Psychogenic polydipsia after traumatic brain injury. A case report.

Electrolyte abnormalities are common medical complications of traumatic brain injury (TBI). Hyponatremia is the most common of these disorders. The syndrome of inappropriate antidiuretic hormone and cerebral salt-wasting are the most well known causes of hyponatremia following TBI. In the presence of polydipsia and polyuria, psychogenic polydipsia should be included in the differential diagnosis. It is important to distinguish among these entities because treatment differs to such an extent that improper diagnosis may lead to a worsening of the patient's condition. We present a patient who presented with a new onset of polyuria and polydipsia after sustaining a TBI. Evaluation, including monitoring of fluid intake and output, serum and urine sodium and osmolarity, as well as a fluid deprivation test revealed the cause to be psychogenic polydipsia. The patient's symptoms improved after institution of a behavioral program and fluid restriction. Various models of drinking behavior have been used to identify the site of dysregulation. Dopaminergic, cholinergic, and hippocampal etiologies have been implicated in this abnormality of fluid homeostasis. If disorders of these systems can lead to psychogenic polydipsia, it is reasonable to believe that a person who has sustained a TBI would be at higher risk of developing psychogenic polydipsia.