Harrison's Q&A: Worsening fatigue, muscle cramping, and abnormal lab results in a 21 YO patient

Harrison's Q&A: Worsening fatigue, muscle cramping, and abnormal lab results in a 21 YO patient

A 21-year-old male college student is evaluated for profound fatigue that has been present for several years but has recently become debilitating. He also reports several foot spasms and cramps and occasionally sustained muscle contractions that are uncontrollable. He is otherwise healthy, takes no medications, and denies tobacco or alcohol use. On examination, he is well developed with normal vital signs including blood pressure. The remainder of the examination is normal. Laboratory evaluation shows a sodium of 138 mEq/L, potassium of 2.8 mEq/L, chloride of 90 mEq/L, and bicarbonate of 30 mmol/L. Magnesium level is normal. Urine screen for diuretics is negative, and urine chloride is elevated. Which of the following is the most likely diagnosis? 

A. Bulimia nervosa 

B. Diuretic abuse 

C. Gitelman syndrome 

D. Liddle syndrome 

E. Type 1 pseudohypoaldosteronism

The answer is C. (Chaps.51 and 309) The patient presents with hypokalemia and hypochloremic metabolic alkalosis in the absence of hypertension. This is most commonly due to surreptitious vomiting or diuretic abuse, but in this case, the urine diuretic screen was negative. In patients with surreptitious vomiting, urine chloride levels are low to preserve intravascular volume, and this was not present in this patient. Bartter syndrome and Gitelman syndrome have hypokalemia and hypochloremic metabolic alkalosis with inappropriately elevated urine chloride levels. Gitelman syndrome is less severe and presents later in life than Bartter syndrome, which is commonly found in childhood due to failure to thrive. Additionally, Gitelman syndrome has more prominent fatigue and muscle cramping. Most forms of Bartter syndrome also have associated hypomagnesemia and hypocalciuria. Patients with type 1 pseudohypoaldosteronism have severe renal salt wasting and hyperkalemia. Liddle syndrome presents with apparent aldosterone excess with severe hypertension, hypokalemia, and metabolic alkalosis.