Myokymia, muscle hypertrophy and percussion "myotonia" in chronic recurrent polyneuropathy.

Three unusual features were observed in a patient with chronic relapsing polyneuropathy: myokymia, muscle hypertrophy, and prolonged contraction in response to muscle percussion. Low nerve conduction velocity and conduction block were demonstrated in all motor nerves tested, indicating a demyelinating peripheral neuropathy. Myokymia was caused by spontaneous motor unit activity which was shown to originate in peripheral nerves, since it persisted after nerve block and was abolished by regional curarization. Muscle hypertrophy was attributed to increased peripheral nerve activity, and the prolonged contraction of muscle in response to direct percussion was attributed to irritability of intramuscular nerve terminals.