Idiopathic Orbital Myositis Revisited.

PURPOSE OF REVIEW: To review current knowledge regarding idiopathic orbital myositis. RECENT FINDINGS: Recent publications have focused on possible causes of orbital myositis and the process to reach a diagnosis of idiopathic orbital myositis. With inflamed and enlarged extraocular muscles, features to distinguish between competing diagnostic possibilities are based on imaging in the context of history and clinical signs. Idiopathic orbital myositis is characterized by the clinical triad of acute onset of orbital pain exacerbated on eye movement, double vision, and redness or swelling of the eyelids or conjunctiva, along with the radiological finding of homogeneous, fusiform enlargement of one or more extraocular muscles. In atypical or inconclusive clinico-radiological findings for a diagnosis of idiopathic orbital myositis, or where the clinical behavior changes or fails to respond to corticosteroid treatment, a systemic and oncologic work-up and muscle biopsy are warranted to exclude specific local or systemic disease as cause of the inflamed and enlarged muscle. As our understanding of idiopathic orbital myositis evolves, the diagnostic focus is shifting toward earlier identification of underlying local or systemic disease through systemic work-up and muscle biopsy.