Neurofibromatosis is a genetic disorder that disturbs cell growth in the nervous system, causing tumors to form on nerve tissue. These tumors may develop anywhere in the nervous system, including in the 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 can become malignant. 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.
There are three distinct types of neurofibromatosis, each with different signs and symptoms.
Neurofibromatosis 1 (NF1) usually appears in childhood. Signs and symptoms include:
- Flat, light brown spots on the skin
- Freckling in the armpits or groin area
- Soft bumps on or under the skin (neurofibromas)
- Tiny bumps on the iris of your eye (Lisch nodules)
- Bone deformities
- Learning disabilities
- Larger than average head size
- Short stature
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:
- Numbness and weakness in the arms or legs
- 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 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, but mainly causes chronic pain, which can occur anywhere in the body.
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.
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.
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 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.
To diagnose neurofibromatosis, doctors will review the symptoms, medical history and family history. Depending on the type of neurofibromatosis suspected, the doctor may conduct or order several tests, which may include:
- Ear exam, such as audiometry, electronystagmography and brainstem auditory evoked response can help determine the level of hearing and balance function in a person with NF2.
- Imaging tests, such as X-rays, CT scans and MRIs, can help identify bone abnormalities, deep tumors in the brain or spinal cord, and very small tumors. An MRI can also help identify optic pathway gliomas in your eye.
- Genetic tests are available for NF1, NF2 and schwannomatosis, and may be done prenatally.
Neurofibromatosis can't be cured, but doctors can monitor and treat your symptoms. If you have a child with NF1 your doctor is likely to recommend yearly age-appropriate checkups.
Surgery may be an option to remove all or part of tumors that are compressing nearby tissues or damaging organs. It may help relieve symptoms of all forms of neurofibromatosis. Complete removal of schwannomas in people with schwannomatosis can ease pain substantially.
In people with NF2 who experience hearing loss, brainstem compression or tumor growth, doctors may recommend surgery to remove vestibular schwannomas. It may help improve hearing, but can carry risks, including hearing loss or damage to the facial nerves.
In patients with NF2, doctors may recommend stereotactic radiosurgery to remove vestibular schwannomas. This procedure allows the doctor to deliver radiation very precisely to the location of the tumor, and it can help preserve your hearing to an extent. However, it may create a concern of radiation-induced cancer, especially if the radiation is applied repetitively and at a young age. Some with NF2 may also be eligible for auditory brainstem implants or cochlear implants to help improve hearing.
Malignant tumors and other cancers associated with neurofibromatosis are treated with standard cancer therapies, such as surgery, chemotherapy and radiation therapy. However, early recognition of malignant tumors and early treatment are the most important factors resulting in good outcome.
If you want further information regarding neurofibromatosis, please visit The Neuro Foundation or the European Neurofibromatosis Group.