Submaximal stimulation and f-wave parameters.

PURPOSE: This study evaluates the effect of submaximal stimulation and varying stimulus rates on F-wave parameters. METHODS: F-waves were recorded from the abductor pollicis brevis muscle from 3 normal subjects stimulating at 25%, 50%, and 75% intensity in comparison with supramaximal stimulation based on peak-to-peak compound muscle action potential amplitude. The effect of varying stimulus intensity (0.5, 1.0, and 2.0 Hz) at 30% stimulus intensity was also evaluated. Data were evaluated based on "true" values obtained after 100 stimuli. F-wave parameters studied included latencies (minimal and mean), amplitudes, persistences, durations, chronodispersions, and mean F amplitudes/maximum compound muscle action potential amplitudes. RESULTS: For varying stimulus intensities and rates, the following results were obtained: (1) no meaningful change in F latencies or durations; (2) mean latency values were more reproducible than minimum; (3) amplitudes, persistence, and mean F amplitudes/maximum M-wave amplitude ratios increase linearly with increase in stimulus intensities; (4) chronodispersion increases with increase in stimulus intensity; (5) 20 stimuli appear adequate for true values at supramaximal stimulation but more are needed at submaximal levels; (6) varying stimulus frequency at submaximal stimulation did not meaningfully affect the results. CONCLUSIONS: F-parameters require more stimuli at submaximal stimulation and, except for latencies and durations, would require different normal values than at supramaximal stimulation.

The peripheral nervous system complications of HTLV-1 myelopathy (HAM/TSP) syndromes.

Human T-cell lymphotropic virus type I (HTLV-1) is a human retrovirus and the etiologic agent for a progressive neurological disease called HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). With its primary site of involvement occurring at the thoracic spinal cord level, HAM/TSP is characterized by muscle weakness, hyperreflexia, lower extremity spasticity, and urinary disturbance. However, HAM/TSP has also been associated with other autoimmune disorders as well as widespread dysfunction within the nervous system that results in less frequent symptoms of cerebral, cerebellar, and cranial nerve involvement. Although masked by the more prominent myelopathy, involvement of the peripheral nervous system also occurs. Syndromes of anterior horn cell, peripheral nerve, and muscle dysfunction have been reported.