Acromegaly and Gigantism Health Article

Definition

Acromegaly is a disease in which an abnormality in the pituitary gland leads to an oversecretion of growth hormone. In adults, this condition results in an enlargement of bones; in children, the abnormality results in excessive height and is called gigantism.

Description

Acromegaly is a disorder in which the abnormal release of a particular chemical from the pituitary gland in the brain causes increased growth in bone and soft tissue, as well as a variety of other disturbances throughout the body. This chemical released from the pituitary gland is called growth hormone (GH). The body's ability to process and use nutrients like fats and sugars is also altered. In children whose bony growth plates have not closed, the chemical changes of acromegaly result in exceptional growth of long bones. This variant is called gigantism, with the additional bone growth causing unusual height. When the abnormality occurs after bone growth stops, i.e. in adults, the disorder is called acromegaly.

Demographics

Acromegaly is a relatively rare disorder, occurring in approximately 50 out of every 1 million people. Gigantism occurs even more rarely, with reported cases in the United States numbering only about 100 by 2004. Males and females are similarly affected. Onset of gigantism is usually at puberty, although some cases of toddlers and young children with gigantism have been reported.

Causes and symptoms

The pituitary is a small gland located at the base of the brain, which releases certain hormones that are important to the functioning of other organs or body systems. The pituitary hormones travel throughout the body and are involved in a large number of activities, including the regulation of growth and reproductive functions. The cause of acromegaly can be traced to the pituitary's production of GH.

Under normal conditions, the pituitary receives input from another brain structure, the hypothalamus, located at the base of the brain. This input from the hypothalamus regulates the pituitary's release of hormones. For example, the hypothalamus produces growth hormone-releasing hormone (GHRH), which directs the pituitary to release GH. Input from the hypothalamus should also direct the pituitary to stop releasing hormones.

In acromegaly, the pituitary continues to release GH and ignores signals from the hypothalamus. In the liver, GH causes production of a hormone called insulin-like growth factor 1 (IGF-1), which is responsible for growth throughout the body. When the pituitary refuses to stop producing GH, the levels of IGF-1 also reach abnormal peaks. Bones, soft tissue, and organs throughout the body begin to enlarge, and the body changes its ability to process and use nutrients like sugars and fats.

The most common cause of acromegaly and gigantism is the development of a noncancerous tumor within the pituitary, called a pituitary adenoma. In the case of pituitary adenomas, the tumor itself is the source of the abnormal release of GH. As these tumors grow, they may press on nearby structures within the brain, causing headaches and changes in vision. As the adenoma grows, it may disrupt other pituitary tissue, interfering with the release of other hormones. These disruptions may be responsible for changes in the menstrual cycle and abnormal production of breast milk in women or delayed development of reproductive organs. In rare cases, acromegaly is caused by the abnormal production of GHRH, which leads to the increased production of GH. Certain tumors in the pancreas, lungs, adrenal glands, thyroid, and intestine can produce GHRH, which in turn triggers production of an abnormal quantity of GH.

In acromegaly, an individual's hands and feet begin to grow, becoming thick and doughy. The jaw line, nose, and forehead also grow, and facial features are described as coarse. The tongue grows larger, and because the jaw is larger, the teeth become more widely spaced. Due to swelling within the structures of the throat and sinuses, the voice becomes deeper and sounds hollower, and patients may develop loud snoring. Children and adolescents with gigantism show a characteristic lengthening and enlargement of bones, principally of the limbs. Some symptoms caused by various hormonal changes are as follows:

• heavy sweating
• oily skin
• increased coarse body hair
• improper processing of sugars in the diet (and sometimes actual diabetes)
• high blood pressure
• increased calcium in the urine (sometimes leading to kidney stones)
• increased risk of gallstones
• swelling of the thyroid gland

People with acromegaly have more skin tags, or outgrowths of tissue, than normal. This increase in skin tags is also associated with the development of growths, called polyps, within the large intestine that may eventually become cancerous. Patients with acromegaly often suffer from headaches and arthritis. The various swellings and enlargements throughout the body may press on nerves, causing sensations of local tingling or burning and sometimes result in muscle weakness.