What is adult-onset growth hormone deficiency?
Adult-onset growth hormone deficiency is a medical condition that occurs when the pituitary gland in brain does not produce enough growth hormone. Growth hormone is made by the anterior pituitary gland. It stimulates the release of another hormone called insulin-like growth factor 1 (IGF-1), which is produced mainly by the liver. Together, these hormones stimulate growth in childhood (especially the height) and in adult life psychological well-being and physical performance.GH also has widespread metabolic effects throughout the body.
Growth hormone deficiency is classified depending on when, or at what stage of life, the deficiency first becomes evident. There are some adults who were diagnosed as growth hormone deficient when they were children (childhood-onset growth hormone deficiency) and there are others who become growth hormone deficient once they reach adult life (adult onset).
What causes adult-onset growth hormone deficiency?
Most cases of adult onset growth hormone deficiency result from damage to the pituitary gland caused by a pituitary tumour or by treatment for this using surgery and/or radiotherapy. Pituitary damage can also result from:
- radiotherapy to the brain for other tumours close to the pituitary gland or for leukemia
- from severe head injury
- autoimmune disease
- from interference with the blood supply to the pituitary gland (as for example in Sheehan’s syndrome, a loss of function of the pituitary gland due to severe blood loss after child birth, or pituitary apoplexy, sudden bleeding in to the pituitary gland).
Most other types of growth hormone deficiency are caused by genetic abnormalities (e.g. Prader-Willi syndrome or Turner syndrome) or by abnormal development of the pituitary gland in the fetus (see the article on childhood growth hormone deficiency). These are usually diagnosed at birth or in early childhood, but growth hormone deficiency is a lifelong condition and treatment may be needed in adult life too (see the article on childhood-onset growth hormone deficiency).
In some cases, no obvious cause for the deficiency can be found and the condition is said to be idiopathic.
What are the signs and symptoms of adult-onset growth hormone deficiency?
Adults with growth hormone deficiency may have a wide range of symptoms. When these symptoms are severe, they can reduce people’s ability to function – both physical and psychological– and this can dramatically lower the quality of their lives.
These symptoms include:
- a decrease in the amount of muscle bulk and strength
- increase in the amount of fat in the body (especially around the waist)
- abnormalities of ‘good’ and ‘bad’ cholesterol. This can lead to an increase in the risk of heart disease
- abnormalities in the blood and in the circulation
- osteoporosis (brittle bones)
- low energy levels and decreased stamina
- impaired concentration and memory.
How common is adult-onset growth hormone deficiency?
It is estimated that in the adult UK population at any given time, approximately one in every 10,000 people will have adult onset growth hormone deficiency. If the adults with childhood-onset and adult-onset growth hormone deficiency are combined, the estimated number is three in every 10,000 people. This works out to approximately 12,600 adults with growth hormone deficiency in England and Wales.
Is adult-onset growth hormone deficiency inherited?
Adult-onset growth hormone deficiency is not an inherited condition. However, there are few rare genetic abnormalities that can cause growth hormone deficiency, but these causes are rare and generally identified in childhood.
How is adult-onset growth hormone deficiency diagnosed?
The most common test is the ‘Insulin tolerance test’. This involves giving an injection of insulin to the patient to lower the blood sugar level. During this stress reaction, the body normally releases growth hormone. Failure to produce an adequate amount of growth hormone in response to this insulin induced stress confirms growth hormone deficiency. Most patients find the test a little uncomfortable but the unpleasant symptoms do not usually last long and, if severe, can be stopped by giving glucose without invalidating the test. The insulin tolerance test should not be carried out in patients with known heart disease or epilepsy. Alternative tests are also available in which growth hormone-releasing hormone, arginine or glucagon are used to cause growth hormone release.
These tests should be carried out in a specialist unit, by experienced staff in performing these tests safely. The tests usually take two to four hours and can be carried out as outpatient or day case procedures. Patients may be asked not to eat before these tests.
How is adult-onset growth hormone deficiency treated?
Adult-onset growth hormone deficiency is treated with growth hormone replacement therapy. . The growth hormone that is used is an artificial preparation that individuals can administer themselves. This is done using daily injections underneath the skin into the fat tissue around the lower abdomen, with an injection device. The needles are the same as those used by people who inject insulin for diabetes and the injections are virtually painless. However, there are needle-free devices available for patients who are unable to overcome the fear of injecting.
Treatment starts as an outpatient clinic with education and support, usually from an endocrine nurse. Once started, individuals are carefully monitored and given regular blood tests. The dosage of the growth hormone is adjusted depending upon the patient’s response and results of blood tests.
In the UK, there are NICE guidelines to regulate the start and continuation of growth hormone therapy.
Are there any side-effects to the treatment?
Side-effects from growth hormone therapy are infrequent and tend to occur when the dose is too high. Fluid retention and discomfort in the joints are reported, but decreasing the dose temporarily can relieve these symptoms. Growth hormone treatment can also increase blood sugar levels. A small number of people can have increased pressure in the brain that can cause headaches and blurred vision. Stopping treatment will resolve this problem.
Taking growth hormone will not cause any increase in height in adults.
What are the longer-term implications of adult-onset growth hormone deficiency?
People with adult-onset growth hormone deficiency have an increased risk of heart disease and strokes as a result of the physical changes that occur in body fat, cholesterol and circulation. Healthy living, a balanced diet and exercise to prevent becoming overweight are essential to reduce this risk. People with adult-onset growth hormone deficiency also have a higher risk of developing osteoporosis or brittle bones and, therefore, have a higher risk of developing fractures from minor injuries. In order to decrease these risks, having a diet that is rich in calcium and taking adequate supplements of vitamin D, along with moderate amount of weight-bearing exercise and resistance training, are all helpful.
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