Acromegaly is characterized by chronic excess circulating growth hormone concentrations. Growth hormone secretion from the pituitary gland is pulsatile and growth hormone appears to stimulate the local production of IGF-1 (somatomedin-C). IGF-1 then acts locally on target tissues to mediate the growth hormone effects. When this syndrome develops in childhood there is a tremendous linear growth of bones resulting in clinical “gigantism.” If this syndrome develops as an adult, most of the bones will not respond to elevated growth hormone since they have stopped growing due to the fusion of their growth plates (epiphyses). Bones without epiphyses will grow with elevated growth hormone, including facial bones. The clinical appearance of acromegaly includes
- enlargement of distal extremities with very big hands and feet
- widening of the spaces between the teeth due to growth of the jaw and facial bones
- carbohydrate intolerance or frank diabetes mellitus
Clinical situations associated with elevated growth hormone concentrations include poorly controlled diabetes mellitus, chronic illness or malnutrition, and stress. These situations differ from acromegaly since they are associated with a low IGF-1 level.
The initial screening test for acromegaly is the circulating growth hormone concentration, ideally drawn after fasting in the morning at the bedside before the person ambulates. False positives are not uncommon, so all positive values must be followed up with either a glucose suppression test (2 hours after a 100 gm glucose load the normal GH is less than 2 ng/mL while in acromegalics it is greater than 5 ng/mL) or an IGF-1 concentration (care must be taken to draw and process blood according to the laboratory specifications since fluctuations in levels are otherwise encountered, false negative IGF-1 concentrations may reflect a low concentration of the IGF binding proteins).