Pathological polydipsia from a brain lesion

摘要

An important diagnostic consideration in the cases of hyponatraemia is psychogenic polydipsia, especially in a predisposed individual. Urine osmolality may help in differentiating psychogenic polydipsia from other causes of hyponatraemia. Besides psychogenic factors and certain medications, no other causes of primary polydipsia have been found. Intracranial processes like tumours and haemorrhage usually cause hyponatraemia by virtue of excess antidiuretic hormone (ADH) production by affecting the hypothalamus-pituitary axis. In rare cases, some intracranial masses have been reported to cause decreased or absent thirst, leading to what is referred to as adipsic hypernatraemia. At least theoretically, the same pathological processes may cause excessive stimulation of the' thirst mechanism and wafer intoxication due to the close anatomical proximity to the thirst centre in the hypothalamus. Here, we report a case of polydipsia causing hyponatraemia from a structural brain lesion. A 2 5-year-old Asian woman was evaluated for hyponatraemia. She had developed the sudden onset of severe headache and nausea, 23 weeks into her first pregnancy. Magnetic resonance imaging revealed an arterio-venous malformation within the region of anterior commissure, anterior fornices reaching the roof of the third ventricle with intracranial bleeding in the lateral, third and fourth ventricles.