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64. Primary hyperaldosteronism

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Primary hyperaldosteronism refers to the state where the adrenal cortex produces too much aldosterone. It’s most commonly caused by hyperplasia or neoplasm of the glomerular zone, and it’s a common cause of secondary hypertension.

Etiology

  • Idiopathic bilateral hyperplasia of the adrenal gland
  • Aldosterone-producing adrenal adenoma (aldosteronoma)
  • Aldosterone-producing adrenal carcinoma
  • Ectopic aldosterone-producing tumors
  • Familial hyperaldosteronism

The latter three are rare. If the primary hyperaldosteronism is caused by an aldosteronoma the condition is called Conn syndrome.

Pathophysiology

The increase in aldosterone level causes the kidney to retain more salt and water, while it loses more potassium and protons. Hypokalaemia and metabolic alkalosis occur but hypertension and hypernatremia does not occur. This is because of the aldosterone escape mechanism:

When salt and water is retained the intravascular volume space will expand. This stimulates secretion of atrial natriuretic peptide (ANP) from the atria. ANP is a natriuretic hormone, meaning that it stimulates the excretion of sodium and water by the kidneys, essentially doing the opposite of aldosterone.

As the increased aldosterone stimulated sodium and water retention, ANP levels will increase as well, counteracting the sodium and water retention effect of aldosterone. ANP does not counteract the potassium and proton excretion, however.

Thanks to the aldosterone escape mechanism significant hypertension is avoided. Oedema and hypernatremia are also rarely present thanks to this.

The plasma renin level is low due to negative feedback.

Clinical features

  • Hypertension (rarely above 150 mmHg systolic)
  • Hypokalaemia
    • Fatigue
    • Muscle weakness
    • Headache

The hypertension is often resistant to drug therapy, and it can occur in young adults, who are less frequently affected by primary hypertension.

Treatment

If the cause is a neoplasm, surgical removal, preferably laparoscopic, is preferred. If the cause is something else, aldosterone receptor blockers like spironolactone are used. Limiting salt intake is also helpful.