Cranial DIABETES INSIPIDUS

What is cranial Diabetes Insipidus (DI)?

It is a disease characterised by the passing excessive amount of urine due to the under production of Anti Diuretic Hormone (ADH), which is produced by the HYPOTHALAMUS and is stored and released by the PITUITARY.

It is a part of the brain, which control the functions of the pituitary gland.

It is a small pea size gland situated in a hollow bony pouch, at the base of the brain, at the back of the bridge of the nose. It is the master gland of the endocrine system and controls the functions of the other endocrine glands.

This hormone controls and regulates the fluid balance of the body. It is produced by the HYPOTHALAMUS and is stored and released by the PITUITARY. When released into the blood circulation it travels to the kidneys. You have two kidneys which cleanse one cup volume of fluid (150mls) each minute. ADH makes the kidneys reabsorb the fluid passing through the kidneys. Without ADH you would pass plenty of urine day and night as the kidneys have to rely on other systems to try and reabsorb fluid but these are not as effective as ADH

Very frequent need to pass urine possibly every hour day and night.
Very thirsty.
Patient can become dehydrated.
The severity of symptoms depends on how much ADH is produced. A simple test is to measure the volume of urine passed over 24hrs. If this is less than 2.5litres then the patient does not have DI.

DI on its own without other pituitary hormone deficiencies is fairly rare.There is an inherited (familial) variety which is usually begins in infancy. Another familial form arises later in childhood and is associated with diabetes mellitus, deafness and visual loss (DIDMOAD) but again this is rare. In some 30% of isolated DI the cause is never found (idiopathic). In some an autoimmune cause is suspected. Other causes can be injury to the pituitary / hypothalamus or their connecting stalk at time of road injury, at surgery on the brain or due to rare diseases which the specialist will check out. In some there is no deficiency of ADH but instead an inability of the kidneys to respond to circulating ADH (known as nephrogenic ADH). DI may also occur as the result of a pituitary adenoma or tumour in the hypothalamus.

No. Diabetes mellitus causing a high blood sugar, high blood calcium, low blood potassium and renal failure can also cause a high urine volume. The commonest cause by far is the patient who gets into the habit of drinking too much liquid (called polydipsia)

The test is called a Water Deprivation Test
This test involves initial measurement of blood and urine concentration at 08.00 a.m. after fasting from mid-night.
You will then be allowed dry food only without any fluid up until 16.00hr.
Body weight, amount of urine output will be measured hourly.
Blood and urine samples will be sent to measure their osmolarity (degree of concentration) at 09.00, 12.00, 15.00 and 16.00hr.
In normal people, hourly urine output will fall and will become more concentrated as you had no fluid intake. Body weight and blood concentration will remain the same.
If you have DI, you will continue to produce large amount of urine despite having no fluid. Urine remains diluted, body weight falls and blood becomes more concentrated.

At 1600 hr DDAVP (manufactured ADH) will be injected and you will be urged to drink plenty of fluid. Urine and blood collections will continue up until 2000hr.
The aim is to see if the kidneys will respond to ADH by reducing urine output.
This test can be done only under medical supervision as it can potentially cause dehydration and fluid and salt imbalance.
In some situations the actual ADH may be measured. This is usually done if a special saline infusion test is required, usually needed for certain borderline DI situations or where nephrogenic DI is suspected.
If DI is proven, you may require additional tests to find for the possible underlying causes as stated above.

This is by replacing the missing ADH hormaone with manufactured hormone called DDAVP (Desmopressin) This comes in three forms; nasal spray, tablets and injection. Some patients settle well on tablets but others do not due to variable absorption of the hormone in the gut and such patients require nasal spray. Your specialist will advise after discussion with you. The injection form is usually reserved for hospital use.

In this condition the hypothalamus and pituitary produce adequate amounts of ADH but the kidneys do not respond. This is a kidney disease which most likely will require you to also see a kidney (renal ) specialist. Treatment is often by special oral medicines.

The Pituitary Foundation
PO Box 1944
Bristol, BS99 2UB.
Tel/Fax 0117 927 3355
e-mail- helpline@pitpat.demon.co.uk

or www.pituitary.org.uk

or

The Diabetes Insipidus Foundation Inc.
http://diabetesinsipidus.maxinter.net/

http://familydoctor.org/handouts/048.html


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Ó NHS Tayside; 2006; version 1.0

Disclaimer; no liability whatsoever is accepted for information given and all such information, especially with regard to drug usage (UK version provided), must be checked with a person’s health provider.