Hypokalemic periodic paralysis (HypoKPP) is characterized by episodes of extreme muscle weakness or paralysis associated with a fall in blood potassium levels (hypokalemia). Episodes (or attacks) typically involve a temporary weakness or inability to move muscles in the arms and legs. On set of episodes usually occur in childhood or adolescence. These episodes can last for hours or days, and frequency varies among patients. The frequency is usually highest between the ages of 15 and 35, and then decreases with age. Some people with HypoPP also develop late-onset proximal myopathy. Triggers to be avoided include carbohydrates, salt (sodium), cold, repetitive exercise, epinephrine, and steroids.

HypoPP can be caused by mutations in the CACNA1S or SCN4A gene. Inheritance is autosomal dominant. Treatment varies depending on the intensity and duration of attacks. Minor attacks may go away on their own, while treatment for moderate to severe attacks may involve taking oral potassium or intravenous (IV) potassium.