Hypokalemic periodic paralysis

Hypokalemic periodic paralysis (HypoPP) is a rare neuromuscular disorder characterized by episodes of muscle weakness or paralysis associated with a fall in blood potassium levels (hypokalemia). It is also known as familial hypokalemic periodic paralysis or Westphall disease. The condition primarily affects skeletal muscles, leading to attacks of flaccid paralysis that can range from mild weakness in a single muscle group to severe, generalized paralysis. Episodes are often triggered by carbohydrate-rich meals, rest after vigorous exercise, stress, cold exposure, or certain medications. Attacks typically begin in adolescence or early adulthood and may last from hours to days. Between episodes, muscle strength is usually normal early in the disease course, though some individuals develop a progressive fixed myopathy (permanent muscle weakness) over time. HypoPP is caused by mutations in genes encoding skeletal muscle ion channels. The most common form, HypoPP type 1, is caused by mutations in the CACNA1S gene (encoding a calcium channel subunit), while HypoPP type 2 is caused by mutations in the SCN4A gene (encoding a sodium channel subunit). Both forms are inherited in an autosomal dominant pattern, though de novo mutations and incomplete penetrance (particularly in females) are recognized. During attacks, potassium shifts from the blood into muscle cells, causing the serum potassium to drop, which impairs muscle excitability. Treatment involves both acute management and long-term prevention of attacks. Acute episodes may be treated with oral potassium supplementation to restore normal serum levels. Preventive strategies include avoidance of known triggers such as high-carbohydrate meals and strenuous exercise, as well as prophylactic medications. Acetazolamide, a carbonic anhydrase inhibitor, is the most commonly used preventive therapy and is effective in many patients. Dichlorphenamide has also been approved for the prevention of attacks. Potassium-sparing diuretics such as spironolactone or triamterene may be used as alternatives. Regular monitoring and a tailored management plan are important, as the disease course and treatment response can vary significantly among individuals.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

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