What is Conn’s syndrome?

Conn’s syndrome is a hormonal condition in which one or both adrenal glands produce more of the hormone aldosterone than normal. Aldosterone helps balance the levels of salt and potassium in the body and helps control blood pressure.

Conn’s syndrome causes:

• high blood pressure (hypertension), which can be quite severe
• lower than normal potassium levels in the blood
• an increased volume of blood in the body

Conn’s syndrome is also known as Conn disease or primary hyperaldosteronism.

What are the symptoms of Conn’s syndrome?

The most common sign of Conn’s syndrome is high blood pressure that is difficult to control, even with medication. Some people also have symptoms such as:

• headaches
• muscle weakness or cramps
• nausea
• frequent urination
• heart palpations

Unless it is treated and controlled, high blood pressure increases your risk of having a stroke, heart disease or kidney disease.

What causes Conn’s syndrome?

In about 2 out of 3 people, Conn’s syndrome develops because the adrenal glands become overactive and produce too much aldosterone.

About 1 in 3 people have a benign (non-cancerous) tumour on the adrenal gland. These tumours are known as adenomas and are often found by accident during a scan to investigate an unrelated issue.

A few people have one of a group of inherited genetic conditions known as familial hyperaldosteronism. Very occasionally, Conn’s syndrome is caused by a cancerous tumour in the adrenal gland. 

Whatever the cause, the excess aldosterone encourages the kidneys to conserve salt and not excrete it in the urine. If you retain salt you retain water as well, so the amount of blood in your body increases. This causes high blood pressure.

When should I see my doctor?

Have your blood pressure checked regularly because it may change. Make sure you get treatment for high blood pressure as soon as possible.

Ask your doctor to consider screening for Conn’s syndrome if:

• you are already being treated with hypertension medication and it is not helping
• you have a family history of high blood pressure
• you developed high blood pressure when you were 40 or older
• tests show low potassium levels in your blood

How is Conn’s syndrome diagnosed?

It is often difficult to diagnose Conn’s syndrome. Doctors may suspect the condition if there is no drop in high blood pressure, despite treatment with several different hypertension medications.

If they suspect you have Conn’s syndrome, your doctor will examine you and take a medical history. You may be referred to a specialist.

The doctor may also order blood tests to check the levels of aldosterone and of another hormone, known as renin, in your blood. It is important that you follow the instructions your doctor or the laboratory gives you before having this blood test. You will need to stop taking certain drugs around 2 weeks before the test.

Other tests for the condition include:

• blood tests to check salt levels and creatinine in the blood
• a computerised tomography (CT) scan of the adrenal glands
• adrenal vein sampling, where blood samples are taken from each adrenal gland to compare the amount of hormones they are producing
• genetic tests for familial hyperaldosteronism

How is Conn’s syndrome treated?

The best treatment for Conn's syndrome will depend on the cause.

If both adrenal glands are overactive, you will be prescribed a medicine to block the effect of too much aldosterone. The most common medicine is spironolactone.

If the condition is caused by an adrenal tumour, you will be referred to a surgeon for an operation to remove the adrenal gland. The operation is known as an adrenalectomy. If the tumour is small and not cancerous, then you may be offered laparoscopic (keyhole) surgery. If the tumour is very large or suspected to be cancerous, you are likely to have open surgery, done through a cut in your back, side or abdomen. For this, you will have a general anaesthetic.

If you have a benign adrenal tumour but can’t have surgery, you should be able to take medication.

Whatever the cause, both medication and surgery are highly effective in reducing the amount of aldosterone you produce. This often reduces your blood pressure and your risk of heart disease or stroke, but not always.

Can Conn’s syndrome be prevented?

If you know that Conn’s syndrome runs in your family, ask your doctor about genetic testing. If you do have the faulty gene for familial hyperaldosteronism, your doctor may suggest you restrict your intake of salt since this can delay the start of high blood pressure and other symptoms.

Resources and support

Find out more about adrenal glands and adrenal surgery here.