A 30-year-old woman presented to the emergency department (ED) of a hospital with sudden-onset flaccid muscle weakness, which was present bilaterally in the proximal lower extremities.1 She had just eaten a meal heavily laden in carbohydrates. She denied nausea, vomiting, diarrhea, fever, and rash. She was not currently taking any medications.
She described three similar attacks during the past year, all of which occurred after consuming a large amount of carbohydrates and drinking alcohol. During those attacks, she was treated in the ED, where she received IV potassium for hypokalemia and experience full symptom resolution. The reason for the hypokalemia remained unknown.
Her family history was notable for sudden cardiac death of unknown etiology in her father, paternal uncle, and brother.
Vitals were within normal limits. Physical exam was notable for symmetrical flaccid muscle paralysis mostly affecting the thighs and calves, areflexia without sensory involvement, and positive Trousseau sign.
Initial labs were notable for severe hypokalemia (1.6 mEq/L), and hypophosphatemia (0.8 mg/dL). ABG revealed respiratory alkalosis (pH 7.48, PaCO2 29 mmHg, PaO2 106 mmHg, bicarbonate 22.3 mmEq/L, oxygen saturation 98.8%), thought to be caused by hyperventilation due to her muscular symptoms.
Urinary excretion of potassium was 2.5 mmol/L, urinary osmolarity was 326 mOsm/kg, and the transtubular potassium gradient was 1.67, as expected in hypokalemia.
Total calcium, LFTs, CBC, plasma renin activity, aldosterone, and thyroid hormone levels were within normal limits. Blood and urine cultures both came back negative. Serology for HBV, HCV, and HIV were all negative. EKG was notable for prolonged QT indicative of hypokalemia.
While in the ED, the patient suddenly developed tetany and severe myalgia in both calves. Urine output decreased, and she began to produce tea-colored urine.
Labs at that time indicated rhabdomyolysis, with elevated creatine phosphokinase (45720 IU/L), and lactate dehydrogenase (1686 U/L). Myoglobin levels were not measured.
She received hydration, spironolactone and 6 hours of IV potassium, with gradual resolution of her symptoms.
What’s the diagnosis?
B. Alcohol intoxication
C. Cushing syndrome
D. Primary hypokalemic periodic paralysis
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.