Congenital melanocytic naevus with associated neurofibroma and schwannoma-like change.

Congenital melanocytic naevus and neurofibromatosis type 1 are distinct clinical entities. A diagnosis of neurofibromatosis is difficult to make in the presence of a congenital melanocytic naevus because nodules may arise in the naevus that have similar histopathological appearances to neurofibromata. A case is reported where nodules arising from a naevus were examined histologically and were found to have neurofibroma and schwannoma like elements but strong positivity for S100 protein in keeping with dermal melanocytes. Lisch nodules were also said to be found in the patient but may represent nodular naevi of the irides. It is important that histopathological findings are interpreted within a clinical context and S100 protein immunohistochemical stain is valuable in helping to differentiate these two conditions.