Myositis of the superior oblique muscle in a patient with suspected superior oblique muscle palsy.

Orbital myositis comprises a subtype of idiopathic orbital inflammation. Symptoms and clinical signs include orbital pain, eyelid swelling, ptosis, and conjunctival chemosis, sometimes concurrent with diplopia. Orbital myositis typically occurs in an idiopathic acute form and affects one or more extraocular muscles. It mainly involves the rectus muscles; cases involving the superior oblique muscle have been rarely reported. We report the case of a 57-year-old man with sudden-onset diplopia. Initial examination was suggestive of right superior oblique muscle palsy; however, myositis of the right superior oblique muscle was confirmed on magnetic resonance imaging (MRI). The patient was started on intravenous steroid pulse treatment. The steroid was tapered for 4 months. Diplopia, exotropia, and excyclotorsion of the right eye disappeared after 3 weeks of treatment. Cranial MRI obtained 2 months after starting treatment showed a normal superior oblique muscle. There has been no recurrence with 8 months of follow-up after completing the steroid taper.