Diabetes insipidus occurs when the kidneys fail to retain water, instead constantly filtering it out of the bloodstream into the urine. This disorder leaves you feeling continually thirsty and at risk of dehydration.
Despite the similar symptoms, this disorder is very different to the better-known diabetes mellitus (Type 1 and Type 2 diabetes or ‘sugar’ diabetes). Nearly 20,000 Australians are thought to live with diabetes insipidus compared to the 1 million with diabetes mellitus.
There are four types of diabetes insipidus:
- Neurogenic (also known as central, cranial, hypothalamic, neurohypophyseal or pituitary diabetes insipidus) – the most common form of this disorder, is usually triggered by disease or trauma to the pituitary gland
- Nephrogenic – a disease of the kidneys, usually inherited
- Dipsogenic – caused by a defect in the hypothalamu
- Gestational – only occurs during pregnancy.
In this fact sheet, only neurogenic (central) diabetes insipidus is discussed.
When we lose water from our body, such as through sweating, it triggers a chain of biological events. The loss of fluid makes our blood more concentrated and this causes the release of an antidiuretic hormone (ADH) called vasopressin. This hormone signals the kidneys to excrete less water, making the urine more concentrated and keeps the body hydrated.
The hypothalamus produces vasopressin and it is stored in and released from the pituitary. Both the hypothalamus and the pituitary are small glands that sit close to each other at the base of the brain.
Put simply, a lack of vasopressin being released into the blood stream causes central diabetes insipidus to develop. This can occur if there is damage to either the pituitary, or the hypothalamus from:
- brain trauma due to injury or brain surgery
- a pituitary tumour or cyst such as craniopharyngioma
- infection such as meningitis
- inflammation (infiltrative disease of the pituitary or hypothalamus such a sarcoidosis)
- other disorders such as Sheehan’s syndrome.
In rare cases, the disorder is inherited, but there’s usually a family history of diabetes insipidus. However, in up to half of all cases the cause is unknown. This is called idiopathic diabetes insipidus.
When the vasopressin levels in the blood stream drop, you start losing water rapidly via your urine. This makes you need to urinate constantly. You also become excessively thirsty.
If you have diabetes insipidus, you’ll find yourself urinating more than 3 litres a day and drinking up to 10 litres of fluid. You’ll also have an imbalance in your blood electrolytes (high sodium and potassium levels). When the fluids aren’t replaced by drinking, you can suffer severe dehydration and even heart failure and seizures.
You may also have symptoms of hypopituitarism if you’ve had surgery on your pituitary or have a pituitary tumour. (see Fact Sheet: Hypopituitarism)
Testing and Diagnosis
The symptoms for diabetes insipidus generally make it easy to diagnose. However, it’s important for your doctor to make a clear distinction between diabetes insipidus and diabetes mellitus as well as to determine the cause of the condition, if possible.
To diagnose diabetes insipidus, your blood and urine concentration will be measured, usually in the morning after an overnight fast. If you have diabetes insipidus your urine will be very diluted. You may also have a water or fluid deprivation test.
To see if there is a tumour or cyst on your brain or if your pituitary is damaged, you’ll most likely also have an MRI or CT scan.
Central diabetes insipidus is treated with replacement vasopressin. A synthetic form of this hormone is available as a nasal spray, nasal drops or tablets. Following surgery, it can be given via an injection. This hormone stops the body from losing water via the kidneys so it’s important to take the medication as prescribed and to drink fluids only when thirsty. Your endocrinologist will prescribe the correct dose for you to ensure normal water balance is maintained.
With treatment, your prognosis with central diabetes insipidus is good. In most cases, the disorder is permanent so you will need to take medication long-term and have regular check-ups every six to 12 months.
If you were diagnosed with idiopathic diabetes insipidus, that is they couldn’t find a cause, you may need to have MRI or CT scans yearly to check you don’t have a slow growing tumour.
Want to know more?
Visit the Pituitary Foundation website: