The muscle fiber conduction velocity and power spectra in familial hypokalemic periodic paralysis.

Surface EMG has been used to determine the average muscle fiber conduction velocity (MFCV) and power spectra of the m. biceps of 10 patients and 15 asymptomatic offspring of a large kinship with familial hypokalemic periodic paralysis (HOPP). The MFCV of the patients was 3.37 +/- 0.35 m/sec (mean +/- SD, n = 9), the median frequency (Fmed) of the power spectra was 55.0 +/- 5.8 Hz (mean +/- SD, n = 9), both values are significantly (P0.001, Student's t-test) lower than the control values: MFCV = 4.55 +/- 0.33 m/sec; Fmed = 88.6 +/- 15.5 Hz (mean +/- SD). In 6 of the 15 asymptomatic relatives, the surface EMG results were also abnormal. It is concluded that the MFCV is reduced in familial HOPP. This results in a predominantly low-frequency content of the power spectra, thereby providing a new model for studying the relationship between the MFCV and the frequency spectrum of surface EMG. Asymptomatic relatives that have inherited the disease probably can be detected with this method.