Abstract
The present study compares the results of sensory evoked potentials after stimulation of the tibial nerve with measurements of short (M1), medium (M2) and long-loop latency (M3) responses of leg muscles in 42 patients suffering from multiple sclerosis. EMG responses were elicited by a movable platform which was tilted in pitch toe-up around the subject's ankle joint. The short latency response of the triceps surae muscle was nearly always normal in latency. The M2 response was lacking in about 30% of the patients and 10% of normals. The long latency response (M3) in the antagonistic anterior tibial muscle was significantly delayed (beyond 162 msec = AM + 2.5 S) in 69% of the patients. The delayed M3 response was found to indicate demyelination as reliably as the delayed somatosensory evoked potential (66% of the patients). The frequency of coincident results in the entire group was 86%. Additional information is gained in cases where SEPs are normal, but M3 is delayed (7%). Furthermore, patients lacking P40 of the SEP still exhibit M3 responses, the latency of which may be measured (24%). The results favour the assumption that M3 is mediated by a supraspinal pathway.
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