A 27-year-old man comes to the office due to recurrent episodes of muscle weakness. He has no other significant past medical history. The patient's weight has been stable for the past few years, and his current BMI is 23 kg/m². His blood pressure is 190/110 mm Hg supine and 195/110 mm Hg standing. His heart rate is 70/min supine and 72/min standing. The rest of the physical examination is unremarkable. Laboratory evaluation shows very low plasma renin activity. Overactivity of which of the following structures is most likely responsible for this patient's symptoms?

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11ec160b_3ab9_0d8d_9249_d3a3cace8539_MD0001_00 This patient has features consistent with primary hyperaldosteronism (PH), a very common cause of secondary hypertension. PH is usually due to increased secretion of mineralocorticoids from bilateral nodular hyperplasia of the adrenal zona glomerulosa or an aldosterone-producing adrenal adenoma (Conn syndrome). The main effect of aldosterone is to stimulate absorption of sodium and excretion of potassium and hydrogen ions in the renal collecting tubules. Aldosterone secretion from the zona glomerulosa is normally regulated by angiotensin II and potassium levels. Overproduction of aldosterone can result in sodium retention, hypertension, and feedback suppression of the renin-angiotensin system (ie, very low renin activity). Some patients also develop metabolic alkalosis and hypokalemia, which can be exacerbated by increased distal tubule sodium delivery (eg, diuretics, increased sodium intake). Symptomatic hypokalemia may cause muscle weakness, cramps, and, occasionally, rhabdomyolysis and cardiac arrhythmias. Despite the increase in sodium absorption, hypernatremia and pedal edema are rarely observed in PH due to the phenomenon of aldosterone escape. The high aldosterone levels lead to increased intravascular volume and therefore cause increased renal blood flow (with resulting pressure natriuresis) and augmented release of atrial natriuretic peptide. This ultimately results in increased sodium excretion by the renal tubules, which limits net sodium retention and prevents the development of overt volume overload and significant hypernatremia. (Choices A and B) Pheochromocytomas are catecholamine-secreting tumors arising from the chromaffin cells of the adrenal medulla or extra-adrenal sympathetic chain, and typically present with severe hypertension. Pheochromocytomas stimulate the renin-angiotensin system due to high circulating catecholamine levels, and are associated with tachycardia and symptoms of catecholamine excess (eg, sweating, palpitations, headache). (Choice C) Increased renin production by the juxtaglomerular apparatus leads to hypertension with elevated aldosterone levels. This typically occurs in the setting of renal artery stenosis with decreased renal blood flow. However, this patient's renin activity is suppressed. (Choices D and F) Hypersecretion from cells of the zona fasciculata or zona reticularis would lead to Cushing syndrome or hyperandrogenism, respectively. Cushing syndrome can cause hypertension and hypokalemia but is usually associated with weight gain and a Cushingoid body habitus (eg, central obesity, moon facies). Educational objective: Primary hyperaldosteronism is caused by excessive aldosterone secretion, typically as a result of bilateral nodular hyperplasia of the zona glomerulosa or an aldosterone-producing adrenal adenoma. Clinical findings include hypertension, low plasma renin activity, hypokalemia, and metabolic alkalosis. __________ References: Case detection, diagnosis, and treatment of patients with primary aldosteronism: an endocrine society clinical practice guideline (http://www.ncbi.nlm.nih.gov/pubmed/18552288)

A 27-Year-Old Man Comes to the Office Due to Recurrent