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