MEDizzy - A 16-year-old female star gymnast presents to your ofce

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Disorders of the Kidney and Urinary Tract

A 16-year-old female star gymnast presents to your ofce complaining of fatigue, difuse weakness, and muscle cramps. She has no previous medical history and denies tobacco, alcohol, or illicit drug use. There is no signifcant family history. Examination shows a thin female with normal blood pressure. Body mass index (BMI) is 18 kg/m2. Oral examination shows poor dentition. Muscle tone is normal, and neurologic examination is normal. Laboratory studies show hematocrit of 38.5%, creatinine of 0.6 mg/dL, serum bicarbonate of 30 mEq/L, and potassium of 2.7 mEq/L. Further evaluation should include which of the following?

ExplanationIn any patient with hypokalemia, the use of diuretics must be excluded. Diuretics or chronic hypokalemia may cause an acute interstitial nephritis with tubular injury. This patient has multiple warning signs for the use of agents to alter her weight, including her age, gender, and participation in competitive sports. Her body mass index is low, and the oral examination may suggest chronic vomiting. Chronic vomiting may be associated with a low urine chloride level. Once diuretic use and vomiting are excluded, the diferential diagnosis of hypokalemia and metabolic alkalosis includes magnesium defciency, Liddle syndrome, Bartter syndrome, and Gitelman syndrome. Liddle syndrome is associated with hypertension and undetectable aldosterone and renin levels. It is a rare autosomal dominant disorder. Classic Bartter syndrome has a presentation similar to that of this patient. It may also include polyuria and nocturia because of hypokalemia-induced diabetes insipidus. Gitelman syndrome can be distinguished from Bartter syndrome by hypomagnesemia and hypocalciuria.