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Difficulty: MediumFormulating a Differential Diagnosis

A 5454-year-old man comes to the clinic for follow-up of hypertension. Over the past three months, his blood pressure has been consistently elevated despite strict adherence to a daily regimen of amlodipine and lisinopril. He reports new-onset muscle cramps and generalized weakness but otherwise feels well. Physical examination shows a blood pressure of 174/98174/98 mmHg and a heart rate of 7676/min. The remainder of the examination, including cardiopulmonary and abdominal assessments, is unremarkable, and there is no peripheral edema.

Laboratory studies show:
Serum sodium: 144144 mEq/L
Serum potassium: 2.72.7 mEq/L
Serum bicarbonate: 3232 mEq/L

Given the unprovoked hypokalemia, his lisinopril is switched to verapamil, and he is prescribed oral potassium supplementation. Two weeks later, his blood pressure remains 168/96168/96 mmHg and his serum potassium is 2.92.9 mEq/L. Further laboratory evaluation reveals markedly suppressed plasma renin activity and a suppressed serum aldosterone concentration.

Based on the clinical and laboratory findings, which of the following is the most likely diagnosis?

  1. A
    Aldosterone-producing adrenal adenoma
  2. B
    Unilateral renal artery stenosis
  3. Excessive consumption of glycyrrhizic acidAnswer
  4. D
    Chronic use of nonsteroidal anti-inflammatory drugs
  5. E
    Liddle syndrome

Answer

The correct answer is excessive consumption of glycyrrhizic acid, which causes a syndrome of apparent mineralocorticoid excess.
The patient's presentation of resistant hypertension, hypokalemia, and metabolic alkalosis strongly suggests mineralocorticoid excess. However, the markedly suppressed levels of both renin and aldosterone rule out primary hyperaldosteronism (where aldosterone is elevated) and secondary hyperaldosteronism (where both are elevated). This specific hormonal profile indicates activation of the mineralocorticoid receptor by a substance other than aldosterone. Glycyrrhizic acid, found in natural black licorice, inhibits the enzyme 11-beta-hydroxysteroid dehydrogenase type 2 in the kidney. This enzyme normally converts active cortisol to inactive cortisone. When it is inhibited, cortisol (which circulates in much higher concentrations than aldosterone) inappropriately binds to and activates the mineralocorticoid receptor. This leads to profound sodium retention, potassium wasting, and a secondary suppression of the endogenous RAAS axis, perfectly matching this patient's clinical and laboratory presentation.

Step-by-Step Solution

1
Identify the primary clinical syndrome from the initial presentation.
The patient has resistant hypertension with spontaneous hypokalemia and metabolic alkalosis.
This triad strongly suggests a state of mineralocorticoid excess, narrowing the differential diagnosis away from essential hypertension.
2
Analyze the renin-angiotensin-aldosterone system (RAAS) laboratory values.
Both plasma renin activity and serum aldosterone concentrations are markedly suppressed.
This step differentiates the underlying mechanism: primary hyperaldosteronism features low renin and high aldosterone, secondary hyperaldosteronism features high renin and high aldosterone, and non-aldosterone mineralocorticoid excess features suppression of both.
3
Correlate the laboratory profile with the patient's demographics to select the most likely etiology.
An acquired non-aldosterone mineralocorticoid excess in a 5454-year-old is most consistent with exogenous ingestion of glycyrrhizic acid (licorice).
To accurately distinguish an acquired dietary/toxicological cause from genetic causes (like Liddle syndrome), which present identically on labs but manifest early in life.

Key Concept

Formulation of a differential diagnosis for mineralocorticoid excess requires sequential evaluation of renin and aldosterone levels to distinguish primary (low renin, high aldosterone), secondary (high renin, high aldosterone), and non-aldosterone-mediated etiologies (low renin, low aldosterone).
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Formulating a Differential Diagnosis

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