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Acromegaly, Gigantism

Acromegaly, Gigantism

Gigantism and acromegaly are hormonal disorders that result from too much growth hormone (GH) in the body. In these conditions, the pituitary produces excessive amounts of GH. Usually the excess GH comes from benign, or noncancerous, tumours on the pituitary.

When GH-producing tumours occur in childhood, the disease that results is called gigantism. In response to GH, the long bones grow in length at the growth plates—areas near either end of the bone. Prolonged exposure to excess GH before the growth plates fuse causes increased growth of the long bones and thus increased height.  In more than ninety percent of individuals, the underlying cause is a benign pituitary tumour. Occasionally it may present as a feature of other conditions such as multiple endocrine neoplasia (MEN) type I, McCune-Albright syndrome (MAS), neurofibromatosis, tuberous sclerosis or Klinefelter syndrome.

Since growth plates fuse after puberty, excessive GH production in adults does not result in increased height. It produces a condition known as acromegaly. The name acromegaly comes from the Greek words for “extremities” and “enlargement,” reflecting one of its most common symptoms—the abnormal growth of the hands and feet. In few patients, acromegaly is caused not by pituitary tumours but by tumours of the pancreas, lungs and adrenal glands that also lead to an excess of GH either because they directly produce GH or, more frequently, because they produce GHRH. Mostly, the overproduction of GH is caused by a benign tumuor of the pituitary gland.

Symptoms :

Growth hormone stimulates the production of another hormone in the liver called insulin-like growth factor 1 (IGF-1) which is the factor that actually causes the physical changes that accompany acromegaly such as the overgrowth of bones, soft tissues and other features of acromegaly. Excessive growth hormone, therefore, leads to abnormally robust growth of all of these tissues.

In children, the long bones grow enormously and the arms and legs lengthen. 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 are 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, thickening of the facial features and weakness.

The person's facial features become coarse, and the hands and feet swell. Larger rings, gloves, shoes, and hats are needed. Overgrowth of the jawbone (mandible) can cause the jaw to protrude (prognathism). The forehead and overlying skin is thickened, which may lead to frontal bossing (an unusually prominent forehead sometimes with a heavy brow ridge). Cartilage in the voice box (larynx) may thicken, making the voice deep and husky. The ribs may thicken, creating a barrel chest. Joint pain is common; after many years, crippling degenerative arthritis may occur.

Later sequelae of the disease include arthritis and carpel tunnel syndrome (compression of the median nerve at the level of the wrist due to pressure from the hypertrophied bone and soft tissue), heart failure, diabetes and hypertension. In addition, the tumor compresses the pituitary gland itself often altering the production of other pituitary hormones. If not treated, this disorder can result in serious illness and premature death.

   

Investigations :

GH is secreted by the pituitary in impulses, or spurts, its concentration in the blood can vary widely from minute to minute. Therefore, a single measurement of an elevated blood GH level is not enough to diagnose acromegaly. Since IGF-I levels are much more stable than GH levels over the course of the day, they are often a more practical and reliable screening measure. Elevated IGF-I levels almost always indicate acromegaly.

More accurate information is obtained when GH is measured under conditions that normally suppress GH secretion. The oral glucose tolerance test is a highly reliable method for confirming a diagnosis of acromegaly. Drinking 75 to 100 grams of glucose solution lowers blood GH levels to less than 1 nanogram per milliliter (ng/ml) in healthy people. In people with GH overproduction, this suppression does not occur.

Magnetic resonance imaging (MRI) scan of the pituitary is used to locate and detect the size of the tumour. If MRI fails to detect a pituitary tumour, the physician should look for non-pituitary “ectopic” tumours in the chest, abdomen, or pelvis as the cause of excess GH. The presence of such tumours usually can be diagnosed by measuring GHRH in the blood and by a CT scan of possible tumor sites.

Rarely, a pituitary tumour secreting GH may be too tiny to detect even with a sensitive MRI scan.

Treatment :

Goals of treatment are to reduce excess hormone production to normal levels, relieve the pressure that the growing pituitary tumour may be exerting on the surrounding brain areas, preserve normal pituitary function or treat hormone deficiencies and improve the symptoms of gigantism/acromegaly.

Surgery by an experienced surgeon is currently regarded as the best first treatment for most people with acromegaly caused by a tumour. It results in an immediate reduction in tumour size and growth hormone production, most often without causing deficiency of other pituitary hormones. The surgeon reaches the pituitary through the nostrils, endoscopically with special tools, removes the tumour tissue in a procedure called transsphenoidal surgery. This procedure promptly relieves the pressure on the surrounding brain regions and leads to a rapid lowering of GH levels. If the surgery is successful, facial appearance and soft tissue swelling improve within a few days. Unfortunately, tumours are often large by the time they are found, and surgery alone does not usually produce a cure.

Radiation therapy is often used as a follow-up treatment, particularly if a substantial amount of the tumour remains after surgery and acromegaly persists. 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.

Following successful treatment, regular follow up is required.

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Dept. of ENT - Head and Neck Surgery and Skullbase Surgery
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