A 36-Year-Old Woman With an Unexpected Cause of Hypokalemia

A 36-year-old woman complained of bilateral lower limb weakness for the last 3 days. She could move her upper limb, neck, and facial muscles and had no respiratory or swallowing difficulties. About 4 years ago, she complained of sudden weakness involving her lower limbs. Two years later, she had another episode involving only the right upper limb. In both cases, she was hypokalemic and received oral and intravenous potassium. She is a known diabetic and has polycystic ovary disease. Her blood pressure was 150/100 mm Hg, and body mass index was 29. Her serum potassium was 2 mEq/L, plasma renin 5 ng/dL, plasma aldosterone 0.63 µIU/mL, and aldosterone to plasma renin activity ratio 8. Cushing syndrome was considered a possibility. Subsequent analysis indicated a baseline cortisol level of 19.6 µg/dL at 8 Am. A screening overnight 1-mg dexamethasone suppression test (DST) showed 17 µg/dL cortisol. The low-dose DST revealed a cortisol level of 10.8 µg/dL. Adrenocorticotropin level was 196 pg/mL, and 24-hour urinary cortisol level was 1284 mg/dL. A high dose of 8-mg DST at 11 Pm to find the source of hypercortisolism performed yielded 15.9 µg/dL. Magnetic resonance imaging of the pituitary displayed a well-defined, heterogeneously enhanced mass lesion (15 × 13 × 11 mm) in the sella with mild suprasellar extension. Transsphenoidal resection and stereotactic radiosurgery were performed on the tumor with hormone replacement and glycemic control following surgery.