Muscle fiber conduction velocity in situ in hypokalemic periodic paralyses.

OBJECTIVES

To clarify the diagnostic yield of conduction velocity along muscle fibers in situ (MFCV) in hypokalemic periodic paralyses (HOPPs).

MATERIAL AND

METHODS

MFCV of the short head of biceps brachii was performed in 3 subjects with primary HOPP and in another 3 with secondary HOPP.

RESULTS

MFCV was reduced during the recovery period in 2 of the patients with hereditary HOPP and in 3 with secondary hypokalemia due to hyperaldosteronism, diuretics, and renal tubular acidosis. One case with familiar HOPP showed fluctuating muscle weakness, but never had paralytic attacks. MFCV slowing was similar in both hereditary and secondary HOPP. Direct stimulation during a major attack with quadriplegia showed inexcitability of most muscle fibers.

CONCLUSIONS

Inexcitability during major attacks and MFCV slowing in interictal or recovery periods evidenced sarcolemmal altered function. MFCV is a sensitive method for the detection of membrane muscle fiber defects in HOPPs and is also an additional diagnostic criterion of these diseases.