Familial Hypokalemic Periodic Paralysis

The periodic paralyses (PPs) are a group of rare neuromuscular disorders related to muscle ion channels, presenting with episodes of sudden muscle weakness. The majority of cases of PP are inherited, resulting from genetic mutations in the subunits of channel proteins of the sodium, potassium, or calcium channels or the SCL4A1 protein. We describe two siblings, a 15-year-old male and an 11-year-old male, presenting with complaints of weakness. Both patients had consumed a large carbohydrate-rich meal the previous night with a history of similar episodes of weakness suggesting a diagnosis of PP. Laboratory investigations were unremarkable except for hypokalemia in both patients, and they were started on potassium supplementation, which resulted in the resolution of symptoms. The elder sibling was started on acetazolamide for prophylaxis, but due to non-response, was put on spironolactone which he tolerated well. Genetic mutation analysis confirmed the diagnosis of familial hypokalemic periodic paralysis (FHPP) with a p. Arg672His mutation in the sodium channel, gene SCN4A (17q23.3) in both siblings. The diagnosis of PP is important to consider in patients with sudden recurring episodes of weakness or paralysis, especially in otherwise healthy adolescents/young adults. The treatment of FHPP is challenging, with cautious potassium supplementation for acute attacks. Workup for other causes should be performed, and genetic analysis is recommended to confirm the diagnosis.