Gigantism is an excessive secretion of growth hormone during childhood, before the closure of the bone growth plates. This excess growth hormone causes overgrowth of the long bones and very tall stature.
Causes, incidence, and risk factors
The cause of excess growth hormone secretion is most often a benign pituitary gland tumor. Giantism may also be caused by an underlying medical condition such as multiple endocrine neoplasia type 1 (MEN-1), McCune-Albright syndrome (MAS), neurofibromatosis, or Carney complex.
If excessive secretion of growth hormone occurs after normal bone growth has stopped, the condition is known as acromegaly.
The vertical growth in height that marks this condition is also accompanied by growth in muscles and organs, which makes the child extremely large for his or her age. The disorder can also delay puberty.
Gigantism is very rare.
- Excessive growth during childhood.
- Frontal bossing and a prominent jaw
- Thickening of the facial features
- Disproportionately large hands and feet with thick fingers and toes
- Increased perspiration
- Secretion of breast milk
- Irregular menstruation
- Delayed onset of puberty
- Double vision or difficulty with peripheral vision
Signs and tests
- An increase in insulin growth factor-I (IGF-I) levels
- A failure to suppress serum growth hormone (GH) levels after an oral glucose challenge (maximum 75g)
- A CT or MRI scan of the head showing pituitary tumor
- High prolactin levels
Other hormone levels may be low due to damage to the pituitary, including thyroid hormone, testosterone (boys), estradiol (girls), or cortisol.
In pituitary tumors with well-defined borders, surgery is the treatment of choice and is curative is about 80% of cases.
For situations in which surgery cannot completely remove the tumor, medication is the treatment of choice. The most effective medications are somatostatin analogs (such as octreotide or long-acting lanreotide), which reduce growth hormone secretion.
Dopamine agonists (bromocriptine mesylate, cabergoline) have also been used to reduce growth hormone secretion, but these are generally less effective. A medication that blocks the effect of growth hormone, pegvisomant, has recently become available.
Radiation therapy has also been used to normalize growth hormone levels. However, it can take 5-10 years for the full effects to be seen and is almost always associated with deficiencies in other pituitary homones. In addition, radiation has been associated with learning disabilities, obesity, and emotional changes in children. Most experts will use radiation only if surgery and medication fail.
Pituitary surgery is usually successful in limiting growth hormone production.
- The development of secondary sexual characteristics may be delayed.
- Surgery and radiation can both lead to deficiencies in other pituitary hormones, causing hypothyroidism, andrenal insufficiency, hypogonadism, and (rarely) diabetes insipidus.
Calling your health care provider
Call your health care provider if signs of excessive growth during childhood are present.
by Amalia K. Gagarina, M.S., R.D.