Professor E W Hillhouse
Coventry & Warwickshire Hospital

Vasopressin (also called Anti-diuretic Hormone or ADH) is a hormone that is made in a region of the brain called the Hypothalamus and is passed to the posterior pituitary via the pituitary stalk. It is then released from the posterior pituitary into the blood stream where it acts upon the kidneys to control the amount of fluid passed out of the body.

Diabetes Insipidus (DI) is a condition where the kidneys are unable to retain water. There are two types of DI - central (cranial) and nephrogenic (within the kidney). Central DI occurs as a result of inadequate secretion of vasopressin from the Pituitary gland. Nephrogenic DI is a very rare condition that occurs due to a kidney abnormality in which the kidneys are resistant to vasopressin and are unable to respond to the hormone. Nephrogenic DI is often inherited.

Central DI can be caused by damage to either the brain or the posterior pituitary. The commonest cause of central DI is trauma such as head injury, road traffic accident, surgery or childbirth, and this accounts for approximately 30% of cases. Other causes are tumours and Idiopathic (of an unknown cause).

Research looking at cell and gene abnormalities, DNA inheritance and copying mutations is ongoing. It may be that idiopathic DI could come into this group but as yet nobody has the answer. There does not appear to be any connection between DI and blood groups.

At primary diagnosis the main concern is fluid balance but patients need to live their lives without becoming obsessed with fluid balance. Cranial DI is treated with a substance called DDAVP (Desmopressin), which is a synthetic analogue of the natural hormone vasopressin. DDAVP contains a variation, which allows it to work for longer than the natural hormone and it is available in different preparations.

• Tablets need to be given in larger doses than other methods as only a rather small proportion are absorbed through the gut.
• The intranasal spray and nasal drops work well unless you have a cold. The intranasal spray provides metered doses whereas nasal drops are administered by tube and the dose can be altered.
• An injection is also available.

There is no simple treatment regime and each person needs to have their care planned to their own requirements. Some people experience difficulty in sleeping through the night even after treatment has been commenced. This may be improved by timing DDAVP and the intake of evening drinks. There are many factors which can affect fluid balance including consuming too much coffee, certain medications which interact with DDAVP e.g. anticonvulsants and possibly stress.