Immunohistochemical studies of selected skin diseases and tumors using monoclonal antibodies to neurofilament and myelin proteins

Differentiating Neurotized Melanocytic Nevi From Neurofibromas Using Melan-A (MART-1) Immunohistochemical Stain

Context.—Neurotized melanocytic nevi and neurofibromas are common, benign cutaneous neoplasms. Usually they are histologically distinct from each other; however, neurotized melanocytic nevi and neurofibromas can be clinically and histologically similar.

Objective.—To determine whether Melan-A (MART-1) immunohistochemical stain is sufficient to differentiate neurotized melanocytic nevi from neurofibromas.

Design.—Forty-nine consecutive specimens of melanocytic nevi with neurotization and 49 specimens of neurofibromas were selected. We used antibodies against Melan-A, S100, and neurofilament protein.

Results.—All of the melanocytic nevi showed Melan-A staining within the neurotized areas, with most of the areas staining strongly positive, whereas all the neurofibromas were completely absent of Melan-A stain. All of the nevi, including the neurotized areas, stained strongly and diffusely for S100, whereas all the neurofibromas showed a distinctive, sharp, wavy pattern of S100 staining. Neurofilament protein showed scattered staining of both melanocytic nevi and neurofibromas.

Conclusions.—Our data indicate that Melan-A immunohistochemical staining is helpful in differentiating neurotized melanocytic nevi from neurofibromas when distinction on histomorphology alone is difficult.

Nevus spilus (speckled lentiginous nevus) associated with a nodular neurotized nevus

We report a case of nevus spilus with neurotized nevus studied by immunohistochemical methods using S-100, leu-6, glial fibrillary acid protein (GFAP), and myelin basic protein (MBP). Histologic findings of the speckled lesion showed irregular rete ridge elongation, increased epidermal melanocytes and melanin in the epidermis, and scattered nevus cell nests in the upper dermis, but showed neurotized nevus in the deep dermis, which has many features of neurofibroma. Diffuse expression of S-100 protein and MBP, focal staining with GFAP, and lack of staining with leu-7 were observed, Leu-7, positive only in neurofibromas and not in neurotized nevus, appears to be the more pertinent method for distinguishing neurotized nevus from neurofibroma.

Immunoenzyme techniques in dermatopathology

The advantages and disadvantages of the immunofluorescence and immunoperoxidase techniques and an introductory description of the major variations of the basic immunoperoxidase method are discussed. The ability to identify intermediate filaments, T and B lymphocyte cell markers, S-100 proteins, myelin basic protein, and carcinoembryonic antigen in tissue sections can assist the dermatopathologist in classifying undifferentiated or histologically similar-appearing tumors. A systematic approach to the diagnosis of a majority of these tumors with the use of immunoenzyme staining is provided.