During a routine follow-up appointment, a 44-year-old female patient reports experiencing … — USMLE Step 3

During a routine follow-up appointment, a $44$ -year-old female patient reports experiencing profound muscle weakness and frequent nocturia over the past $3$ months. She has a $3$ -year history of hypertension that remains poorly controlled despite daily adherence to a regimen of lisinopril and hydrochlorothiazide. Her current blood pressure is $165/102\text{ mmHg}$ , and her heart rate is $78\text{/min}$ . Physical examination demonstrates a normal body mass index, no striae or central adiposity, an absence of peripheral edema, and normal deep tendon reflexes.

A comprehensive metabolic panel reveals the following:

Test	Result
Serum sodium	$147\text{ mEq/L}$
Serum potassium	$2.6\text{ mEq/L}$
Serum chloride	$102\text{ mEq/L}$
Serum bicarbonate	$32\text{ mEq/L}$
Blood urea nitrogen	$15\text{ mg/dL}$
Serum creatinine	$0.8\text{ mg/dL}$

To further evaluate the refractory hypertension and electrolyte abnormalities, additional serologic testing is obtained:

Test	Result	Reference Range
Plasma aldosterone concentration	$32\text{ ng/dL}$	$3-16\text{ ng/dL}$
Plasma renin activity	$0.1\text{ ng/mL/hr}$	$0.6-4.3\text{ ng/mL/hr}$
Aldosterone-to-renin ratio	$320$	$< 20$

Based on these laboratory findings, which of the following pathophysiologic mechanisms is the most accurate interpretation of this patient's condition?

A
Thiazide-induced volume contraction and secondary neurohormonal activation
B
Reduced renal arterial perfusion stimulating the juxtaglomerular apparatus
Autonomous adrenal hypersecretion of mineralocorticoidsCevap
D
Constitutive activation of collecting tubule sodium channels
E
Renal microvascular thrombosis impairing local cortical perfusion

Cevap

Autonomous adrenal hypersecretion of mineralocorticoids

The correct answer identifies autonomous adrenal hypersecretion of mineralocorticoids. This patient presents with the classic triad of primary hyperaldosteronism: hypertension, hypokalemia, and metabolic alkalosis. The diagnosis is strongly supported by the interpretation of the endocrine laboratories, which show an elevated plasma aldosterone concentration and suppressed plasma renin activity, leading to an aldosterone-to-renin ratio (ARR)

> 20

. In primary hyperaldosteronism, an adrenal adenoma or bilateral adrenal hyperplasia autonomously produces excessive aldosterone. This excess aldosterone causes distal tubular sodium retention and volume expansion, which subsequently suppresses renin secretion from the juxtaglomerular apparatus via negative feedback. Notably, the patient's renin remains suppressed despite concurrent therapy with a thiazide and an ACE inhibitor, both of which typically increase renin levels, further confirming the autonomous nature of the aldosterone excess.

Adım Adım Çözüm

Identify the primary clinical and basic laboratory abnormalities.

The patient exhibits treatment-resistant hypertension, marked hypokalemia (

2.6\text{ mEq/L}

), and metabolic alkalosis (serum bicarbonate

32\text{ mEq/L}

Recognizing the classic triad of hypertension, hypokalemia, and metabolic alkalosis is the critical first step in directing the diagnostic focus toward a state of mineralocorticoid excess.

Interpret the specific endocrine laboratory findings.

The patient has an elevated plasma aldosterone concentration (

32\text{ ng/dL}

) and suppressed plasma renin activity (

0.1\text{ ng/mL/hr}

), yielding an abnormally high aldosterone-to-renin ratio of

320

This ratio differentiates primary causes (where aldosterone is autonomously produced, suppressing renin) from secondary causes (where renin is overproduced, driving aldosterone secretion).

Synthesize the laboratory data to determine the underlying pathophysiology.

The combination of high aldosterone and low renin confirms a diagnosis of primary hyperaldosteronism, which is driven by autonomous adrenal production.

Other conditions causing hypokalemic hypertension display different hormone profiles (e.g., both renin and aldosterone elevated in secondary hyperaldosteronism; both suppressed in Liddle syndrome).

Anahtar Kavram

Primary hyperaldosteronism is characterized by the triad of hypertension, hypokalemia, and metabolic alkalosis, with laboratory testing confirming an elevated plasma aldosterone concentration and a suppressed plasma renin activity (high aldosterone-to-renin ratio).

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