Psychogenic polydipsia

Primary polydipsia
Synonyms	Psychogenic polydipsia, compulsive drinking, psychosis-intermittent hyponatremia-polydipsia (PIP) syndrome
Classification and external resources
Specialty	Psychiatry
ICD-10	R63.1
ICD-9-CM	783.5
DiseasesDB	10318
MedlinePlus	003085
MeSH	D059607
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Primary polydipsia is a form of polydipsia characterised by excessive fluid intake in the absence of physiological stimuli to drink. This includes psychogenic polydipsia (PPD), which is caused by mental disorders, often schizophrenia, and often accompanied by the sensation of dry mouth. Some forms of primary polydipsia are explicitly non-psychogenic. Primary polydipsia is a diagnosis of exclusion.

Psychogenic polydipsia may occasionally be referred to as psychosis-intermittent hyponatremia-polydipsia (PIP) syndrome or compulsive water drinking.

In diagnosis, primary polydipsia is usually categorised as:

The terms primary polydipsia and psychogenic polydipsia are sometimes incorrectly used interchangeably - to be considered psychogenic, the patient needs to have some other psychiatric symptoms, such as delusions involving fluid intake or other unusual behaviours. Primary polydipsia may have physiological causes, such as autoimmune hepatitis.

Since primary polydipsia is a diagnosis of exclusion, the diagnosis may be made for patients who have medically unexplained excessive thirst, and this is sometimes incorrectly referred to as psychogenic rather than primary polydipsia.

As a diagnosis of exclusion, a diagnosis of primary polydipsia may be the result of elimination of the possibility of diseases causing similar signs and symptoms, such as diabetes inspidus. Diagnosis may be complicated by the fact that chronic and extreme compulsive drinking may impair the response of the kidneys to vasopressin, thus reducing the kidney's ability to concentrate the urine. This means that psychogenic polydipsia may lead to test results (e.g. in a water restriction test) consistent with diabetes inspidus or SIADH, leading to misdiagnosis.

Dry mouth is often a side effect of medications used in the treatment of some mental disorders, rather than being caused by the underlying condition. Such medications include antipsychotics, antidepressants, anticonvulsants, alpha agonists and anticholinergics. It should also be ensured that the thirst isn't caused by diuretic use (particularly thiazide diuretics), MDMA use, excessive solute intake or chronic alcoholism. Alcoholism may cause physiological thirst since ethanol inhibits vasopressin, the hormone primarily responsible for water retention in osmoregulation. The following conditions should also be excluded: DI, cerebral salt wasting, pseudohyponatraemia caused by hyperlipidemia or hyperparaproteinemia, SIADH, mineralcorticoid deficiency, salt-wasting nephropathy, nephrotic syndrome, chronic heart failure and cirrhosis.

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