Nystagmus in motor neuron disease: clinicopathological study of two cases.

Two patients with amyotrophic lateral sclerosis proved postmortem had nystagmus in addition to typical clinical signs of motor neuron disease. The first patient had gaze-evoked rotatory nystagmus that was followed by horizontal nystagmus in the primary position with supranuclear paresis of horizontal gaze and upgaze. The second patient had rotatory nystagmus that was evoked by lateral gaze, with normal range of eye movements. Nystagmus is so rare in motor neuron disease that these observations may imply another disease, but postmortem examination did not provide any other explanation. These two cases add to the increasing evidence that motor neuron disease comprises a heterogeneous group of disorders.