Clinical and echographic findings in idiopathic orbital myositis.

We performed a retrospective chart review of 100 patients with idiopathic orbital myositis, who were of ages 9 to 84 years. Data from 75 patients gave the following results. Females were affected more than twice as often as males. Fifty-one patients (68%) had single muscle involvement, with the lateral and medial recti affected most frequently (38 cases [33%] and 33 cases [29%] of muscles, respectively). In 34 patients (45%), affected muscles functioned normally; the remaining 55% (63 muscles) were fairly equally distributed between paretic (20%), restrictive (20%), or combined paretic and restrictive (15%) myopathies. Analysis of muscle function, echographic findings, and duration of symptoms indicates that within days of onset of symptoms, the affected muscle is initially enlarged but retains normal function. Within the first two weeks, continued enlargement results in muscle paresis. The muscle may then enter a partially or completely restrictive phase, which may become permanent. Fifty-one patients (68%) responded well to systemic corticosteroids, although 11 patients (15%) had further recurrences of the disease. Seven patients (9%) later developed thyroid eye disease after initially having unimuscular orbital myositis. We advocate early institution of corticosteroids in order to avoid permanent restrictive myopathies.