Hypokalemic periodic paralysis is a relatively rare disease in which individuals experience transient, severe episodes of hypokalemia as a result of rapid intracellular potassium shift into skeletal muscle. The attacks typically manifest as muscle cramps, muscle paralysis, or cardiac arrhythmias, and may are classically precipitated by rest following exercise, catecholamine excess, or carbohydrate-rich meals.
The acquired form in most instances is associated with thyrotoxicosis. Even though more women than men suffer from hyperthyroidism, there is a huge male predominance (up to a 70:1 M:F ratio) of hyperthyroid-induced hypokalemic periodic paralysis. The disorder seems to be especially common in Asian populations.
In contrast, the hereditary forms of hypokalemic periodic paralysis have a roughly equal M:F ratio, have a younger age of onset (<20 years of age), is most common in Caucasians, and the hypokalemic episodes tend to last longer. It is inherited in an autosomal dominant fashion and thus far mutations have been identified in the genes CACNA1S (a calcium channel subunit expressed in skeletal muscle), SCN4A (a skeletal muscle Na channel), and KCNE3 (a skeletal muscle K channel).