Overview

Growth hormone is famous for helping children grow; however, its functions do not come to an end once the growth plates fuse. In adults, it plays a part in body composition, bone metabolism, lipids, exercise tolerance, and overall well-being. Adult growth hormone deficiency, which is also referred to as adult GHD, takes place when there is insufficient production of growth hormone by the pituitary gland.

Because there are several possible symptoms that can also be signs of aging and some other disorders, adult-onset GHD cannot be established based on symptoms. The right diagnosis should include medical history, examination of the pituitary gland, and lab tests.

What Is Adult Growth Hormone Deficiency?

GH is secreted by the pituitary gland that lies at the base of the brain. Its secretion is pulsatile in nature, which means there is variation in the concentration during the course of the day. Most of its actions are mediated by insulin-like growth factor 1 (IGF-1) secreted by the liver.

GHD in adults can either be childhood onset or adult onset. While childhood onset GHD persists even when the person stops growing, retesting is done for most of them as they enter adulthood. GHD in adults occurs much later in life, especially following disease or injury to the pituitary or hypothalamus.

It may exist alone but is more frequently seen along with other pituitary hormone deficiencies.

What Causes Growth Hormone Deficiency in Adults?

Growth hormone deficiency in adults is particularly common where there are conditions that affect the hypothalamus-pituitary region. These include tumors in the pituitary gland or near the pituitary, surgery on the pituitary or brain, radiation on the head, and any inflammatory, infiltrating, vascular, or structural conditions of the pituitary gland.

Severe injuries to the brain may be associated with pituitary conditions as well. Those with growth hormone deficiency during their childhood may still experience this condition in adulthood, particularly if the underlying cause was genetic, structural, or due to pituitary gland disorder.

Since the pituitary gland controls several hormone systems, GHD is usually coupled with hypothyroidism, hypoadrenalism, or hypogonadism.

Symptoms of Growth Hormone Deficiency in Adults

The symptoms of adult growth hormone deficiency can be quite subtle. These might include fatigue, decreased exercise tolerance, increase in body fat especially abdominal fat, decreased muscle mass, poor muscle function, and decreased bone mineral density. Additionally, some individuals have had poor cholesterol and other lipid profiles, as well as a decrease in the quality of life.

These symptoms do not point exclusively to GHD. Symptoms like fatigue, weight gain, poor strength, decreased mood, and low bone density may be seen in various other medical problems, medications, or even normal aging.

The presence of these symptoms along with previous problems involving the pituitary gland, cranial irradiation, pituitary surgery, major head injury, or deficiencies in other pituitary hormones might suggest a diagnosis of GHD, but these symptoms by themselves are insufficient for the diagnosis.

Growth Hormone Deficiency vs. Normal Aging

The secretion of growth hormones tends to fall with age. It should not be confused with the condition known as adult GHD that affects people of a certain age.

It is important to differentiate because muscle weakness, high body fat around the abdomen, limited physical capacity, and fatigue may result from aging as well as GHD. The same symptoms may arise due to sleep disorder, thyroid dysfunction, anemia, depression, side effects of some medications, and chronic illness.

In relation to growth hormone deficiency vs aging, one has to take into account medical context and perform testing in case of doubt. Guidelines do not recommend the use of GH therapy based on falling levels of GH and IGF-1 with age.

How Is Growth Hormone Deficiency Diagnosed?

Growth hormone deficiency testing starts with the clinical background. For example, an endocrinologist may consider symptoms, medical history in childhood, diseases of the pituitary gland and the brain, surgery, radiotherapy, trauma to the head, as well as other pituitary hormones deficiencies.

Random growth hormone blood level testing is typically not recommended since the secretion of this hormone is pulsatile. Thus, a low result obtained at a certain point can be completely normal. That is why current guidelines use dynamic testing in most adults.

The IGF-1 test may be included in the diagnostic protocol because the IGF-1 levels are less variable through the day compared to GH. The lower IGF-1 value may be used to support the diagnosis if done in an appropriate clinical context.

Nevertheless, the interpretation of the IGF-1 value should include age-specific normal values and also the general condition of the individual, because many other conditions may affect the IGF-1 result.

• Growth Hormone Stimulation Tests

In cases where confirmation is required, a GH stimulation test will be done to check the pituitary’s reaction after a stimulus is employed to release GH.

The insulin tolerance test has for many years been used as a reference standard, but this test actually induces hypoglycemia and cannot be applied to some individuals, especially those with a history of seizures and heart problems. The glucagon stimulation test is a popular substitute. Macimorelin, which is an orally administered GH secretagogue, is yet another alternative that can be employed under certain circumstances. Test selection and the cut-off levels are dependent on the test and the individual at hand. BMI is especially critical in some tests like the glucagon stimulation test.

How Is Adult Growth Hormone Deficiency Treated?

Prescription Growth Hormone Replacement

For adults with confirmed GHD and no contraindication, treatment may involve recombinant human growth hormone. Somatropin is a recombinant form of human growth hormone used medically and is commonly administered by subcutaneous injection.
When growth hormone replacement is prescribed, HGH injections may involve different somatropin formulations and delivery systems. The appropriate product, dose, and treatment plan depend on the diagnosis, age, response, medical history, and concurrent hormone therapies, so treatment should be prescribed and monitored by a qualified healthcare professional.

Treatment Is Individualized

There is no single approach to the management of adult deficiency of growth hormone. Modern therapy relies on personalized medication doses that do not rely on body weight alone.

Age, gender, estrogen consumption through oral administration, metabolism, and other therapies for the other pituitary hormones are factors that influence the need for hormone replacement. The ultimate aim of therapy is to compensate for growth hormone deficiency without overexposure to GH.

Benefits and Possible Side Effects of Growth Hormone Therapy

GH replacement therapy may help improve body composition, physical fitness, bone mass, and quality of life in appropriately chosen adult patients with GH deficiency. There are no guarantees for weight reduction, increase in energy, or reversing aging processes associated with aging. Recombinant human growth hormone may also cause adverse reactions. One such side effect is fluid accumulation causing swelling, joint pain or muscle pain, tingling or carpal tunnel syndrome in case of high doses of the drug.

Other adverse reactions caused by somatropin are associated with glucose metabolism. Somatropin may also cause additional risks for certain medical conditions. Most adverse reactions associated with the use of somatropin and caused by dose have been observed to decrease in response to lowering the dose.

Monitoring During Growth Hormone Treatment

Monitoring is a standard practice during growth hormone treatment. Evaluation will involve the assessment of symptoms, treatment objectives, side effects, and serum IGF-1 levels. The dose may be altered appropriately to maintain serum IGF-1 levels within the appropriate age-related range while minimizing adverse effects.

Other factors that can be evaluated include glucose metabolism, lipids, body composition, blood pressure, and bone health. Where there are deficiencies of other hormones from the pituitary gland, thyroid, adrenal, and reproductive hormones may require evaluation. Patients who have had pituitary tumors in the past may need monitoring based on their conditions.

When Should You See an Endocrinologist?

It may be sensible to speak about the possibility of testing with an endocrinologist if any signs of possible GHD appear with the existence of some risk factors like pituitary pathology, previous pituitary or brain surgeries, irradiation of the brain, severe brain injury, deficiencies in multiple pituitary hormones, or GHD during childhood.

Fatigue, weight gain, depression, or lack of muscle mass alone do not suffice to prove adult GHD. The fact is that these symptoms may have various other causes.

It is possible for an endocrinologist to decide about the necessity of testing, choose the most harmless test, assess multiple pituitary hormones, and provide information on the therapy if the GHD exists. This way, one can distinguish between adult GHD and aging or avoid uncontrolled use of hormones.