MUSCLE-FIBER CONDUCTION-VELOCITY IN THE DIAGNOSIS OF FAMILIAL HYPOKALEMIC PERIODIC PARALYSIS - INVASIVE VERSUS SURFACE DETERMINATION

Muscle fiber conduction velocity (MFCV) in the brachial biceps muscle was determined in a large family of patients with hypokalemic periodic paralysis (HOPP) by both a surface and an invasive method. Other surf ace EMG parameters and the muscle force were also determined. Both the surface and the invasive method showed a significantly lower mean MFC V in the proven gene carriers but only the invasive method showed a lo wer MFCV in all proven carriers. It can be concluded that MFCV determi nation is a reliable method to detect the membrane defect in HOPP carr iers and that the invasive method is not only easy to perform, but als o more sensitive. The muscle force and the integrated EMG at maximal v oluntary contraction were lower in the carrier group. A positive corre lation between the surface MFCV and the neuromuscular efficiency (the quotient of force and integrated EMG) was found in the controls but no t in the HOPP carriers. Since type II fibers have a higher neuromuscul ar efficiency, this suggests a preferential involvement of type II fib ers in HOPP. (C) 1994 John Wiley & Sons, Inc.