Dermatomyositis is a clinically distinct myopathy characterized by rash and a complement-mediated microangiopathy that results in the destruction of muscle fibers. In some patients the condition becomes resistant to therapy and causes severe physical disabilities.

We conducted a double-blind, placebo-controlled study of 15 patients (age, 18 to 55 years) with biopsy-proved, treatment-resistant dermatomyositis. The patients continued to receive prednisone (mean daily dose, 25 mg) and were randomly assigned to receive one infusion of immune globulin (2 g per kilogram of body weight) or placebo per month for three months, with the option of crossing over to the alternative therapy for three more months. Clinical response was gauged by assessing muscle strength, neuromuscular symptoms, and changes in the rash. Changes in immune-mediated muscle abnormalities were determined by repeated muscle biopsies.

The eight patients assigned to immune globulin had a significant improvement in sores of muscle strength (P < 0.018) and neuromuscular symptoms (P < 0.035), whereas the seven patients assigned to placebo did not. With crossovers a total of 12 patients received immune globulin. Of these, nine with severe disabilities had a major improvement to nearly normal function. Their mean muscle-strength scores increased from 74.5 to 84.7, and their neuromuscular symptoms improved. Two of the other three patients had mild improvement, and one had no change in his condition. Of 11 placebo-treated patients, none had a major improvement, 3 had mild improvement, 3 had no change in their condition, and 5 had worsening of their condition. Repeated biopsies in five patients of muscles whose strength improved to almost normal showed an increase in muscle-fiber diameter (P < 0.04), an increase in the number and a decrease in the diameter of capillaries (P < 0.01), resolution of complement deposits on capillaries, and a reduction in the expression of intercellular adhesion molecule 1 and major-histocompatibility-complex class I antigens.

High-dose intravenous immune globulin is a safe and effective treatment for refractory dermatomyositis.