A Middle-Aged Man With Diplopia, Headache, and Hyperglycemia.

A 60-year-old man with a history of diabetes mellitus and hypertension presented with diplopia and vertigo for two days. These symptoms had a gradual onset, were progressive, and were associated with a headache that had been present for 15 days. His blood sugar level was 376 mg/dl. His convergence and ability to adduct when looking laterally were affected bilaterally. Additionally, he presented with right exotropia on primary gaze and no ptosis. Brain imaging was normal. Following the rest of the work-up, diabetes mellitus was independently established as the cause of bilateral internuclear ophthalmoplegia in this patient. High blood sugar affects the brain at the molecular level by causing vascular damage, oxidative stress, and decreasing neuroplasticity.