Acromegaly and Gigantism
Overproduction of growth hormone causes excessive growth. In children, the condition is called gigantism; in adults, it is called acromegaly.
Growth hormone stimulates the growth of bones, muscles, and many internal organs. Excessive growth hormone, therefore, leads to abnormally robust growth of all of these tissues. Overproduction of growth hormone is almost always caused by a noncancerous (benign) pituitary tumor (adenoma). Certain rare tumors of the pancreas and lungs also can produce hormones that stimulate the pituitary to produce excessive amounts of growth hormone, with similar consequences.
Symptoms
If excessive growth hormone production starts before the growth plates have closed (that is, in children), the condition produces gigantism. The long bones grow enormously. A person grows to unusually great stature, and the arms and legs lengthen. Puberty may be delayed, and the genitals may not develop fully.
In most cases, excessive production of growth hormone begins between the ages of 30 and 50, long after the growth plates of the bones have closed. Increased growth hormone in adults produces acromegaly, in which the bones become deformed rather than elongated. Because changes occur slowly, they are usually not recognized for years.
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). 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.
In both gigantism and acromegaly, the tongue may enlarge and become more furrowed. Coarse body hair, which typically darkens, increases as the skin thickens. The sebaceous and sweat glands in the skin enlarge, producing excessive perspiration and often an offensive body odor. The heart usually enlarges, and its function may be so severely impaired that heart failure occurs. Sometimes a person feels disturbing sensations and weakness in the arms and legs as enlarging tissues compress the nerves. Nerves that carry messages from the eyes to the brain may also be compressed, causing loss of vision, particularly in the outer visual fields. The pressure on the brain may also cause severe headaches.
Nearly all women with acromegaly have irregular menstrual cycles. Some women produce breast milk even though they are not breastfeeding (galactorrhea) because of either too much growth hormone or a related increase in prolactin. About one third of men who have acromegaly develop erectile dysfunction (impotence). There is also an increased likelihood of developing diabetes mellitus, high blood pressure (hypertension), heart failure, sleep apnea, and certain tumors, particularly affecting the large intestine, which may become cancerous. Life expectancy is reduced in people with untreated acromegaly.
Diagnosis
In children, rapid growth may not seem abnormal at first. Eventually, however, the abnormality of the extreme growth becomes clear.
In adults, because the changes induced by high levels of growth hormone occur slowly, acromegaly often is not diagnosed until many years after the first symptoms appear. Serial photographs (those taken over many years) may help a doctor establish the diagnosis. An x-ray of the skull may show thickening of the bones and enlargement of the nasal sinuses. X-rays of the hands show thickening of the bones under the fingertips and swelling of the tissue around the bones. Blood sugar levels and blood pressure may be high.
The diagnosis is confirmed by blood tests, which usually show high levels of both growth hormone and insulin-like growth factor I (IGF-I). Because growth hormone is released in short bursts and the levels of growth hormone often fluctuate dramatically even in people without acromegaly, a single high level of growth hormone in the blood is insufficient to make the diagnosis. Doctors must give something that would normally suppress growth hormone levels, most commonly a glucose drink (the oral glucose tolerance test), and show that normal suppression does not occur. This test is not necessary when the clinical features of acromegaly are obvious, the IGF-I level is high, or a tumor is seen in the pituitary on scanning.
A computed tomography (CT) or magnetic resonance imaging (MRI) scan is usually performed to look for abnormal growths in the pituitary gland. Because acromegaly is usually present for some years before being diagnosed, a tumor is seen on these scans in most people.
Treatment
Stopping or reducing the overproduction of growth hormone is not easy; thus, doctors may need to use a combination of surgery, radiation, and drug therapy.
Surgery by an experienced surgeon is currently regarded as the best first treatment for most people with acromegaly caused by a tumor. It results in an immediate reduction in tumor size and growth hormone production, most often without causing deficiency of other pituitary hormones. Unfortunately, tumors 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 tumor remains after surgery and acromegaly persists.
Radiation therapy involves the use of supervoltage irradiation, which is less traumatic than surgery. This treatment may take several years to have its full effect, however, and often results in later deficiencies of other pituitary hormones, as normal tissue is often also affected. More directed radiation therapy, such as stereotactic radiosurgery, is being tried to speed results and spare the normal pituitary tissue.
Drug therapy can also be used to lower growth hormone levels. Occasionally, bromocriptine and other dopamine agonists are of some benefit. The most effective drugs, however, are those that are forms of somatostatin, the hormone that normally blocks growth hormone production and secretion. These drugs include octreotide and its new long-acting analogs, which only have to be given about once a month. These drugs are effective in controlling acromegaly in many people as long as they continue to be taken (they do not provide a cure). Their use has been limited by the need to inject them and by their high cost. This may change as such drugs become longer acting and more readily available. Several new growth hormone blocker drugs are being investigated.
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