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Key Features

  • Episodes of flaccid weakness or paralysis occur, sometimes in association with abnormal plasma potassium level

  • May have a familial (dominant inheritance) basis

  • The hypokalemic variety is commonly associated with hyperthyroidism in young Asian men

Clinical Findings

  • Hypokalemic periodic paralysis

    • Attacks tend to occur on awakening, after exercise, or after a heavy meal and may last for several days

    • Strength is normal between attacks

  • Hyperkalemic periodic paralysis: attacks also tend to occur after exercise but usually last for < 1 h

  • Normokalemic periodic paralysis: similar clinically to the hyperkalemic variety, but the plasma potassium level remains normal during attacks

Diagnosis

  • Clinical diagnosis combined with plasma potassium and, when relevant, thyroid function tests (free T4, TSH)

Treatment

  • Hypokalemic periodic paralysis

    • Patients should avoid excessive exertion

    • Attacks may be prevented by a low-carbohydrate, low-salt diet; acetazolamide, 250–750 mg once daily orally; nonselective β-adrenergic blockers

    • An ongoing attack may be aborted by potassium chloride given orally or by intravenous drip, provided the ECG can be monitored and kidney function is satisfactory

    • Treatment of associated hyperthyroidism prevents recurrences

  • Hyperkalemic periodic paralysis

    • Attacks may be terminated by intravenous calcium gluconate (1–2 g) or by intravenous diuretics (furosemide, 20–40 mg), glucose, or glucose and insulin

    • Daily acetazolamide or chlorothiazide may prevent recurrences

  • Normokalemic periodic paralysis

    • Treatment is with acetazolamide, 250–750 mg once daily orally

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