Description

Hypokalemic periodic paralysis is a syndrome characterized by episodes of motor weakness accompanied by low serum potassium levels in between periods of well-being.

Epidemiology

• There are primary and secondary forms. The primary form is genetic and follows an autosomal dominant pattern of inheritance. The secondary forms may complicate a number of medical disorders including, but not limited to, primary and acquired distal renal tubular acidosis, primary and acquired Fanconi syndrome, thyrotoxicosis, hyperaldosteronism, Bartter syndrome, Gitelman syndrome, and medication reactions (theophylline, amphotericin, diuretics, laxatives, chemotherapy agents such as cisplatin).
• Although rare, this is the most common cause of primary periodic paralysis. Prevalence is around 1 in 100,000.
• The primary form usually manifests in the first 2 decades of life and is more common in men than women (displaying incomplete penetrance phenotypes). Late-onset hypokalemic periodic paralysis is usually secondary and is characterized by hypokalemia, which may be persistent in contrast to primary where hypokalemia is periodic.

Etiology and Pathophysiology

Calcium channelopathy impairs muscle depolarization, causing flaccid paralysis. Sodium channelopathies are seen in a smaller subset of patients and cause clinical manifestations by impairing depolarization muscle action potentials. Potassium channelopathy increases potassium intracellular entry.

Genetics
Mutations in genes encoding for calcium (CACNL1A3), sodium (SCN4A), potassium (KCNJ18) channels have been described. Calcium channel mutations are the most common, present in 80% of all primary cases (1).

Risk Factors

Attacks are typically triggered by vigorous exercises, stress, and high-carbohydrate meals. Hyperadrenergic drive worsens the hypokalemia by promoting intracellular shift of the K⁺ ion.