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

Nimish J Thakore,R John Leigh,Erik P Pioro,Janet C Rucker

doi:10.1186/1471-2377-6-3

Nimish J Thakore, R John Leigh + Show 2 more

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https://doi.org/10.1186/1471-2377-6-3

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BackgroundEye 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 presentationAll 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.ConclusionThe 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.

Highlights

Eye movements are clinically normal in most patients with motor neuron disorders until late in the disease course
We report 3 patients with a distinctive, sporadic motor neuronopathy characterized by early wrist drop, prolonged survival, and downbeat nystagmus
The key features of the syndrome we have described are (1) clinical and electrodiagnostic findings of progressive loss of anterior horn cells, (2) early and disproportionately severe involvement of finger and wrist extensors, (3) relative sparing of facial, pharyngeal, tongue and respiratory musculature, (4) prolonged survival, (5) lack of a family history of similar disorder, and (6) eye movement abnormalities, downbeat nystagmus

Summary

Background

Eye movements are usually spared in motor neuron disorders, such as amyotrophic lateral sclerosis (ALS), spinal muscular atrophy, Kennedy's disease and poliomyelitis. Standing apart from this classic picture is a subset of patients ALS in whom disordered eye movements are clinically evident early in the course Such patients are variously reported to show slowing of vertical saccades [6], gaze-evoked horizontal or rotary nystagmus[7], and impairment of smooth pursuit[8]. Eye movement measurements confirmed downbeat nystagmus, which increased on lateral and down gaze, following head shaking (especially vertically) and during convergence (Fig. 1). Optic fundi and visual fields were normal She had a full range of eye movements, but downbeat nystagmus was evident, especially on lateral and down gaze. Patient 3 was examined by various neurologists at two institutions between 1984 and 1990 and was subsequently lost to follow-up His first symptoms were weakness of extension of the left little finger in 1982 at the age of 40 years.

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