Hyperexcitability of motor and sensory neurons in neuromyotonia

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Ann Neurol. 1979 Jun;5(6):523-32.

Hyperexcitability of motor and sensory neurons in neuromyotonia.

Lance JW, Burke D, Pollard J.

Two members of a family with a neuropathy resembling Charcot-Marie-

Tooth disease were unable to relax their muscles after voluntary

contraction. Muscle spasm often outlasted voluntary contraction by 30

seconds or more before subsiding into myokymia and fasciculations.

The posture of the hand during muscle spasm resembled that of tetany,

and Trousseau's and Chvostek's signs were present although no

abnormality of calcium or magnesium metabolism could be demonstrated.

Muscle spasms ceased during medication with carbamazepine, 600 mg

daily.

Nerve stimulation, electromyography, and regional neuromuscular

blockade with curare indicated that the condition originated in

peripheral nerve, while microneurographic recordings showed that

sensory as well as motor fibers were hyperexcitable. Sural nerve

biopsy revealed axonal degeneration involving myelinated and

unmyelinated fibers.

It was concluded that the neural hyperexcitability is caused by a

membrane defect resulting in a low threshold for excitation

throughout the length of the axon.