Motor neuronopathy with dropped hands and downbeat nystagmus: a distinctive disorder? A case report

Abstract

Background: Eye movements are clinically normal in most patients with motor neuron disorders until late in the disease course. Rare patients are reported to show slow vertical saccades, impaired smooth pursuit, and gaze-evoked nystagmus. We report clinical and oculomotor findings in three patients with motor neuronopathy and downbeat nystagmus, a classic sign of vestibulocerebellar disease.

Case presentation: All patients had clinical and electrodiagnostic features of anterior horn cell disease. Involvement of finger and wrist extensors predominated, causing finger and wrist drop. Bulbar or respiratory dysfunction did not occur. All three had clinically evident downbeat nystagmus worse on lateral and downgaze, confirmed on eye movement recordings using the magnetic search coil technique in two patients. Additional oculomotor findings included alternating skew deviation and intermittent horizontal saccadic oscillations, in one patient each. One patient had mild cerebellar atrophy, while the other two had no cerebellar or brainstem abnormality on neuroimaging. The disorder is slowly progressive, with survival up to 30 years from the time of onset.

Conclusion: The combination of motor neuronopathy, characterized by early and prominent wrist and finger extensor weakness, and downbeat nystagmus with or without other cerebellar eye movement abnormalities may represent a novel motor neuron syndrome.

Figure 1

Representative record of downbeat nystagmus in Patient 1, which increased with convergence. Positive values indicated rightward, upward, or convergence movements.

Figure 2

MRI brain of patient 2 showing atrophy of cerebellum.

Figure 3

Representative record from Patient 2, showing downbeat nystagmus on left-gaze and a burst of horizontal saccadic oscillations. On the inset at right, the saccadic oscillations are shown at a different time scale; note that an intersaccadic interval (marked by asterisk) is present for some, but not all, cycles. Same conventions as in Figure 1.