A 37-year-old Asian nonsmoking man with no known medical or drug history presented with an insidious onset of left-eye ptosis (only brought to attention by his friends on review of recent photographs) and subsequent painless vertical diplopia for 1 year. He did not complain of headaches, facial numbness, dysarthria, facial droop, dysphagia, or limb weakness or numbness. There was no history of joint pain or constitutional symptoms.
Neurological examination revealed a nonfatigable partial left-eyelid ptosis, left-eye hypotropia at primary position, and impaired left eye supraduction (Figure 1) with a nonreactive left pupil on direct and consensual light reflexes. There were no other cranial nerve deficits. Limb reflexes, motor testing, and sensory testing results were normal, and the plantar responses were flexor.