LabMed

Acromegaly

At a Glance

Acromegaly is a rare chronic endocrine disorder caused by the hypersecretion of growth hormone (GH) from the anterior pituitary gland in adults. A GH-secreting adenoma of the pituitary gland is the most common cause of acromegaly. Rarely, GH may be secreted by some malignancies.

Acromegaly is indolent with symptoms often preceding diagnosis by several years. Visual field defects and persistent headaches are common complaints caused by expansion of the adenoma. The tumor may also compromise normal pituitary tissue leading to deficiencies of other pituitary hormones.

Because GH stimulates the hepatic synthesis of insulin-like growth factor 1 (IGF-1), other symptoms of acromegaly are related to the excess GH and IGF-1 secretion and include:

  • Enlargement of the extremities

  • Increase in ring and/or shoe size

  • Coarsening of facial features

  • Prognathism (growth of mandible)

  • Macroglossia

  • Excessive sweating

Acromegalics have an increased risk of developing diabetes mellitus, hypertension, cardiovascular disease, and congestive heart failure. They also show a greater incidence of premalignant colon polyps that increases the risk of colon cancer.

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

GH and IGF-1 testing is indicated for individuals with headaches and musculoskeletal growth. Because GH secretion is pulsatile, its concentration in acromegaly may be within the established reference interval. In contrast, serum concentrations of IGF-1 are relatively constant and are usually elevated in acromegaly. Thus, IGF-1 is the best single test for diagnosis. Acromegaly is excluded, if the GH concentration is less than 0.3 ng/mL in conjunction with a concentration of IGF-1 within the established reference interval.

GH secretion is inhibited by glucose. Individuals with active acromegaly are unable to suppress GH concentration after an oral glucose tolerance test. After administering 75 grams of glucose, samples are obtained over 120 minutes. Failure to suppress GH (<0.3 ng/mL) at 120 minutes is diagnostic of acromegaly. If GH is suppressed, then acromegaly is excluded.

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. Starvation, obesity, and diabetes mellitus decrease and pregnancy increases concentrations of IGF-1.

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