Diabetes insipidus

What causes it?

Diabetes insipidus occurs when the body doesn't produce enough antidiuretic hormone (ADH) or doesn't respond correctly to its effects.

ADH helps to control the balance of water in the body by regulating the production of urine. It's produced by the hypothalamus and stored in the pituitary gland until it's needed.

There are two forms of diabetes insipidus.

Cranial diabetes insipidus occurs when the body doesn't produce enough ADH. This may be the result of a tumour in the hypothalamus or pituitary gland, infection, radiotherapy, surgery to the gland or a head injury.

Nephrogenic diabetes insipidus occurs when the kidneys don't respond to ADH. It may be caused by certain medicines, follow kidney damage or be inherited.

What are the symptoms?

Someone with diabetes insipidus passes excessive amounts of urine, sometimes more than three litres over 24 hours. They're always thirsty and drink almost constantly.

People with diabetes insipidus may need to urinate every 15 to 20 minutes. Disturbed sleep - and daytimes - are the consequence of having to pass water so frequently.

Dehydration is common when diabetes insipidus is left undiagnosed or untreated, causing high levels of sodium in the blood. This in turn can lead to tiredness, lethargy, confusion and the risk of fits and coma.

Babies and young children with diabetes insipidus may display failure to thrive.

How is it diagnosed?

Specific tests are performed when someone is suspected of having diabetes insipidus. These measure:

• The volume of urine produced over a 24-hour period
• The amount of urine produced after fluid input has been restricted (if diabetes insipidus is present, large volumes will still be produced)
• How the body responds to being given ADH (if it lowers the amount of urine, cranial diabetes insipidus is the likely cause; if it remains high, the nephrogenic form is likely)

Scans are also used to identify specific causes.

Antenatal diagnosis of diabetes insipidis is possible.

What's the treatment?

If a treatable cause of cranial diabetes insipidus is found, this will be treated. Otherwise, synthetic ADH can be given on daily basis.

Nephrogenic diabetes insipidus is treated with a low-sodium diet and medication to reduce the amount of urine produced. If an underlying cause is found and can be treated, this form should resolve.