Unless a person comes from a family with definite Schwannomatosis, the diagnosis is only considered after the more likely possibility of NF2 has been excluded. Patients with suspicious symptoms are usually referred to one of the specialist Neurofibromatosis (NF) Centres, or reviewed by Consultants working within a regional genetics service skilled at differentiating this diagnosis. The doctors there will undertake a series of tests to look for signs of NF2 including skin and eye checks, head and spine MRI scans and genetic testing. It may be necessary for the genetic testing to be done both on schwannomas that have been removed and blood samples before the diagnosis is clarified.
There may be a period of time when the diagnosis is unclear. For example, a patient may present initially with multiple schwannomas and complain of pain, but have no hearing problems. In time that patient may go on to develop the hallmark bilateral vestibular schwannomas that would confirm a diagnosis of NF2. This would only be apparent by serial annual MRI scans.
A diagnosis is made more complicated by the fact that about a third of NF2 patients with no family history are described as having “mosaic” NF2 – in other words where only a part of their body carries the NF2 gene fault.
The problem for doctors is that mosaic NF2 and mosaic Schwannomatosis can present in exactly the same way. On examination and on scan the schwannomas look the same - the only clinical clue is if the patient has a lot of pain...but even this is not always the case. In this situation, the skill in diagnosis is particularly important and the doctor will rely on information from symptoms, physical examination, scans and tests (including mutation analysis) to come to a conclusion. This may take a frustrating length of time. In Schwannomatosis about 30% of patients have a mosaic presentation with the tumours being confined to one particular area of the body, one arm or a leg only for example.
In an individual with at least 2 non-intradermal (i.e. within the layers of the skin) schwannomas, an MRI scan will be undertaken to confirm or exclude the diagnosis of NF2. If no vestibular schwannomas are present and there is no other evidence of NF2, then a diagnosis of Schwannomatosis will be considered.
There is no confirmatory blood test available at present.
Inheritance of Schwannomatosis
Most people with Schwannomatosis are the only person in their family to be affected. There are some families with two or more affected people and here inheritance is dominant (as for NF1 and NF2) but the difference is that not all family members with the gene develop schwannomas.
Genes and Schwannomatosis
The genetics of Schwannomatosis is much more complicated than in NF1 and NF2-related-Schwannomatosis. So far two genes have been identified; the first (called SMARCB1 or INI1) was identified in 2007 with the second LZTR1 being found in 2013. Mutations have been found in these genes in 60-70% of people from affected families’ cases, but in only about 20-25% of people who are the only person in the family. The SMARCB1 and LZTR1 genes are on chromosome 22 close to the NF2 gene. Schwannomas in NF2 and Schwannomatosis have different genetic changes and this is proving helpful in providing a clear diagnosis. However, it is likely that at least 3 more genes remain to be found.