Neurofibromatosis Type II
What Is Neurofibromatosis Type II?
Neurofibromatosis type II (NF2) is a tumor syndrome. It results in the growth of benign nervous system tumors. It is an inherited condition, which means that it is passed from parents to children genetically. It is estimated to occur in around 1:50,000 people.
What Causes NF2?
It is caused by a mutation in a tumor suppressor gene known as schwannomin. This gene regulates the growth of cells in the nervous system. The mutated gene allows cells to grow out of control resulting in tumor formation. It may be passed from parent to offspring, or it may arise from a spontaneous mutation in the first patient in a family.
Everyone has 2 copies of the gene. One mutation may occur spontaneously. This does not cause a problem because the other copy is there to prevent a tumor from forming. However, in NF2 patients they are born with one mutation. When the second mutation occurs spontaneously, a tumor will arise.
There is a 50% chance of inheriting the mutated gene from a parent with NF2. This type of inheritance pattern is known as autosomal dominant. Symptoms are first noted in the teenage years or early 20s.
What Types of Tumors Occur?
NF2 affects many types of nerve cells including: Schwann cells, arachnoid cells, glial cells, and ependymal cells. Schwannomas, meningiomas, gliomas, and ependymomas result from these cell types respectively. Neurofibromas, for which the disease is named for, may grow from the peripheral nerves. This results in many soft bumps on or under your skin. Tumors may occur in the brain, along the spinal cord, or in the peripheral nervous system.
What Symptoms Do These Tumors Cause?
Gradual hearing loss and ringing in the ears results from the growth of schwannomas from the vestibular nerves, or vestibular schwannomas. They are typically bilateral and over time can cause deafness. Dizziness and balance issues also may arise from vestibular schwannomas, either by direct impact on the vestibular nerve or by compression on the brainstem and cerebellum. Headaches can occur from increased pressure on the brain.
Schwannomas may occur on other cranial nerves resulting in other symptoms such as vision loss, double vision, facial droop, trouble swallowing, hoarseness, shoulder paralysis or tongue paralysis. Spinal and peripheral tumors may cause numbness, pain, or weakness in the trunk or extremities.
NF2 patients are also at increased risk for cataracts.
How Is Nf2 Diagnosed?
NF2 can be diagnosed by clinical criteria or genetic testing. Neurological symptoms prompt your doctor to obtain an MRI. Bilateral vestibular schwannomas are diagnostic for NF2. Clinical diagnosis can also be made if you have one vestibular schwannoma and a family member with NF2, if you have one vestibular schwannoma and 2 other benign brain tumors previously listed, or if you have a cataract at a young age and a family member with NF2.
Genetic testing can be performed on a blood sample. A mutation in one copy of your schwannomin gene is diagnositic of NF2.
How Is Nf2 Treated?
Unfortunately, there is no cure for NF2. Treatment of the various tumors that occur is recommended based the characteristics of each tumor. Some tumors may need no treatment. Others may require radiation. Some may need to be removed surgically. These decisions are complex and are best made by a team of doctors each with different areas of expertise.
Treatment of vestibular schwannomas is required so that they do not become so large that they compress the brainstem where centers for basic functions of life occur. The brainstem plays an important role in regulation of breathing, heart rate, blood pressure and wakefulness.
Hearing status is very important when deciding how to treat vestibular schwannomas. This is because hearing in both ears will likely be threatened over the patient’s life. If hearing is not yet affected, treatment risks worsening hearing. If hearing loss is already profound, treatment has much less risk.
Large tumors with poor hearing are removed surgically. The worse hearing ear is operated on first. Small tumors with good hearing are typically observed, although hearing preservation surgery is possible. Medium, large, or growing tumors with good hearing are difficult. If the other ear has poor hearing it is extremely difficult. These tumors may be irradiated, or they may be observed until they are compressing the brainstem. Avastin is a medication that decreases blood supply to the tumor. It is currently being given in research studies. It may stop tumor growth and is an alternative to surgery and radiation when useful hearing remains in the ear with the growing tumor.
Hearing loss is difficult to treat. Hearing aids usually do not help with profound hearing loss. Cochlear implants are useful if the cochlear nerve is not damaged but surgical removal of tumor often requires removal of the cochlear nerve or at the very least damages it. Auditory brainstem implants (ABIs) are an option in these cases.