Summary

Conn's syndrome (primary hyperaldosteronism, PA) is the most common cause of secondary hypertension, accounting for 5-15% of all hypertensive patients. It is caused by autonomous aldosterone secretion, typically from an aldosterone-producing adenoma (APA) or bilateral adrenal hyperplasia (BAH). Excess aldosterone causes sodium retention (hypertension) and potassium loss (hypokalaemia, though present in only ~50%). Screening is with the aldosterone-to-renin ratio (ARR); confirmatory testing includes saline suppression test or fludrocortisone suppression test. Adrenal CT and adrenal vein sampling (AVS) distinguish unilateral disease (adenoma — surgery) from bilateral disease (hyperplasia — medical therapy with mineralocorticoid receptor antagonists).

Key Facts

• Prevalence: 5-15% of all hypertensives; >20% of resistant hypertension
• Aetiology: Bilateral adrenal hyperplasia (~60%) > Aldosterone-producing adenoma (~35%) > Rare (carcinoma, familial)
• Classic triad: Hypertension + Hypokalaemia + Metabolic alkalosis (but hypokalaemia only in ~50%)
• Screening: Aldosterone-to-Renin Ratio (ARR); High aldosterone + Suppressed renin
• Confirmation: Saline suppression test; Fludrocortisone suppression test
• Localisation: CT adrenals + Adrenal vein sampling (AVS)
• Treatment: Unilateral (adenoma) = Laparoscopic adrenalectomy; Bilateral = Spironolactone/Eplerenone

Clinical Pearls

"Hypokalaemia Is NOT Required": Classic teaching describes hypokalaemia, but it's only present in ~50% of cases. Screen for PA in resistant hypertension even with normal potassium.

"ARR = Screening Test": The Aldosterone-to-Renin Ratio (ARR) is the screening test. A high ratio (high aldosterone, suppressed renin) suggests PA. But medications affect results — ACE inhibitors, ARBs, beta-blockers, diuretics all interfere.

"AVS Is the Gold Standard for Localisation": Adrenal CT may miss small adenomas and cannot distinguish unilateral from bilateral disease. Adrenal vein sampling (AVS) determines lateralisation and guides surgical vs medical management.

"Spironolactone Works but Has Side Effects": Spironolactone is first-line for bilateral PA, but anti-androgenic side effects (gynaecomastia, erectile dysfunction, menstrual irregularity) limit use. Eplerenone is more expensive but selective.

"PA Causes Target Organ Damage Beyond BP": Aldosterone excess causes cardiovascular and renal damage independent of blood pressure. Treating PA reduces cardiovascular risk beyond BP control alone.

Why This Matters Clinically

Primary hyperaldosteronism is underdiagnosed. Identifying and treating PA improves blood pressure control, reduces cardiovascular risk, and may achieve cure with surgery. All patients with resistant hypertension should be screened.[1,2]

Examination Findings

General:

• Usually unremarkable
• No specific signs of PA itself

Cardiovascular:

• Elevated blood pressure
• Signs of end-organ damage (LVH — heave, S4)

Neuromuscular:

• Muscle weakness (if hypokalaemic)
• Reduced reflexes (severe hypokalaemia)

Surgical Outcomes

Medical Outcomes

Key Guidelines

Key Evidence

TAIPAI Study

• Surgical treatment of APA leads to greater BP reduction than medical therapy
• Supports adrenalectomy for unilateral PA

What is Conn's syndrome?

Conn's syndrome (primary hyperaldosteronism) is a condition where one or both adrenal glands produce too much of a hormone called aldosterone. This causes high blood pressure and sometimes low potassium.

Why does it matter?

It's the most common treatable cause of high blood pressure. Finding and treating it can cure or significantly improve blood pressure and reduce the risk of heart attacks and strokes.

What are the symptoms?

• High blood pressure (often hard to control with tablets)
• Low potassium levels (may cause muscle weakness, cramps)
• Often no specific symptoms

How is it diagnosed?

• Blood tests measuring aldosterone and renin
• Confirmatory tests (salt loading or saline infusion)
• CT scan and sometimes sampling blood from the adrenal veins

What is the treatment?

• If one adrenal gland is affected: Keyhole surgery to remove it (often curative)
• If both glands are affected: Tablets to block the effects of aldosterone

High-Yield Exam Topics

Sample Viva Questions

Q1: A 45-year-old has resistant hypertension on 4 antihypertensives. How do you screen for primary hyperaldosteronism?

Model Answer: I would screen with an Aldosterone-to-Renin Ratio (ARR). Before testing, I would correct hypokalaemia if present (low K+ suppresses aldosterone) and ideally stop interfering medications (ACE inhibitors, ARBs, diuretics, beta-blockers, spironolactone) for at least 4 weeks, using calcium channel blockers or alpha-blockers for BP control. An elevated ARR (high aldosterone + suppressed renin) suggests PA. Confirmatory testing with saline suppression test would follow: failure to suppress aldosterone after 2L saline confirms autonomous aldosterone secretion. Then CT adrenals and adrenal vein sampling for localisation.

Q2: How do you distinguish aldosterone-producing adenoma from bilateral adrenal hyperplasia?

Model Answer: CT adrenals can identify an adenoma, but it cannot reliably distinguish between unilateral and bilateral disease. Adrenal vein sampling (AVS) is the gold standard for lateralisation. Selective catheterisation of both adrenal veins measures aldosterone and cortisol. A lateralisation ratio >4:1 suggests unilateral disease (adenoma) — suitable for surgery. No lateralisation suggests bilateral hyperplasia — treated medically with mineralocorticoid receptor antagonists.

Q3: What are the treatment options for confirmed primary hyperaldosteronism?

Model Answer: Treatment depends on subtype:

• Unilateral (adenoma): Laparoscopic adrenalectomy is curative in 50% (normotensive) and improves BP in 90%. Pre-operative spironolactone corrects potassium and BP.
• Bilateral (hyperplasia): Medical therapy with mineralocorticoid receptor antagonists — Spironolactone 12.5-50 mg initially, titrated up to 400 mg if needed. Eplerenone is an alternative with fewer anti-androgenic side effects. Additional antihypertensives may be required.

Common Exam Errors

Last Reviewed: 2025-12-24 | MedVellum Editorial Team

Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists.