Growth Hormone Excess: Gigantism and Acromegaly

Growth hormone is secreted by the anterior pituitary and stimulates hepatic IGF-1. IGF-1 mediates growth of cartilage, bone, soft tissue, and viscera. Growth hormone itself increases insulin resistance, explaining the impaired glucose tolerance associated with excess secretion.

Excess growth hormone before epiphyseal closure causes gigantism with increased linear bone growth. Excess after growth-plate closure causes acromegaly, characterized by enlargement of acral tissues rather than renewed linear growth.

Acromegaly develops slowly and produces a characteristic tissue-growth pattern.

• Hands and feet enlarge.
• Facial features coarsen, with forward and downward mandibular growth.
• Tongue and soft tissues enlarge.
• Cardiac and visceral enlargement may occur.

Serum IGF-1 is the useful screening measurement because growth hormone fluctuates during the day. Failure of growth hormone suppression after oral glucose supports the diagnosis. A pituitary lesion is then assessed by MRI after biochemical overproduction has been established.