Primary Hyperaldosteronism

Autonomous production of aldosterone independent of its regulators (angiotensin II/potassium)

Aetiology

Adrenal adenoma (Conn's syndrome)

  • ~30% cases
  • Do not suppress ACTH - adjacent and contralateral adrenal tissue is not atrophic
Genetic features
  • KCNJ5 channel is a rectifying selective channel which maintains membrane hyperpolarisation
  • Mutations lead to loss of ion selectivity; Na+ entry and depolarisation and therefore increased aldosterone production

Bilateral adrenal hyperplasia

  • Idiopathic
  • Accounts for ~60% cases

Rare causes

  • Genetic mutations - several familial forms of hyperaldosteronism recognised as well as recurrent somatic mutations observed in sporadic cases
  • Unilateral hyperplasia

Pathophysiology

  • Commonest secondary cause of hypertension

Cardiac actions of aldosterone

  • Increased cardiac collagen
  • Cytokines and ROS synthesis
  • Increased sodium retention
  • Abnormal endothelial function
  • Increased sympathetic outflow
  • All contribute to increased BP, LVH and atheroma

Clinical presentation

  • Significant hypertension
  • Hypokalaemia (~30%)
  • Alkalosis

Investigations

Confirm aldosterone excess

  • Measure plasma aldosterone: renin ratio
  • If ratio raised investigate further with saline suppresion test
    • Failure of plasma aldosterone to suppress by > 50% with 2 litres of normal saline confirms PA

Confirm subtype

  • Adrenal CT to demonstrate adenoma
  • Sometimes adrenal vein sampling to confirm adenoma is true source of aldosterone excess

Management

Adrenal adenoma

  • Unilateral laproscopic adrenalectomy
  • Cures hypokalaemia
  • Cures hypertension in 30-70% of cases

Bilateral adrenal hyperplasia

  • Mineralocorticoid receptor antagonists - spironolactone or eplerenone