The arthritis of inflammatory childhood myositis syndromes

Arthritis has been an associated finding in juvenile dermatomyositis (JDM), but its prevalence, course, and response to therapy has not been well described. We investigated the frequency, course, and clinical and radiographic features in a large cohort of patients with JDM.

The charts of 94 patients with idiopathic myositis (1984-99) were reviewed: 80 JDM, 3 juvenile polymyositis (JPM), 5 amyopathic JDM, and 6 overlap myositis syndromes. Compiled data included demographics, clinical features, a detailed description of the arthritis, investigations (radiographs, autoantibodies), course, and response to therapy. All radiographs were independently reviewed by a single radiologist.

Sixty-one percent (95% CI 50-72%) of patients with JDM had arthritis. The arthritis was reported a median 4.5 mo (range -73.6 to 76.6 mo) after the JDM onset. When compared to patients with no arthritis, the occurrence of arthritis was not significantly related to sex, race, positive antinuclear antibody or rheumatoid factor, calcinosis, nodules, vasculitis, or Raynaud's phenomenon. The initial involvement was pauciarticular in 67% and polyarticular in 33%. In the pauci group, asymptomatic knee effusions were the predominant finding (n = 19, 58%), and in 18 patients may have been the result of steroid therapy. Two patients evolved from a pauci onset to a polyarticular course. All responded to therapy (corticosteroids; 47 were taking other medications) with remission of the arthritis within a median of 2.0 mo (range 0.1-64.5 mo). However, the arthritis recurred in 39% as the corticosteroids were tapered. Four patients with JDM eventually required corticosteroid wrist injections, with resolution of the arthritis. The arthritis was nonerosive in all cases. No patient with JPM had arthritis. Three of 5 patients with amyopathic JDM and 4 of 6 with overlap myositis syndrome had a nonerosive polyarthritis.

Nonerosive arthritis involving the knees, wrists, elbows, and fingers is a frequent manifestation of JDM and other idiopathic childhood myositis. The arthritis is seen early in the course of JDM and often responds to treatment. However, the arthritis may recur with tapering of corticosteroids despite remission of the JDM. In a significant proportion of JDM cases, arthritis is the major sequela and may warrant further medical therapy or intraarticular corticosteroid injections.