Transient reduction in the posterior pituitary bright signal preceding water intoxication in a malnourished child.

We describe a 4 year-old boy with hypothalamic dysfunction and weight loss, attributed to psychosocial deprivation. Reduced intensity of the posterior pituitary bright signal (PPBS) on MRI, associated with a normal urinary concentrating ability, was documented in the 24 hours prior to the development of the syndrome of inappropriate secretion of antidiuretic hormone (ADH) and severe hyponatraemia. The PPBS was normal on MRI 2 months later, following weight gain and resolution of the other hypothalamic abnormalities. This report shows that the abnormalities of ADH associated with decreased intensity of the PPBS include increased secretion and abnormal regulation as well as ADH deficiency. The association of osmotically unregulated ADH secretion with undernutrition and stress suggests that particuar caution should be used when fluid intake in such children is not driven by thirst.