Context. Changes in body weight, statural growth rate and puberty may be the presenting symptoms of hypothalamic-pituitary tumors.

Objective. To assess the relationship between the tumor and its treatment, and the weight, growth rate and onset of puberty, using the diencephalic syndrome of emaciation (DS) as model.

Patients. Eleven patients seen before one year old, except one aged 9 yr, for DS due to hypothalamic pilocytic astrocytoma, were treated by surgical resection (n = 9), cranial irradiation (n = 7) and/or chemotherapy (n = 10).

Results. At diagnosis, growth rate was normal, despite the emaciation, and there was no hypothalamic-pituitary deficiency, except in the oldest patient. After tumor treatment, all had growth hormone and thyroid stimulating hormone deficiencies, but only 3, who underwent major surgical resection, also had ACTH deficiency and diabetes insipidus. Eight became obese and all but the older had transient precocious puberty.

Plasma leptin concentrations were very low at diagnosis, increased after tumor treatment and decreased transiently in one boy when the testosterone increased. The plasma soluble leptin receptor (sOB-R) concentrations changed in the opposite direction, leading to an increase in the free leptin index (FLI), including in the 3 patients whose tumor was reduced without surgery.

The BMI was correlated positively with plasma leptin (Rho=0.73, P = 0.0004) and FLI (Rho=0.63, P < 0.004) and negatively with ghrelin (Rho= -0.49, P < 0.03) concentrations.

Conclusions. The obesity that occurs after treatment of hypothalamic tumors is not due to dysregulation of leptin secretion, as it and sOB-R remain regulated by factors like testosterone. This study also shows the influence of weight, possibly via leptin secretion, on the transient hypothalamic-pituitary-gonadal activation that occurs during the first year of life.