Psychogenic polydipsia is an excessive water intake seen in some patients with mental illnesses such as schizophrenia, and/or the developmentally disabled. It should be taken very seriously, as the amount of water ingested exceeds the amount that can be excreted by the kidneys,and can on rare occasions be life-threatening as the body's serum sodium level is diluted ( in other words dilutional hyponatremia ) to an extent that seizures and cardiac arrest can occur.
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
Excessive urination and extreme thirst (especially for cold water and sometimes ice or ice water) are typical for DI. Symptoms of diabetes insipidus are quite similar to those of untreated diabetes mellitus, with the distinction that the urine does not contain glucose and there is no hyperglycemia (elevated blood glucose). Blurred vision is a rarity. Signs of dehydration may also appear in some individuals since the body cannot conserve much (if any) of the water it takes in.
In order to distinguish DI from other causes of excess urination, blood glucose levels, bicarbonate levels, and calcium levels need to be tested. Measurement of blood electrolytes can reveal a high sodium level (hypernatremia as dehydration develops). Urinalysis demonstrates a dilute urine with a low specific gravity. Urine osmolarity and electrolyte levels are typically low.
Habit drinking (in its severest form termed psychogenic polydipsia) is the most common imitator of diabetes insipidus at all ages. While many adult cases in the medical literature are associated with mental disorders, most patients with habit polydipsia have no other detectable disease. The distinction is made during the water deprivation test, as some degree of urinary concentration above isosmolar is usually obtained before the patient becomes dehydrated.