Water diabetes; DI
Anti-diuretic hormone (also called vasopressin) is produced in the hypothalamus and then secreted by the pituitary gland into the bloodstream at the base of the brain. Anti-diuretic hormone is needed to control the fluid balance in the body. It does this by making the kidneys produce more concentrated urine.
There are two types of diabetes insipidus, cranial and nephrogenic. Cranial diabetes insipidus is a condition in which the hypothalamus does not produce enough anti-diuretic hormone. Nephrogenic diabetes insipidus is a condition in which the kidneys fail to respond to anti-diuretic hormone. Both conditions mean that the kidneys are unable to retain water, leading to the passing of too much dilute urine (pale urine). In severe cases, up to 20 litres of urine are passed in one day. This can occur even when the body is dehydrated and should be trying to save fluid by producing concentrated urine (dark urine).
Diabetes insipidus is not related to diabetes mellitus (often just called diabetes).
Usually diabetes insipidus is thought to have no clear, definable cause. This is known as idiopathic. However, some causes can be found:
The symptoms of diabetes insipidus include:
These symptoms are similar to those of diabetes mellitus, but there is no sugar present in the urine and blood sugar levels are normal.
Providing there is adequate provision of water to satisfy the excess thirst, the signs of diabetes insipidus can be minimal. Dehydration can occur if fluid intake cannot keep pace with the amount of urine passed. This can result in an imbalance of electrolytes in the blood, possibly causing symptoms such as headache, fatigue or muscle pain.
Diabetes insipidus is rare in the general population, affecting approximately one in 25,000 people. In patients who have had pituitary surgery, 10–20% can experience symptoms temporarily after the operation. A similar percentage of patients who have had a severe head injury develop short-term diabetes insipidus. A minority of individuals have persistent symptoms after pituitary surgery and head injury.
Genetic causes of diabetes insipidus are very rare.
In most cases diabetes insipidus is not inherited. Very rarely, it can be due to inherited conditions such as a mutation in the genes that produce anti-diuretic hormone or faults in the genes that produce receptors within the kidney cells that enable anti-diuretic hormone to function.
Certain blood and urine tests can point to a diagnosis of diabetes insipidus such as a high sodium level (hypernatraemia) and high concentration of the blood (serum or plasma osmolality), along with a low urine concentration (urine osmolality).
To be certain of the diagnosis, a ‘water deprivation test’ is commonly undertaken. This takes several hours and involves attending hospital early in the day and being deprived of any fluid intake. Initial blood and urine tests are done to measure the concentration and salt levels in both. At hourly intervals, the same tests are repeated along with measurements such as blood pressure, weight and the amount of urine passed. If the blood sodium or concentration levels rise significantly above normal along with low urine concentration, then it is likely that the patient has diabetes insipidus.
To test if the diabetes insipidus is cranial or nephrogenic, an injection of desmopressin (a manufactured form of anti-diuretic hormone) is given. An hour after this injection is given, the urine concentration is tested again. If there is an increased concentration of more than 50% then cranial diabetes insipidus is most likely. Patients with nephrogenic diabetes insipidus will have a poor response to the desmopressin injection.
If cranial diabetes insipidus is diagnosed, an MRI scan of the head may be performed to look for any obvious abnormality in the hypothalamus (the region of the brain which makes anti-diuretic hormone) or in the pituitary gland (which releases anti-diuretic hormone).
In mild cases of cranial diabetes insipidus, treatment is not always needed. Those patients might just need to increase the amount of water they drink to compensate for the increased fluid loss through urination. Cranial diabetes insipidus can be treated with a manufactured version of anti-diuretic hormone, called desmopressin, in the form of a nasal spray or tablet. The dose given and how often medication needs to be taken, will depend on the severity of diabetes insipidus and the symptoms the patient has. In cases of nephrogenic diabetes insipidus, a water tablet (diuretic) called hydrochlorothiazide or amiloride may help, but desmopressin will not.
Side-effects are very rare. Too much desmopressin can lead to low salt levels in the blood and a gathering of excess fluid in the body. This occurs because the desmopressin prevents the kidneys from excreting enough urine. If the patient is concerned about any side-effects, he or she should talk to their endocrinologist or GP.
With appropriate treatment, patients with diabetes insipidus should be able to pursue a normal lifestyle. However, it is possible they will require long-term monitoring by their GP and/or endocrinologist. Patients need to be careful to avoid dehydration. In cranial diabetes insipidus, desmopressin is a life-sustaining therapy and should only be stopped following specialist advice, especially when patients are admitted to hospital for any reason.
Last reviewed: Mar 2018