Introduction

Conn’s syndrome is primary hyperaldosteronism – an excess of aldosterone.
Hyperaldosteronism is an important cause of secondary hypertension. 
The epidemiology is unclear, due to a selection bias in some of the studies that have attempted to assess this. The prevalence amongst those with resistant hypertension is thought to be 5-10%, but amongst the general population it is probably around 1% (estimates vary from 0.1 – 4%).
It is a recognised cause of hypertension. It can also cause alkylosis (due to the exchange of sodium for hydrogen by some channels in the tubule).
It is often symptomless, but may present with symptoms of hypokalaemia – such as muscle weakness, fatigue, polyuria, cramps.

Causes

  • About 80% of cases are due to a solitary mineralocorticoid producing adrenal adenoma.
    • Classically this is “Conn’s Syndrome” and other causes technically are not. In reality, the terms hyperaldosteronism and Conn’s syndrome are often used interchangeably
  • About 20% of cases are due to adrenal hyperplasia.
    • 15% of cases are bilateral
    • <5% of cases are unilateral
  • Adrenal carcinoma can also cause hyperaldosteronism

Pathology

Excess aldosterone acts on the distal renal tubule, resulting in retention of sodium.
 

Presentation

  • Hypertension
  • Hypokalaemia
    • 70% of patients have normal potassium
    • May cause weakness
  • Hypernatraemia
    • Most patients have sodium in the normal range
  • Metabolic alkalosis
  • Polyuria and polydipsia

Investigations

  • U+E – may show hypernatraemia and hypokalaemia – but often not
  • Renin and aldosterone levels
    • Increased aldosterone
    • Decreased renin – if renin is normal then primary aldosteronism is excluded
    • Aldosterone/renin ratio is the usual way that diagnosis is confirmed
    • Ratio >800 confirms diagnosis and prompts need to investigate for the cause
    • Results can be altered by antihypertensives
  • ECG – signs of hypokalaemia
  • CT / MRI
    • To look for adrenal mass or hyperplasia
  • Salt loading and renin and aldosterone levels
    • Patients are loaded with salt tablets and high salt diet for two weeks
    • In the normal physiological state, this should suppress plasma aldosterone
    • In primary hyperaldosteronism, aldosterone is not suppressed
    • Rarely used – doesn’t seem to enhance diagnostic rate and is fiddly and time-consuming
  • Lying and standing aldosterone and renin levels
    • Can differentiate between adrenal hyperplasia and adrenal adenoma
    • Samples taken after lying down for several hours and repeated after standing for several hours
    • Need careful interpretation by a specialist
    • In adrenal hyperplasia – aldosterone increases after 4 hours of standing by >30%
    • In adrenal adenoma – there is not change in postural results

Differentials

There are many possible differentials, although clinically the most important is renal artery stenosis (RAS) which often presents with a similarly hypertensive patient. In these circumstances, performing an USS of the renal tract is important to exclude RAS as a differential. Other findings in RAS include:

  • Raised renin AND aldosterone
  • Renal arteriogram is the gold standard of diagnosis
  • U+E may show hypokalaemia and impaired renal function

Other differentials include:

  • Cushing’s disease
    • Aldosterone and renin levees are low
  • Congenital adrenal hyperplasia
  • Nephrotic syndrome

Management

  • Adrenal adenoma (Conn’s Syndrome)
    • Surgical removal of the adenoma
    • In the meantime, medical management may be required:
      • Spironolactone (aldosterone antagonist)
    • Hypertension may persist after removal of tumour due to secondary effects of hypertension on the vasculature
  • Bilateral adrenal hyperplasia
    • Medical management with aldosterone antagonists
      • Spironolactone – blocks both aldosterone and testosterone receptors, which can cause gynaecomastia, menstrual irregularities and erectile dysfunction
      • Amiloride – another potassium sparing diuretic, although its effects are generally weaker than spironolactone
      • Eplerenone – selective aldosterone antagonist and thus does not suffer from the same testosterone effects as spironolactone. More evidence is needed to evaluate its effectiveness in adrenal hyperplasia

References

  • Hyperaldosteronism - patient.info
  • Murtagh’s General Practice. 6th Ed. (2015) John Murtagh, Jill Rosenblatt
  • Oxford Handbook of General Practice. 3rd Ed. (2010) Simon, C., Everitt, H., van Drop, F.

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