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What is diabetes insipidus?
Diabetes insipidus (DI) is an uncommon condition in which the body is unable to effectively retain water. It can cause people to be very thirsty and pass large amounts of urine.
The brain regulates the concentration of your blood by controlling the amount of fluid that you take in through drinking and eating, and the amount of fluid you pass through urine.
A region of the brain called the hypothalamus can sense when blood is too concentrated and, in response, triggers the release of a hormone called vasopressin (also known as antidiuretic hormone), which is stored in the pituitary gland.
When vasopressin is released into the bloodstream by the pituitary gland, it acts on the kidneys, causing them to retain water and reduce the amount of fluid that is excreted via urine. When the concentration of the blood drops too low, the hypothalamus reduces its stimulation of vasopressin release. This causes the kidneys to excrete more fluid.
Diabetes insipidus results from a deficiency in the levels or action of vasopressin.
There are three main types of diabetes insipidus: central DI, nephrogenic DI and gestational DI.
In central DI, an abnormality in the brain causes too little vasopressin to be produced.
- Head injuries;
- Infections such as meningitis and encephalitis;
- Tumours in the brain;
- Brain surgery or radiotherapy;
- Conditions that affect the blood vessels in the brain including aneurysm, bleeding, sickle-cell anaemia, and;
- Inherited conditions such as Wolfram syndrome.
In some cases, no underlying cause can be identified.
In nephrogenic DI, the kidneys no longer respond to vasopressin, even though normal levels are still produced by the brain.
- Kidney diseases such as chronic kidney disease and renal tubular acidosis;
- Hypercalcaemia - elevated levels of calcium in the blood;
- Some medications such as lithium, orlistat and certain antibiotics;
- Hypokalaemia - reduced levels of potassium in the blood, and;
- Rare inherited conditions.
In some cases, no underlying cause can be identified.
Gestational DI can occur in the last trimester of pregnancy and in the period just after birth.
- A hormone produced by the placenta called vasopressinase destroys the vasopressin circulating in the bloodstream;
- An abnormality in the thirst mechanism, and;
- Reduced sensitivity to vasopressin in the kidneys.
In some cases, no underlying cause can be identified, but it usually resolves 4-6 weeks after birth.
Gestational DI may run in some families. Once it has occurred in one pregnancy, it may occur again in later pregnancies.
Signs and symptoms
The main features of DI are:
- Sudden onset in symptoms;
- Abnormally high thirst, particularly for cold water, that is unable to be quenched despite drinking large amounts of fluids, and;
- Passing very high amounts of colourless urine.
The amount of urine passed will vary, but in severe cases can be up to 20 litres a day.
Because of the need to urinate frequently, people with DI will often wake frequently during the night in order to go to the toilet, or experience bedwetting.
Other symptoms can include:
In babies with DI, symptoms can include:
- Persistent crying and irritability despite efforts to comfort or settle them;
- Very wet nappies that require frequent changing;
- Vomiting and fever;
- Reduced growth or weight loss, and;
- A tendency to be cold, particularly in their hands and feet.
Methods for diagnosis
When diagnosing DI, it is important for the doctor to rule out other medical conditions that may be causing the symptoms and to determine the underlying cause.
Your doctor will perform a physical examination, ask questions about your symptoms and order some tests. Tests include:
Analysis of the urine can determine its concentration. If the concentration is low, it can indicate DI.
Blood may be taken to measure the concentration of the blood and the amount of glucose (in order to check for diabetes mellitus).
Fluid deprivation test
A fluid or water deprivation test is generally done in hospital, so your health can be closely monitored while it occurs. During the test, no water or other fluids are taken for a number of hours. During this time, you will be monitored for:
- Changes in your body weight;
- How much urine you produce;
- The concentration of your urine, and;
- The concentration of your blood.
If fluid control is normal, during the test you will tend to produce less urine and it will become more concentrated.
However when you have DI, urine of low concentration will continue to be produced in large amounts. This means that during this test, you will tend to become dehydrated and your blood concentration will rise.
During this test, levels of vasopressin may be monitored. If it appears as though DI is causing symptoms, a dose of artificial vasopressin may be given to help determine whether the DI is central or nephrogenic. In central DI, artificial vasopressin will tend to increase the concentration of urine, while in nephrogenic DI it does not tend have an effect.
Magnetic resonance imaging
Because DI is often caused by brain problems or injury, a magnetic resonance imaging (MRI) scan can help to identify such an underlying cause of the condition.
If it is suspected that the cause of DI is inherited, genetic screening may be recommended.
Types of treatment
Treatment depends on the type and severity of DI. In mild cases, drinking enough fluids to cover the increased production of urine may be all that is required. This may mean being careful to ensure that you always have access to plenty of drinking water.
Eating a low-salt diet, which can help to reduce the amount of urine you produce, may be recommended and you may need to be particularly careful to drink enough fluids in warm weather or when exercising.
You may be recommended to wear a medic-alert bracelet, so that health care providers can be easily alerted to your condition if you become ill.
For children with DI, parents and carers may need to monitor their condition and their fluid intake and urine output, particularly with young children who are less able to regulate their fluid intake or describe symptoms. Discussing the child's condition and care needs with their school is important, including that they may require extra toilet breaks.
Underlying conditions that cause central DI, such as brain infections or tumours, may require treatment. In some cases, such as with some brain injuries, the symptoms may gradually get better on their own.
DI can be managed by supplementing the inadequate amount of vasopressin that the brain is producing with an artificial version of vasopressin called desmopressin. This may be taken in a variety of ways including injection, nasal spray, wafers and tablets.
Underlying conditions that can cause nephrogenic DI, such as hypercalcaemia, may require treatment. It may also be recommended that you stop taking any medications that may be contributing to the condition. However, it is important not to stop taking medications except under your doctor's supervision, because this may cause other side effects or health problems to get worse.
Mild cases of gestational DI may not require any treatment, although closer monitoring may be required to make sure that fluid levels in the body stay within safe levels.
In some cases, desmopressin may be prescribed to help reduce urine production.
If severe DI is untreated, it can lead to chronic dehydration. While it is rare when water is available, severe dehydration caused by DI can lead to kidney and brain damage, and eventually to the failure of the heart and circulatory system and death.
It is important to take the correct dose of desmopressin, as taking too much can cause the body to retain too much fluid and have reduced levels of sodium in the blood. This can cause symptoms such as confusion, nausea, weakness and lethargy. Untreated, severe cases can lead to seizures and death.
Prognosis depends on the underlying cause of DI. In some cases, such as following brain surgery or injury, DI may get better over time. Gestational DI usually goes away around 4-6 weeks after birth.
When it persists, DI can generally be managed well with appropriate treatment, although ongoing monitoring by a specialist is often necessary.
It is generally not possible to prevent diabetes insipidus.