Growth hormone deficiency can occur for a variety of reasons, either in isolation or part of panhypopituitarism (a deficiency of all pituitary hormones). The cells of the pituitary gland that produce growth hormone (somatotrophic cells) are very sensitive to trauma, radiation, and compression. Isolated growth hormone deficiency has been reported after closed head injury, and growth hormone is one of the first hormones to be depressed by compression of the pituitary gland from a lesion such as a tumor.
Growth hormone binds to its receptors in various tissues to cause different effects. In the liver, it causes the generation of a protein called IGF-I. IGF-I from the liver accounts for about 90% of circulating IGF-I. Other tissues, and in particular bone, also make IGF-I in response to growth hormone. Growth hormone and IGF-I result in long bone growth, in conjunction with other hormones, and cause an increase in stature. Growth hormone, and probably IGF-I, cause salt and water retention at the level of the kidney. Growth hormone does a number of things to build muscle. It also burns fat, especially the visceral fat located in the stomach, and is responsible for body composition.
In children, growth hormone deficiency can lead to short stature and delay in puberty, and it is the most common symptom in children with pituitary lesions.
In adults symptoms include:
- decreased energy
- a feeling of social isolation
- increase in fat and decrease in lean muscle mass
- poor exercise tolerance
- sleep disturbance
- skin abnormalities (fine wrinkling, dryness, thinning)
Some studies show that growth hormone deficiency may contribute to a higher risk of cardiovascular disease and higher cholesterol levels. Many patients also show psychological symptoms such as depression, social isolation, poor short-term memory and impaired concentration.
Once a diagnosis of growth hormone deficiency is confirmed, growth hormone replacement should be considered in the context of current symptoms and signs, lifestyle and risks. Synthetic growth hormone has improved treatment of growth hormone deficiency. There is no oral replacement therapy and treatment requires daily injections.
In children, growth hormone replacement is critical for growth and development. Horomone replacement is used not only to treat the growth hormone deficiency, but also to promote growth and to increase height. In adults, replacement therapy has been controversial but is now widely accepted. The goal of therapy for adults is to improve the overall sense of well-being and reverse the symptoms and signs of growth hormone deficiency, such as weight gain and poor bone density. For patients with normal IGF-1 levels, there may not be any benefit from growth hormone therapy. For patients with diminished IGF-1, growth hormone can be titrated to normalize IGF-1 and the benefits usually are noted in six to 18 months.
Patients who have had long-term and severe GH deficiency may develop symptoms of growth hormone excess just after starting GH replacement therapy even though the IGF-I levels are normal. The symptoms might include swelling in the hands and feet, pain in the large joints, and carpal tunnel syndrome.
Growth hormone replacement is not indicated in the presence of an active pituitary tumor or in patients who have not yet completed antitumor therapy.