Pain may be classified according to pathophysiology (eg, nociceptive or neuropathic pain), etiology (eg, arthritis or cancer pain), or the affected area (eg, headache or low back pain).
Nociceptive pain is caused by activation or sensitization of peripheral nociceptors, specialized receptors that transduce noxious stimuli. Neuropathic pain is the result of injury or acquired abnormalities of peripheral or central neural structures.
Acute pain is caused by noxious stimulation due to injury, a disease process, or the abnormal function of muscle or viscera. It is almost always nociceptive.
Chronic pain is pain that persists beyond the usual course of an acute disease or after a reasonable time for healing to occur, typically 1 to 6 months. Chronic pain may be nociceptive, neuropathic, or mixed.
Modulation of pain occurs peripherally at the nociceptor, in the spinal cord, or in supraspinal structures. This modulation can either inhibit (suppress) or facilitate (intensify) pain.
At least three mechanisms are responsible for central sensitization in the spinal cord: (1) wind-up and sensitization of second-order wide dynamic range neurons; (2) dorsal horn neuron receptor field expansion; and (3) hyperexitability of flexion reflexes.
Chronic pain may be caused by a combination of peripheral, central, and psychological mechanisms.
Moderate to severe acute pain, regardless of site, can affect the function of nearly every organ and may adversely influence perioperative morbidity, mortality, and convalescence.
The evaluation of any patient with pain should include several key components. Information about location, onset, and quality of pain, as well as alleviating and exacerbating factors, should be obtained along with a pain history that includes previous therapies and changes in symptoms over time.
Psychosocial evaluation is useful whenever medical evaluation fails to reveal an apparent cause for pain, pain intensity is disproportionate to disease or injury, or when psychological or social issues are apparent.
Myofascial pain syndromes are common disorders characterized by aching muscle pain, muscle spasm, stiffness, weakness, and, occasionally, autonomic dysfunction.
Ninety percent of disc herniations occur at L5–S1 or L4–L5. Symptoms usually develop following flexion injuries or heavy lifting and may be associated with bulging, protrusion, or extrusion of the disc.
Back pain caused by spinal stenosis usually radiates into the buttocks, thighs, and legs. Termed pseudoclaudication or neurogenic claudication, this pain is characteristically worse with exercise and relieved by rest, particularly sitting with the spine flexed.
Diabetic neuropathy is the most common type of neuropathic pain.
Complex regional pain syndrome (CRPS) is a neuropathic pain disorder with significant autonomic features that is usually subdivided into two variants: CRPS 1, formerly known as reflex sympathetic dystrophy (RSD), and CRPS 2, formerly known as causalgia. The major difference between the two is the absence or presence, respectively, of documented nerve injury.
Trigeminal neuralgia (tic douloureux) is classically unilateral and usually located in the V2 or V3 distribution of the trigeminal nerve. It has an electric shock quality, with episodes lasting from seconds to minutes, and ...