The changes in nerve conduction in acute idiopathic polyneuritis

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Abstract
Serial electrophysiological measurements of both motor and sensory nerve function of the hand were made in a patient with acute idiopathic polyneuritis. It was hoped that this study would aid in explaining the nature of the reversible disturbance of nerve conduction associated with this disease. In the acute stage of the illness there is an actual failure of nervous conduction in myelinated fibres, probably to the elbow, and this agrees with the clinical impairment of sensation. At this time there was almost complete paralysis and this must have been due to a failure of conduction in nearly all the motor axons. During the recovery stage sensation was noted as early as the twenty-fourth day and completely restored seven weeks after the onset of the illness. Clinical testing showed that motor power returned to normal again. This indicated that a large proportion of previous nonconducting fibers had functionally re-innervated muscle fibers. The conduction velocity, however, of the fastest fibers was somewhat slower than that of the fibers still conducting during the acute stage of the illness. This indicated that those fibers which had survived the first stage of the disease were affected subsequently. This continuation of the disease process was not apparent clinically. In acute polyneuritis only the terminal portions of the motor and sensory fibers are severely affected. This may aid in explaining the rapid recovery. The electrical excitability of the nerve membrane is not lost but the "local" circuit currents necessary for conduction are inactivated. This process may be similar to experimental "demyelina-tion". Although Wallerian degeneration may occur in severe cases of acute idiopathic polyneuritis, in milder cases with recovery it is more likely that the myelin sheath is damaged but the nerve retains its structural integrity.

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