Treatment of “permanent” muscle weakness in familial hypokalemic periodic paralysis

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Abstract
Three patients with Hypokalemic Periodic Paralysis (HOPP)‐associated progressive interattack muscle weakness, who became unresponsive or worsened by acetazolamide, responded favorably to dichloro‐phenamide, a more potent carbonic anhydrase inhibitor. Dichloro‐phenamide in single‐blind placebo‐controlled trials, considerably improved functional strength in two of the patients and had a moderate but definite effect in the third. Muscle groups graded 4/5 (MRC scale) returned to normal; very weak (0–3/5) atrophic muscles, improved to a minor degree. In one patient with acetazolamide‐resistant paralytic attacks, dichlorophenamide also diminished the frequency and severity of the acute attacks. Dichlorophenamide had, in the present study, less effect than acetazolamide in reducing serum HCO and elevating Cl−. Its effectiveness may be related to the degree of sensitivity of certain HOPP patients to alterations of Cl− and/or HCO serum levels or to a different action of the drug unrelated to carbonic anhydrase inhibition or acidosis. Dichlorophenamide should be considered as an alternate to acetazolamide in the treatment of patients with HOPP‐associated interattack muscle weakness who have become unresponsive or worsened by acetazolamide.