Common electrolyte imbalance, uncommon cause

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Figure 1
Striae on the patient’s abdomen (arrow).
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Figure 2
Hyperpigmentation of the patient’s knuckles (arrows).

TABLE 1

Patient’s laboratory test results

Laboratory test	Results (reference range)^{^a}
Arterial blood gas
pH	7.665 (7.35–7.45)
Partial pressure of carbon dioxide	43.4 mm Hg (35–48)
Partial pressure of oxygen	95.9 mm Hg (83–108)
Bicarbonate	48.4 mmol/L (21–28)
Sodium	138 mEq/L (135–145)
Fasting plasma glucose	210 mg/dL (70–100)
Magnesium	2.2 mg/dL (1.8–2.5)
Thyroid-stimulating hormone	2.2 mIU/L (0.4–4.8)
Urine electrolytes, 24-hour
Potassium	117 mmol/24 hours (< 15)
Sodium	86 mmol/24 hours (40–220)
Calcium	172 mg/24 hours (< 228)
Magnesium	84 mg/24 hours (73–122)
Urine creatinine, 24-hour	16 mg/kg/24 hours (15–20)
Transtubular potassium gradient	9 (< 2 in hypokalemia)
Plasma aldosterone concentration	5.24 ng/dL (2.2–35.3)
Direct renin concentration	6.09 mIU/L (4.4–46.1)
Serum cortisol
Measured at 8 AM	50.3 μg/dL (6.2–18.0)
Overnight 1-mg dexamethasone suppression test	48.0 μg/dL (< 2.0)
High-dose (8 mg) dexamethasone suppression test	42.7 μg/dL (> 50% reduction from baseline)
Urine cortisol, 24-hour	2,800 μg/24 hours (28.5–213.7)
Plasma adrenocorticotropic hormone	326 pg/mL (15–65)