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Neurofibromatosis -fī-ˌbrō-mə-ˈtō-səs

by Margaret C. McBride, MD

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 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.

Neurofibromas are flesh-colored growths of Schwann cells (which form a wrapping around peripheral nerve fibers—see Figure: Typical Structure of a Nerve Cell) and other cells that support peripheral nerves (the nerves outside the brain and spinal cord). 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 on the skin and just outside the spinal cord. Sometimes tumors develop in the nerves 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 and around the brain.

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

In a few people, tumors develop in the brain.

Causes

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 have been identified.

In the rest of the people, neurofibromatosis results from a spontaneous 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

Type 1

Most people notice no symptoms, and the disorder is first suspected during a routine examination when doctors find the café-au-lait spots or lumps under the skin in nerves. Some people notice these skin spots or lumps themselves, and some then notice tingling or weakness in areas near the spots or 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 on 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.

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 or weakness may result. Tumors that affect nerves in the head can cause blindness, dizziness, incoordination, or weakness.

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

Type 2

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.

Diagnosis

Doctors base the diagnosis on findings during examination. They 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 during pregnancy to check for the mutation in the fetus.

Treatment

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.

Because neurofibromatosis can be hereditary, genetic counseling is recommended when people with this disorder are considering having children. 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.