Diagnosed as definite or possible but limited to one limb or ≤5 contiguous segments of spine.Another set of criteria are:

Two or more nonintradermal (cutaneous) schwannomas
No evidence of vestibular tumor
No known NF-2 mutationor

One pathologically confirmed nonvestibular schwannoma plus a first degree relative who meets the above criteria. Treatment
Schwannomatosis patients represent 2.4% to 5% of patients undergoing surgical resection of their schwannomas. In isolated regions of the body schwannomas are small and difficult to locate. Intraoperative sonography offers invaluable assistance in such cases by localizing small schwannomas and decreasing operative time and extent of the surgical incision. If feasible, the schwannomas can be surgically removed. Any tumor-associated pain usually subsides after tumor removal. Damaged nerves and scar tissue can be a result of surgery and pain can be an ongoing problem. Sometimes, a tumor will reappear at the same site after surgery. If surgery is unfeasible, then pain management will have to be used. Schwannomatosis can sometimes cause severe, untreatable pain over time. Other than surgery and/or pain management, there are no other medical treatments available. There are no drugs available to treat Schwannomatosis. Gamma knife radiosurgery can be performed on head tumors to help stop growth of a tumor, although there is no guarantee that it will work. The University of Pittsburgh published their experience with over 829 cases and reported 97% of patients had long term tumor control (defined as requiring no further treatment) with Gamma knife radiosurgery. Recently, many advances are being made in the treatment of schwannomas. Of interest is CyberKnife, manufactured by Accuray.
However, molecular analysis of the NF2 gene in schwannomatosis patients has shown the presence of inactivating mutations in the tumor cells, but no evidence of the germline mutations that are found in NF2 patients.A mechanism involving both the SMARCB1 and NF2 genes may be responsible for the development of the disease because tumor analysis of schwannomas indicates the presence of inactivating mutations in both the SMARCB1 and NF2 genes. However, there is speculation about the involvement of an unidentified schwannomatosis gene(s) in most cases. This is because one study found no SMARCB1 germinal mutations in patients with familial schwannomatosis. Some schwannomatosis patients do not have SMARCB1 or NF2 mutations. Furthermore, many patients exhibit somatic mosaicism for mutations in the NF2 or SMARCB1 gene, which means that some somatic cells have the mutation and some do not in the same patient. Ultimately, the tumorigenesis of schwannomas is not solely dependent on one gene locus alone. In regards to the SMARCB1 and NF2 genes, it is important to understand constitutional mutations and somatic mutations. Constitutional mutations are the first inactivation events that are often small mutations, such as point mutations and deletion/insertion of single base pairs. Somatic mutations are the second mutations that occur and may also be another small mutation or the loss of the remaining allele of the gene. Schwannomas from one patient share the same constitutional mutations but have distinct somatic mutations. In addition, the constitutional mutation may be present in non-tumor.SMARCB1 is also known as INI1, hSNF5, or BAF47.