Polydipsia is a medical condition in which the patient ingests abnormally large amounts of fluids by mouth. The word is made from the words poly meaning many and dipsia which means thirst. The fluid is usually water, though some people may think of alcohol because of the etymologically related term dipsomaniac, meaning an alcoholic.
Polydipsia is almost always associated with dehydration due to polyuria (excessive urination), if the condition is prolonged beyond a few hours in those with functioning kidneys.
It is often, and 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 is also caused by other conditions featuring osmotic diuresis and by diabetes insipidus ("water diabetes"), and forms part of the differential diagnostic tree for them, as well. Polydipsia is also a symptom of atropine or belladonna poisoning. Another cause can be due to medication (such as diuretics) or inadvertent consumption of caffeine. One who drinks nothing but coffee or soda can be easily misdiagnosed by a medical professional as psychogenic polydipsia, as they may be unaware they are consuming diuretics.
Polydipsia in Psychiatric Subsets
Psychogenic polydipsia is a type of polydypsia with described in patients with mental illnesses and/or the developmentally disabled. It is present in a subset of schizophrenics. These patients, most often chronic schizophrenics with a long history of illness, often exhibit enlarged ventricles and shrunken cortex on MRI, making the physiological mechanism difficult to isolate from the psychogenic. It is a serious disorder and often leads to institutionalization as it can be very difficult to manage outside the inpatient setting. It should be taken very seriously - it can be life threatening as serum sodium is diluted to an extent that seizures and cardiac arrest can occur. Patients have been known to seek fluids from any source possible.
In treatment resistant polydipsic psychiatric patients, regulation in the inpatient milieau can be accomplished by use of a weight-water protocol. First, baseline weights must be established and correlated to serum sodium levels. Weight will normally fluctuate during the day, but as the water intake of the polydipsic goes up, the weight will naturally rise. The physician can order a stepped series of interventions as the weight rises. The correlation must be individualized with attention paid to the patient's normal weight and fluctuations, diet, co-morbid disorders (such as a seizure disorder) and urinary system functioning. Progressive steps might include redirection, room restriction, and increasing levels of physical restraint with monitoring. Such plans should also progressive increases in monitoring, as well as a level at which a serum sodium level is drawn.
It is important to note that the majority of psychotropic drugs (and a good many of other classes) can cause dry mouth, but this is not to be confused with true polydipsia in which a dangerous drop in serum sodium will be seen.
While psychogenic polydipsia is generally not found outside the population of those with serious mental disorders, there is some anecdotal evidence of a milder form (typically called 'habit polydispsia' or 'habit drinking') that can occasionally 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.
Polydipsia is a symptom, not a disease (cause). To diagnose the cause of polydipsia a fluid deprivation test is used, which may require a patient to abstain from water, and for blood and urine tests to be undertaken. Additional blood work may be required to test for the presence of diuretics, such as caffeine, or recreational drugs. Finally neurological testing may be required to determine if there has been damage to the hypothalamus.