Paralysis, Periodic

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 beta-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