Neuromuscular reaction to paired stimuli.

A modification of the twin pulse method is described, by which the nerve tested is stimulated at one proximal site percutaneously and the neuromuscular response to it is derived from a dependent muscle. An electronic subtraction procedure provides separation of the conditioned muscle action potential for measurement by means of a microcomputer. Several parameters were determined in the conditioned action potential and compared to the same criteria in an unconditioned single action potential. Changes of the conditioned action potential were measured at fixed stimulus intervals between 2 and 6 msec. Preliminary normal ranges interindividually and intraindividually were established. Their dependency on skin surface temperature was determined. In polyradiculoneuropathy, the data for motor nerve conduction velocity were characteristically pathologic, and neuromuscular reaction to paired stimuli data deviated minimally from normal. In vincristine neuropathy, motor nerve conduction velocity was normal, but neuromuscular reaction to paired stimuli data fell outside the normal range early in the clinical course. Since polyradiculoneuropathy is a primary demyelinating and remyelinating process and vincristine neuropathy is an example of axonal degeneration, neuromuscular reaction to paired stimuli can facilitate the differential diagnosis in polyneuropathy. Furthermore, this method seems apt to quantify axonal degeneration. In a mixed form of polyneuropathy, peroneal muscular atrophy, motor nerve conduction velocity, as well as neuromuscular reaction to paired stimuli, were abnormal, the latter resulting in abnormally high relative amplitudes. In muscle disorders such as Duchenne muscular dystrophy, neuromuscular reaction to paired stimuli data was abnormal, contrasting experiments using double stimulation of the diseased muscle itself.