Chapter 90. Common Pain Syndromes

1. Central sensitization is a cardinal element of chronic pain syndromes. Targeting factors contributing to this process is the cornerstone of managing chronic pain.

2. Chronic pain has a complex pathophysiology. Treatment should be multidisciplinary and aim for functional restoration.

3. Myofascial pain syndromes are characterized by the presence of trigger points, which have distinctive features that differentiate them from tender points.

4. Fibromyalgia is increasingly diagnosed. It is characterized by widespread pain and the presence of specific tender points. Multiple effective pharmacologic agents are now available.

5. Osteoarthritis (OA) is the most common joint disorder, is one of the most common chronic diseases in the elderly, and is a leading cause of disability. Certain measures may help prevent or slow the progression of OA. Conservative management options may delay or eliminate the need for surgery.

6. Tricyclic antidepressants, serotonin reuptake inhibitors, and antiepileptic drugs, especially calcium channel modulators, are considered good first-line options for treatment of most neuropathic pain syndromes.

7. Treatment of complex regional pain syndrome remains controversial but should start early and focus on mobility of the affected limb. Sympathetic blocks and multimodality analgesia help facilitate this. In advanced cases, more invasive options may be needed such as spinal cord stimulation or intrathecal analgesia.

8. Neck and back pain can be generated by a variety of different anatomic structures, which are targeted in the treatment plan. A careful history and physical examination along with imaging data will help reach the most specific pain generator, which should be targeted in the treatment plan instead of following a blind approach to target all potential generators.

9. Headache syndromes are numerous. The International Headache Society guidelines make the diagnosis of different headache syndromes easy and simple.

10. Tension and migraine headache are the most common primary headache. Preventative therapy is essential to their management.

Many pain conditions are encountered in clinical practice. This chapter provides a concise, practical, updated review of the most common pain syndromes. Along with the other chapters in this book on pain, a comprehensive review of pain is given.

Knowing the pathophysiology of chronic pain is essential for understanding the clinical features of different pain and the rationale of different treatment options used in the field. Chapter 89 covers this topic in detail. This chapter briefly summarizes the mechanisms of pain.

Pain sense starts by detecting noxious stimuli at the level of nociceptors, which are specialized receptors in the peripheral nervous system. An electrical signal is generated (transduction) and transmitted by the afferent fibers, A-δ fibers (slow, thin myelinated fibers), and C-fibers (the unmyelinated slowest fibers) of the spinal and cranial nerves. The first-order neurons of these fibers are located in the dorsal root ganglia or cranial nerve ganglia. Visceral afferent nociceptive fibers (A-δ and C) travel with sympathetic and parasympathetic fibers; their cell bodies also are found in the dorsal root ganglia. Muscles are also innervated by both A-δ and C-fibers. The pain signal then is transmitted to the sensory (second-order) neurons of the dorsal horn of the spinal cord. The ascending nociceptive tracts convey nociceptive stimuli from the dorsal horn of the spinal cord to higher centers in the central nervous system (CNS). These tracts include the spinothalamic, spinohypothalamic, spinoreticular, and spinopontoamygdala tracts. Multiple cortical and subcortical neural structures contribute to processing the pain signal, leading to pain perception. Pain is modified by the CNS via inhibitory descending tracts. Many inhibitory and excitatory neurotransmitters and other biochemical mediators mediate the physiologic process of pain perception.

Repeated peripheral tissue injury may result in a maladaptive phenomenon—peripheral sensitization—which refers to a decreased threshold and an increased response to stimulation, and is maintained by various endogenous biochemicals. Moreover, sensitization of the entire nociceptive pathway can arise secondary to chronic neuroplastic changes in the CNS, resulting in a phenomenon called central sensitization. As a result, multiple clinical features may arise and produce neuropathic pain (see Chapter 89). Once sensitization is established, it may be impossible to separate central contributions from peripheral contributions to the process of sensitization. Because of sensitization, pain may persist or may partially respond to therapy even when the primary injury is no longer active.

Treatment of chronic pain targets the different components contributing to the sense of pain by blocking the signal before it travels to the CNS, potentiating the inhibitory descending tracts, modifying the process of sensitization, or a combination of 1 or more of these mechanisms.

Myofascial Pain Syndromes

Myofascial pain originates from active trigger points (TPs) within muscle structures and/or surrounding connective tissue. A typical TP is characterized by the presence of a taut band in the muscle, tenderness to palpation, and a reference pain zone distant from the TP center. Myofascial pain syndrome (MPS) can be primary or secondary to other painful conditions.

Although no clear mechanism has been defined, TPs are believed to begin after an initial macro or micro injury, which in vulnerable individuals evolves into a chronic MPS through the cascade of peripheral and central sensitizations.

Patients with myofascial pain usually present with muscle ache that is well localized to certain muscles with distinct radiating patterns or is of vague location and radiation. The pain usually is persistent but may fluctuate in intensity. It usually is associated with other symptoms such as joint ache, stiffness, paresthesias, decreased range of motion, fatigue, poor sleep, or headache. When the pain is chronic, autonomic features such as edema and hyperemia may appear.

Diagnosis of MPS is established by identifying TPs. TPs should be sought in a systematic manner. Figure 90-1 illustrates some of the common TPs. TPs are best identified by palpation with the fingertips and application of steady incremental pressure over different areas until hypersensitive points are found and the patient's pain is reproduced. Tight bands are felt by rubbing the fingers across the muscle fibers. When the applied pressure is altered quickly, a brief local muscle twitch response can be observed.1

Treatment of MPS should focus on eliminating TPs to break the cycle enhancing chronic pain and to restore normal tone and function of the affected muscles. TP injections have been widely used to facilitate this process. Although clinicians use different solutions and medications for TP injections, no specific solution has been shown to be superior to others. Repeated steroid injection is associated with a risk for local muscle atrophy.

An alternative to injections is spraying of TPs with a vapocoolant such as chlorofluoromethane or ethyl chloride, with simultaneous stretching of the muscle. In combination with these treatments, muscle rehabilitation with exercises and thermal modalities is also useful. If analgesia is required, nonsteroidal anti-inflammatory drugs (NSAIDs) usually are given. Despite the wide use and acceptance of these therapies, no clear evidence supports their efficacy. Chronic MPS can be complex and refractory to treatment.

Fibromyalgia

Fibromyalgia (FM) is a multisymptomatic syndrome defined by the core feature of chronic, widespread pain. FM is a common entity that affects women more than men and increases steadily with age.2

Although a definitive causal relation has not been established, FM usually is precipitated by trauma, stress, infections, or other factors. It commonly accompanies a wide range of medical conditions, including rheumatoid arthritis (RA), low back pain, systemic lupus erythematosus, Sjögren syndrome, osteoarthritis (OA), inflammatory bowel disease, irritable bowel syndrome, headache, mood disorders, restless legs syndrome, and sleep disturbance, particularly stage 4. Research shows that certain individuals might have vulnerability to FM because of past life events or a complex genetic component interacting with environmental insults.2,3

Patients typically present with chronic, widespread stiffness and pain that is described as a constant dull ache worsened by muscle overactivity. FM is usually associated with a constellation of symptoms such as easy fatigability, nonrestorative sleep, cognitive dysfunction, depression, and somatic complaints other than musculoskeletal pain.2

The diagnosis of FM is usually based on the 1990 recommendations of the American College of Rheumatology (ACR) classification criteria, which comprise 1 historical feature (widespread pain of at least 3 months' duration) and 1 physical finding (the presence of tender points over at least 11 of 18 specified tender point sites on palpation at a force of 4 kg—the amount of pressure required to blanch a thumbnail).2 The locations of the 18 tender points are shown in Figure 90-2. Palpation of control sites that typically are not tender is recommended. Some of these sites are the forehead, the medial third of the clavicle, the dorsum of the middle phalanx of the third digit, and the medial malleolus. If tenderness is present in these sites, the diagnosis of FM is questionable. Tenderness points are different from TPs in that they lack the other associated features. FM is distinguished from MPS by the absence of true TPs.

Treatment of FM is multidisciplinary and should consist of psychological intervention; physical therapy, especially aquatic-based exercises; treatment of comorbid mental disorders and associated sleep disorders; and pharmacologic therapies. Multiple medications have proven effective for the management of pain in FM and are now approved by the Food and Drug Administration (FDA). These are Pregabalin,4 Duloxetine,5 and Milnacipran.6 Tricyclic antidepressants (TCAs) have also been shown effective in FM and have the added benefit improving sleep. NSAIDs have varying degrees of success. Tramadol, a dual reuptake inhibitor of norepinephrine and serotonin with weak μ-receptor affinity, is proving useful. Pramipexole, an antiparkinsonian dopamine agonist, at a dose of 4.5 mg also appears to be a promising option for treatment of FM.7,8

Opioids have not been shown to be effective. Most FM patients tend to have a chronic course, with exacerbations, remissions, and fluctuating symptoms.

Bursitis and Tendinitis

Tendinitis, bursitis, and other periarticular painful conditions are common causes of regional pain. Understanding of the musculoskeletal anatomy and a careful clinical examination are essential in determining the true cause of pain. Whereas arthritis (or synovitis) causes effusions in the synovial space or diffuse swelling of the synovium, producing global joint swelling, bursitis causes an effusion or swelling limited to the bursa only, and tendinitis causes little, if any, swelling limited to the tenosynovial structure. In synovitis, direct palpation of the synovium elicits diffuse tenderness over the entire synovial surface area. In bursitis, tenderness is localized to the bursal structure and spares the synovium. The tenderness in tendinitis is elicited best by active range of motion and active isometric loading against resistance, but can be detected by direct palpation. Tendinitis is painful with active or passive range of motion as the inflamed tendon experiences loading. Passive range of motion elicits tenderness only if the inflamed tendon is stretched and passively loaded, and active range of motion or isometric testing elicits tenderness by actively loading the tendon.

Table 90-1 lists each anatomic region and the more common periarticular conditions for each region.

In general, treatment of bursitis, tendinitis, and other periarticular conditions is similar and usually conservative. Physical therapy is helpful in most cases and may be more successful when therapy includes a combination of passive modalities, such as ice and heat, and active modalities, such as strengthening exercises to improve any biomechanical imbalances. Ultrasound is sometimes helpful and is of proven benefit for symptomatic calcific tendinitis of the shoulder. NSAIDs are helpful as analgesics but are of limited usefulness in alleviating chronic conditions. Judicious intralesional injections of steroids are helpful. However, caution should be exercised when considering intralesional steroids for bicipital and Achilles tendinitis because tendon rupture is a risk. Surgery may be required for refractory conditions.

Arthritides

Arthritides and related syndromes are common causes of pain, with a steady increase of prevalence. An estimated 15% (40 million) of Americans had some form of arthritis in 1995. By the year 2020, an estimated 18.2% (59.4 million) of Americans will be affected.9 Thus, although pain specialists may not be the primary treating physicians, they should be familiar with these syndromes and be able to recognize them and participate in the overall management plan to help in reducing the associated morbidity and disability. Detailed coverage of these syndromes is beyond the scope of this chapter.

Osteoarthritis

Osteoarthritis (OA) is by far the most common joint disorder, is one of the most common chronic diseases in the elderly, and is a leading cause of disability. Increased weight is the most significant independent predictor of both incidence and progression of OA in weight-bearing joints. The risk for development of OA is increased by high-impact repetitive activities. Smoking and osteoporosis increase the frequency of OA.

The joints most commonly involved in OA are the metatarsophalangeal (MTP) joint of the great toe (hallux valgus or "bunion"), proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints of the fingers, and carpometacarpal (CMC) joint of the thumb, hips, knees, and both lumbar and cervical spines. Other joints, even major weight-bearing joints such as the ankle, are regularly spared unless they are involved in secondary forms of OA. Pain is the main symptom leading to the diagnosis of OA. The pain is most often described as a deep ache, accompanied frequently by joint stiffness that follows periods of inactivity (on arising in the morning or after sitting). Pain is aggravated by using the involved joints, may radiate, or may be referred to surrounding structures. In the early stages of the disease, pain is commonly relieved by rest. With more severe disease, pain may be persistent, interfering with normal function and preventing sleep, even with medical management.

On physical examination, the joints may demonstrate tenderness, crepitus, and a limited range of motion. Joint swelling may be due to an accompanying synovial effusion or to bony enlargement and the presence of osteophytes. Radiographic findings help confirm the diagnosis. Joint space narrowing, subchondral bone sclerosis, subchondral cysts, and osteophytosis are characteristic.2

Nonpharmacologic management of OA includes correction of body mechanics and posture, weight loss, and physical therapy. Analgesia can be achieved by using acetaminophen and NSAIDs as first-line therapy. Intraarticular corticosteroid injections might have a positive role but should be judiciously implemented and not repeated more than 3 times per year because of possible secondary cartilage damage. The structure-modifying effects of drugs are being evaluated, and both glucosamine sulfate and diacerein have shown different results in treating pain.10-12 Doxycycline has been proved to slow the rate of joint space narrowing in knees with established OA.13

Intraarticular injection of a viscosupplement such as Hylan has been shown to be effective in reducing pain in knee OA.14 When conservative therapy fails, joint replacement surgery might be the only option to help with analgesia.

Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic multisystem disease with inflammatory polyarthritis of symmetric distribution affecting the peripheral joints of the hands (sparing DIP joints), feet, wrists, elbows, shoulders, hips, knees, and ankles. The cervical spine is generally the only axial skeleton affected by RA.

RA manifests in constitutional symptoms of fatigue, low-grade fever, weight loss, and morning stiffness. Synovitis (inflammation of the synovium) is the hallmark of RA. It produces pain, swelling, and tenderness of the joints. RA is characterized by a waxing-and-waning course with relapses and remissions. Pain in RA is multifactorial. In the early stages, it is secondary to inflammation. At later stages, the damaging effects of erosion of cartilage and bone also cause pain. RA can be accompanied by FM. RA complications can also result in pain such as vertebral body fractures, compression of the median nerves by synovial tissue in the carpel tunnel, rheumatoid vasculitis, cervical spine instability at the C1-2 level, and septic arthritis.15

Diagnosis is based on the history and physical examination and is supported by the presence of rheumatoid factor, which is present in 80% of patients with RA. Radiographically, soft-tissue swelling, juxtaarticular osteopenia, symmetric space narrowing, and bony erosions are seen.

Pharmacologic treatment of RA relies on NSAIDs, corticosteroids, analgesics, and disease-modifying antirheumatic drugs (DMARDs). Early and aggressive use of DMARDs is essential once the diagnosis is confirmed. Anti–tumor necrosis factor α agents, such as infliximab, etanercept, and adalimumab, have very potent anti-inflammatory properties and provide dramatic improvements in symptoms and signs. Interleukin-1 receptor antagonists such as anakinra also have been shown to be effective in slowing the damage of cartilage and progression of arthritis.

When pain is unresponsive to treatment, surgical options should be pursued, including synovectomy, arthroplasty, and joint replacement. Opioids might be the only option to provide adequate analgesia in advanced cases refractory to treatment or when contraindications to other analgesics exist.

Other Arthritides

Multiple other arthritic syndromes may have pain as a cardinal feature. They include spondyloarthropathies, gout, and pseudogout. Arthritis can also accompany other systemic diseases, such as systemic lupus erythematosus, scleroderma, polymyalgia rheumatica, giant cell arteritis, Reiter syndrome, and inflammatory bowel disease.

Treatment should always focus on treating the underlying condition. NSAIDs usually provide acceptable analgesia. Often, opioids are required for more severe cases.

Neuropathic pain is a pathologic pain that results from sustained transmission of pain signals in the absence of ongoing tissue injury or activation of pain-sensitive afferent peripheral nerves. Neural injury or dysfunction at any point along the somatosensory system from the peripheral nerve endings to the brain can cause neuropathic pain. Multiple mechanisms (peripheral and central) are responsible for sustaining neuropathic pain. Although its role is less identified than in nociceptive pain conditions, primary sensitization of nociceptive nerve endings might be a contributing factor to sustaining neuropathic pain. Damaged nerve fibers, especially neuromas, may generate ectopic action potentials, which contribute to neuropathic pain. When input from peripheral nociceptors into the dorsal horn of the spinal cord decreases, as encountered in deafferentation conditions such as shingles and after amputation, the dorsal horn neurons become hyperexcitable and may even develop spontaneous activity. In addition, the reduction of peripheral sensory input leads to ephaptic sprouting of the neurons neighboring the affected central neurons, resulting in magnification of the perceived pain field. Central sensitization, as outlined, also plays a major role in neuropathic pain. Because the inhibitory interneurons normally are excited by peripheral input, attenuation of this input will decrease inhibition and amplify the pain signal. In general, the inhibitory circuits of pain signal are downregulated at the level of both the spinal cord and the brain. At the level of the brain, different sites are involved in the processing of pain signal, and the somatosensory-pain homunculus is not quite preserved. The initial neural injury and subsequent evolving mechanisms explain the complexity of clinical features encountered in neuropathic pain syndromes.

Some clinical features are common among neuropathic syndromes, whereas others are unique to specific syndromes. Patients usually have different types of pain. A stimulus-independent pain is a spontaneous pain experienced by patients without sensory stimulation. It consists of a background constant pain, intermittent exacerbations, and brief episodes of other symptoms. The pain usually is burning, aching, crushing, gnawing, lancinating, shooting, electrical, or lightning in quality, and associated with painful numbness and paresthesias (dysesthesias). The stimulus-evoked pain includes a variety of signs, such as hyperalgesia, mechanical and thermal allodynia, and hyperpathia. Table 90-2 summarizes some features of neuropathic pain.

Associated clinical features include abnormalities of reflexes and muscle function. Increased reflexes and tone are indicative of an upper motor neuron disease and suggest a central lesion such as stroke, whereas reduced reflexes or tone suggest peripheral origin as in compressive radiculopathies or neuropathies. Secondary motor changes could be a result of disuse and abnormal position. Autonomic abnormalities can be seen and include changes in color and temperature in the affected tissues, swelling due to abnormal leakage of intravascular fluid, and growth of skin, hair, nails, and other cutaneous structures. Other systemic features of autonomic dysfunction that could be seen include orthostatic hypotension, impotence, delayed gastric emptying, abnormal sweating and/or thermoregulation, difficulties with elimination, and occasionally cardiac arrhythmias. The management of specific neuropathic pain syndromes will be discussed in this chapter, but in general a common management algorithm may be followed for all neuropathic pain syndromes.16

Table 90-3 lists the most common neuropathic pain syndromes.17 The following is a brief discussion of common neuropathic pain conditions.

Painful Peripheral Neuropathies

A wide variety of etiologies lead to peripheral neuropathies. It is important to realize that not all neuropathies are painful, as is the case with most of the inherited neuropathies. Some patients with neuropathy have chronic pain due to other conditions, and their pain should not be immediately attributed to the concomitant nonpainful neuropathy. The distribution of neuropathy can be generalized and symmetric (polyneuropathy), such as diabetic and alcoholic polyneuropathy; multifocal (mononeuropathy multiplex), such as collagen vascular disease–related neuropathies; or focal (mononeuropathy), as seen in trauma and entrapment neuropathies. Polyneuropathy usually is symmetric and starts in a distal-to-proximal gradient in a "glove and stocking" distribution. Mononeuropathy multiplex affects multiple peripheral nerves arbitrarily and sometimes can be difficult to differentiate from polyneuropathy. Mononeuropathy follows the distribution of the affected nerve. Neuropathies may result from injury to the axons (axonal neuropathies), to myelin (demyelinating neuropathies), or mixed lesions. Most of the neuropathies encountered in pain medicine practice are axonal neuropathy types. Acute (AIDP) and chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) are examples of demyelinating neuropathies usually seen in pain practice. Table 90-4 highlights most of the painful neuropathies a pain physician might encounter.

Although the evaluation of neuropathy usually is conducted by neurologists, it is important for the pain medicine practitioner to be familiar with the diagnostic workup. Figure 90-3 shows a simple diagnostic approach that leads to the diagnosis of most neuropathies.18

Small-Fiber Neuropathy

Small-fiber neuropathy (SFN) is the most common type of painful neuropathy. The smaller axons A-δ (small myelinated) and C (unmyelinated) are affected. The larger fibers usually are preserved but could be involved at a later stage. SFN is a disease of late middle age, but symptoms could start as early as the third decade or as late as the ninth decade.19 SFN is vastly under recognized, and most cases are "idiopathic." SFN may predate diabetes mellitus20 and neoplastic conditions by many years. Although SFN is more common in men, patients presenting with pain of SFN are more likely to be women.21

Pain and decreased temperature sensation are the predominant features. Proprioception, vibratory sensation, and muscle-stretch reflexes usually are intact because they are mediated by the larger nerve fibers A-β and A-α, which are not involved in the pathologic process.

Injury of affected fibers cannot be detected by standard nerve conduction studies (NCS) and electromyography (EMG), so these tests usually are unrevealing. Therefore, the diagnosis usually is clinical and relies on ruling out other possibilities. A definite diagnosis of SFN could be reached by autonomic testing or a skin biopsy if warranted. When fasting blood glucose or glycosylated hemoglobin (HgA1C) levels are diagnostic of diabetes mellitus, obtaining an oral glucose tolerance test may unveil impaired glucose tolerance or early diabetes mellitus.22-24

The distinction between SFN and "large-fiber" neuropathies is important because the underlying cause is more likely to be identifiable when both large and small fibers are affected.

Diabetic Peripheral Neuropathic Pain

Current estimates suggest that more than 22 million Americans have diabetes.25 Peripheral neuropathy is one of the most common complications of diabetes,26 and conversely diabetes is the most common cause of peripheral neuropathy in developed countries.27 Studies suggest that 30% to 60% of all diabetics have signs and/or symptoms of peripheral neuropathy.25,28-30 The risk is greater than 50% in individuals who have had diabetes for more than 20 years. The prevalence of any neuropathy is 66% for patients with Type 1 diabetes mellitus and 59% for those with Type 2.26 Neuropathy can be seen at any stage of diabetes progression, and approximately 10% of newly diagnosed Type 2 diabetics may have neuropathy.26 Neuropathic symptoms may be the presenting complaint leading to the diagnosis of diabetes. Neuropathy also has been reported in patients with impaired glucose tolerance, or "prediabetes."26 Multiple risk factors contribute to the risk of diabetic neuropathy, including duration of diabetes, age, male gender, increased height, hypertension, and smoking.28 Poor glycemic control is a major modifiable risk factor for neuropathy, as demonstrated by the reduction in risk of neuropathy with intensive glucose lowering. This is demonstrated by a decrease of approximately 60% in Type 1 diabetic patients treated with intensive insulin therapy compared to those who received conventional therapy.31

The clinical manifestations of diabetic peripheral neuropathy depend on the specific nerves affected. Because all branches of the peripheral nervous system are susceptible to damage from diabetes, patients can exhibit abnormalities of sensory, motor, or autonomic function. Deficits frequently overlap or coexist.

Diabetic peripheral neuropathy is a heterogeneous condition that can manifest clinically as several types,26 which can exist individually or overlap. Table 90-5 lists the different types of diabetic peripheral neuropathy.

NCS and quantitative sensory testing (eg, quantitative vibration threshold testing) can be used to confirm neuropathy suggested by the physical examination or to confirm the diagnosis in patients with symptoms but no abnormalities on physical examination. Normal NCS do not necessarily rule out neuropathy as a cause of pain because neuropathic symptoms may be due to SFN.

Multiple pharmacologic agents have been used for treatment of diabetic peripheral neuropathic pain. Duloxetine32,33 and pregabalin34-37 are the only FDA-approved drugs for diabetic peripheral neuropathic pain. Multiple other medications have been shown to be effective, such as TCAs,38,39 gabapentin,27,40 venlafaxine,41-43 tramadol, capsaicin,29,44-48 opioids,49-51 and a combination of more than one of these medications.50,52 Zonisamide53 also appears to be promising. Antiepilepsy drugs (AEDs)54 and many other drugs have been used extensively, with varying degrees of success.17,18,55 In a small case series, spinal cord stimulation was successful in the treatment of diabetic peripheral neuropathic pain refractory to conventional therapies, including opioids.56,57

HIV/AIDS-Related Neuropathy

Neuropathic pain occurs in approximately one-third of patients with human immunodeficiency virus (HIV) and acquired immunodeficiency syndrome (AIDS).58 A variety of disorders can result in neuropathic pain in HIV and AIDS patients. The different types of HIV/AIDS-related neuropathies are summarized in Table 90-6.59,60

Treatment of HIV/AIDS-related neuropathic pain relies on treatment of the underlying infection(s) and removal of toxic agent if possible. Neuropathic agents have been used, with variable results. Lamotrigine61,62 and probably ziconotide63 have documented efficacy.

Carpal Tunnel Syndrome

Carpal tunnel syndrome (CTS) is the most common painful mononeuropathy of the upper limb. It results from compression (entrapment) of the median nerve as it passes under the ligamentous canal in the wrist. Multiple factors predispose to or precipitate CTS, such as fractures, ganglions, synovial disorders, wrist arthritides, ergonomic stressors, repetitive use, pregnancy, obesity, chronic renal insufficiency, and other systemic disorders such as diabetes and acromegaly.

CTS is characterized by paresthesias and dysesthesias over the median nerve sensory area of the hand, which includes the thumb, index, and median half of the middle fingers. Weakness of the thenar muscles can occur. Symptoms are most pronounced upon awakening.

Physical examination shows decreased sensation over the palmer aspect of the thumb through the lateral half of the middle finger. At later stages, the thenar muscles are weak and could be atrophied. Tinel sign and Phalen test are not sensitive but help support the diagnosis when they are present.64,65 Tinel sign is the elicitation of distal paresthesias by percussion on the wrist or at the base of the palm. Phalen test attempts to elicit paresthesias by applying pressure (inflating a tourniquet to 60 mm Hg) on the arm or holding the wrist in a flexed position. The diagnosis of CTS can be confirmed by NCS and EMG.

Most patients respond well to conservative treatment, which includes wrist splinting, NSAIDs, or steroid injections. If treatment fails, surgical decompression at the wrist may be necessary, especially when weakness progresses.

Acute Herpes Zoster

Acute herpes zoster (shingles) is the most common cause of sensory neuropathy. It results from infection reactivation of the dormant varicella-zoster virus in the ganglionic neurons or satellite cells, followed by transmission of the virus particles to the nerve endings proximally and distally. The incidence of herpes zoster varies with age and immune status, ranging from 0.4 to 1.6 cases per 1000 among healthy people younger than 20 years to 4.5 to 11 cases per 1000 among those 80 years or older.66 The risk of a second attack is as high as the risk of a first attack.67 The risk of acute herpes zoster is higher among patients with HIV infection or cancer and particularly among children with leukemia and transplant recipients.66,68-71

Dermatomal distribution and vesicular rash are the hallmarks of acute herpes zoster. The most affected nerves follow this order: thoracic spinal roots, ophthalmic division of the trigeminal nerve (V1), maxillary division of the trigeminal nerve (V2), cervical spinal roots, and sacral spinal roots.72 The involvement is unilateral in most cases but can rarely be bilateral.

The earliest clinical features of acute herpes zoster noticed by patients are dermatomal dysesthesias associated with pruritus. This could be accompanied or followed shortly by the appearance of the typical rash, which matures through different stages until it crusts and heals. The pain worsens with progression and consists of dysesthesias, burning, and shooting pain. It tends to resolve spontaneously as the crust falls off, a process that takes 4 to 5 weeks.

Treatment of acute herpes zoster is discussed in the section on postherpetic neuralgia because of the close therapeutic strategies.

Postherpetic Neuralgia

Many definitions have arbitrarily been used for postherpetic neuralgia (PHN). Results of recent research distinguishes among 3 phases of pain: acute pain (which occurs within 30 days after rash onset; described earlier), PHN (pain that persists ≥120 days after rash onset), and subacute herpetic neuralgia (pain that persists beyond the acute phase but resolves before the diagnosis of PHN is made).73,74 PHN may develop after a pain-free interval. Nearly all patients have pain in association with acute herpes zoster, and 10% to 70% of these patients go on to have PHN.66,67,75 Not only does the risk of PHN increase with age, but so does the intractability of the pain.66 The presence of prodrome, female gender, greater rash severity, and greater acute herpes zoster pain severity have been associated with increased risk for PHN.74 The risk of PHN is not increased in immunocompromised patients.69,75 Symptoms consist of a background dermatomal burning pain and dysesthesias with superimposed intermittent lancinating pain. Hypoesthesia, hyperalgesia, allodynia, and hyperpathia may be present.

Treatment

The goal of treatment of acute herpes zoster is to alleviate the symptoms, shorten its course, and prevent the evolution of PHN. Antiviral drugs (famciclovir, valacyclovir, acyclovir) started within 72 hours after the rash appears reduce acute pain in immunocompetent patients, thus providing relief in the greatest number of patients and possibly reducing the likelihood of evolution of PHN.66,76,77 Although corticosteroids do not alter the course of PHN, they improve the quality of life after zoster, thus justifying their administration in combination with an antiviral drug in high-risk patients 50 years or older with moderate to severe pain in whom corticosteroids are not contraindicated.66

Some reports suggest the efficacy of infiltration of the skin, peripheral nerves, sympathetic nerve blockade, or paravertebral or epidural spaces with local anesthetic drugs with or without steroids in patients with acute herpes zoster.66,78-80

A large retrospective study suggested that any benefits of somatic nerve blocks are limited to the first 2 months of pain.66

Treatment of pain associated with established PHN can be challenging. In general, drugs used for neuropathic pain are used for treatment of PHN. TCAs have well-documented efficacy.39 Anticonvulsants are widely used.81 Gabapentin82-84 and pregabalin85-87 have documented efficacy and are FDA approved. Opioids may be required for more severe cases. Topical lidocaine patches have been shown to be effective for PHN, especially in alleviating allodynia.43,88,89 Data suggest the possible efficacy of epidural or intrathecal steroid injections in chronic PHN.90-92

Numerous other treatment modalities have been attempted, such as the transcutaneous electrical nerve stimulation unit,93 topical agents, acupuncture, and hypnosis, with various results. In refractory PHN, more invasive surgical options have been implemented, including dorsal root entry zone lesions, cordotomy, rhizotomy, spinal cord stimulation, and sympathectomy.

Meralgia Paresthetica

Meralgia paresthetica is an entrapment mononeuropathy of the lateral femoral cutaneous nerve as it passes under the inguinal ligament. It is associated with a number of conditions and factors, such as increased pressure on the nerves, as occurs with tight belts, pregnancy, CTS, regional operations, obesity, or after rapid weight changes.94,95

Meralgia paresthetica is characterized by a patch of dysesthesias and decreased sensation over the anterolateral thigh. Diagnosis can be easily confirmed by blocking the nerve. Management is conservative. Corticosteroid injections also can be used. The prognosis is very good, with most patients experiencing spontaneous remission in 6 to 12 months. Surgery might be helpful in refractory cases.96

Trigeminal Neuralgia

Trigeminal neuralgia, previously called tic douloureux, is a disorder of the trigeminal nerve. It is characterized by brief electric shock–like pain that is abrupt in onset and termination and is limited in distribution to 1 or more divisions of the trigeminal nerve. Pain is commonly evoked by trivial trigger factors such as washing, shaving, talking, and/or brushing the teeth. Small areas in the nasolabial fold and/or chin may be particularly susceptible to the precipitation of pain (trigger areas). The pain usually remits for variable periods.

Trigeminal neuralgia classically starts in the second or third division and affects the cheek or chin. The first division is involved in less than 5% of patients. Trigeminal neuralgia is a unilateral disorder but in rare cases is bilateral, in which case a central lesion such as multiple sclerosis should be excluded. Between paroxysms, patients usually are asymptomatic but may have a persistent dull background pain. In some cases, the trigeminal root in the posterior fossa is compressed by tortuous or aberrant vessels. Classic trigeminal neuralgia usually is responsive, at least initially, to pharmacotherapy.

Table 90-7 lists the International Headache Society (IHS) diagnostic criteria for trigeminal neuralgia.97

Carbamazepine is still the first-line treatment. Other AEDs, such as gabapentin, also have been shown to be effective.98 TCAs are effective.99 In refractory cases, invasive procedures (eg, ablative lesioning or decompression of the trigeminal ganglion) may be required.100

Glossopharyngeal Neuralgia

Glossopharyngeal (cranial nerve IX) neuralgia is a severe transient stabbing pain experienced in the distribution of this nerve and the distribution of the auricular and pharyngeal branches of the vagus nerves. The pain is felt in the ear, base of the tongue, tonsillar fossa, or beneath the angle of the jaw. The pain is commonly provoked by swallowing, talking, or coughing and may remit and relapse as in trigeminal neuralgia. Table 90-8 lists the IHS diagnostic criteria for glossopharyngeal neuralgia.97

In Eagle syndrome, the nerve is compressed by a calcified or ossified stylohyoid ligament, which is visible on x-ray or computed tomography (CT) scan.101 Pharmacologic treatment of glossopharyngeal neuralgia is similar to that of trigeminal neuralgia. In Eagle syndrome, resection of the stylohyoid ligament is effective.

Occipital Neuralgia

Occipital neuralgia is a paroxysmal stabbing jabbing pain in the distribution of the greater or lesser occipital nerves or the third occipital nerve, sometimes accompanied by diminished sensation or dysesthesias in the affected area. It is associated with tenderness over the affected nerve. Table 90-9 lists the IHS diagnostic criteria for occipital neuralgia.97

Treatment can be conservative using different analgesics, including TCAs and AEDs, or application of nerve blocks. For refractory cases, neuroablative measures can be used.102

Central pain is a "deafferentation" pain that can result from any lesion found in the CNS.103 Virtually any type of lesion can produce this type of pain, including demyelinating, vascular, infectious, inflammatory, and traumatic. Pain onset may be delayed by several months after the initial insult, reflecting the slow degeneration process within the CNS. Pain usually correlates to the anatomic site of the causative lesion. The pain features are those of neuropathic pain.

Brain central pain results from a variety of etiologies. Thalamic pain (Dejerine-Roussy syndrome) is the prototype of central pain, but lesions in the brainstem and other sites also can produce central pain. Strokes are the most common cause, with pain reported to occur in up to 8% of poststroke patients.104 Other etiologies include multiple sclerosis, brain abscess, encephalitis, and tumors.

Spinal cord central pain is a common complication of spinal cord injuries. Trauma is the most common etiology.105 Iatrogenic, inflammatory, demyelinating, vascular, neoplastic, and congenital lesions are other possible causes. The most common level of injury associated with pain is cauda equina followed by the central cord injuries. Syringomyelia and syringobulbia can occur as delayed consequences of trauma or congenital malformations and produce neuropathic pain of segmental pattern.

Central pain is one of the most difficult pain states to effectively treat. Pregabalin106 and lamotrigine107,108 show encouraging results. Some evidence exists for the benefit of TCAs.39 Other agents used for neuropathic pain, such as AEDs and opioids, have been used, but no sound evidence supports their efficacy.

Sympathetically Maintained Pain and Complex Regional Pain Syndromes

Sympathetically maintained pain (SMP) is defined as "pain that is maintained by sympathetic efferent innervation or by circulating catecholamines."109 Thus SMP is not a clinical diagnosis but rather a pathophysiologic mechanism in chronic pain marked by improvement of pain when sympathetic blockade is performed. When the pain does not respond to sympathetic blockade, it is called sympathetically independent pain (SIP). SMP is thought to be a major culprit in many chronic pain states, such as peripheral and central neuropathic pain syndromes.110-112

Complex regional pain syndrome (CRPS) is considered to be a neuropathic SMP syndrome. The 2 types of CRPS are type I (previously called reflex sympathetic dystrophy) and type II (previously called causalgia). CRPS is more common in women than in men, and the incidence reaches its peak in the fifth decade.113,114 It involves 1 limb in most cases,115 and there is a history of noxious traumatic injury with or without nerve involvement.114 There is no correlation between the severity of injury and the severity of the ensuing pain syndrome. Direct injuries to CNS structures have been reported as causative, including spinal cord116 and brain117 injuries. In CRPS type II particularly, there may be a stretch injury to the nerve, without interruption of the nerve. Multiple risk factors have been postulated to predispose to CRPS, including immobilization,118 smoking,119 genetic predisposition,120 and psychological factors.121

The exact mechanism of CRPS is not known, but it appears to be a disease of both the CNS and the peripheral nervous system122,123 Peripherally, α-adrenergic sensitization of the nociceptive afferent fibers occurs. As a result, nociceptors are activated by release of norepinephrine by sympathetic postganglionic fibers. Release of certain mediators, such as prostaglandins, by sympathetic fibers can further sensitize the nociceptive afferents. If the injury results in myelin loss of the fibers, artificial synapses develop between the affected sensory afferents and sympathetic efferents, a process called ephaptic transmission. The dorsal root ganglion is thought to be another site for ephaptic transmission resulting from sprouting of sympathetic postganglionic fibers around sensory neurons. At the level of the dorsal horn of the spinal cord, the wide dynamic range neurons, which are second-order neurons, are activated and sensitized by the active injured C-fibers. Sensitized wide dynamic range cells are thought to be activated by other stimuli, such as light touch, explaining the phenomenon of allodynia. At the level of the brain, there is altered sensorimotor processing and increased hyperexcitability.124,125 Thus CRPS results from interaction between the CNS and the periphery. Central changes are reflected as alterations in somatic sensation (including pain), the motor system, and the peripheral autonomically regulated effector systems (vasculature, sweat glands, inflammatory cells).122

In most cases the presenting symptom of CRPS is pain, which most often is burning and does not follow a dermatomal pattern.113,126 Other common symptoms and signs include decreased range of motion, weakness, hyperpathia, allodynia, hyperalgesia, color change, altered skin temperature, edema, hyperesthesia, hypoesthesia, sweating change, nail or hair changes, and dystonia.113,126 Although symptoms typically start in a distal limb, CRPS has been reported to start in other regions of the body, such as the head, proximal limbs, and genitalia.127 Spread of CRPS features proximally or to other regions of the body has been well described.

The diagnosis of CRPS can be made only in the absence of any other diagnosis explaining the findings. Table 90-10 summarizes the International Association for the Study of Pain (IASP) diagnostic criteria for CRPS.128-131 These criteria are very sensitive and less specific. Criteria with improved specificity are proposed and summarized in Table 90-11.129,131

No specific diagnostic test is available for CRPS.132 Several tests can help confirm the diagnosis or rule out other conditions. Blood tests, including erythrocyte sedimentation rate, blood cell count, and rheumatologic testing, may be necessary to help rule out infection or a rheumatologic condition.132 When vasomotor features are present, vascular studies can exclude a vascular etiology. NCS and EMG may clarify the presence of nerve injury necessary for the diagnosis of CRPS type II. An important distinction between CRPS type II and peripheral mononeuropathy is that the somatosensory symptoms in CRPS extend beyond the distribution of the affected nerve.132 Radiographic studies including magnetic resonance imaging (MRI) often are necessary to exclude bone or soft-tissue pathology as the source of pain. Plain radiographic studies may show findings of bony demineralization, which is not specific to CRPS and could be the result of disuse.133 A 3-phase bone scan of the affected extremity has variable sensitivity and is relatively nonspecific in the diagnosis of CRPS. Classic findings include increased periarticular uptake throughout the 3 phases (blood pool, blood phase, scan phase).132 Thermography can assist in confirming thermal dysregulation. Simple measures also can provide this information, using infrared thermometer or skin temperature probes that document the temperature of the normal and the affected limbs. A temperature difference of 0.6°C between limbs is considered significant.134 Quantitative sudomotor axonal reflex testing evaluates autonomic function by measuring sweat output in response to a cholinergic agent. Although a positive response to a sympathetic block can help in establishing the diagnosis, it is not required to diagnose CRPS.132 A pharmacologic sympathetic block can be performed with intravenous infusion of phentolamine. However, the more common approach is performance of a local anesthetic sympathetic trunk block. A lumbar paravertebral sympathetic block is performed for lower limbs, and a cervicothoracic block (stellate ganglion block) or upper thoracic sympathetic block is performed for upper limbs. Evidence of a satisfactory sympathetic block (eg, thermography) in the absence of a somatic nerve block should be demonstrated.132 If favorable results are achieved by sympathetic blocks, then their continued administration may be useful.

Treatment of CRPS remains controversial because of the lack of adequate evidence on most therapies implemented in clinical practice. A consensus statement released in 2002 by an interdisciplinary expert panel produced a reasonable treatment approach135,136 Rapid initiation of multidisciplinary treatment is recommended, with advancement to higher levels of intervention if initial therapy shows no benefit in 2 weeks. Simultaneous physical rehabilitation, psychological therapy, and provision of adequate analgesia are key elements in the treatment plan. The primary goal of treatment is functional restoration of the affected region. In some studies, physical therapy has shown to be effective and thus should be started as soon as possible while effective analgesia is provided. Multiple physical and occupational therapy measures can be used in the process of rehabilitation, starting with desensitization and stress loading, then gentle active range of motion and stretching to increase flexibility, and eventually normalization of use and general conditioning.137

Psychological therapy should focus on educating patients that pain sensations in CRPS type I do not indicate tissue damage, and that reactivation of the affected limb is important. With persistent symptoms, clinical psychological assessment is recommended, eventually followed by cognitive behavioral therapy. Comorbid conditions such as depression, sleep disturbance, anxiety, and generalized physical deconditioning should be treated.

Analgesia is achieved using oral or topical neuropathic pain agents, including TCAs, AEDs, NSAIDs, opioids, and other agents.138 Corticosteroids may be effective, especially if the inflammatory component is profound.139 Calcitonin, topical dimethylsulfoxide (DMSO), and α1-adrenoceptor antagonists (eg, terazosin, phenoxybenzamine) may be helpful. Many other drugs have been anecdotally used, with varied results (including prazosin, clonidine, mexiletine, ketamine, baclofen, bisphosphonates, muscle relaxants, and calcium channel blockers).140

When symptoms are persistent, patients who had favorable results with diagnostic sympathetic blockade are often offered intravenous regional sympathetic blocks (IRSBs). IRSBs using phentolamine, guanethidine, reserpine, droperidol, and atropine have been shown to be ineffective.121 Patients who have not had good results with sympathetic blockade may require a combined somatic/sympathetic block using indwelling catheters to allow adequate physical therapy and rehabilitation. Epidural catheters also have been used in this fashion.135 If sympathetic blocks are effective in producing analgesia but duration is limited, neurolysis with either neurolytic injections or radiofrequency-lesioning techniques can be considered.141 Spinal cord stimulation appears to be an effective treatment, especially for CRPS type I.142,143 Spinal analgesia may be an effective treatment of CRPS when other modalities fail.135,144,145

Postamputation Pain

Stump Pain

Stump pain is a chronic sensation of pain at the site of amputation. It also is referred to as residual limb pain.146 It may occur with phantom limb pain or alone. Several factors may account for stump pain and should be evaluated, including surgical trauma, ischemia, local infection, ill-fitting prostheses, or a painful neuroma formation.

Treatment should focus on treating the underlying etiology. Treatment of painful neuromas ranges from simple injections to surgical interventions, with varying degrees of success.147

Phantom Pain

Phantom sensation is the perception of the amputated part and occurs in almost all amputees. Phantom pain is the perception of pain distal to the amputation site. It has unclear etiology, but deafferentation of central neurons seems to play a major role in the development of phantom pain. Its incidence peaks approximately 1 month after amputation and gradually improves as the pain "telescopes" toward the stump. The pain results in paroxysms of burning and twisting sensation in the amputated part. Phantom pain should be differentiated from stump pain.

Treatment of phantom pain is challenging. Pharmacologic agents for neuropathic pain should be attempted. TCAs, tramadol, and gabapentin have been shown to be effective.148,149 Nerve blocks can be tried for more difficult cases. In refractory cases, surgical options (eg, dorsal root entry zone lesions) and more invasive procedures might be the only effective methods for treating the pain. Preemptive analgesia may prevent phantom pain, although this remains controversial.150

Back and Neck Pain

Low back pain is one of the most common symptoms that prompt patients to seek medical care and is the leading cause of disability among workers younger than 45 years. Current data suggest that more than three-fourths of people will have back pain at one point in their life, with an annual prevalence up to 45%.151,152

Neck pain is a less common complaint but still has a point prevalence of approximately 10% to 35% and a lifetime prevalence of approximately 15% to 50%. It is more common in women.153

Pain can originate due to pathology in a variety of neuraxial structures, including vertebral bodies, intervertebral disks, ligaments, muscle structures, joints (facet, sacroiliac), nerve roots, meninges, and epidural space. A combination of etiologies is common and may be difficult to delineate. Table 90-12 summarizes the most common etiologies of back and neck pain.

Obtaining an adequate history and physical examination is crucial for reaching the correct diagnosis and implementing a successful treatment plan. Special attention should be given to excluding emergency situations, such as epidural infection, epidural hemorrhage, cauda equine syndrome, spinal cord compression, spine metastasis, and aortic aneurysm. This chapter discusses only the more common pain syndromes.

Discogenic Pain

Discogenic pain is believed to occur as a result of damage to the annular lamellae by the disrupted inner internal disk and the resultant decreased pain threshold to mechanical loading. Usually a deep axial ache radiates to shoulders and scapular areas from cervical disks and to buttocks and posterior thighs from lumbar disks. The pain is worsened by mechanical loading maneuvers such as sitting, standing, and particularly bending forward.

Although CT scanning and MRI of the spine may show signs of disk degeneration, establishing clinical correlation with imaging findings is difficult.154 A provocative discography test that consists of dye injection into the disk material followed by CT imaging has been advocated to confirm discogenic pain.155

Treatment is conservative, consisting of physical therapy, weight reduction, and NSAIDs. Patients with 1 or 2 diseased disks who are refractory to conservative therapy may benefit from intradiscal electrothermal therapy (see Chapter 92).156-158

Radicular Pain

Radicular pain originates as a result of irritation of a nerve root due to a herniated nucleus pulposus or degenerative neuroforaminal narrowing. The most commonly affected levels in the lower back are L5-S1 and L4-5. In the neck, the affected levels are C5-6 and C6-7. Typically, the pain radiates from the neck or back in a dermatomal pattern (Fig. 90-3). Usually the patient has associated sensory disturbance and reflex decrease in the distribution of the affected root. A positive straight-leg raising (SLR) test while the patient is in a supine or sitting position indicates nerve root irritation. SLR test is considered positive when pain is reproduced in a dermatomal distribution. However, nerve root irritation is not always present in patients with low back pain or posterior thigh discomfort. MRI is helpful in identifying anatomy and changes near the nerve roots. NCS/EMG can help confirm the diagnosis and assess the severity of injury.

Conservative treatment, including NSAIDs and PT, is sufficient for most cases. Epidural steroid injections can provide symptomatic management.159,160 Transforaminal steroid injections might be superior and prevent from surgery but may result in more complications, especially at the cervical spine level.161-164 Surgical intervention may be required for refractory pain, especially if neurologic deficits are present. Microdiscectomy is the gold standard treatment for uncomplicated herniated nucleus pulposus.

Facet Arthropathy

The facet joints (zygapophysial or Z joints) are true synovial joints whose main function is to limit rotation and resist compression during lordosis. Facet joint pain results from conditions that increase the load on them, such as arthritis, decreased disk space, and increased lordosis (as in obesity).

Pain usually is a gradual-onset deep axial ache that radiates to the scapular regions in the neck or to the buttocks and posterior thighs. It is associated with morning stiffness. The pain is reproduced by facet loading maneuvers by hyperextension and lateral rotation, which provokes pain ipsilaterally. Paraspinal tenderness often is present.165-166

MRI or CT can reveal arthritic changes in the facet joints, such as hypertrophy and joint space narrowing. The diagnosis can be confirmed by diagnostic block of the joints or of the medial branches innervating them.

Treatment is conservative, consisting of oral analgesics, weight loss, and physical therapy (PT). Intrajoint steroid injection can be attempted. Radiofrequency ablation of the medial branches appears to be promising.167,168

Sacroiliac Arthropathy

The sacroiliac joint connects the sacrum to the iliac bones. It is subject to degenerative and inflammatory arthritides as well as mechanical dysfunction. The pain usually is precipitated by an injury, such as falling, lifting, or turning. The pain is a unilateral ache that radiates to the buttock, groin, and thigh area. It rarely goes below the knee. The pain is worsened by loading the joint, as occurs during prolonged sitting, standing, or bending. There is tenderness over the joint area, and the pain typically is reproduced by the Patrick test, in which the hip is forced into external rotation by placing the ankle on the opposite knee or thigh and pushing down on the knee. Intraarticular local anesthetic block can help confirm the diagnosis.

Treatment with NSAIDs and PT can be helpful. Fluoroscopy-guided intraarticular steroid injection has been the mainstay of treatment in clinical practice. Lateral branch block and radiofrequency ablation have been reported useful in advanced cases.169

Spinal Stenosis

Spinal stenosis results from narrowing of the central canal, lateral recesses, or neuroforamina due to age-related degenerative changes, including osteophyte formation, facet hypertrophy, ligamentum flavum hypertrophy, and diffuse broad-based disk bulge. Its occurrence in the cervical spine is referred to as cervical "spondylosis." When spinal stenosis occurs in people younger than 60 years, other comorbidities, such as diabetes or congenital stenosis due to short pedicles, scoliosis, and spondylolisthesis, should be ruled out.

Pain manifests as radicular when the narrowing occurs in the lateral recesses or neuroforamina. In the case of lumbosacral spinal canal stenosis, axial low back pain and neurogenic claudication are the predominant features.170 Neurogenic claudication worsens with walking (especially downhill) and with extension of the spine. Rest and flexion of the spine usually provide temporary relief.

Cervical spondylosis can progress and cause cervical spondylotic myelopathy (CMS) and cord compression of varying severity. Motor weakness, spasticity, hyperreflexia, Babinski sign, Hoffman sign, paresthesias, imbalance, bowel and bladder function, and other features of spinal cord compression should be carefully assessed. Acute cervical spondylotic myelopathy can occur as a result of abrupt hyperextension of the neck. Radiographic changes reflecting degeneration associated with stenosis are common with aging; thus clinical correlation is critical in the assessment and management of related symptom complexes.170

Treatment of spinal stenosis should start with conservative measures, including oral analgesics, translaminar or transforaminal epidural steroid injections, and PT. Surgical options should be preserved for cases with rapid neurologic progression, CMS, or cauda equina syndrome, or for patients who remain symptomatic despite a course of nonsurgical therapy and who have advanced imaging studies that correspond to existing symptoms. Surgical management of lumbar and cervical stenosis includes discectomy, neural decompression, and spinal arthrodesis. Several studies report that surgical treatment produces better outcomes than nonsurgical treatment in the short term; however, improved results tend to regress over time.171-175

Failed Back Surgery Syndrome

Failed back surgery syndrome refers to the persistence or recurrence of low back pain after surgical intervention on the lumbosacral spine. Potential causes of surgical intervention failure include the following60: (1) poor patient selection, (2) unindicated surgery, (3) inadequate surgical decompression, (4) recurrence of lesions, (5) established neural injury, (6) complications of diagnostic and/or surgical intervention, and (7) secondary instability or degeneration. One study found that the predominant specific diagnoses in patients with failed back surgery syndrome were (in order) foraminal stenosis, painful disk(s), pseudarthrosis, neuropathic pain, instability, and psychological problems. Recurrent disk herniation is seen less often than in the past.176

Physical examination and imaging studies are essential to confirm the diagnosis and rule out other emerging etiologies. Treatment should be focused on the specific underlying etiology and may include repeated surgical intervention. Epidurolysis of adhesions via epiduroscopy or by catheter technique has limited evidence of efficacy.177,178 Spinal cord stimulation was found to be both more effective and less costly than conservative medical management over the lifetime of a patient.179-181

Whiplash Injury

Whiplash injury refers to neck injury caused by abrupt hyperextension due to indirect force, as occurs with acceleration–deceleration mechanisms. Whiplash injury is estimated to occur in 1% of the general population and to become chronic in up to 25% of these patients. Up to 60% of car accident victims evaluated in emergency departments have neck pain and up to 26% of them have persistent symptoms after 1 year.177 Cervical facet joint pain is the most common source of pain after whiplash injury. The most common cervical segments involved are C2-3 and C5-6.182,183

Physical examination is nonspecific and may reveal tenderness and limited range of motion. Patients who have normal plain radiographic findings and no evidence of a neurologic deficit do not require additional MRI.184

Diagnostic medial branch block is helpful in delineating etiologies and differentiating between facet arthropathy and other causes of neck pain. Treatment of acute whiplash injury is conservative and includes oral NSAIDs, PT, and transcutaneous electrical nerve stimulation unit.185 In chronic conditions where facet arthropathy is confirmed with diagnostic blocks, radiofrequency ablation appears to be promising.183,186

Head Pain

Headache is one of the most common symptoms encountered in clinical practice. A pain medicine physician should be familiar with the common types of syndromes and be able to provide appropriate management. The IHS provides valuable sources for the classification and diagnosis of different syndromes.97

The prevalence of headache in the United States is estimated to be 78% in women and 68% in men. In general, headache is classified as primary or secondary. Primary headaches are diseases by themselves, as seen with migraine, tension-type, and cluster headaches. Secondary headaches are caused by an underlying condition. Most headaches seen in clinical practice are primary headaches (˜90% or more).187 The most common headache is tension headache, with a prevalence of 78%. Migraine also is very common, with an estimated prevalence of 16%. Among secondary headaches, the most common cause is attributable to fasting. Nasal- and sinus-related headaches and head trauma are less common. Many fear that headaches are caused by intracranial disease such as tumors; however, this actually occurs in a very small percentage of the population (0.5%).188

Evaluation of headache requires thorough history and physical examination. Special attention should be given to any "red flags" that may point to a secondary disorder. In the absence of warning signs, most likely the headache is of a primary disorder, with most headaches being either tension-type or migraine. Even in the absence of warning signs, possible secondary headache disorder may exist in patients presenting with "atypical features," such as migraine with prolonged aura lasting more than 60 minutes, migraine that lacks characteristic features (eg, no nausea, photophobia, or phonophobia), and migraine that does not quite meet all the diagnostic criteria, especially if they do not respond to normal therapy. These are the signals that are frequently elicited in a headache evaluation.

The most important feature is the temporal profile of the headache, specifically the mode of onset. Headache with a rapid time to peak intensity should always suggest an underlying cause of secondary headache. Not only the mode of onset but also the age at onset is important, as headache onset after age 50 years should raise concern of secondary headache. Other "red flags" include association with systemic signs or symptoms; the presence of a new or different headache, particularly in those with systemic malignancy, which may signify intracranial disease (eg, metastases); a change in headache pattern, such as progressive headache with loss of headache-free period; and a change in frequency or severity of a previously existing headache disorder (because underlying secondary causes in patients with a history of migraine can mimic normal headache patterns). Any, even subtle, abnormal neurologic findings also should raise suspicion.189

Electroencephalography is not useful in the routine evaluation of patients with headache. However, electroencephalography may be useful in patients with headache who have an alteration of consciousness, encephalopathy, or focal neurologic deficits and atypical symptoms.190 Lumbar puncture (LP) is indicated in the evaluation of thunderclap or sudden headache to exclude the possibility of subarachnoid hemorrhage. CT can be negative in up to 25% of patients within 24 hours of occurrence of subarachnoid hemorrhage and can be negative in up to 50% of patients 1 week after initial presentation of headache resembling thunderclap. LP is indicated in any patient with subacute and progressive headache in order to exclude infections, an inflammatory condition, or carcinomatous meningitis. Any patient who presents with headache and fever, confusion, or seizure should be suspected of having acute intracranial infection. LP should be performed in patients with high or low intracranial pressure syndrome (idiopathic intracranial hypertension), even in the absence of papilledema. LP should be performed to confirm low-pressure states, as occurs with cerebrospinal fluid (CSF) leaks. In the absence of "red flags," CT or MRI typically is not performed unless a change in headache pattern occurs or the patient experiences changes in neurologic status as evidenced by seizures or focal neurologic signs or symptoms.191

Following is a discussion of IHS criteria for common headaches and a brief review of major treatment options.

Migraine

Multiple types of migraine exist. The more common types are discussed here.

Migraine Without Aura

Migraine without aura previously was called common migraine. Table 90-13 lists the IHS diagnostic criteria97 for migraine without aura.

Migraine with Aura

This type of headache previously was called classic migraine. It fulfills the criteria of migraine as described earlier and is associated with aura. The aura is a complex of neurologic symptoms that occurs just before or at the onset of migraine headache. A typical aura consists of visual and/or sensory and/or speech symptoms. It has gradual development, duration no longer than 1 hour, and complete reversibility.97 Some patients have typical aura without having a typical migrainous headache.

Treatment of migraine headaches is abortive and preventive. Abortive treatment is directed toward the acute attacks as they occur. Many drugs have been shown to be effective abortive medications. Nonspecific treatments, such as acetaminophen, aspirin and caffeine combination (Excedrin), and NSAIDs, are effective for simple and less severe migraines. Other nonspecific migraine agents include corticosteroids, antiemetics, and opioid analgesics. The migraine-specific agents are considered the mainstay abortive treatment of migraine. They include ergotamine, dihydroergotamine, and the more selective serotonin antagonists (triptans). Multiple triptans are available in different forms, half-lives, and potencies. Preventive treatment of migraine should focus on modifying and/or eliminating the triggering factors, such as sleep disturbance, caffeine intake, analgesics overuse, and stressors. Pharmacologic preventive treatment is indicated when migraine intensity, duration, or frequency is severe enough to warrant chronic use of a daily medication. Preventive treatment also is indicated for more serious forms of migraine, such as basilar-type migraine (migraine with neurologic signs of posterior circulation dysfunction), migraine with complications (focal neurologic features), and hemiplegic migraine. TCAs (eg, amitriptyline), nonselective beta-blockers (eg, propranolol), and AEDs (eg, topiramate and divalproex sodium) are effective preventive agents.

Tension-Type Headache

Tension-type headaches are the most common primary headache. Many features distinguish them from migraines. Each attack of tension-type headache can be much shorter or much longer than migraine. The pain generally is bilateral, is of mild to moderate intensity, is constant, and is not aggravated by movement or activity. Photophobia or phonophobia may be present but usually not both, and the patient experiences no nausea or vomiting. Tension-type headaches have a wide spectrum of frequency that varies from sporadic episodes to chronic forms.97

Infrequent episodes of tension-type headaches can be treated with simple analgesics. For more frequent and chronic forms, preventive treatment is essential.

Cluster Headache

Cluster headaches are much less common than tension-type and migraine headaches but are excruciatingly painful and devastating. Table 90-14 lists the IHS diagnostic criteria for cluster headaches.97

As for treatment of migraine headaches, treatment of cluster headaches is abortive and preventive. Abortive treatment consists of inhaled oxygen; triptans, especially the injectable form (sumatriptan); or dihydroergotamine. Multiple preventive agents can be tried. They include corticosteroids, hypertension medications (beta-blockers and calcium channel blockers), and lithium. In refractory cases, invasive treatments might be required. They include sphenopalatine ganglion blockade, trigeminal nerve and/or ganglion blockade, or deep brain stimulation.

Postdural Puncture Headache

Low-CSF pressure headache results from a dural tear and subsequent CSF leak. Postdural puncture headache is the more common type of low-CSF headache. The IHS diagnostic criteria for postdural puncture headache are listed in Table 90-15.97

Epidural blood patch at the expected site of leak remains the mainstay treatment. Conservative therapy includes bedrest, aggressive hydration, caffeine, and analgesics.

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