Psychogenic polydipsia

Psychogenic polydipsia is a special form of polydipsia, caused by mental disorders.

Clinical presentation
The patient drinks large amounts of water, which raises the pressure of the extracellular medium. As a side effect, the antidiuretic hormone level is lowered. The urine produced by these patients will have a low electrolyte concentration and it will be produced in large quantities (polyuria). If the patient is institutionalised, close monitoring by staff is necessary to control fluid intake. In extreme episodes, the patient's kidneys will be unable to deal with the fluid overload, and weight gain will be noted.

Causes and background
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.

Treatment
In treatment-resistant polydipsic psychiatric patients, regulation in the inpatient milieu 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, comorbid 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.

Atypical patient profiles
While psychogenic polydipsia is usually not seen outside the population of those with serious mental disorders, it may occasionally be found among others in the absence of psychosis, although there is no extant research to document this other than anecdotal observations. Such persons typically prefer to possess bottled water that is ice cold, consume water and other fluids at excessive levels, and may be falsely diagnosed as suffering from diabetes insipidus, since the chronic ingestion of excessive water can produce symptoms and diagnostic results that mimic mild diabetes insipidus.