Pituitary dwarfism
Definition
Dwarfism is a condition in which the growth of the individual is very slow or delayed, resulting in less than normal adult stature. The word pituitary refers to the pituitary gland, which regulates the production of certain chemicals called hormones. Therefore, pituitary dwarfism is decreased bodily growth due primarily to hormonal problems. The end result is a proportionate little person, because the height and the growth of all other structures of the individual are decreased.
Description
Pituitary dwarfism is caused by problems arising from the pituitary gland. The pituitary gland, also called the hypophysis, is a gland at the base of the brain that produces many different hormones. This gland is divided into the anterior (front) and posterior (back) halves. The anterior pituitary produces six hormones: growth hormone, adrenocorticotropin (corticotropin), thyroid stimulating hormone (thyrotropin), prolactin, follicle stimulating hormone, and lutenizing hormone. The posterior pituitary gland only produces two hormones: antidiuretic hormone (vasopressin) and oxytocin.
The growth process begins in the lower part of the forebrain in a small organ called the hypothalamus. The hypothalamus releases hormones that regulate the production of other hormones. When the hypothalamus releases growth hormone-releasing hormone (GHRH), the anterior pituitary is stimulated to release growth hormone (GH). Growth hormone then acts on the liver and other tissues and stimulates them to secrete insulin-like growth factor-1 (IGF-1). IGF-1 directly promotes the development of bone and muscle, causing bones to grow in length, and muscles to increase protein synthesis (make more protein).
Since growth is a complex phenomenon, it may be slowed down or stopped by abnormalities arising at any point in the process. Thus, dwarfism can result if there is a deficiency in any of these hormones, if there is a failure in the receptor cells receiving the hormonal stimuli, or if the target cells are unable to respond.
At its most basic, pituitary dwarfism results from decreased production of hormones by the anterior pituitary. When none of the hormones of the anterior pituitary are adequately produced, this is called panhypopituitarism. A common form of pituitary dwarfism is due to deficiencies in the production of growth hormone (GH). When less GH than normal is produced during childhood, an individual's arms, legs, and other structures continue to develop in normal proportions, but at a decreased rate.
Demographics
It is estimated that between one in 14,000 and one in 27,000 babies born each year have some form of dwarfism. In 2004, more than 20,000 children in United States were receiving supplemental GH therapy. It is estimated that about one quarter of them had organic causes of GH deficiencies. There appears to be no racial or ethnic component to pituitary dwarfism, but males seem to be afflicted more than females.
Causes and symptoms
Investigations are underway to determine the specific genetic mutations that can cause dwarfism. Pituitary dwarfism can be caused by:
- genetics
- accident-related trauma to the pituitary gland
- surgical injury of the pituitary
- central nervous system tumor
- central nervous system trauma
- central nervous system radiation
- leukemia
In most cases, the cause of dwarfism is not known (idiopathic).
A child with a growth hormone deficiency is often small with an immature face and chubby body build. The child's growth does not follow the normal growth curve patterns. In cases of tumor, most commonly craniopharyngioma (a tumor near the pituitary gland), children and adolescents may have neurological symptoms such as headaches, vomiting , and problems with vision. The child may also have symptoms of double vision. The symptom, however, that all children with pituitary dwarfism share is that they do not grow at the same rate as their peers.
When to call the doctor
If a child appears to be smaller than children two or more years younger than he or she is, the doctor should be consulted.
Diagnosis
Growth hormone deficiency is present at birth, but since the primary symptoms of pituitary dwarfism are height and growth at a reduced rate, the condition is not diagnosed until later in childhood. Charting a child's growth in comparison to age norms will help lead to a diagnosis. Another diagnostic technique uses an x ray of the child's hand to determine the child's bone age by comparing this to the child's actual chronological age. The bone age in affected children is usually two or more years behind the chronological age. This means that if a child is 10 years old, his or her bones will look like they are those of an eight-year-old. The levels of growth hormone and IGF-1 may also be measured with blood tests.
The doctor will do a complete examination to make sure that delayed growth is not caused by other underlying problems, such as tumor. X rays of the area where the pituitary gland is located, or more advanced imaging such as magnetic resonance imaging (MRI) or computed tomography (CT), may help the doctor make a diagnosis and may show whether there have been any changes to the pituitary gland itself.
Treatment
Growth hormone replacement therapy can be administered if the child is lacking growth hormone. A pediatric endocrinologist, a doctor specializing in the hormones of children, administers this type of therapy before a child's bone growth plates have fused or joined. Once the growth plates have fused, GH replacement therapy is rarely effective.
Until 1985, growth hormone was obtained from the pituitary glands of human cadavers. However, some disease complications resulted, and the United States Food and Drug Administration (FDA) banned this source of GH. In 1985, recombinant DNA techniques produced a safe and unlimited supply of GH in the lab. Now, the only growth hormone used for treatment is that which is made in a laboratory.
If growth hormone is not the only hormone deficiency, the doctor must prescribe ways to raise the levels of the other deficient hormones, if these options are available. A careful balancing of all of the hormones produced by the pituitary gland is necessary for patients with panhypopituitarism, making this form of dwarfism complex and difficult to manage.
Prognosis
The prognosis depends on the cause of the dwarfism. A panhypopituitarism dwarf does not pass through the initial onset of adult sexual development ( puberty ) and never produces enough gonadotropic (sex) hormones to develop adult sexual function. These individuals also have other medical conditions that may prove fatal. Dwarfism due only to growth hormone deficiency has a much better prognosis if treated early with replacement GH. These individuals do pass through puberty and mature sexually; however, without treatment, they remain proportionately small in stature.
The success of treatment with GH varies. An increase in height of 4–6 in. (10–15 cm) can occur in the first year of treatment. Following this first year, the response to the hormone replacement therapy is less pronounced. Even after this first year, however, the child usually continues to grow at a faster rate than he or she would without GH therapy. Long-term use is considered successful if the individual grows at least 0.75 in. (2 cm) per year more than he or she would without the hormone. However, if GH therapy is not given before the growth plates of the long bones—such as the legs and arms—fuse, the individual will not grow. Prognosis is generally better the earlier a child starts GH replacement therapy.
Improvement for individuals with other causes of dwarfism, such as a tumor, varies greatly. The prognosis usually depends on successful resolution of the underlying problem, whether there is any permanent damage, and the age of the child.
Prevention
There is no known way to prevent pituitary dwarfism, although in some cases it may be caused by traumatic injury to the pituitary gland. Engaging in safe behaviors may reduce the risk of injury-induced pituitary deficiencies.
Parental concerns
Children with pituitary dwarfism are smaller than other children, but they are just as smart and can lead long, healthy lives. It is important for parents not to expect less of their child with pituitary dwarfism simply because the child looks younger than he or she actually is. Chores and conversations should be appropriate to the actual age of the child. Children with pituitary dwarfism may face thoughtless comments from others on occasion, and the parents' reaction to such comments can strongly determine how the child feels about himself or herself.
KEY TERMS
Adrenocorticotropic hormone (ACTH) —Also called adrenocorticotropin or corticotropin, this hormone is produced by the pituitary gland to stimulate the adrenal cortex to release various corticosteroid hormones.
Antidiuretic hormone (ADH) —Also called vasopressin, a hormone that acts on the kidneys to regulate water balance.
Craniopharyngioma —A tumor near the pituitary gland in the craniopharyngeal canal that often results in intracranial pressure.
Deprivational dwarfism —A condition where emotional disturbances are associated with growth failure and abnormalities of pituitary function.
Follicle-stimulating hormone (FSH) —A pituitary hormone that in females stimulates the ovary to mature egg capsules (follicles) and in males stimulates sperm production.
Growth hormone —A hormone that eventually stimulates growth. Also called somatotropin.
Hormone —A chemical messenger secreted by a gland or organ and released into the bloodstream. It travels via the bloodstream to distant cells where it exerts an effect.
Luteinizing hormone —A hormone secreted by the pituitary gland that regulates the menstrual cycle and triggers ovulation in females. In males it stimulates the testes to produce testosterone.
Oxytocin —A hormone that stimulates the uterus to contract during child birth and the breasts to release milk.
Panhypopituitarism —Generalized decrease of all of the anterior pituitary hormones.
Prolactin —A hormone that helps the breast prepare for milk production during pregnancy.
Puberty —The point in development when the ability to reproduce begins. The gonads begin to function and secondary sexual characteristics begin to appear.
Thyroid-stimulating hormone (TSH) —A hormone produce by the pituitary gland that stimulates the thyroid gland to produce the hormones that regulate metabolism. Also called thyrotropin.
Resources
BOOKS
Ghigo, C. et al, eds. Growth Hormone Secretagogues. New York: Elsevier, 1999.
Melmed, Shlomo, ed. The Pituitary. Malden, MA: Blackwell Pub., 2002.
PERIODICALS
Klotter, Jule. "Growth Hormone Replacement Therapy." Townsend Letter for Doctors and Patients 251 (June 2004): 28.
"Message to Parents: Hold Off on Growth Hormone for Short Kids." Life Science Weekly (Sept. 14, 2004): 1172.
Sandberg, David E. et al. "Height and Social Adjustment: are Extremes a Cause for Concern and Action?" Pediatrics 114, no. 3 (Sept. 2004): 744–51.
ORGANIZATIONS
Human Growth Foundation. 997 Glen Cove Avenue, Suite 5 Glen Head, NY 11545. (800) 451-6434 Fax: (516) 671-4055 http://www.hgfound.org
Little People of America, Inc. 5289 NE Elam Young Parkway, Suite F-700 Hillsboro, OR 97124. (888) LPA-2001 or (530) 846-1562 Fax: (503) 846-1590. http://www.plaonline.org.org
Tish Davidson, A.M. Jason S. Schliesser, D.C.