Multiple unilateral schwannomas: segmental neurofibromatosis type 2 or schwannomatosis?

Schwannomas are benign solitary tumours of the peripheral nerve sheaths. The occurrence of multiple schwannomas usually implies hereditary disease. The most frequent syndrome associated with multiple schwannomas is neurofibromatosis type 2 (NF2), which is defined by bilateral vestibular schwannomas. Schwannomatosis is a distinct disease characterized by multiple pathologically proven schwannomas in the absence of vestibular schwannomas. It is not currently known if the presence of multiple schwannomas confined to a limb may represent a mosaic form of NF2 or a distinct disease, because mutation analysis of these tumours is not routinely performed. We report a 31-year-old patient who presented with multiple slowly growing subcutaneous tumours on his left arm. His family history was negative for cutaneous tumours or central nervous system disease, and he did not have additional features of NF2. Magnetic resonance tomography and ophthalmological examination excluded vestibular schwannoma and eye stigmata of NF2. After resection of three tumours, histological analysis confirmed the diagnosis of benign schwannomas. Molecular genetic analysis by temperature gradient gel electrophoresis and microsatellite marker analysis demonstrated two distinct mutations of the NF2 gene (NF2) in two different schwannomas, with concomitant loss of heterozygosity in both tumours. In contrast, neither normal skin nor peripheral blood lymphocytes revealed mutations of NF2. The clinical and molecular genetic findings suggest that the diagnosis in our patient is schwannomatosis rather than segmental NF2 because the mutations found in different tumours were not identical. The possibility of a localized predisposition for the acquisition of NF2 mutations is discussed.