Dermatomyositis

A humorally mediated autoimmune disease characterized by vascular lesions and degeneration of the skin and muscle, leading to a typical rash, symmetric weakness, and some muscle atrophy, principally of proximal limb muscles.

Women are affected more often than men. Natural history data for onset after age 40 are not available. This immune disease results from a humorally dependent, antibody-mediated process directed against capillaries and other small blood vessels in muscle. About 10% of patients have a malignancy; breast and lung tumors are the most common, with a disproportionate increase in tumors of the ovary, uterus, and bowel. No consistent relationship exists between tumor discovery and onset of dermatomyositis.

Symptoms, Signs, and Diagnosis

A rash (usually the presenting feature) and muscle weakness are the major clinical signs; the rash can occur without the muscle weakness. The rash is reddish purple (heliotrope) and involves the periorbital regions; a more erythematous rash occurs on the malar regions, neck, shoulders, or extensor surfaces of the arms and legs. Gottron's papules are reddish, raised, scaly lesions over the extensor surfaces of the proximal interphalangeal and distal interphalangeal joints. Thickened, cracked cuticles with dilated capillary loops in the nail beds are also characteristic.

Weakness develops over weeks or months. Proximal limb muscles are typically weaker than distal muscles. Neck flexors are particularly weak. Muscles supplied by cranial nerves are typically spared, except for those involved with swallowing. Dysphagia, myalgia, and muscle tenderness occur in about 50% of patients. Involvement of other organs is not uncommon and includes the joints (arthralgias and arthritis), gastrointestinal tract (delayed gastric emptying and microvasculopathy causing intestinal ulceration or perforation), lungs (interstitial lung disease), and heart (conduction abnormalities and cardiomyopathy).

Blood muscle enzyme levels (especially CK levels) are elevated. The ESR is elevated in about 50% of patients, and the antinuclear antibody titer is elevated in about 25 to 50%.

Diagnosis is suggested by the clinical findings and elevation of muscle enzyme levels. Muscle biopsy shows characteristic perifascicular atrophy of muscle fibers, a decreased number of capillaries, and perivascular infiltrates. Electromyographic findings indicate muscle inflammation.

Prognosis and Treatment

Death may follow severe and progressive muscle weakness accompanied by dysphagia, malnutrition, aspiration pneumonia, or respiratory failure with superimposed pulmonary infection. Prognosis in patients with malignancy-associated myositis is generally determined by the prognosis of the tumor. Prognosis is usually poorer if the rash is necrotizing and muscle weakness is present.

During the acute stages, most patients benefit from immunosuppressive therapy and bed rest. Usually, prednisone is started at 1 to 2 mg/kg/day (60 to 100 mg/day) po. To permit use of the lowest possible dosage of prednisone for the shortest time, another immunosuppressant (eg, azathioprine 2 to 3 mg/kg/day in divided doses) po may be used concomitantly; in many patients, azathioprine is effective as monotherapy after 12 to 18 months of treatment. IV immune globulin therapy is effective and offers an excellent second-choice therapy, even before other immunosuppressants (eg, azathioprine, methotrexate), in patients who cannot achieve full recovery with corticosteroid treatment. Immune globulin can produce headaches, fever, flu-like illness, and, occasionally, meningitis or renal failure. However, these adverse effects are less likely to occur if the drug is given in small infusions (0.4 to 0.5 g/kg/day) to reach a total dose of 2 g/kg. Long-term management includes physical therapy, frequent monitoring of muscle strength, and regular physical activity.

Elderly patients require frequent evaluation for occult tumors, especially in the breast and lung. No predictable relationship exists between tumor removal and resolution of myopathy, but some patients have remarkable recoveries.