Why does excess pituitary growth hormone cause acromegaly in adults?

Acromegaly occurs in adults when the pituitary gland produces excess growth hormone after the epiphyses (the growing ends of bones) have closed.12

In children, excess growth hormone leads to gigantism because the bones are still capable of longitudinal growth. However, once an individual reaches adulthood and these growth plates have fused, the bones can no longer increase in length. Consequently, the continued overproduction of growth hormone causes the bones and soft tissues to thicken and enlarge rather than lengthen.213

This results in the characteristic clinical features of acromegaly, including the enlargement of the hands, feet, nose, and jaw, as well as the thickening of the skin and the enlargement of internal organs. The condition is typically caused by a benign tumor (adenoma) of the pituitary gland's somatotroph cells.13