A 35-year-old man is evaluated due to poor exercise tolerance and muscle weakness. He has no past medical history. Blood pressure is 175-185 mm Hg systolic and 105-115 mm Hg diastolic on repeat measurements, and pulse is 78-95/min. Laboratory results are as follows:
| Sodium | 146 mEq/L |
| Potassium | 2.4 mEq/L |
| Glucose | 95 mg/dL |
| Creatinine | 0.7 mg/dL |
CT scan of the abdomen reveals a 3-cm mass in the left adrenal gland. Which of the following additional findings would be expected in this patient?
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This patient has significant hypertension at a relatively young age, which raises suspicion for secondary causes of hypertension. In particular, his hypokalemia associated with a 3-cm adrenal mass is highly suggestive of primary hyperaldosteronism (Conn syndrome). Conn syndrome is characterized by the excessive, unregulated secretion of aldosterone, usually due to adrenal adenoma or bilateral adrenal hyperplasia.
Aldosterone stimulates renal reabsorption of sodium, leading to expanded blood volume and hypertension. However, hypernatremia is generally mild due to increased renal blood flow and secretion of natriuretic factors (ie, aldosterone escape). The hypertension causes a compensatory drop in renin production (Choice E); low plasma renin activity (PRA) with an elevated serum aldosterone level confirms the diagnosis of Conn syndrome.
In addition, aldosterone causes wasting of potassium, leading to hypokalemia, which can cause muscle weakness and decreased exercise tolerance. Aldosterone also stimulates nephrons to secrete hydrogen ions into the urine, resulting in increased reabsorption of bicarbonate, elevated serum bicarbonate levels (Choices A and D), and metabolic alkalosis.
(Choice B) Secondary hyperaldosteronism is characterized by elevated aldosterone with elevated PRA and metabolic alkalosis. Typical endogenous causes include renovascular hypertension and renin-secreting tumor. However, this patient's 3-cm adrenal mass makes renovascular hypertension less likely, and a renin-secreting tumor would typically be found in the kidneys, not the adrenal glands.
Educational objective:
Primary hyperaldosteronism (Conn syndrome) causes hypertension, hypokalemia, and metabolic alkalosis. The diagnosis is confirmed by low plasma renin activity with an elevated serum aldosterone level.