Primary hyperaldosteronism

Primary hyperaldosteronism was previously thought to be most commonly caused by an adrenal adenoma, termed Conn's syndrome. However, recent studies have shown that bilateral idiopathic adrenal hyperplasia is the most common cause. Differentiating between the two is important as this determines treatment.

Causes

• bilateral idiopathic adrenal hyperplasia: the cause of around 60-70% of cases
• adrenal adenoma: 20-30% of cases
• unilateral hyperplasia
• familial hyperaldosteronism
• adrenal carcinoma

Features

• hypertension
  • increasingly recognised but still underdiagnosed cause of hypertension
• hypokalaemia
  • e.g. muscle weakness
  • this is a classical feature in exams but studies suggest this is seen in only 10-40% of patients, and is more common with adrenal adenomas
• metabolic alkalosis

Investigations

• guidelines vary but certain patients should be screened for primary hyperaldosteronism, e.g.
  • hypertension with hypokalemia
  • treatment-resistant hypertension
• the 2016 Endocrine Society recommend that a plasma aldosterone/renin ratio is the first-line investigation in suspected primary hyperaldosteronism
  • should show high aldosterone levels alongside low renin levels (negative feedback due to sodium retention from aldosterone)
• following this a high-resolution CT abdomen and adrenal vein sampling is used to differentiate between unilateral and bilateral sources of aldosterone excess
  • if the CT is normal adrenal venous sampling (AVS) can be used to distinguish between unilateral adenoma and bilateral hyperplasia

Management

• adrenal adenoma: surgery (laparoscopic adrenalectomy)
• bilateral adrenocortical hyperplasia: aldosterone antagonist e.g. spironolactone

CT abdomen showing a right-sided adrenal adenoma in a patient who presented with hypertension and hypokalaemia. The adenoma can be seen 'next to' or 'below' the liver.