Association of lower motor neuron disorders with fasciculation, neuromyotonia and myoclonus.

Fasciculations may be generated at any point on a hyperexcitable lower motor neuron. Physiological ('benign') fasciculations often begin suddenly and persist for years without development of muscular wasting or weakness. Fasciculations may be a sign of degeneration of lower motor neurons in which case they may be associated with muscle cramps and neuromyotonia. Both sensory and motor axons are overactive in neuromyotonia, the symptoms of which are relieved by administration of anticonvulsants such as carbamazepine. Spinal muscular atrophy is a feature in some cases of progressive myoclonic epilepsy of the systems degeneration type that may be overlooked because muscular wasting is overshadowed by the dramatic appearance of action myoclonus.