Dermatomyositis and Polymyositis

Both diseases belong to a group of connective tissue disorders known as idiopathic inflammatory myopathies. They are a multisystem disease characterized by necrotizing inflammatory myopathy of striated muscles and a skin rash, both of unknown etiology.

Approximately 5-10:100,000 in the general population. Female preponderance (male-to-female ratio = 1:2) but no racial predisposition.

Both are autoimmune-mediated diseases, but the mechanisms are different and the exact etiology is unknown.

• Primary idiopathic polymyositis (adult)
• Primary idiopathic dermatomyositis (adult)
• Childhood dermatomyositis or polymyositis with necrotizing vasculitis
• Polymyositis associated with connective tissue disorder (i.e., overlap syndrome, mixed connective tissue syndrome)
• Polymyositis or dermatomyositis associated with malignant tumors

Whether the pathophysiologies for dermatomyositis and polymyositis are different or the same is controversial. For some authors, these two diseases differ from each other mainly by the presence of dermatologic features (dermatomyositis) or the lack thereof (polymyositis). In the opinion of the proponents of a different pathophysiology, the two diseases differ as follows:

• Dermatomyositis: Activation of the humoral part of the immune system with antibodies directed against small arterioles and capillaries of the muscles seems to be the main culprit. Deposition of the complement factors C5b-9 (so-called membrane attack factor) results in antibody-mediated cell death. As the inflammatory process continues, capillary destruction results in atrophy, necrosis of muscle fibers, and, finally, muscle weakness and muscle tenderness.
• Polymyositis: Abnormal cellular immune response is considered responsible for the symptoms of this disease. Some evidence exists for a cytotoxic, T-cell-mediated attack directed toward muscular components. The factors triggering this cascade are unknown, but viruses could play a role (picornavirus-like structures have been found in affected muscle cells). Electron microscopy revealed tubular inclusions in endothelial cells of affected skin and muscle vessels and in surrounding monocytes, similar to those seen in other viral infections. Other viruses that have been blamed include retroviruses (HIV, HTLV-1) and coxsackievirus B.

Pathognomonic features are heliotrope rash (violaceous erythema and edema) of the periorbital region and the eyelids, a reddish rash on the face and upper torso, and Gottron papules (violaceous-colored papules found on metacarpophalangeal and distal interphalangeal joints [knuckles] and the extensor aspects of knees and elbows). Sun exposure can exacerbate the skin lesions. Dilated cuticular telangiectasias at the base of the fingernails also are characteristic for dermatomyositis. Muscle biopsy, if obtained, detects degeneration and necrosis of muscle fibers that cause them to lose their staining characteristics so that the cytoplasm appears empty, resulting in the term ghost fibers. These changes combined with inflammatory cell infiltrates around blood vessels enforce the diagnosis of dermatomyositis. Four of the five following diagnostic criteria must be present for definite diagnosis: (1) cutaneous lesions typical for dermatomyositis; (2) elevated muscle enzyme levels (creatine kinase, transaminases, aldolase, lactate dehydrogenase); (3) progressive, proximal, symmetrical muscle weakness (shoulder and hip) developing over weeks to months; (4) pathologic electromyography (EMG), and (5) typical findings on muscle biopsy.

Childhood onset usually occurs between 5 and 15 years of age. Dermatomyositis in children is similar to the adult form. However, healing of affected muscles by fibrosis, which may result in incapacitating contracture deformities (flexion contractures of the ankles often result in a tiptoe gait), gastrointestinal ulcers, and infections, seem to be more common in children. Anemia is common as a result of gastrointestinal ulcerations and hemorrhages. In addition to these ulcerations with melena and/or hematemesis, extensive bowel infarctions caused by necrotizing arteritis can complicate the course of the disease. Progressive weakness of proximal muscles is present, usually in combination with elevated serum levels of creatinine phosphokinase (not mandatory), transaminases (aspartate aminotransferase [ASAT], alanine aminotransferase [ALAT]), lactate dehydrogenase, and aldolase. Results of EMG are abnormal. The degree of weakness can range from mild to severe, and even quadriparesis has been reported. Weakness of swallowing musculature (dysphagia), intercostal muscles, and the diaphragm may lead to problems with airway protection and respiration (10% of cases). Myocardial fibrosis can cause arrhythmias (heart block), ventricular dysfunction (dilated cardiomyopathy), and heart failure. Interstitial lung disease may be present and usually is mild (these patients often are anti-Jo-1 antibody [a myositis-specific antibody] positive). Use of steroids has improved mortality but with the expense of inherent problems of steroid therapy. Additional immunosuppressive drugs may be needed. A negative nitrogen balance is present when the disease is active. Sensation is not altered, and tendon reflexes are preserved unless the muscle strength is severely compromised by the inflammatory process. Death usually results from respiratory failure, heart failure, or a complicating infection. Up to 20% of adult cases (especially when the rash is present and the age of onset is late) are associated with occult neoplasms (lung, breast, ovary, stomach, prostate, nonmelanoma skin cancer), and dermatomyositis is considered a paraneoplastic syndrome in these patients. Steroids, salicylates, and immunosuppressives (azathioprine, cyclophosphamide, intravenous immunoglobulins) are used to suppress the inflammatory process. Subcutaneous calcifications can cause skin ulcerations and infections when they protrude through the skin.

Obtain a full history of motor milestones and of complications following previous surgeries. Evaluate pulmonary function (forced vital capacity [FVC], peak expiratory flow rate, forced expiratory volume in 1 second [FEV1], FEV1:FVC ratio, arterial blood gas analysis). Evaluate cardiac function (ECG, echocardiography, radionuclide imaging when necessary). Preoperative laboratory investigations should include hemoglobin level, arterial blood gas analysis, and serum levels of total protein and albumin. Calculate the nitrogen balance if active disease is present. Serum creatinine phosphokinase and serum myoglobin levels are said to be the most sensitive indicators of disease activity. Perform a systemic assessment for other associated autoimmune disorders. Review drug therapy and possible complications. Continue steroid coverage and give additional perioperative stress prophylaxis.

A high complication rate is expected in the presence of muscle weakness, respiratory insufficiency, and cardiac dysfunction. Mechanical ventilation may be necessary following major surgery. Endotracheal intubation should be performed to minimize the risk of pulmonary aspiration in view of difficulties with swallowing and the resulting pooling of oral secretions. A rapid-sequence induction should be used if pharyngeal, esophageal, or gastric symptoms are present. Some papers have recommended avoiding malignant-hyperthermia triggering agents in the presence of muscle pathology. Avoid intramuscular injections. Extubation and termination of assisted ventilation should follow measurement of lung volumes (e.g., tidal volume, minute volume). Because of the risk of aspiration, tracheal extubation may be performed with the patient in the lateral position. If preoperative pulmonary function was significantly reduced, short-term postoperative ventilatory support following major surgery should be anticipated. Postoperative chest physiotherapy should be provided when necessary to minimize pulmonary complications.

In the presence of muscle weakness, small incremental doses of neuromuscular blockers should be used and the effects monitored by a peripheral nerve stimulator. Normal response to neuromuscular blockers has been reported. Both normal and increased sensitivity to nondepolarizing neuromuscular blockers have been reported. Acute inflammation of muscles is present in the acute form of the disease, so suxamethonium should be avoided because of the possibility of hyperkalemia. Titrate opioids to avoid respiratory depression.

Amyotrophic Lateral Sclerosis: Degenerative motor neuron disease evolving to progressive muscle weakness resulting in paralysis.

Myasthenia Gravis: Neuromuscular disorder characterized by muscle weakness and rapid muscle fatigue. Usually apparent during adulthood, but onset may occur at any age. Most individuals present eyelid ptosis, diplopia, and excessive muscle fatigue following exercise. Other features commonly include dysarthria, dysphagia, and proximal limb weakness. Approximately 10% may develop potentially life-threatening complications as a result of severe respiratory depression (myasthenic crisis).