Hyperaldosteronism occurs when there are excessive circulating levels of aldosterone. Hyperaldosteronism can be subdivided into two main types:
- Primary hyperaldosteronism (~95% of cases)
- Secondary hyperaldosteronism (~5% of cases)
Primary hyperaldosteronism is the most common and curable form of secondary hypertension and has an estimated prevalence of approximately 5-10%.
Primary hyperaldosteronism occurs when there are excessive levels of aldosterone independent of the renin-angiotensin axis. Secondary hyperaldosteronism occurs due to high renin levels.
The causes of primary hyperaldosteronism include:
- Adrenal adenoma (Conn’s syndrome) – the most common cause of hyperaldosteronism (~80% of all cases). These are usually unilateral and solitary and are more common in women.
- Adrenal hyperplasia – this accounts for ~15% of all cases. Usually bilateral adrenal hyperplasia (BAH) but can be unilateral rarely. More common in men than women.
- Adrenal cancer – a rare diagnosis but essential not to miss
- Familial aldosteronism – a rare group of inherited conditions affecting the adrenal glands
The causes of secondary hyperaldosteronism include:
- Drugs – diuretics
- Obstructive renal artery disease – renal artery stenosis and atheroma
- Renal vasoconstriction – occurs in accelerated hypertension
- Oedematous disorders – heart failure, cirrhosis and nephrotic syndrome
Patients are often asymptomatic. When clinical features are present, the classically described presentation of hyperaldosteronism is with:
- Metabolic acidosis
- Sodium levels can be normal or slightly raised
Other, less common, clinical features include:
- Muscle weakness (from persistent hypokalaemia)
- Polyuria and polydipsia
- Intermittent paraesthesia
- Tetany and paralysis (rare)
Often the earliest sign of hyperaldosteronism is from aberrant urea and electrolytes showing hypokalaemia and mild hypernatraemia. If the patient is taking diuretics, and the diagnosis is suspected, these should be repeated after the patient has taken off diuretics.
If the diagnosis is suspected, plasma renin and aldosterone levels should be checked. Low renin and high aldosterone levels (with a raised aldosterone: renin ratio) is suggestive of primary aldosteronism.
If the renin: aldosterone ratio is high, then the effect of posture on renin, aldosterone and cortisol can be investigated to provide further information about the underlying cause of primary hyperaldosteronism. Levels should be measured lying at 9 am and standing at noon:
- If aldosterone and cortisol levels fall on standing, this is suggestive of an ACTH dependent cause, e.g. adrenal adenoma (Conn’s syndrome)
- If aldosterone levels rise and cortisol levels fall on standing, this is suggestive of an angiotensin-II dependent cause, e.g. BAH
Other investigations that can help to distinguish between an adrenal adenoma and adrenal hyperplasia include:
- CT scan
- MRI scan
- Selective adrenal venous sampling
The management of hyperaldosteronism varies depending upon the underlying cause.
Adrenal adenoma (Conn’s syndrome):
- Medical management and hypertension control with aldosterone antagonists, e.g. spironolactone and eplerenone
- Surgical management with adrenalectomy
Adrenal hyperplasia is usually treated medically with aldosterone antagonists.
Management of secondary hyperaldosteronism is with the treatment of the underlying cause.
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