Primary polydipsia and psychogenic polydipsia are forms of polydipsia characterised by excessive fluid intake in the absence of physiological stimuli to drink. 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:
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. Hypervolemia, leading to oedema, hypertension and weight gain (due to the kidneys being unable to filter the excess blood) in extreme episodes
Tonic-clonic seizure
Behavioural changes, including fluid-seeking behaviour; patients have been known to seek fluids from any available source, such as toilets and shower rooms.The most common presenting symptom is tonic-clonic seizure, found in 80% of patients. 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. Brain differences
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). 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.
Simple hypoplasia
Kidneys that are small for age but still have normal renal architecture. This leads to a decrease in the number of nephrons, or functional units of the kidney. Dysplasia
Malformation of kidney or bladder architecture. A dysplastic kidney is typically small for age and may contain cysts. A multicystic dysplastic kidney is an extreme example of renal dysplasia. Isolated collecting duct dilation
Dilation of the renal pelvis, ureters, or both. Also called hydronephrosis. Anomalies of position
Kidneys and ureters located in incorrect position, including horseshoe kidney and ectopic ureters. See also
Overflow incontinence

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