[Ipsilateral oculomotor nerve palsy and contralateral downbeat nystagmus due to unilateral paramedian thalamopenduncular infarction--a case report].

A case of midbrain and thalamic infarction which showed complete oculomotor nerve palsy of the ipsilateral eye and monocular downbeat nystagmus, ptosis, upward movement disturbance and adduction disturbance of the contralateral eye was reported. The patient is a 53-year-old woman who was admitted to our hospital because of sudden onset of double vision. Head magnetic resonance imaging showed unilateral midbrain and thalamic infarction. The midbrain lesion was located in the paramedian area and the bilateral ptosis, bilateral upward gaze palsy and adduction disturbance of the contralateral eye were considered to be caused by the lesion involving the unilateral oculomotor nucleus. This case is considered to be important because the association of contralateral monocular downbeat nystagmus is very rare.