Primary polydipsia

Primary polydipsia is a form of polydipsia^[1] 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, such as in patients with autoimmune chronic hepatitis with severely elevated globulin levels.^[2] Primary polydipsia is a diagnosis of exclusion.

Diagnosis

Psychogenic and non-psychogenic

In diagnosis, primary polydipsia is usually categorised as:

• Psychogenic - caused by underlying psychiatric symptoms, such as psychoses
• Non-psychogenic - another cause, including unknown causes

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 psychosis, delusions involving fluid intake or other unusual and repetitive behaviours.

Diagnostic considerations

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.^[3] 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.^[4] 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.^[5]

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.^[6] Such medications include antipsychotics, antidepressants, anticonvulsants, alpha agonists and anticholinergics.^[7] 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. The following conditions should also be excluded: DI, cerebral salt wasting, pseudohyponatraemia, SIADH, mineralcorticoid deficiency, salt-wasting nephropathy, nephrotic syndrome, chronic heart failure and cirrhosis.^[8]

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 patients.^[9] It may also be found in people with developmental disorders, such as those with autism.^[10] 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.^[11] 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.

Signs and symptoms

Signs and symptoms of psychogenic polydipsia include:^[12]

• 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.^[13]
• Hypervoelemia, leading to oedema, hypertension and weight gain (due to the kidneys being unable to filter the excess blood)^[11] in extreme episodes
• Tonic-clonic seizure^[14]
• Behavioural changes, including fluid-seeking behaviour; patients have been known to seek fluids from any available source, such as toilets and shower rooms.^[11][15]

The most common presenting symptom is tonic-clonic seizure, found in 80% of patients.^[16] 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.^[12]

Treatment

Treatment for psychogenic polydipsia depends on severity and may involve behavioural and pharmacological modalities.^[17]

Acute hyponatraemia

If the patient presents with acute hyponatraemia (severe dehydration) 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.^[18]

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.^[19] 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.^[17] 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.^[20]

Psychogenic polydipsia often leads to institutionalisation of mentally ill patients, since it is difficult to manage in the community.^[11] 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.^[18]

Pharmaceutical

A number of pharmaceuticals may be used in an attempt to bring the polydipsia under control, including:

• Atypical antipsychotics, such as clozapine,^[21] olanzapine and risperidone^[22]
• Demeclocycline, a tetracycline antibiotic, which is effective due to the side effect of inducing nephrogenic diabetes insipidus causing syndrome of inappropriate antidiuretic hormone secretion (SIADH)^[18][23]

There are a number of emerging pharmaceutical treatments for psychogenic polydipsia, although these need further investigation:^[24]

• ACE Inhibitors, such as enalapril^[25]
• Clonidine, an alpha-2 adrenergic agonist^[25]
• Irbesartan, an angiotensin II receptor antagonist^[22]
• Propranolol, a sympatholytic beta blocker^[26]
• Vasopressin receptor antagonists, such as conivaptan^[27]
• Acetazolamide, a carbonic anhydrase inhibitor^[28]

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.^[29]

Other animals

Psychogenic polydipsia is also observed in some nonhuman patients, such as in rats.^[30]

See also

• Water intoxication
• Fluid deprivation test

References

Further reading

• Risk factors for the development of hyponatremia in psychiatric inpatients. Arch Intern Med. 1995 May 8;155(9):953-7. PMID 7726704
• Efficacy of clozapine in a nonschizophrenic patient with psychogenic polydipsia and central pontine myelinolysis. Hum Psychopharmacol. 2002 Jul;17(5):253-5. PMID 12404683

External links

• Psychogenic Polydipsia at GPnotebook
• Advice for clinicians on Psychogenic Polydipsia from BMJ Best Practice (subscription required)
• Psychogenic Polydipsia (Exessive Fluid seeking Behaviour) by Donald “Don” Hutcheon on the APA's website