Schwannomatosis (pronounced SHWA-NOMA-TOSIS) is a genetic disorder that causes the growth of benign tumors called schwannomas along the nerves of the body and in the skull. Schwannomatosis is difficult to diagnosis because the main symptom is pain, and the tumors can be small and difficult to detect. It is a complex genetic condition that is still being characterized by the neurofibromatosis (NF) medical community of doctors and researchers.
Schwannomatosis is closely linked with NF2, in that both disorders lead to schwannoma growth through the same mechanism. In NF2, a mutation in one copy of the NF2 gene is inherited or occurs sporadically at birth and that mutation causes an increased risk of the growth of schwannoma, meningioma, and ependymoma tumors. In schwannomatosis, a different gene is mutated which then leads to the loss of NF2 which then causes tumor growth. Because more steps are required for a tumor to develop, the risk of tumor growth is lower. People with schwannomatosis have little to no additional risk of meningiomas and ependymomas, and only rarely lose hearing in both ears, unlike in NF2. In 40 percent of people with schwannomatosis, a mutation in the genes LZTR1 and SMARCB1 is detected. The remaining 60 percent of people with schwannomatosis likely have some other genetic reason to explain the growth of multiple nerve sheath tumors, but a cause has yet to be identified. They are said to have a “clinical” diagnosis even though a genetic cause cannot be found. With more NF research, additional causes of schwannomatosis are likely to be discovered in the future. Finally, some mutations in LZTR1 and SMARCB1 are detected but do not lead to loss of NF2 and tumor growth, i.e. someone may have a mutation in these genes and still have no clinical signs of schwannomatosis. It is important to be examined by an NF expert to determine whether a diagnosis of schwannomatosis is accurate.
Criteria for a clinical diagnosis of schwannomatosis includes any one of the following:
- One deep tissue schwannomas, including at least one that has been definitively diagnosed from a biopsy or surgery, AND no more than one vestibular schwannoma on MRI imaging of the brain with high resolution of the inner ear canal.
- One confirmed schwannoma, or at least one meningioma seen on brain MRI imaging, AND a parent or sibling diagnosed with schwannomatosis.
- The diagnosis is considered “possible” if there are at least two deep tissue nerve tumors that have not been proven on biopsy or resection, and the tumors cause long-term pain.
There is no genetic cure for schwannomatosis. Treatment involves standard imaging and appointments with an NF expert to monitor the growth of associated tumors. Tumors that are painful and those which cause weakness or numbness may need to be surgically removed, and radiation may be recommended. The Neurofibromatosis Clinic at Mount Sinai includes orthopedic and neuro-surgeons, radiologists, ENT doctors, neuro-otologists (hearing specialized neurologists), pain experts, and oncologists, and is dedicated to clinical trials research in schwannomatosis to improve the physical and mental health of our patients.