Gigantism

Overview

What is gigantism?

Gigantism, also called pediatric acromegaly and pituitary gigantism, is a very rare condition that happens when a child or adolescent has high levels of growth hormone (GH) in their body, which causes them to grow very tall. The pituitary gland normally produces GH, but a tumor on their pituitary can produce excess GH in gigantism.

Your pituitary gland is a small, pea-sized endocrine gland located at the base of your brain below your hypothalamus. Your pituitary gland releases eight important hormones, including GH.

Growth hormone, also known as human growth hormone (hGH) and somatotropin, is a natural hormone that acts on many parts of the body to promote growth in children. Once the growth plates (epiphyses) in your bones have fused, GH no longer increases height. Instead, it helps to maintain normal bone, cartilage and organ structure and metabolism. GH is closely connected to insulin-like growth factor 1 (IGF1), a hormone your liver releases. These hormones work together to carry out growth and metabolism functions.

In gigantism, the excessive amount of growth hormone (GH) accelerates the growth of muscle, bones and connective tissue. This leads to an abnormally increased height as well as several soft tissue changes. When left untreated or uncontrolled, some people with gigantism have grown over 8 feet tall.

Because of this, early diagnosis and treatment are crucial in cases of gigantism.

What is the difference between gigantism and acromegaly?

Gigantism and acromegaly are both conditions that result from excess growth hormone (GH). The difference is in who the conditions affect — adults develop acromegaly, whereas children and teenagers who are still growing develop gigantism.

In children, gigantism occurs when they experience excess GH before the growth plates in their bones fuse (before the end of puberty).

Once your growth plates have fused, excess GH causes acromegaly. In this case, you don’t grow in height, but the excess GH affects your bones’ shape and your organ size as well as other health factors.

Gigantism is rarer than acromegaly.

Who does gigantism affect?

Though it’s very rare, gigantism can affect any child whose growth plates in their bones haven’t fused yet (they haven’t finished puberty). Gigantism more commonly affects children assigned male at birth more than children assigned female at birth.

How common is gigantism?

Gigantism is very rare. There’ve been approximately 100 cases recorded in the United States so far.

How does growth normally happen in children?

Growth hormone (GH) regulates growth during childhood by promoting measured bone, muscle and tissue growth and helping to control metabolism. Growth is normally a relatively stable process until a child reaches puberty.

During puberty, the release of sex hormones (estrogen and testosterone) increases significantly and causes the growth plates (epiphyses) at the ends of your child’s long bones to slowly fuse. Height growth stops at the end of puberty when the growth plates have completely joined.

The rate at which a child grows and their final height reached after puberty is determined by a combination of several genes they inherit from their parents, environmental factors and their sex.

In cases of gigantism, a child grows very rapidly and significantly more than other children of the same sex and age. But gigantism can still be difficult for parents to detect since symptoms of gigantism might seem like normal childhood growth spurts at first.

If you have any questions or concerns about the rate at which your child is growing, talk to their healthcare provider.

Symptoms and Causes

What are the signs and symptoms of gigantism?

Excessive amounts of growth hormone (GH) cause the signs and symptoms of gigantism. Children with gigantism can also develop certain symptoms as their pituitary tumor applies pressure to their nearby brain and nerve tissues. The main sign of gigantism is excessive growth. Children with gigantism grow rapidly in height.

Aside from being very tall/large for their age, physical characteristics of gigantism include:

  • Very prominent forehead and a prominent jaw.
  • Gaps between their teeth.
  • Thickening of their facial features.
  • Large hands and feet with thick fingers and toes.

Other symptoms of gigantism include:

If your child experiences these symptoms, it’s important to talk to their healthcare provider as soon as possible.

What causes gigantism?

The most common cause of gigantism is a benign (noncancerous) tumor on your child’s pituitary gland (a pituitary adenoma) that releases excess growth hormone (GH). Children with gigantism almost always have large pituitary tumors called macroadenomas (a pituitary adenoma that’s 10 millimeters in diameter or larger) at diagnosis. Gigantism can also be caused by pituitary hyperplasia, which is when your pituitary gland becomes enlarged.

Many children with gigantism have a genetic mutation that causes the pituitary tumor to form. The most common genetic mutations associated with gigantism are AIP gene mutations or deletions, making up approximately 29% of the population of people with gigantism.

Gigantism can occur as a part of several rare genetic disorders that lead to an increased risk of developing GH-secreting pituitary tumors, including:

  • Carney complex: This is a genetic condition that affects skin color (pigmentation) and causes benign tumors of your skin, heart and endocrine system. GH-secreting pituitary adenomas occur in about 10% to 13% of Carney complex cases and usually have a slow progression.
  • McCune-Albright syndrome: This is a genetic condition that affects your bones, skin and endocrine system, causing café-au-lait skin pigmentation, scar tissue forming on bones and early (precocious) puberty. Excess GH is present in 20% to 30% of McCune-Albright syndrome cases. It’s often caused by pituitary gland enlargement (hyperplasia) but pituitary adenomas can be the cause as well.
  • Multiple endocrine neoplasias (MEN) type 1 or type 4: These are genetic conditions in which one or more of your endocrine glands are overactive and/or form a tumor, which can include a GH-secreting pituitary tumor.
  • Neurofibromatosis: This is a condition that’s a part of a group of genetic conditions known as neurocutaneous disorders that affect your skin and nervous system. These types of disorders are caused by abnormal increases in cell growth. This results in the formation of tumors all over your body, which can include a GH-secreting tumor.
  • Familial isolated pituitary adenomas (FIPA): This is an inherited condition characterized by the development of pituitary adenomas, which can include a GH-secreting adenoma.

Diagnosis and Tests

How is gigantism diagnosed?

Gigantism can be difficult to diagnose due to how rare it is and because growth rates can vary widely from child to child due to genetics and environmental factors.

In general, healthcare providers suspect gigantism when a child’s height is three standard deviations above the normal average height for their sex and age or two standard deviations above the adjusted average based on the height of their biological parents.

If your child’s healthcare provider thinks they may have gigantism, they’ll likely recommend you see an endocrinologist, a healthcare provider who specializes in hormone-related conditions. They’ll make a diagnosis based on your child’s medical and family history, a thorough clinical evaluation and specialized tests such as blood tests and imaging tests.

What tests will be done to diagnose gigantism?

If your child’s healthcare provider suspects they have gigantism, they may order the following tests to help diagnose the condition:

  • Growth hormone and IGF-1 (insulin-like growth factor 1) blood tests: These tests measure different hormone levels in your child’s blood from a sample taken from their vein. Higher than normal levels may indicate gigantism.
  • Glucose tolerance test: This test can assess whether your child’s growth hormone levels react to glucose (sugar) the way they should. For this test, a provider will draw blood samples from your child’s vein at different intervals after your child drinks a glucose (sugar) solution.
  • Imaging tests: If blood tests confirm that your child has gigantism, their provider will probably recommend an MRI (magnetic resonance imaging) scan or CT (computed tomography) scan, which can clearly show the size and location of a pituitary tumor and help determine the proper treatments.

If your child has been diagnosed with gigantism, their provider may order additional tests to see if the condition has affected other parts of their body. These tests may include:

Management and Treatment

How is gigantism treated?

The goals of treating gigantism include:

  • Safely controlling growth hormone (GH) and insulin-like growth factor 1 (IGF1) levels.
  • Controlling pituitary tumor growth.
  • Reducing the effects of the pituitary tumor on nearby structures, such as brain tissue and the optic nerve.
  • Treating or reducing the effects of GH on other body systems.

Healthcare providers typically use a combination of treatments, specifically surgery and radiation therapy, for gigantism.

Medications are available and effective in treating acromegaly (excess GH in adults) but the effects of these drugs on children haven’t been adequately studied.

Surgery for gigantism

Surgery is the most common treatment option for gigantism. The goal is to remove or reduce the size of the pituitary tumor. Since the pituitary tumors that cause gigantism are often large, children with gigantism may need multiple surgeries to remove the tumor and effectively control GH levels.

Your child’s surgeon may use a type of surgery called transsphenoidal surgery to remove the pituitary tumor, which involves going through your child’s nose and sphenoid sinus, a hollow space in your child’s skull behind the nasal passages and below your child’s brain, to perform surgery.

Radiation therapy for gigantism

Radiation therapy can help lower growth hormone levels when surgery isn’t effective in doing so. Radiation therapy uses specialized equipment to target the tumor with radiation beams. This therapy works slowly. It may require several treatment courses, with breaks in between, and may take several years to fully take effect.

What are the possible complications of gigantism treatment?

As a result of surgeries and/or radiation therapy, approximately 60% of people with gigantism develop hypopituitarism after treatment, a condition in which there’s a lack of one, multiple or all of the hormones made by your pituitary gland. Hypopituitarism is treated with hormone replacement medications.

Complications from surgery to remove a pituitary tumor can include:

Possible side effects of radiation therapy include:

  • Impaired fertility.
  • Vision loss and brain injury (rare).
  • Tumor development several years after treatment (rare).

Prevention

Can gigantism be prevented?

Unfortunately, there’s nothing you can do to prevent gigantism, though early diagnosis is crucial. Prompt treatment can help prevent or slow the changes that cause your child to grow very tall.

Outlook / Prognosis

What is the prognosis (outlook) for gigantism?

The prognosis (outlook) for children and adolescents diagnosed with gigantism depends on several factors, including:

  • How early or late they’re diagnosed.
  • How effective treatment is at controlling growth hormone levels.
  • If they develop complications related to gigantism.

In general, people who are older at diagnosis tend to have more complications than people who are diagnosed at a younger age, probably due to longer exposure to excess growth hormone and insulin-like growth factor 1.

Because of this, it’s essential to talk to your child’s healthcare provider as soon as possible if you’re noticing abnormal or unexpected changes in their growth and/or physical features.

What is the life expectancy of someone with gigantism?

Early diagnosis and treatment of gigantism are crucial to prevent excessive height and associated complications and improve life expectancy.

If gigantism is left untreated, it’s associated with significant complications and an increased death rate of around twice the normal average.

What are the complications of gigantism?

Long-term complications that some people with gigantism might experience due to excessive height and the overall effects of excess growth hormone include:

Issues participating in everyday tasks such as buying clothes and traveling due to a very tall height can also diminish the quality of life of people with untreated gigantism.

Living With

When should I see my child’s healthcare provider about gigantism?

If your child has been diagnosed with gigantism, they’ll need to see their healthcare provider and/or endocrinologist regularly to monitor treatment and to make sure their hormone levels are in an optimum range.

A note from Cleveland Clinic

If you’re noticing changes in the rate at which your child is growing and/or changes in their physical features, it’s important to talk to their healthcare provider as soon as possible. While it may be unlikely that gigantism is the cause, any concerning changes are worth evaluating. People with gigantism who are diagnosed early have the best outlook and usually lead healthy lives. If you have any questions about what to expect with your child’s growth, don’t be afraid to reach out to their provider. They’re there to help.

Last reviewed by a Cleveland Clinic medical professional on 05/09/2022.

References

  • Beckers A, Petrossians P, Hanson J, Daly AF. The Causes and Consequences of Pituitary Gigantism. (https://pubmed.ncbi.nlm.nih.gov/30361628/) Nat Rev Endocrinol. 2018; 14(12): 705-720. Accessed 5/9/2022.
  • Bello MO, Garla VV. Gigantism And Acromegaly. [Updated 2021 Apr 7]. In: StatPearls [Internet]. Treasure Island, FL: StatPearls Publishing; 2021. Accessed 5/9/2022.
  • MedlinePlus. Gigantism. (https://medlineplus.gov/ency/article/001174.htm) Accessed 5/9/2022.
  • Rostomyan L, Daly AF, Beckers A. Pituitary Gigantism: Causes and Clinical Characteristics. (https://pubmed.ncbi.nlm.nih.gov/26585365/) Ann Endocrinol (Paris). 2015; 76(6): 643-9. Accessed 5/9/2022.
  • Society for Endocrinology. Gigantism. (https://www.yourhormones.info/endocrine-conditions/gigantism/) Accessed 5/9/2022.

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy