S-100 negative myxoid neurothekeoma: a new type of neurothekeoma?*

Dear Editor, Neurothekeomas are rare benign dermal tumors, which originate from the peripheral nerve sheath. They are divided into myxoid, intermediate, and cellular types, based on the amount of myxoid matrix and on the immunohistochemical study. We report an unusual S-100 negative case of myxoid neurothekeoma, which is currently described in the literature as a new type of neurothekeoma. A 73-year old male patient presented with an asymptomatic erythematous nodule (0.8 x 0.6 x 0.5 cm in size) in the right inframandibular region for about a year (Figure 1). Diagnostic hypothesis were adenoid basal cell carcinoma, neurofibroma, and others skin adnexal neoplasms. After surgical excision with 3-mm margins, pathological studies showed multiple nodules of varying sizes, containing abundant mucin and sparse stellate cells in the dermis, consistent with myxoid neurothekeoma (Figure 2). Immunohistochemistry was focally positive for CD-68 and diffusely positive for vimentin, but negative for S-100, CD-10, CD-57, EMA, and GFAP (Figure 3). Histopathological and immunohistochemical findings corroborated the diagnosis of S-100 negative myxoid neurothekeoma, also described as myxoid neurothekeoma cell. The term neurothekeoma was coined in 1980 by Gallagher and Helwig to de-