Gigantism

Definition

Gigantism is abnormally large growth due to an excess of growth hormone during childhood, before the bone growth plates have closed.

Alternative Names

Giantism

Causes

The most common cause of too much growth hormone release is a noncancerous (benign) tumor of the pituitary gland. Other causes include:

• Carney complex
• McCune-Albright syndrome (MAS)
• Multiple endocrine neoplasia type 1 (MEN-1)
• Neurofibromatosis

If excess growth hormone occurs after normal bone growth has stopped, the condition is known as acromegaly.

Gigantism is very rare.

Symptoms

The child will grow in height, as well as in the muscles and organs. This excessive growth makes the child extremely large for his or her age.

Other symptoms include:

• Delayed puberty
• Double vision or difficulty with side (peripheral) vision
• Frontal bossing and a prominent jaw
• Headache
• Increased sweating
• Irregular periods (menstruation)
• Large hands and feet with thick fingers and toes
• Release of breast milk
• Thickening of the facial features
• Weakness

Exams and Tests

• CT or MRI scan of the head showing pituitary tumor
• Failure to suppress serum growth hormone (GH) levels after an oral glucose challenge (maximum 75g)
• High prolactin levels
• Increased insulin growth factor-I (IGF-I) levels

Damage to the pituitary may lead to low levels of other hormones, including:

• Cortisol
• Estradiol (girls)
• Testosterone (boys)
• Thyroid hormone

Treatment

In pituitary tumors with well-defined borders, surgery is the treatment of choice and can cure many 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 release.

Dopamine agonists (bromocriptine mesylate, cabergoline) have also been used to reduce growth hormone release, but these are generally less effective. Pegvisomant, a medication that blocks the effect of growth hormone, may be used.

Radiation therapy has also been used to bring growth hormone levels to normal. However, it can take 5 - 10 years for the full effects to be seen and this almost always leads to low levels of other pituitary hormones.

Radiation has also been linked to learning disabilities, obesity, and emotional changes in children. Most experts will use radiation only if surgery and medication fail.

Outlook (Prognosis)

Pituitary surgery is usually successful in limiting growth hormone production.

Possible Complications

• Delayed puberty

Surgery and radiation can both lead to low levels of other pituitary hormones, which can cause:

• Adrenal insufficiency
• Diabetes insipidus (rarely)
• Hypogonadism
• Hypothyroidism

When to Contact a Medical Professional

Call your health care provider if your child has signs of excessive growth.

References

Melmed S, Kleinberg D. Pituitary masses and tumors. In: Kronenberg HM, Melmed S, Polonsky KS, Larsen PR. Williams Textbook of Endocrinology. 12th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 9.

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