Temperature dependence of nerve conduction and EMG in neuropathy associated with gammopathy

The effects of warming on nerve conduction variables and electromyography were studied in 15 patients with a polyneuropathy associated with monoclonal gammopathy of undetermined significance. In each patient median nerve (motor, sensory) and tibial nerve (motor) conduction parameters were measured before and after warming in water at 36 degrees C. Warming: (1) increased the conduction velocity (CV); (2) decreased the distal motor latency, amplitude, and duration of the compound muscle or nerve action potential; and (3) caused fibrillations to appear in 1 patient. The increase in CV with temperature depended upon the CV after warming: the lower this CV, the smaller the increase in CV with temperature (delta CV/delta T). Correction of median nerve motor CV before warming with 2.2 m/s per degree C yielded CV values which were higher than the CV values after warming, because in most patients delta CV/delta T was less than 2.2 m/s per degree C. Because of differences in delta CV/delta T values, it is more accurate to warm the extremity than to correct for temperature.