LAUSR

A 62-year-old man presented with the acute onset of diplopia. His medical history included well-controlled hypertension, hypercholesterolemia, and polymyalgia rheumatica (PMR) that was treated 2 years previously with steroids. The PMR was in remission at the time of presentation. The patient presented to an outside ophthalmologist with binocular vertical diplopia and moderate-to-severe headache of 1-week duration. On examination, he was found to have a 10-prism diopter exotropia with reduced adduction of the left eye and horizontal dissociated abduction nystagmus of the right eye on right gaze, suggestive of an internuclear ophthalmoplegia (INO). He also had a left hypertropia in right gaze (Fig. 1).