[Isolated inferior rectus muscle paresis from midbrain infarction]

A 74-year-old woman, with hypertension and dilated cardiomyopathy, presented with sudden onset of diplopia without vertigo and other neurological symptom. Examination revealed left inferior rectus muscle paresis. Other neurological findings were normal. She had no cerebellar ataxia and sensori-motor dysfunction. Magnetic resonance imaging showed increased signal intensity on T2-weighted and proton density-weighted images in the right ventral midbrain, compatible with infarction involving the fascicular oculomotor fibers. Complete resolution of the diplopia and normal ocular motility were noted 3 months after the onset of the diplopia. Focal ischemic midbrain lesions should be considered in cases of isolated partial oculomotor nerve paresis.