Shaky hands are a part of motor neuron disease phenotype: clinical and electrophysiological study of 77 patients.

Involuntary movements are common, but poorly recognized feature of motor neuron disease that may add to functional impairment. Results of our study suggest that involuntary movements are likely of peripheral origin, with a non-fused contraction of enlarged motor units being a common driving mechanism. Minipolymyoclonus appears if no synchronization of motor units occurs. When synchronization occurs via stretch reflex, mechanical-reflex tremor is generated.