Primary polydipsia and psychogenic polydipsia are forms of
polydipsia[1] characterised by excessive fluid intake in the absence of physiological stimuli to drink.[2] Psychogenic polydipsia which is caused by psychiatric disorders, often
schizophrenia, is often accompanied by the sensation of
dry mouth. Some forms of polydipsia are explicitly non-psychogenic. Primary polydipsia is a
diagnosis of exclusion.
Signs and symptoms
Signs and symptoms of psychogenic polydipsia include:[3]
Excessive thirst and
xerostomia, leading to overconsumption of water
Hyponatraemia, causing headache, muscular weakness, twitching, confusion, vomiting, irritability etc., although this is only seen in 20–30% of cases.[4]
Hypervolemia, leading to
oedema, hypertension and weight gain (due to the kidneys being unable to filter the excess blood)[5] in extreme episodes
Behavioural changes, including fluid-seeking behaviour; patients have been known to seek fluids from any available source, such as toilets and shower rooms.[5][7]
The most common presenting symptom is tonic-clonic seizure, found in 80% of patients.[8] Psychogenic polydipsia should be considered a life-threatening condition, since it has been known to cause severe hyponatraemia, leading to cardiac arrest, coma and
cerebral oedema.[3]
Brain differences
Location of the
insular cortex, a structure implicated in PPD
Psychogenic polydipsia in individuals with schizophrenia is associated with differences seen in
neuroimaging. MRI scans may be used to help with differentiating between PPD and diabetes insipidus, such as by examining the signal of the
posterior pituitary (weakened or absent in central DI).[9] Some patients, most often with a history of mental illness, show a shrunken cortex and enlarged ventricles on an
MRI scan, which makes differentiation between psychogenic and physiological cause difficult.[5] However, these changes will likely only develop after chronic PPD associated with severe mental illness, as opposed to less severe forms of the disorder as seen in those with
anxiety and
affective disorders. PPD is also linked with significant reductions in
insular cortex volume,[10] although this may be caused by the secondary hyponatraemia. It has been suggested that these deficits lead to moderate to severe
cognitive impairments, especially affecting
working memory, verbal memory,
executive function, attention and motor speed.[11]
Other areas with volume reductions (both white and grey matter) include:[10][11]
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 insipidus.[12] 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.[13] This means that psychogenic polydipsia may lead to test results (e.g. in a water restriction test) consistent with diabetes insipidus or
SIADH, leading to misdiagnosis.[14]
Tobacco smoking is an often overlooked factor linked to hyponatremia, due to the ADH-releasing effect of
nicotine, although this is usually limited to heavy smokers.[21] One study suggested that around 70% of patients with self-induced polydipsia were tobacco smokers.[22] Diagnostic tests for primary polydipsia usually involves the
fluid deprivation test to exclude ADH problems. The
desmopressin test is also used, in which the synthetic hormone is used as a
diagnostic workup to test for inappropriate secretion of vasopressin, as seen in DI and SIADH.
Patient profiles
Psychogenic polydipsia is found in patients with mental illnesses, most commonly schizophrenia, but also anxiety disorders and rarely affective disorders, anorexia nervosa and personality disorders. PPD occurs in between 6% and 20% of psychiatric inpatients.[23] It may also be found in people with developmental disorders, such as those with
autism.[24] 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 existent 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.[medical citation needed] However, a preference for ice-cold water is also seen in diabetes insipidus.[25][26]
Treatment
Estimation of serum sodium levels from weight gain and suggested interventions[27]
Treatment for psychogenic polydipsia depends on severity and may involve
behavioural and
pharmacological modalities.[28]
Acute hyponatraemia
If the patient presents with acute hyponatraemia (overhydration) caused by psychogenic polydipsia, treatment usually involves administration of intravenous
hypertonic (3%)
saline until the
serum sodium levels stabilise to within a normal range, even if the patient becomes asymptomatic.[29]
Fluid restriction
If the patient is
institutionalised, monitoring of behaviour and serum sodium levels is necessary. In treatment-resistant polydipsic psychiatric patients, regulation in the inpatient setting can be accomplished by use of a weight-water protocol.[30] First, base-line 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 include progressive increases in monitoring, as well as a level at which a serum sodium level is drawn.
Behavioural
Behavioural treatments may involve the use of a
token economy to provide
positive reinforcement to desirable behaviour.[28] Furthermore,
cognitive therapy techniques can be used to address the thought patterns that lead to compulsive drinking behaviour. Success has been seen in trials of this technique, with emphasis on the development of coping techniques (e.g. taking small sips of water, having ice cubes instead of drinks) in addition to challenging
delusions leading to excessive drinking.[31][better source needed]
Psychogenic polydipsia often leads to
institutionalisation of mentally ill patients, since it is difficult to manage in the community.[5] Most studies of behavioural treatments occur in institutional settings and require close monitoring of the patient and a large degree of time commitment from staff.[29]
Pharmaceutical
Risperdal (risperidone) tablets
A number of pharmaceuticals may be used in an attempt to bring the polydipsia under control, including:
Lithium was previously used for treatment of PPD as a direct competitive ADH antagonist, but is now generally avoided due to its toxic effects on the
thyroid and
kidneys.[29]
It is important to note that the majority of
psychotropic drugs (and a good many of other classes) can cause dry mouth as a side effect, but this is not to be confused with true polydipsia in which a dangerous drop in serum sodium will be seen.[40]
Terminology
In diagnosis, primary polydipsia is usually categorised as:
Non-psychogenic – another non-psychological cause, including
idiopathic (unknown cause)
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.[13]
Non-psychogenic
Although primary polydipsia is usually categorised as psychogenic, there are some rare non-psychogenic causes. An example is polydipsia found in patients with
autoimmune chronic hepatitis with severely elevated
globulin levels.[41] Evidence for the thirst being non-psychogenic is gained from the fact that it disappears after treatment of the underlying disease.
Non-human animals
Psychogenic polydipsia is also observed in some non-human patients, such as in rats and cats.[42]
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