Unilateral Isolated Trochlear Nerve Palsy due to Ipsilateral Midbrain Infarction.

Ischemic stroke is a very rare etiology in cases of isolated trochlear nerve palsy, and no reports of ipsilateral trochlear nerve palsy caused by unilateral stroke have so far been published. However, we now report a case of isolated trochlear nerve palsy due to ipsilateral dorsal small midbrain infarction in a 70-year-old woman who presented with acute onset of diplopia. There were no other clinical manifestations, but brain magnetic resonance imaging revealed a small ischemic lesion in the right dorsal midbrain, showing that isolated trochlear nerve palsy can be caused by stroke.