gigantism

Gigantism is what happens when a child is exposed to far too much growth hormone while the bones can still grow longer, producing strikingly tall stature. It is essentially the childhood version of growth hormone excess, before the growth plates have closed.

The usual cause is a benign growth-hormone-secreting tumor of the pituitary gland, which pours out hormone without regard to normal feedback. The excess growth hormone drives high IGF-1, and because the epiphyseal plates are still open, the long bones keep lengthening, so the child grows abnormally tall and fast.

The same hormone excess in an adult, after the plates have fused, cannot add height and instead causes acromegaly, with enlargement of the hands, feet, jaw, and internal organs. Gigantism and acromegaly are thus two faces of the same underlying problem, separated only by whether the growth plates are open or closed.

An honest caveat: gigantism is very rare, and most very tall children are simply tall for genetic or familial reasons, not because of a tumor. Diagnosis rests on documenting growth hormone excess, typically a high IGF-1 and failure of growth hormone to suppress during an oral glucose tolerance test, plus pituitary imaging.