Acromegaly: Symptoms, Complications, Causes, Diagnosis and Treatments

It is due to excessive production of growth hormone (GH), usually by a secretory adenoma of pituitary growth hormone.

It is usually due to a tumor of the pituitary gland , known as a pituitary adenoma.

Pituitary tumors : in more than 95% of cases, the excessive growth hormone is caused by a pituitary tumor, usually a benign microadenoma of the pituitary gland.

Non-pituitary tumor : tumors of the adrenal glands, lungs and pancreas are involved in some cases. These tumors secrete growth hormone or growth hormone-releasing hormone.

Its prevalence is estimated at 40-130 cases per million inhabitants. If the disorder occurs in childhood, it leads to gigantism instead of acromegaly.

Elevated levels of growth hormone stimulate the liver to produce insulin-like growth factor-1 (IGF-1, for its acronym in English). Elevated levels of insulin-like growth factor stimulate the excessive growth of body tissues.

Growth hormone, also known as somatotropin , is a peptide hormone that stimulates growth , cell reproduction and cell regeneration in humans and other animals. Therefore, it is important in human development.

It is a type of mitogen that is specific only for certain types of cells. Growth hormone is a stress hormone that increases the concentration of glucose and free fatty acids.

A recombinant form of human growth hormone called somatropin is used as a prescription medication to treat growth disorders in children and growth hormone deficiency in adults.

In the United States, it is only available legally in pharmacies, by prescription of a doctor.

In recent years in the United States, some doctors have begun to prescribe growth hormone in elderly patients with growth hormone deficiency (but not in healthy people) to increase vitality.

While it is legal, the efficacy and safety of this use for human growth hormone has not been proven in a clinical trial.

In its role as an anabolic agent, human growth hormone has been used by competitors in sports since at least 1982, and has been banned by the International Olympic Committee and the National Collegiate Athletic Association.

The traditional analysis of urine does not detect doping with human growth hormone, so the ban could not be applied until the early 2000s, when blood tests began to develop that could distinguish between natural human growth hormone and artificial.

Blood tests conducted by the World Anti-Doping Agency at the 2004 Olympic Games in Athens, Greece, focused mainly on human growth hormone.

In the United States, the only approved use of growth hormone for livestock is the use of a cow-specific growth hormone called bovine somatotropin to increase milk production in dairy cows.

Retailers can label milk containers produced with or without bovine somatotropin.

Acromegaly affects muscle strength, bone health and energy levels, and can cause unusual physical characteristics and medical complications. It can be years until the changes appear.

Early death is possible and life expectancy can be reduced by 10 years. Three to four people in every million are diagnosed with acromegaly in the United States each year, and affect 60 people in every million at the same time.

The initial symptom is typically the extension of the hands and feet. There may also be enlargement of the forehead, jaw and nose. Other symptoms may include joint pain, thicker skin, increased voice, headaches and vision problems.

Complications of the disease can include type 2 diabetes, sleep apnea, and  high blood pressure . Acromegaly is usually caused by the pituitary gland producing too much growth hormone. The condition is not inherited from the parents of a person.

The diagnosis is by measuring growth hormone after a person has drunk glucose or by measuring growth factor I similar to insulin in the blood. After diagnosis, medical images of the pituitary are made to look for an adenoma.

If excess growth hormone is produced during childhood, the result is gigantism. Treatment options include surgery to remove the tumor, medications, and radiation therapy. Surgery is usually the preferred treatment and is most effective when the tumor is smaller.

In those in whom surgery is not effective, drugs of the somatostatin-like or growth hormone receptor type can be used. The effects of radiation therapy are more gradual than those of surgery or medication.

Without treatment, those affected live on average 10 years less; however, with the treatment, the life expectancy is usually normal. Acromegaly affects approximately 6 per 100,000 people worldwide.

It is diagnosed more frequently in middle age. Men and women are affected with the same frequency.

The first medical description of the disorder occurred in 1772 by Nicolas Saucerotte . The term is from the Greek ἄκρον akron meaning “extreme” and mega μ queγαmeaning “big”.

Signs and symptoms of acromegaly

Acromegaly is characterized by somatic disfigurement acquired slowly progressive (mainly with the face and extremities) and systemic manifestations.

When it is caused by a pituitary tumor, as is usually the case, the patient may experience effects of the tumor mass, such as headaches, visual impairment and facial pain due to the participation of the fifth cranial nerve.

Characteristics that result from the high level of growth hormone or expanding tumor include:

  • Visibly soft tissue that produces increased hands, feet, nose, lips and ears, and a general thickening of the skin.
  • Pronounced protrusion of the eyebrows, often with ocular distension (frontal protuberance).
  • Acrocordón (benign tumor that forms on the skin).
  • Indications of the carpal tunnel .

The changes caused by acromegaly take time to develop. Changes in physical appearance can be dramatic. They include:

  • A big jaw and tongue.
  • Gaps between the teeth.
  • A more prominent front.
  • Swollen hands
  • Big feet.
  • Rough and oily skin.

Other changes include:

  • Tingling and lack of sensitivity in the hands and feet.
  • Intense sweating
  • Headaches.
  • Vision problems.

There may also be an enlargement of the internal organs, including the heart, liver, lungs and kidneys. It can lead to a condition called gigantism.

Complications

The excess of growth hormone interrupts the metabolism of carbohydrates, which causes resistance to insulin, possibly diabetes and high cholesterol. Complications can be life threatening. They include:

Acromegaly leads to pituitary gigantism if it occurs in children before the epiphyseal fusion of the bones. High levels of growth hormone can cause pain and arthritis in joints or narrow bone tunnels, such as carpal tunnel syndrome and spinal stenosis.

It feeds the abnormal growth of the head and face, such as prognathism (a protruding jaw), malocclusion of the teeth and enlargement of the forehead, tongue, ears, fingers and extremities.

In addition, with acromegaly, the hair may thicken and the skin may thicken. The respiratory tract also thickens, resulting in sleep apnea and deepening of the voice.

Heart disease often occurs, either because of direct heart detriment or hypertension, high cholesterol and overwork. In fact, heart disease is the most common cause of death among patients with this condition.

In addition to the effect of high levels of growth hormone and insulin-like growth factor 1, acromegaly can cause other disorders of another pituitary axis, such as hyperprolactinemia, which can cause amenorrhea , galactorrhea, impotence and loss of libido, hyperthyroidism and disease of Cushing .

These conditions can cause thyroid, adrenal, or gonadal insufficiency.

Acromegalic patients are more susceptible to neoplasms, possibly due to the increase in insulin-like growth factor-1 in the growth of cancer cells, and 46% have colonic polyps, which can lead to carcinoma.

Additional complications include cholelithiasis (gallstones), hypercalcemia, and hyperphosphatemia .

Causes

Adenoma pituitario

Approximately 98% of cases of acromegaly are due to the overproduction of growth hormone by a benign tumor of the pituitary gland called adenoma.

These tumors produce an excessive growth hormone and compress the surrounding brain tissues as they grow.

In some cases, they can compress the optic nerves. Tumor expansion can cause headaches and visual disturbances.

In addition, the compression of surrounding normal pituitary tissue can alter the production of other hormones, which causes changes in menstruation and discharge in women and impotence in men due to reduced testosterone production.

There is a marked variation in growth hormone production rates and tumor aggressiveness. Some adenomas grow slowly and the symptoms of excess growth hormone are often not noticed for many years.

Other adenomas grow rapidly and invade the areas of the surrounding brain or the paranasal sinuses, which are located near the pituitary gland. In general, younger patients tend to have more aggressive tumors.

Most pituitary tumors arise spontaneously and are not genetically inherited. Many pituitary tumors arise from a genetic alteration in a single pituitary cell that leads to greater cell division and tumor formation.

This genetic change, or mutation, is not present at birth, but it is acquired during life. The mutation occurs in a gene that regulates the transmission of chemical signals within pituitary cells; permanently activates the signal that tells the cell to divide and secrete growth hormones.

The events within the cell that cause the disordered growth of pituitary cells and the secretion of growth hormone are currently under intense investigation.

Pituitary adenomas and diffuse somatomamotropic hyperplasia may be the result of the GNAS gene of somatic activating mutations, which may be acquired or associated with the McCune-Albright syndrome.

Other tumors

In some patients, acromegaly is not caused by pituitary tumors, but by tumors of the pancreas, lungs, and adrenal glands. These tumors also lead to an excess of growth hormone.

Either because they produce the growth hormone themselves or, more often, because they produce the growth hormone-releasing hormone, the hormone that stimulates the pituitary gland to produce growth hormone.

In these patients, the hormone releasing excess growth hormone can be measured in the blood and states that the cause of acromegaly is not due to a defect of the pituitary gland.

When these non-pituitary tumors are removed surgically, they decrease the levels of growth hormone and improve the symptoms of acromegaly.

In patients with non-pituitary tumors producing growth hormone-releasing hormone, the pituitary gland may still be enlarged and confused with a tumor.

Therefore, it is important that doctors carefully analyze all “pituitary tumors” taken from patients with acromegaly so as not to overlook the possibility that a tumor elsewhere in the body is causing the disorder.

Diagnosis of acromegaly

If acromegaly is suspected, medical images and medical laboratory investigations are usually used together to confirm or rule out the presence of this condition.

Insulin growth factor 1 (IGF-1) provides the most sensitive laboratory test for the diagnosis of acromegaly.

And a test of growth hormone suppression after an oral glucose load, which is a very specific laboratory test, will confirm the diagnosis after a positive test result for insulin growth factor 1 (IGF-1, for its acronym in English).

A single value of growth hormone is not useful in view of its pulsatility (levels in the blood vary greatly, even in healthy individuals).

The levels of growth hormone taken 2 hours after a glucose tolerance test of 75 or 100 grams are useful in the diagnosis.

Growth hormone levels are suppressed below 1μg / l in normal people and levels higher than this limit are confirmatory of acromegaly.

Other pituitary hormones should be evaluated to treat the secretory effects of the tumor, as well as the effect of tumor mass on the normal pituitary gland.

They include thyroid-stimulating hormone (HST), gonadotropic hormones (FSH, LH), adrenocorticotropic hormone, and prolactin.

A magnetic resonance imaging of the brain focused on the sella turcica after administration of gadolinium allows a clear delineation of the pituitary and hypothalamus and the location of the tumor.

Several other syndromes of overgrowth can cause similar problems.

Pseudoacromegalia

Pseudoacromegaly is a condition with the usual acromegaloid characteristics, but without an increase in growth hormone and insulin-like growth factor 1 (IGF-1, for its acronym in English).

It is frequently associated with insulin resistance. Cases have been reported due to minoxidil at an unusually high dose.

It can also be caused by a selective defect of post-receptor insulin signaling, which leads to metabolic disruption, but the preservation of mitogenic signaling.

Treatments

The treatment is aimed at correcting (or preventing) the tumor compression of the surrounding tissues by excising the lesion causing the disease, and reducing the levels of growth hormone and insulin growth factor 1 to normal values.

The treatment will depend on the location of the tumor, the age of the person and their medical history.

Surgical treatment

The surgery can be carried out to eliminate the pituitary tumor. This would stop the overproduction of growth hormone and relieve pressure on the surrounding tissue.

Transsphenoidal endonasal surgery: a minimally invasive surgery involves the insertion of an endoscope through a small incision in the nasal cavity or upper lip to access the pituitary gland and extract the pituitary adenoma.

The endoscope will pass from the nasal cavity to the sphenoid bone, which is a bone that separates the brain from the rest of the facial structures, it will quickly relieve the symptoms of pressure, as well as the lower levels of high growth hormone.

The recovery time is shorter compared to traditional transsphenoidal surgery.

Transnasal transsphenoidal microscopic surgery : this is a traditional pituitary surgery that uses direct visualization of the tumor with a microscope.

Recent retrospective studies showed a gross total resection with a resolution of the endonasal approach of insulin-like growth factor 1 (IGF-1) that is comparable to microscopic transsphenoidal transnasal surgery.

Removing the tumor should lead to a drop in growth hormone levels. However, even if the tumor is successfully removed, hormone levels may not return to normal, and additional therapies may be necessary.

When surgery (the usual first-line treatment) does not correct the hypersecretion of growth hormone / insulin growth factor 1, medical treatment with dopamine agonists (particularly cabergoline), somatostatin analogues and / or radiotherapy can be used.

Radiation therapy

Radiation therapy can be used alone or as part of a combined approach.

After surgery, radiation therapy can remove the remaining tumor cells. It can also be used together with medications to reduce growth hormone levels.

Conventional radiation therapy is given 5 days a week, for up to 6 weeks, but it can take up to 10 years for growth hormone levels to return to normal.

In stereotactic radiosurgery, it is a precision radiotherapy that directs intensely focused radiation beams to the tumor, minimizing damage to the surrounding tissue.

This involves fewer sessions than conventional radiation therapy, and can reduce growth hormone levels in a shorter time.

It is often administered as an adjunct to surgery to prevent relapse or when surgery can not achieve acceptable reduction in growth hormone levels. It is associated with the risk of irradiating adjacent brain tissues.

Medication to control growth

Whether as an adjunct to surgery or when surgery is not desirable, acromegaly can be treated with medications only if surgery is considered too risky or impossible due to the location of the tumor.

These aim to stop the rapid growth triggered by the prevention of the secretion or action of growth hormone. A combination of treatments is probably the best option.

Somatostatin analogues (octreotide, Lanreotide) : these act on the somatostatin receptor to cause the inhibition of growth hormone secretion.

It is usually given as intramuscular injections once a month. It can also be used to reduce large pituitary adenomas before surgery.

Dopamine receptor agonists (cabergoline, bromocriptine) : these act on D2 receptors and are not as effective as somatostatin analogues. They are often used as attachments.

Growth hormone receptor antagonist (Pegvisomant) : this novel drug blocks the growth hormone in the receptors, decreasing the levels of insulin growth factor 1 (IGF-1), while the levels of the Growth hormone are not affected.

It is useful in patients who are resistant to somatostatin analogues. Thanks to this therapeutic strategy of multiple steps, adequate hormonal control is achieved in most patients, which gives them a normal life expectancy.

Comorbidities associated with acromegaly usually improve after treatment, but persistent sequelae can, however, affect quality of life.