The correct answer is D. Primary hypokalemic periodic paralysis
Using a step-wise approach that ruled out other causes of hypokalemia (e.g. thyrotoxicosis, hyperaldosteronism, renal or GI loss), the patient was diagnosed with primary hypokalemic periodic paralysis. Family history and past history of attacks supported the diagnosis. The patient refused DNA analysis, so the diagnosis could not be confirmed.
Hypokalemic periodic paralysis represents a rare cause of rhabdomyolysis, a medical emergency that can cause life-threatening complications, including kidney injury, disseminated intravascular coagulation, and cardiac arrythmias. Causes of rhabdomyolysis include: muscle trauma, muscle enzyme deficiency, electrolyte abnormalities, infection, toxins, endocrinopathy, and drugs (e.g. β-mimetics, insulin, laxatives or diuretics).
While the mechanism of hypokalemic rhabdomyolysis remains unknown, it may be related to muscle ischemia. Potassium is an important regulator of muscle blood flow. Severe hypokalemia is associated with capillary contraction, reduced blood supply to muscles, and muscle cell damage.
Primary periodic paralaysis (PPP) represents a rare cause of hypokalemic rhabdomyolsis. PPP is a rare genetic disease that causes periodic attacks of muscle weakness related to decreased or increased potassium levels (though potassium levels can also be normal). The disorder is inherited in an autosomal dominant fashion, and is caused by mutations that affect potassium-sensitive muscle membrane excitability. Common triggers include: a high carbohydrate meal, alcohol, and strenuous activity.
Diagnosis is based on patient history and symptoms, and confirmed by the long exercise test (LET, which measures the action potential that triggers muscular contraction), or genetic testing. Treatment depends on whether the patient has hyperkalemic or hypokalemic periodic paralysis. In hypokalemic periodic paralysis, carbonic anhydrase inhibitors or potassium sparing diuretics are used, along with potassium supplementation when necessary.
Take home points
• Primary periodic paralysis is a rare genetic disorder with autosomal dominant inheritance and characterized by attacks of flaccid muscle weaknes and levels that are increased or decreased (though sometimes normal)
• Hypokalemic periodic paralysis is a rare cause of rhabdomyolysis, which may result when very low potassium levels contribute to muscle ischemia and injury
1. Jung YL, Kang JY. Rhabdomyolysis following severe hypokalemia caused by familial hypokalemic periodic paralysis. World J Clin Cases. 2017;5:56-60. https://www.wjgnet.com/2307-8960/full/v5/i2/56.htm. Accessed October 19, 2018.