Neurofibromatosis

DEFINITION

Neurofibromatosis is a genetic disorder that disturbs cell growth in your nervous system, causing tumors to form on nerve tissue. These tumors may develop anywhere in your nervous system, including in your brain, spinal cord and nerves. Neurofibromatosis is usually diagnosed in childhood or early adulthood.

The tumors are usually noncancerous (benign), but in some cases these tumors become cancerous (malignant) tumors. People with neurofibromatosis often experience only mild symptoms. Effects of neurofibromatosis can range from hearing loss, learning impairment, and heart and blood vessel (cardiovascular) complications to severe disability due to nerve compression by tumors, loss of vision and severe pain.

Neurofibromatosis treatment aims to maximize healthy growth and development and to manage complications as soon as they arise. When neurofibromatosis causes large tumors or tumors that press on a nerve, surgery may help ease symptoms. Some people may benefit from other therapies, such as stereotactic radiosurgery, medications to control pain or physical therapy.

CAUSES

Neurofibromatosis is caused by genetic defects (mutations) that either are passed on by a parent or occur spontaneously at conception. Each form of neurofibromatosis is caused by mutations in different genes.

Neurofibromatosis 1 (NF1)

The NF1 gene is located on chromosome 17. Normally, this gene produces a protein called neurofibromin, which is abundant in nervous system tissue and helps regulate cell growth. A mutation of the NF1 gene causes a loss of neurofibromin, which allows cells to grow uncontrolled.

Neurofibromatosis 2 (NF2)

A similar problem occurs with NF2. The NF2 gene is located on chromosome 22, which produces a protein called merlin. A mutation of the NF2 gene causes loss of merlin, which also leads to uncontrolled cell growth.

Schwannomatosis

Schwannomatosis may be associated with a mutation of the SMARCB1 gene located on chromosome 22. Other gene mutations may be involved in schwannomatosis. The occurrence of schwannomatosis may be inherited or may be sporadic (spontaneous), but these are not known yet.

SYMPTOMS

Three distinct types of neurofibromatosis exist, each with different signs and symptoms.

Neurofibromatosis 1 (NF1)

Neurofibromatosis 1 (NF1) usually appears in childhood. Signs and symptoms include:

• Flat, light brown spots on the skin. These harmless spots, also called cafe au lait (ka-FAY oh LAY) spots, are common in many people. If you have more than six of them, it’s a strong indication of NF1. In NF1, cafe au lait spots are usually present at birth or appear during the first years of life and then stabilize. They aren’t serious but can sometimes be a cosmetic concern.
• Freckling in the armpits or groin area. Freckling usually appears by age 4 or 5.
• Soft bumps on or under the skin (neurofibromas).Neurofibromas are benign tumors that can be located anywhere in the body. Many people develop tumors in the skin or under the skin, but neurofibromas can also grow inside of the body. Sometimes, a growth will involve multiple nerves (plexiform neurofibroma).
• Tiny bumps on the iris of your eye (Lisch nodules). Lisch nodules — harmless lesions in your eye — can’t easily be seen just by looking at them, and they don’t affect your vision. However, your doctor can detect these lesions using a special instrument.
• Bone deformities. Abnormalities in the way bones grow and a deficiency in bone mineral density can cause bone deformities such as a curved spine (scoliosis) or bowed lower leg.
• Learning disabilities. Impaired thinking skills (cognition) are common in children with NF1, but are usually mild. Children may have difficulty with language and visual-spatial skills. Children with NF1 often may have a specific learning disability, such as attention-deficit/hyperactivity disorder (ADHD).
• Larger than average head size. Children with NF1 tend to have a larger than average head size and higher brain volume, but it’s unknown whether this is related to cognitive impairment.
• Short stature. Children with NF1 often have a short stature and are below average in height.

Neurofibromatosis 2 (NF2)

Neurofibromatosis 2 (NF2) is much less common than NF1. Signs and symptoms of NF2 usually result from the development of vestibular schwannomas (also known as acoustic neuromas) in both ears.

These benign tumors grow on the nerve that carries sound and balance information from the inner ear to the brain (the eighth cranial nerve). Resulting signs and symptoms generally appear in the late teen and early adult years and may include:

• Gradual hearing loss
• Ringing in the ears
• Poor balance

In some cases, NF2 can lead to growth of schwannomas in other nerves of the body, including the cranial, spinal, visual (optic) and peripheral nerves. Associated signs and symptoms may include:

• Facial drop
• Numbness and weakness in the arms or legs
• Pain
• Balance difficulties

In addition, NF2 may result in vision problems due to abnormal growth on the retina (mostly in children) or due to the development of cataracts.

Schwannomatosis

Schwannomatosis is a rare form of neurofibromatosis only recently recognized. It rarely affects people before their 20s or 30s. Schwannomatosis causes painful tumors called schwannomas to develop on cranial, spinal and peripheral nerves, but not on the nerve that carries sound and balance information from the inner ear to the brain (the eighth cranial nerve).

Because tumors don’t grow on this nerve, schwannomatosis doesn’t cause hearing loss, making it different from NF2. As with NF2, though, schwannomatosis doesn’t cause cognitive impairment. Schwannomatosis mainly causes chronic pain, which can occur anywhere in your body.

When to see a doctor

If you notice signs or symptoms of neurofibromatosis in your child or yourself, call your doctor for an appointment or bring it up at your next visit. The tumors associated with neurofibromatosis are often benign and slow-growing. So although it’s important to obtain a timely diagnosis and monitor for complications, the situation isn’t an emergency.