Idiopathic orbital myositis.

Idiopathic orbital myositis is a subtype of nonspecific orbital inflammation primarily involving the extraocular muscles. It occurs most frequently in young to middle-aged adults with a 2 to 1 female predominance. The cardinal clinical feature is orbital pain exacerbated by eye movement. Other common findings include diplopia, proptosis (which is generally minimal), conjunctival injection and chemosis, and periorbital edema. Thyroid eye disease is commonly confused with orbital myositis, but the latter is characterized by a more acute onset, more severe pain, and a rapid response to systemic corticosteroid therapy. Echography and CT scanning reveal enlarged muscle bellies and thickened tendons, with low internal reflectivity echographically. Although the cause of orbital myositis is unknown, an immune-mediated pathophysiologic mechanism is likely. This review summarizes recent findings regarding the epidemiology, diagnosis, pathophysiology, and treatment of idiopathic orbital myositis.