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HealthInfo Canterbury

Diabetes insipidus

If you have cranial diabetes insipidus, it means you don't have enough anti-diuretic hormone (ADH). This hormone is also called arginine vasopressin (AVP).

You make ADH in an area of your brain called the hypothalamus, which is just above your pituitary gland. Your pituitary gland releases the ADH into your blood.

ADH acts on your kidneys, allowing you to make concentrated urine. If your body doesn't make enough ADH then your kidneys make a lot of dilute urine. As a result, you'll feel thirsty and have to urinate (wee) a lot. These symptoms are similar to those that people have with sugar diabetes (diabetes mellitus). However, people with diabetes insipidus have normal blood sugar levels. Their symptoms are caused by lack of ADH.

What causes diabetes insipidus?

Almost any disease that affects the pituitary region of the brain can cause diabetes insipidus. Causes include pituitary tumours, and damage caused by surgery or trauma. Sometimes there might be a genetic cause.

Sometimes people's kidneys can't respond to ADH. This is called nephrogenic diabetes insipidus (NDI). NDI can be caused by some medications, in particular lithium. If you're taking lithium, it's important that you tell your doctor about any symptoms such as feeling very thirsty and passing lots of urine. You should also have regular blood tests to check your lithium level.

Symptoms and diagnosis

FDP woman drinking waterFeeling very thirsty, drinking lots of fluid (often preferring cold water) and passing lots of urine are the symptoms of diabetes insipidus.

We diagnose diabetes insipidus with blood and urine tests. Usually we will ask you to stop drinking any fluid for a time to see if your urine becomes concentrated.

How long you have to go without drinking depends on how serious your symptoms are. You may simply need to have a urine test done after having nothing to drink overnight. Or we might need to keep you in hospital for several hours and monitor your blood and urine while you're not drinking. This is called a fluid deprivation test. At the end of the test we give you ADH to see if your kidneys respond normally.

You might also need scans of the pituitary region of your brain.

Some people develop diabetes insipidus after pituitary surgery, so we always monitor surgery patients closely. If this happens to you it may be temporary, or it might be permanent.

How is diabetes insipidus treated?

Usually we give a synthetic form of the ADH hormone called DDAVP (Minirin), which people spray into their nostrils. Most people need one or two sprays of DDAVP each day. Some people need more. If someone has problems with the nasal spray they can use a special tube to blow DDAVP into their nose. This is a bit fiddly. A tablet form of DDAVP is also available, however you might not absorb it properly, and it costs about $2 a tablet.

If you have a cold, or an allergy affecting your nose, you might absorb less of the hormone. Always clear your nose well before using the spray. Tablets might help in this situation.

How do I know I am on the right dose?

Different people need different doses of DDAVP. We generally find the best long-term dose by trial and error. If you're not taking enough DDAVP, you'll feel thirsty and need to urinate a lot. This is called breakthrough.

If you're taking too much DDAVP, the level of sodium in your blood will fall. At first this might not cause you any symptoms or you may feel nauseated, headachy and generally just a little unwell. If your sodium level becomes very low you can become confused.

To stop this from happening we usually recommend that once every two weeks you stop taking DDAVP until you've had symptoms of thirst and passing a lot of urine (breakthrough) for about two hours. Then take your usual dose of DDAVP. This is a safeguard and, as long as you drink when you're thirsty, lets your own body correct its sodium level.

If you have symptoms suggesting your sodium is too low, your GP can easily arrange a blood test to check.

What happens if I miss a dose or don't absorb it properly?

If this happens, you'll start urinating a lot and getting thirsty. If it happens within two hours of taking a dose, then it's safe to take the dose again.

But if several hours have passed since you had your DDAVP, one option is to "drink yourself out of trouble". Keep drinking as your thirst tells you until your next regular dose. Or you could take your next regular dose earlier.

What if a person with diabetes insipidus doesn't feel thirsty?

Sometimes the thirst centre in the brain may be damaged. It's very important to know if you have no sense of thirst. If this happens to you, you may be told to drink a set amount of fluid each day.

What to do if you get sick or need surgery

FDP abdominal painIf you become unwell with vomiting or diarrhoea, you should take half your usual dose of DDAVP. If you're unwell for more than one to two days you should see your doctor and have your blood sodium level checked.

If you have an operation it's important that your fluid balance is monitored (by measuring what you drink and how much urine you pass). Your blood sodium level also needs to be monitored. This will help decide if you need to change your dose of DDAVP. Make sure you tell your surgeon or medical specialist that you have diabetes insipidus.

Pregnancy is not likely to change the dose of DDAVP spray you need. But you might need to increase your dose if you're taking DDAVP tablets.

Effect of medication

Some medicines can affect the action of ADH. For example, if you're taking steroid-like drugs you might need a higher dose of DDAVP. Other drugs, such as anti-inflammatory drugs (NSAIDS) may lower the amount you need. Other drugs may affect your blood sodium levels – for example antidepressants, diuretics, epilepsy medications. Check any new medicine with your doctor and, if in doubt, get your blood sodium level checked.

Medical alert bracelet

It's wise to wear a medical alert bracelet or pendant so medical staff know how to treat you in an emergency. Search online for medical bracelets NZ to find medical bracelet suppliers.

People with diabetes insipidus can live normal lives with no restrictions. But we recommend you see your doctor once a year to review your diabetes insipidus and check your blood sodium level.

Written by the Department of Endocrinology, Christchurch Hospital. Adapted by HealthInfo clinical advisers. Last reviewed February 2018.

Images courtesy of FreeDigitalPhotos.net. Woman drinking by mikumistock, stomach ache by Ohmega1982

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Review key: HIDII-70635