A 50-year-old man comes to the physician complaining of 2 months of muscle cramps. He also complains of weakness and fatigue. He has a 20-pack-year smoking history but does not drink alcohol. The patient's past medical and family histories are noncontributory. His temperature is 36.7 C (98 F), blood pressure is 150/96 mm Hg, and pulse is 78/min. His body mass index is 28 kg/m². The rest of the examination is within normal limits. Laboratory results are as follows: Which of the following is the most appropriate next step in management of this patient?

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11ec25c8_d3b1_6d72_bc81_ad5bd4ce808f_MD0003_00 Primary hyperaldosteronism should be suspected in any hypertensive patient presenting with hypokalemia. Patients with mild primary hyperaldosteronism may not have spontaneous hypokalemia, but they are prone to develop diuretic-induced hypokalemia. Severe hypokalemia can cause muscle cramps/weakness. Other findings include metabolic alkalosis and mild hypernatremia (143-147 mEq/L). Patients usually do not have peripheral edema due to spontaneous diuresis (aldosterone escape). The best screening test is early-morning plasma aldosterone concentration (PAC) to plasma renin activity (PRA) ratio. However, drugs that significantly alter the PAC/PRA ratio (eg, spironolactone, eplerenone, amiloride, triamterene) should be withdrawn for 4 weeks before testing. A PAC/PRA ratio >20 with plasma aldosterone >15 ng/dL suggests primary hyperaldosteronism and requires further confirmatory adrenal suppression testing. Adrenal suppression testing usually involves salt loading and documenting inability to suppress serum aldosterone. Patients with positive adrenal suppression testing should then undergo adrenal imaging, usually by computed tomography (CT) scan (Choice C). Hyperaldosteronism is most commonly due to bilateral adrenal hyperplasia (50%-60%) or aldosterone-producing adrenal adenoma (40%-50%). If CT scan does not reveal a discrete unilateral mass, adrenal vein sampling is recommended to differentiate between hyperplasia and adenoma. Surgery is preferred for adenoma, and medical therapy is preferred for hyperplasia. (Choice A) Chest CT scan can diagnose a lung cancer, which can sometimes be associated with syndrome of inappropriate antidiuretic hormone or Lambert-Eaton syndrome. Lambert-Eaton syndrome usually presents with progressively worsening proximal muscle weakness, fatigue, ptosis, and autonomic dysfunction (eg, dry mouth). Syndrome of inappropriate antidiuretic hormone causes hyponatremia instead of hypernatremia. (Choice B) Dexamethasone suppression test can diagnose Cushing's syndrome. Patients typically develop findings such as central obesity, purple striae, proximal muscle wasting, glucose intolerance, and hypertension. (Choice D) Measurement of 24-hour urinary potassium excretion was used previously to document inappropriate potassium excretion. A 24-hour urinary potassium level >30 mEq in the presence of hypokalemia suggests hyperaldosteronism. However, this test is no longer commonly used. (Choice E) Plasma free metanephrines would be elevated in pheochromocytoma, a secondary cause of hypertension. Patients usually develop hypertension and the classic triad of episodic headache, sweating, and palpitations with tachycardia. However, pheochromocytoma does not usually cause the degree of hypokalemia seen in this patient. Educational objective: The ratio of plasma aldosterone concentration to plasma renin activity is the preferred initial screening test for primary hyperaldosteronism. Adrenal suppression testing can confirm the diagnosis, and positive tests require further adrenal imaging. Adrenal venous sampling is the most sensitive test for differentiating adrenal adenoma and bilateral adrenal hyperplasia in patients without discrete unilateral adrenal mass on imaging.

A 50-Year-Old Man Comes to the Physician Complaining of 2