Cranial diabetes insipidus
The 3 most common causes of cranial diabetes insipidus are:
- a brain tumour that damages the hypothalamus or pituitary gland
- a severe head injury that damages the hypothalamus or pituitary gland
- complications that occur during brain or pituitary surgery
No cause can be found for about a third of all cases of cranial diabetes insipidus.
These cases, known as idiopathic, appear to be related to the immune system attacking the normal healthy cells producing AVP.
It's unclear what causes the immune system to do this.
Less common causes of cranial diabetes insipidus include:
- cancers that spread from another part of the body to the brain
- Wolfram syndrome, a rare genetic disorder that also causes vision loss
- brain damage caused by a sudden loss of oxygen, which can occur during a stroke or drowning
- infections, such as meningitis and encephalitis, that can damage the brain
Nephrogenic diabetes insipidus
Your kidneys contain nephrons, which are tiny intricate structures that filter waste products from the blood and help produce urine.
They also control how much water is reabsorbed into your body and how much is passed in the urine when you pee.
In a healthy person, AVP acts as a signal to the nephrons to reabsorb water into the body.
In nephrogenic diabetes insipidus, the nephrons in the kidneys are not able to respond to this signal, leading to excessive water loss in large amounts of urine.
Your thirst increases to try to balance this loss from the body.
Nephrogenic diabetes insipidus can be present at birth (congenital) or develop later in life as a result of an external factor (acquired).
These are described in more detail below.
Congenital nephrogenic diabetes insipidus
Two abnormal changes in genes that leads to them not working properly (genetic mutations) have been identified that cause congenital nephrogenic diabetes insipidus.
The first, known as the AVPR2 gene mutation, is responsible for 90% of all cases of congenital diabetes insipidus.
But it's still rare, occurring in an estimated 1 in 250,000 births.
The AVPR2 gene mutation can only be passed down by mothers (who may appear to not be affected) to their sons (who are affected).
The remaining 10% of cases of congenital nephrogenic diabetes insipidus are caused by the AQP2 gene mutation, which can affect both males and females.
Acquired nephrogenic diabetes insipidus
Lithium is the most common cause of acquired nephrogenic diabetes insipidus.
It's a medication often used to treat bipolar disorder.
Long-term lithium use can damage the cells of the kidneys so they no longer respond to AVP.
Just over half of all people on long-term lithium therapy develop some degree of nephrogenic diabetes insipidus.
Stopping lithium treatment often restores normal kidney function, although in many cases the damage to the kidneys is permanent.
Because of these risks, it's recommended that you have kidney function tests every 3 months if you're taking lithium.
Other causes of acquired nephrogenic diabetes insipidus include:
- hypercalcaemia – a condition where there's too much calcium in the blood (high calcium levels can damage the kidneys)
- hypokalemia – a condition where there's not enough potassium in the blood (all the cells in the body, including kidney cells, require potassium to function properly)
- pyelonephritis (kidney infection) – where the kidneys are damaged by an infection
- ureteral obstruction – where 1 or both tubes that connect the kidneys to the bladder (ureters) become blocked by an object, such as a kidney stone, which damages the kidneys