FAMILIAL PERIODIC PARALYSIS

any of the forms of a rare disorder that is characterized by relatively short-term, recurrent attacks of muscle weakness. Usually (but not invariably) the disorder is inherited; it is probably sex-linked, and it occurs three times more often in males than in females. The disorder is most often associated with abnormally high or abnormally low serum potassium concentration; these two forms are known as hyperkalemic or hypokalemic periodic paralysis, respectively, and they have some clinical features in common. Hypokalemic paralysis is the more severe form. It generally begins late in childhood or in adolescence. Onset of paralysis occurs most frequently at night during sleep. An attack of this type may last longer than 24 hours. A form of hypokalemic paralysis that is associated with hyperthyroidism has been noted among adult males of Japanese and Chinese extraction. It is clinically similar to hypokalemia but carries a greater risk of cardiac involvement. Treatment of the hyperthyroidism prevents further attacks. Hyperkalemic paralysis begins in infancy and is characterized by more frequent but milder attacks that last minutes or hours; it may also be accompanied by mild myotonia (muscle spasm), of the tongue, for example. Normokalemia is another form of familial periodic paralysis. In this form of the disorder the potassium level remains stable. Symptoms are generally more severe than those typical of hyperkalemia. Neither normokalemia nor hypokalemia are associated with myotonia. In familial periodic paralysis, attacks may take from several minutes (generally characteristic of hyperkalemia) to several hours to develop; they range in severity from general weakness to total paralysis. Typically, weakness in the legs is the first sign of onset, followed by weakness in the arms. Usually, only trunk and limb muscles are affected, and the affected person is able to speak and breathe. The heart muscle is only rarely involved. The attacks may come at intervals of days, months, or years. In later years a degeneration of the muscle fibres may occur. Factors that seem to precipitate attacks include relaxation after periods of exertion or strenuous exercise. Mild exercise, however, may sometimes alleviate a mild attack. In a few other diseases, such as diabetes, Addison's disease, and kidney insufficiency, there may be brief episodes of paralysis similar to that in familial paralysis, often following administration of glucose. Treatment of hypokalemic periodic paralysis includes the administration of potassium chloride. In hyperkalemic paralysis, short-term treatment involves injections of a calcium gluconate solution, and long-term treatment may include insulin and dialysis of the blood. Both of the better-known forms of the disorder seem to respond to small doses of acetazolamide, a diuretic. See also paralysis.