Diabetes Insipidus

The condition 'diabetes insipidus' (DI) is characterised by the passage of large volumes of urine (>3 litres/24hrs), and persistent thirst.  It is distinguished from diabetes mellitus (sugar diabetes) by 'insipid' urine, i.e., lacking taste, in contrast to the 'sweet tasting' urine of diabetes mellitus.  A common cause of DI is inadequate secretion of Vasopressin, the antidiuretic hormone, from the posterior pituitary.  However, some patients suffer from renal conditions in which the kidneys fail to respond correctly to vasopressin; this is nephrogenic DI. 

Trauma, infection, granulomatous disease (e.g., sarcoidosis) or tumours in the region of the Hypothalamus or pituitary may reduce vasopressin secretion.  Pituitary surgery not infrequently causes DI which is usually transitory lasting a few hours or days; occasionally it may be permanent and be accompanied by loss of other pituitary hormones.  Pituitary surgery also causes other forms of hypopituitarism which are covered elsewhere (factsheet 6).

Presenting symptoms

• Polyuria, in excess of 3 litres/24hrs in adults
• Thirst and polydipsia (excessive drinking)
• Tiredness, lethargy and reduced concentration (often the result of lack of sleep due to night-time visits to the toilet).

Investigations

The diagnosis is suggested by copious volumes of dilute urine with normal or slightly raised serum sodium.  A water-deprivation test for up to 8 hours with measurements of serum sodium, blood and urine osmolalities and urine volume at 2 hour intervals followed by observation of urinary responses to Desmopressin (DDAVP - an artificial vasopressin), can differentiate DI from other causes of polyuria (i.e., persistent excessive drinking or nephrogenic DI).  An MRI scan of the pituitary region to include the hypothalamus and posterior pituitary is necessary.

Treatment

Mild cases of DI (urine output 3-4 litres/24hrs) can be managed by ingestion of water to quench thirst.  Others require desmopressin (DDAVP) which can be given orally, intranasally or parenterally.  It is essential to avoid chronic overdosage which will cause Hyponatraemia (low serum concentration of sodium).

Long-term management

Because of the risk of hyponatraemia, occasional (1-3 monthly) measurements of serum sodium are advised. Some recommend missing desmopressin treatment one day each week to avoid the development of hyponatraemia.

Resources for patients

Please go to the Resource Library of this website to access resources for patients.  Our library includes literuature, newsletters and articles available from The Pituitary Foundation as well as the contact information for other organisations who provide support and information.  All of our patient leaflets are available to read as well as downloadable in PDF format from this website. 

Resources for GPs