polydipsia

Polydipsia is a medical symptom in which the patient displays excessive thirst.^[1] The word derives from the Greek πολυδιψία,^[2] which is derived from πολύς (polys, "much, many") + δίψα (dipsa, "thirst"). An etymologically related term is dipsomaniac, meaning an alcoholic.

Causes

This symptom is characteristically found in diabetics, often as one of the initial symptoms, and in those who fail to take their anti-diabetic medications or whose dosages have become inadequate. It can also be caused by a change in the osmolality of the extracellular fluids of the body, hypokalemia, decreased blood volume (as occurs during major hemorrhage), and other conditions that create a water deficit.^[1] This is usually a result of osmotic diuresis (increased urination), such as in diabetes insipidus ("tasteless" diabetes, as opposed to diabetes mellitus, "sweet" diabetes).^[1] Polydipsia is also a symptom of anticholinergic poisoning.

Polydipsia in Psychiatric Subsets

For the main article, see Psychogenic polydipsia.

Psychogenic polydipsia is an excessive water intake^[1] seen in some patients with mental illnesses such as schizophrenia, and/or the developmentally disabled. It should be taken very seriously, as the amount of water ingested exceeds the amount that can be excreted by the kidneys,^[1] and can on rare occasions be life-threatening as the body's serum sodium level is diluted to an extent that seizures and cardiac arrest can occur.

While psychogenic polydipsia is generally not found outside the population of serious mental disorders, there is some anecdotal evidence of a milder form (typically called 'habit polydipsia' or 'habit drinking') that can be found in the absence of psychosis or other mental conditions. The excessive levels of fluid intake may result in a false diagnosis of diabetes insipidus, since the chronic ingestion of excessive water can produce diagnostic results that closely mimic those of mild diabetes insipidus.

Diagnosis

Polydipsia is a symptom (evidence of a disease state), not a disease in itself. As it is often accompanied by polyuria, investigations directed at diagnosing diabetes insipidus and diabetes mellitus can be useful. Blood serum tests can also provide useful information about the osmolality of the body's extracellular fluids. A decrease in osmolality caused by excess water intake will decrease the serum concentration of red blood cells, blood urea nitrogen (BUN), and sodium.^[1]

See also

• Water intoxication
• Human homeostasis
• Polyphagia

References