Conn's Syndrome

What is Conn's syndrome?


Conn's syndrome is a condition that affects the adrenal glands and involves excess production of a hormone called aldosterone. This condition is also known as primary hyperaldosteronism.

Conn's syndrome is significant in that it is a potentially curable cause of high blood pressure (hypertension). Some studies suggest that Conn's syndrome is rare i.e. one new case in a million people each year. However, when detailed investigations have been performed in patients with high blood pressure, up to 15% may have this condition.




The excess secretion of the hormone aldosterone into the blood from an abnormal adrenal gland or glands causes Conn's syndrome. One of two types of abnormality may be present: a benign tumour on one adrenal gland, called an adenoma or a general enlargement of both adrenal glands, called hyperplasia.

The underlying reasons for the development of an adenoma or hyperplasia are unknown.



What else could be the cause?

The most common cause of high blood pressure is essential hypertension, and this may mimic Conn's syndrome. Thus, high blood pressure and low blood potassium may be due to essential hypertension, which is treated with diuretic drugs that cause a loss of potassium in the urine.


In addition, plasma renin activity may be suppressed by some drugs that are commonly used to treat hypertension (for example, beta-blockers). The suppression may mislead the doctor to an incorrect diagnosis of primary hyperaldosteronism (Conn's syndrome).


There are also a few very rare conditions your doctor might need to exclude.




High blood pressure is the main, and often the only, symptom of Conn's syndrome. Other symptoms may occur because high aldosterone levels in the blood affect the kidneys by increasing the loss of the mineral potassium in the urine. This in turn may lead to a decrease in blood potassium, resulting in tiredness, muscle weakness and passing large volumes of urine (polyuria) especially at night (nocturia). However, these symptoms are also found in many other conditions (for example, diabetes mellitus or hypercalcaemia) and do not alone establish a diagnosis of Conn's syndrome. Also, many patients with Conn's syndrome do not necessarily have a low blood potassium level.




Conn's syndrome should be suspected in all patients with high blood pressure.


Investigation for Conn's syndrome has traditionally been limited to patients who have low blood potassium, or in whom blood pressure is moderate to severe (i.e. more than 160/110 mm Hg), or is difficult to control with medication. However, using these criteria, many patients with Conn's syndrome will not be diagnosed. For example, about 40% of patients with Conn's syndrome have normal blood potassium levels.


The most rigorous method of diagnosis is to measure the blood levels of two hormones: aldosterone and renin (which plays a role in stimulating aldosterone production). In Conn's syndrome, the aldosterone level is elevated and the renin level is low or undetectable.



Seeing a specialist

Your family doctor may refer patients with high blood pressure and low blood potassium to a specialist in endocrinology (diagnosing conditions that affect your glands or endocrine system), kidney disease or clinical pharmacology.


Other patients who should be referred for investigation include those with severe high blood pressure, or those who are poorly controlled on medication or who have a family member with an endocrine tumour.


However, there is motivation for all patients with high blood pressure (i.e. more than 140/90 mm Hg) to have their aldosterone and plasma renin activity measured. The difficulty is that the blood samples must be taken under controlled conditions, usually at 09.00am after lying down for 30 minutes. Blood samples require correct interpretation, as your diet, drug therapy and other factors could affect the results of these tests. Thus, in practice, aldosterone and plasma renin activity measurements are specialist investigations.



What can you do for yourself?

A low-salt diet may reduce some symptoms by improving the low blood potassium and blood pressure. However, lowering your dietary salt intake may also cause an increase in the plasma renin activity (potentially masking the correct diagnosis).


To ensure a proper evaluation some patients may be asked to ingest a fixed intake of salt tablets for 72 hours before blood is tested for potassium, aldosterone and plasma renin.



What can your doctor do?

While awaiting evaluation at a specialist centre, potassium supplement tablets may be given to improve the low blood potassium. Some patients may have very low blood potassium, warranting urgent in-patient treatment.


Patients with Conn's syndrome will have special scans of the adrenal glands done. This will allow the important distinction to be made between a single adenoma and hyperplasia of both adrenal glands. Blood may also be taken directly from the adrenal veins (via a catheter passed through a vein in the groin) to determine whether both adrenals are over-secreting aldosterone.


Treatment for an aldosterone-producing adenoma is surgical removal (unilateral adrenalectomy). This may be performed via laparoscopic (keyhole) surgery in some advanced centres.

Patients with bilateral hyperplasia (and also those with an adenoma awaiting surgery) may be treated with the drug spironolactone (e.g. Aldactone), which acts by blocking the effect of aldosterone. Spironolactone is somewhat similar in chemical structure to the female sex hormone, oestradiol, and therefore has some female hormonal effects.


Without drug or surgical treatment, high blood pressure in many patients with Conn's syndrome is difficult to control. Poorly-controlled high blood pressure is associated with increased rates of stroke, heart disease and kidney failure.




Treatment of Conn's syndrome is usually successful. Many patients with a single adrenal adenoma will be able to stop drug treatment and will have normalised blood pressure.


Nevertheless, many specialist centres will evaluate and monitor a patient with Conn's syndrome for life to help prevent the rare possibility of growth of a second adenoma.  


Patients with bilateral hyperplasia should undergo life-long monitoring of the effectiveness and side effects of drug treatment. For these patients, quality of life is generally good, although some may not be able to tolerate spironolactone treatment.