"Mind, body, and water!" - Postherpetic polydipsia masquerading as obsessive-compulsive disorder.

Polydipsia has always been an intriguing entity in clinical psychiatry, since long. Other than being commonly associated with patients of chronic schizophrenia, as described in past, it can also mimic and present in other psychiatric disorders; and thus may be elusive for diagnosis and treatment. Here we describe a patient having polydipsia with prominent obsessive compulsive symptoms, which, after detailed investigations, was found to be secondary to herpes encephalitis. The organic nature of the illness was ascertained by distinct signal changes in right uncus, hippocampus and cingulate cortex; whereas conventional workup for polydipsia ruled out both central and nephrogenic diabetes insipidus. Treatment with fluoxetine, proper behavioural management and psychoeducation resulted in slow but sustained improvement in this patient. We then deconstruct the clinical manifestations and discuss the neurobiological explanation.