Idiopathic orbital myositis: report of six cases.

Idiopathic orbital myositis, a subgroup of inflammatory orbital pseudotumor, occurred in six patients with acute onset periorbital pain, diplopia, and in most cases, eyelid swelling. Proptosis, ductional restrictions, and responsiveness to oral prednisone administration were characteristic. Computed tomography and orbital ultrasonography showed enlargement of one or more extraocular muscles, with sparing of other orbital soft tissues. One patient had involvement of all recti muscles in both orbits. The distinction of orbital myositis from Graves' ophthalmopathy is made on clinical grounds, with acute orbital pain and corticosteroid responsiveness being uncharacteristic of the latter. The possibility of orbital myositis being an immune-mediated process is discussed.