Gigantism - Wikipedia

Gigantism is characterized by an excess of growth hormone (GH). The excess of growth hormone that brings about gigantism is virtually always caused by pituitary growths (adenomas).[7] These adenomas are on the anterior pituitary gland. They can also cause overproduction of GH's hypothalamic precursor known as growth hormone releasing hormone (GHRH).[10]

As a result of the excessive amounts of growth hormone, children achieve heights that are well above normal ranges.[11] The specific age of onset for gigantism varies between patients and gender, but the common age that excessive growth symptoms start to appear has been found to be around 13 years.[6] Other health complications, such as hypertension, may occur in pediatric patients with hyper-secretion of growth hormone. Characteristics more similar to those seen in acromegaly may occur in patients that are closer in age to adolescence since they are nearing growth plate fusion.[12]

Hormonal cause

Growth hormone (GH) and insulin-like growth factor-I (IGF-I) are two substances that have been identified as influencing growth plate formation and bone growth and, therefore, gigantism. Their specific mechanisms are still not well understood.[6][13]

More broadly, GH and IGF have both been identified to be involved in most stages of growth: embryonic, prenatal, and postnatal.[14][15] Moreover, the receptor gene for IGF has been shown to be particularly influential throughout various stages of development, especially prenatally. This is the same for GH receptor genes which have been known to drive overall growth throughout various pathways.[14][16]

Growth hormone is a precursor (upstream) of IGF-I, but each has its independent role in hormonal pathways. Yet both seem to ultimately come together to have a joint effect on growth.[15]

Diagnostic testing

Evaluation of growth hormone hypersecretion cannot be excluded with a single normal GH level due to diurnal variation. However, a random blood sample showing markedly elevated GH is adequate for diagnosis of GH hyper-secretion. Additionally, a high-normal GH level that fails to suppress with administration of glucose is also sufficient for a diagnosis of GH hyper-secretion.[17]

Insulin-like growth factor-1 (IGF-1) is an excellent test for evaluation of GH hyper-secretion. It does not undergo diurnal variation and will thus be consistently elevated in GH hyper-secretion and therefore patients with gigantism. A single normal IGF-1 value will reliably exclude GH hypersecretion.[17]