Long-term Outcome in 7 Patients With Idiopathic Orbital Myositis

PURPOSE: Idiopathic orbital myositis, a rare disease of unknown cause, presents a diagnostic puzzle because the diagnosis is based on the exclusion of other diseases. This study aims at elucidating its long-term outcome to answer a clinical question whether idiopathic orbital myositis would be a distinct clinical entity. METHODS: Retrospective review was made on 7 consecutive patients (6 men and 1 woman) with the age at the initial visit ranging from 33 to 69 years (mean, 45.8 years) who were diagnosed with idiopathic orbital myositis and followed for 5 years or more (mean, 9.2 years) at a referral-based hospital. RESULTS: Chief complaint at the initial visit was diplopia in 4 patients, blurred vision in 2 patients, and proptosis in 1 patient. On magnetic resonance imaging, 4 patients showed enlargement of a single extraocular muscle on unilateral side while 3 patients showed enlargement of multiple extraocular muscles on unilateral side or bilateral sides. No patient developed systemic diseases or other orbital lesions in the long-term follow-up. All patients at the last visit were free from symptoms, including diplopia, after tapering of prednisolone at the initial dose of 20 to 60 mg daily. CONCLUSION: Idiopathic orbital myositis had a favorable long-term outcome with corticosteroid administration and appears to be a distinct clinical entity without systemic involvement.