Isolated Unilateral Ptosis due to Paramedian Midbrain Infarction

A 59-year-old man who had hypertension, dyslipidemia, diabetes mellitus, and left eye glaucoma developed sudden vertigo and left ptosis; he did not notice diplopia. He visited our hospital on day 3 after onset and neurologic examination showed left ptosis. His left visual acuity was counting fingers, and the light reflex was sluggish owing to glaucoma. Pupil sizes were equal, and eye movements and the lower lid were unremarkable. Magnetic resonance images revealed an acute infarction of the left paramedian midbrain. We considered that selective damage to the oculomotor fascicles innervating the left levator palpebrae superioris caused ipsilateral ptosis. As the fascicles for this ocular muscle run in the small area adjacent to those for the medial rectus, inferior rectus and superior rectus muscles, this is an extremely rare case of midbrain infarction presenting with isolated unilateral ptosis.