Electrolyte and water distribution in familial hypokalaemic periodic paralysis

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Abstract
Distribution of water, Na and K was studied by means of a multiple isotope technique in 6 patients with familial hypokalemic periodic paralysis. Untreated patients, between attacks of paralysis, have a markedly reduced body K and intracellular K concentration. Total body water, water distribution, exchangeable Na and residual Na are normal. In 1 patient treated with a Na diet and K there was a marked change in electrolyte distribution and clinical improvement. Intracellular K concentration returned to normal and residual Na concentration was elevated well above normal. During the period of paralysis in an induced attack, intracellular K concentration fell slightly due to entry of relatively greater amounts of water than K into the cells. The ratio of intercellular to extracellular potassium concentration was normal both during paralysis and when muscle power was fully restored upon being treated with a low-Na diet and K supplements. Abnormality in muscle function is not due to hyperpolarization of the muscle membrane. Recently, the transport of K was related to the sarcoplasmic reticulum. In muscle biopsies from cases of both familial hypokalemic periodic paralysis and familial hyperkalemic periodic paralysis structural abnormalities of the sarcoplasmic reticulum are seen. This may well account for the abnormalities of permeability to K found in these patients.