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

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Abstract
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 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.