At a Glance

Gigantism is a rare endocrine disorder caused by the hypersecretion of growth hormone (GH) from the anterior pituitary gland in growing children prior to the fusion of the epiphyseal growth plates. Although a GH-secreting adenoma of the pituitary gland is the cause of giantism in some children, hypersecretion of GH in children is more often due to an excess of hypothalamic growth hormone releasing hormone (GHRH).

Gigantism can be suspected in children who are more than three standard deviations above the normal mean height for their age. Keeping in mind that the majority of children with tall stature do not have the disorder, other causes of rapid linear growth should be excluded.

Gigantism is usually sporadic but may occur as part of a coexisting disorder, including McCune Albright syndrome, multiple endocrine neoplasia type 1, and Carney complex.

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What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

GH stimulates the hepatic synthesis of insulin-like growth factor 1 (IGF-1), and serum concentrations of IGF-1 are an indicator of GH secretion. Further, although the secretion of GH is pulsatile, the concentration of IGF-1 is relatively constant. Thus, serum IGF-1 testing is a valuable screening test for possible GH excess.

If IGF-1 is elevated, a GH suppression test is warranted. This provocative test measures the serum GH response after an oral glucose tolerance test. After administering 75 grams of glucose, samples are obtained over 120 minutes. A normal response is the suppression of GH to less than 0.3 ng/mL at 120 minutes.

Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications – OTC drugs or Herbals – that might affect the lab results?

Age- and gender-specific reference intervals are required for accurate interpretation of IGF-1, because concentrations rise gradually throughout childhood and are substantially higher during puberty than during the pre- or post-pubertal years.

A GH suppression test can produce false-positive results in unaffected children undergoing pubertal growth spurts as GH may fail to suppress and may be paradioxically increased.