Primary polydipsia

Primary polydipsia
Other names	Psychogenic polydipsia, compulsive drinking, psychosis-intermittent hyponatremia-polydipsia (PIP) syndrome
Patients with PPD often prefer ice cold water
Specialty	Psychiatry
Symptoms	Xerostomia, polydipsia, fluid-seeking behavior
Complications	Water intoxication

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
• Tonic-clonic seizure^[6]
• 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

Psychogenic polydipsia in individuals with schizophrenia is associated with differences seen in

Other areas with volume reductions (both white and grey matter) include:[10]^[11]

• Right posterior lobe
• Right inferior temporal gyrus
• Parahippocampal gyrus
• Both left and right superior temporal gyri
• Right cuneus
• Left medial frontal gyryus and inferior frontal gyrus
• Right lingual gyrus

Diagnosis

As a

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

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

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

• Atypical antipsychotics, such as clozapine,^[32] olanzapine and risperidone^[33]
• Demeclocycline, a tetracycline antibiotic, which is effective due to the side effect of inducing nephrogenic diabetes insipidus.^[29][34] Demeclocycline is used for cases of psychogenic polydipsia, including those with nocturnal enuresis (bed-wetting). Its mechanism of action involves direct inhibition of vasopressin at the DCTs, thus reducing urine concentration.^[29]

There are a number of emerging pharmaceutical treatments for psychogenic polydipsia, although these need further investigation:^[35]

• ACE Inhibitors, such as enalapril^[36]
• Clonidine, an alpha-2 adrenergic agonist^[36]
• angiotensin II receptor antagonist^[33]
• Propranolol, a sympatholytic beta blocker^[37]
• Vasopressin receptor antagonists, such as conivaptan^[38]
• Acetazolamide, a carbonic anhydrase inhibitor^[39]

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:

• psychiatric symptoms, including those caused by psychoses and rarely by affective disorders
• 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]

See also

• Water intoxication
• Fluid deprivation test

References