A 38-year-old woman presents with a 6-month history of progressive headaches and palpitations. On examination, blood pressure is 168/110 mmHg bilaterally, heart rate 98 bpm, and there is a palpable abdominal mass. Laboratory investigations show serum potassium 3.2 mEq/L, serum sodium 148 mEq/L, and plasma glucose 156 mg/dL (fasting). Plasma renin activity is suppressed at 0.3 ng/mL/hr (normal 0.5–1.6). Abdominal CT reveals a 3 cm left adrenal nodule with high lipid content. What is the most likely diagnosis?

Explanation

## Clinical Presentation & Diagnosis **Key Point:** The triad of hypertension, hypokalemia, and metabolic alkalosis with suppressed plasma renin activity is pathognomonic for primary aldosteronism (Conn syndrome). ### Diagnostic Features in This Case | Feature | Finding | Significance | |---------|---------|---------------| | **Blood pressure** | 168/110 mmHg | Moderate-to-severe hypertension | | **Serum potassium** | 3.2 mEq/L | Hypokalemia (aldosterone-induced urinary K+ loss) | | **Serum sodium** | 148 mEq/L | Hypernatremia (aldosterone-mediated Na+ reabsorption) | | **Plasma renin activity** | 0.3 ng/mL/hr (suppressed) | **Hallmark of primary aldosteronism** | | **Imaging** | Left adrenal nodule, lipid-rich | Consistent with aldosterone-producing adenoma (APA) | | **Fasting glucose** | 156 mg/dL | Secondary hyperglycemia (aldosterone effect) | ### Pathophysiology 1. **Autonomous aldosterone secretion** from an adrenal adenoma → sodium retention and potassium wasting 2. **Suppressed renin** because increased plasma volume and sodium inhibit the renin-angiotensin system 3. **Metabolic alkalosis** from hypokalemia (H+ shifts intracellularly to replace K+) 4. **Hypertension** from sodium and fluid retention **High-Yield:** The **suppressed plasma renin activity** in the setting of hypertension + hypokalemia + adrenal nodule is the diagnostic linchpin — this rules out secondary causes (renal artery stenosis, renovascular disease) where renin would be elevated. ### Diagnostic Workup ```mermaid flowchart TD A[Hypertension + Hypokalemia]:::outcome --> B{Plasma renin activity?}:::decision B -->|Suppressed| C[Primary aldosteronism likely]:::action B -->|Elevated| D[Secondary aldosteronism]:::action C --> E[Aldosterone-to-renin ratio]:::action E -->|Elevated| F[Adrenal imaging: CT/MRI]:::action F --> G[Unilateral nodule]:::outcome G --> H[Aldosterone-producing adenoma]:::outcome D --> I[Investigate renal artery stenosis]:::action ``` **Clinical Pearl:** Hypokalemia in a hypertensive patient should always raise suspicion for primary aldosteronism — it is present in ~50% of cases and is the most common secondary cause of hypertension in developed countries. [cite:Harrison 21e Ch 297]