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Neurofibromatosis

The neurofibromatoses are genetic disorders that cause tumors to grow in the nervous system. The tumors start in the supporting cells that make up the nerves and the myelin sheath - the thin membrane that envelops and protects the nerves. These conditions cause tumors to grow on nerves and, less often, in the brain and spinal cord, causing other abnormalities such as skin changes and bone abnormalities. While many affected individuals inherit the condition, between 30 and 50 percent of new cases arise spontaneously from mutation (change) in someone's genes. Once this change has taken place, the mutant gene can be passed on to subsequent generations. There are three types of neurofibromatosis (NF): NF1 is the most common type of the condition. Symptoms of NF1, which may be visible at birth and almost always by the time the child is 10 years old, may include light brown spots on the skin (cafe au lait spots), two or more growths on the iris of the eye, a tumor on the optic nerve, a larger than normal head circumference and abnormal development of the spine, cranial bone or tibia. NF2 is less common and is characterized by slow-growing tumors on the vestibular branch of the right and left eighth cranial nerves called vestibular schwannomas or acoustic neuromas. The tumors press on and damage neighboring nerves and impair hearing. The distinguishing feature of schwannomatosis is the development of multiple schwannomas (tumors made up of certain cells) anywhere in the body except on the vestibular branch of the 8th cranial nerve. The dominant symptom is pain, which develops when a schwannoma enlarges or compresses nerves or adjacent tissue. Some people may experience numbness, tingling, or weakness in the fingers and toes.

Therapy

Treatment may include surgery, targeted radiation, or chemotherapy. In April 2020, the US Food and Drug Administration approved selumetinib (Koselugo) for the treatment of children 2 years of age and older with neurofibromatisis type 1. The drug helps stop tumor cell growth. Surgery to completely remove NF2 tumors is an option. Surgery for vestibular schwannomas does not restore hearing and usually reduces hearing. Sometimes surgery is not performed until after complete loss of functional hearing. Surgery can cause facial nerve damage and some degree of facial paralysis. Targeted radiation of vestibular schwannoma has a lower risk of facial paralysis than open surgery, but is more effective in shrinking small to moderate tumors than in larger tumors. Chemotherapy with a drug that targets the blood vessels of vestibular schwannoma can shrink the tumor and improve hearing, but some tumors do not respond at all and sometimes only respond temporarily. Bone abnormalities can often be corrected surgically, and surgery can also correct cataracts and retinal abnormalities. Pain usually disappears when tumors are completely removed.

Prognosis

In most cases, the symptoms of NF1 are mild and individuals lead normal and productive lives. In some cases, however, NF1 can be severely disabling and cause cosmetic and psychological problems. The course of NF2 varies greatly from person to person. Hearing loss in both ears develops in most people with NF2. In some cases of NF2, the damage to nearby vital structures, such as other cranial nerves and the brain stem, can be life-threatening. Most people with schwannomatosis have significant pain. In some extreme cases, the pain will be severe and disabling.

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