Adipsia and hypernatraemia in a dog with focal hypothalamic granulomatous meningoencephalitis.

A 7-year-old Doberman was presented with a history of progressive neurological disease of 4 weeks duration. Initially there were episodes of aimless wandering and uncharacteristic aggression, however, the dog was obtunded at presentation. Serum biochemical analysis revealed profound hypernatraemia and moderate hyperproteinaemia. Despite correction of the hypernatraemia by the infusion of hypotonic fluids, the dog continued to periodically exhibit pacing and head pressing. A patchy, ill-defined contrast-enhancing area was evident in the ventral midbrain on computed tomography of the brain. Analysis of the cerebrospinal fluid revealed a mild increase in protein concentration, positive Pandy's test and mild pleocytosis. Because of the poor prognosis, euthanasia and necropsy were performed. Histopathological analysis of the brain revealed a severe focal meningoencephalitis affecting hypothalamic nuclei and mammillothalamic tracts. Destruction of osmoreceptors in the hypothalamus responsible for recognition of thirst is believed to have resulted in adipsia and subsequent hypernatraemia.