An uncommon cause of diplopia: do not forget Brown syndrome

A 30-year-old woman developed a new-onset orbital pain and vertical binocular diplopia in the right upgaze within 3 days. An examination revealed normal primary gaze position and left hypotropia in the right upgaze ([Figure 1]), unreversed with forced duction. The pupils and left eye excycloduction were normal. A magnetic resonance imaging (MRI) scan revealed superior oblique muscle (SOM) tenosynovitis ([Figure 2]). No infectious, autoimmune, metabolic or rheumatological etiologies were identified, and we concluded it was a case of idiopathic Brown syndrome (BS). The symptoms were resolved within one week of the administration of prednisone.