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Neurofibromatosis

By Margaret C. McBride, MD, Professor of Pediatrics;Pediatric Neurologist, NeuroDevelopmental Science Center, Northeast Ohio Medical University;Akron Children’s Hospital ; M. Cristina Victorio, MD, Assistant Professor in Pediatrics;Director, Headache Program; Pediatric Neurologist, Northeast Ohio Medical University;Akron Children's Hospital

Neurofibromatosis is a group of genetic disorders in which many soft, fleshy growths of nerve tissue (neurofibromas) form under the skin and in other parts of the body, and flat spots that are the color of coffee with milk (café-au-lait spots) often develop on the skin.

  • In addition to growths under the skin and café-au-lait spots on the skin, people may have abnormalities in bone, lack of coordination, weakness, abnormal sensation, or hearing or vision problems.

  • Doctors do a physical examination and sometimes an imaging test to check for lumps and growths.

  • No treatment can cure the disorder, but growths can be removed surgically or, if cancerous, may be treated with radiation therapy or chemotherapy.

Neurofibromas are flesh-colored growths of Schwann cells (which form a wrapping around peripheral nerve fibers) and other cells that support peripheral nerves (the nerves outside the brain and spinal cord).

Typical Structure of a Nerve Cell

A nerve cell (neuron) consists of a large cell body and nerve fibers—one elongated extension (axon) for sending impulses and usually many branches (dendrites) for receiving impulses.

Each large axon is surrounded by oligodendrocytes in the brain and spinal cord and by Schwann cells in the peripheral nervous system. The membranes of these cells consist of a fat (lipoprotein) called myelin. The membranes are wrapped tightly around the axon, forming a multilayered sheath. This myelin sheath resembles insulation, such as that around an electrical wire. Nerve impulses travel much faster in nerves with a myelin sheath than in those without one.

Neurofibromas, which can be felt under the skin as small lumps, usually start appearing after puberty.

Types

There are three types of neurofibromatosis:

  • Type 1 (or NF1, also known as von Recklinghausen disease) affects about 1 of 2,500 to 3,000 people. Neurofibromas develop along peripheral nerves—for example, under or within the skin and just outside the spinal cord. Sometimes tumors develop in the nerves that connect the brain to the eyes (optic nerves). Bone and soft tissues (such as muscle) may also be affected.

  • Type 2 (or NF2) affects about 1 of 35,000 people. It causes tumors of the auditory nerve (which connects the inner ear and the brain), called acoustic neuromas, and sometimes tumors in the brain or in the tissues that cover the brain or spinal cord (meninges). Tumors in the meninges are called meningiomas. They are not cancerous.

  • Schwannomatosis is less common than the other two types. Neurofibromas develop around peripheral nerves, but not the auditory nerve.

Causes of Neurofibromatosis

About half the people with neurofibromatosis inherit it. Only one gene for neurofibromatosis—from one parent—is required for the disorder to develop, and each child of an affected parent has a 50% chance of inheriting the disorder. Most of the genes involved in neurofibromatosis have been identified.

In the rest of the people, neurofibromatosis results from a spontaneous (not inherited) gene mutation. Thus, these people have no family history of the disorder.

Different types of mutations—whether inherited or spontaneous—may occur. The severity of the disorder depends on the type of mutation.

Symptoms of Neurofibromatosis

Type 1

Type 1 neurofibromatosis usually causes no symptoms, other than the characteristic café-au-lait spots or lumps (neurofibromas) under the skin. People may not notice these skin spots or lumps. However, if neurofibromas put pressure on the nerve they surround, people may notice tingling or weakness in areas near the lumps.

Café-au-lait spots develop in about 90% of affected children. They develop on the skin of the chest, back, pelvis, and creases of the elbows and knees. These spots typically exist at birth or appear during infancy. Children who do not have neurofibromatosis may have two or three café-au-lait spots, but children with type 1 have six or more of these spots.

Between ages 10 and 15, neurofibromas of varying sizes and shapes may begin appearing in the skin. There may be fewer than 10 of these growths or up to thousands of them.

Rarely, neurofibromas under the skin or an overgrowth of bones causes structural abnormalities, such as an abnormally curved spine (kyphoscoliosis), rib deformities, enlarged long bones in the arms and legs, and bone defects of the leg bones or skull. If the bone surrounding the eyeball is affected, the eyes bulge. Some children have slightly larger heads.

Neurofibromas may affect any nerve in the body but frequently grow on spinal nerve roots (the parts of the spinal nerve that emerge from the spinal cord through the spine). There, they often cause few or no problems. However, if they put pressure on (compress) the spinal cord, they can cause paralysis or disturbances in sensation in different parts of the body, depending on which part of the spinal cord is compressed. If neurofibromas compress peripheral nerves, the nerves may not function normally, and pain, tingling, numbness or weakness may result. Tumors that affect nerves in the head can cause blindness, dizziness, incoordination, or weakness.

Other problems may develop. They include

  • A tumor on the optic nerve (called an optic glioma)

  • Lisch nodules (benign growths on the iris, the colored part of the eye)

  • Bulges in the walls of arteries (aneurysms) or blockages in arteries

  • Learning problems

  • Leukemia

  • Cancerous tumors, sometimes in the brain or along the peripheral nerves

Optic gliomas may not cause any symptoms, or they may enlarge enough to put pressure on the optic nerve and impair vision or even cause blindness. These tumors can usually be identified by the time children are 5 years old and rarely develop after age 10.

Neurofibromatosis usually progresses slowly. As the number of neurofibromas increases, more neurologic problems may develop.

Type 2

In type 2 neurofibromatosis, auditory nerve tumors develop on one or both auditory nerves. The tumors may cause hearing loss, ringing in the ears (tinnitus), unsteadiness, dizziness, and sometimes headache or weakness in parts of the face. Symptoms may start during childhood or early adulthood.

People may also have other types of tumors, including gliomas and meningiomas (see Table: Tumors That Originate in or Near the Brain), and some develop cataracts prematurely.

Schwannomatosis

In schwannomatosis, benign tumors (called schwannomas) can develop on almost any nerve in the body, except the auditory nerves. Some people have many schwannomas, but others have only a few.

The first symptom of schwannomatosis is usually pain, which may become chronic and severe. Some people have numbness, tingling, or weakness in the fingers and toes. Other symptoms may develop, depending on the location of the schwannomas.

Diagnosis of Neurofibromatosis

  • A doctor's evaluation

  • Computed tomography or magnetic resonance imaging

In most people, neurofibromatosis is identified when people have a routine examination, see the doctor because of cosmetic complaints, or need to be evaluated because they have a family history of neurofibromatosis.

Doctors base the diagnosis on findings during examination, such as café-au-lait spots or lumps under the skin along nerves.

Doctors usually do computed tomography (CT) or magnetic resonance imaging (MRI) to check for growths in the head and near the spinal cord in people who have neurologic symptoms.

Genetic testing is not usually done, although if testing has identified a mutation in a parent with type 1, testing can be done to check for the same mutation in the child.

Treatment of Neurofibromatosis

  • Surgery or radiation therapy

  • For cancerous tumors, chemotherapy or radiation therapy

No known treatment can stop the progression of neurofibromatosis or cure it.

Individual neurofibromas can usually be removed surgically or shrunk with radiation therapy. Sometimes surgical removal of the neurofibroma requires removing the nerve as well.

If cancerous tumors develop, chemotherapy or radiation therapy may be used.

Because neurofibromatosis can be hereditary, genetic counseling is recommended when people with this disorder are considering having children. The children of people with neurofibromatosis have a 50% chance of having the disorder. For people who have a child with the disorder but do not have the disorder themselves, the risk of having another child with the disorder is very small.

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