Trichoblastoma and nodular basal cell carcinoma are generally held to be distinctive epithelial neoplasms with some overlapping features. We investigated 30 trichoblastomas in which the basaloid cells expressed cytokeratins (CK) CK5/6, CK14, CK17, CK19, and, in a few cells, vimentin. The cells of the periphery of small and large cysts showed the same profile. Cells lining the lumen of small cysts expressed CK14, CK17, and involucrin, and those in larger cysts showed a positivity for CK1, CK4, CK10, CK14, CK17, and involucrin. The remaining tested antibodies (CK7, CK8, CK13, CK18, CK20, alpha-smooth-muscle actin) were negative in all cases. The cells of the stroma expressed vimentin and in 22 cases, the CD34 antigen. Seventeen nodular basal cell carcinomas showed exactly the same staining pattern. Furthermore, there are striking immunohistochemical similarities between the neoplastic basaloid cells of both neoplasms and the cells of the hair germ. Therefore, trichoblastoma and nodular basal cell carcinoma cannot be distinguished by their pattern of cytokeratin expression in paraffin sections. The virtually identical cytokeratin pattern seen in trichoblastoma, basal cell carcinoma, and the developing fetal hair follicle is compelling evidence for common differentiation pathway.

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Background: Buschke-Ollendorff syndrome is an autosomal dominant disorder clinically characterized by the appearance of disseminated white papules and osteopoikilosis. Histologically most cases show normal collagen and increased elastic tissue. Abortive forms of Buschke-Ollendorff syndrome are described, which show characteristic skin involvement, absence of skeletal changes and decreased elastic tissue. Papular elastorrhexis is characterized by nonfollicular, white papules, decreased elastic tissue, no genetic inheritance and no osteopoikilosis. Objective: Is papular elastorrhexis a new entity or an abortive form of Buschke-Ollendorff syndrome? Methods: We examined three members of one family (brother, sister and mother) presenting with nonfollicular, distributed, white papules on the trunk and extremities. Skin biopsies were examined by histological and electron-microscopic methods. Results: The histological and electron-microscopic examinations of skin biopsies showed decreased, fragmented elastic fibers and normal collagen. By X-ray examination, no osteopoikilosis was found. The family presented here supports a genetic background of the disease. Conclusion: The clinical appearance with the absence of osteopoikilosis and the histological findings of our cases suggest the diagnosis of papular elastorrhexis. Papular elastorrhexis however was reported to be nonfamilial. Because of the genetic background found here we believe that papular elastorrhexis is an abortive form of Buschke-Ollendorff syndrome. Summarizing our data and reviewing the literature, we suggest that connective tissue nevi with the most prominent alterations in the elastic tissue should be classified under the term elastic tissue nevi.

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Summary Reactive perforating collagenosis (RPC) is a rare skin disorder characterized by reddish papules with a central keratotic plug which appear mainly on the extensor aspects of the limbs. An idiopathic or classical variant has been delineated from an acquired one which occurs in diabetes mellitus and renal failure. Histopathological examination of the lesions shows transepidermal elimination of abnormally staining bundles of collagen. To clarify the origin of this collagenous material we performed an immunohistochemical study including biopsies of two patients with RPC, one classical and one acquired. Staining reactivity to antibodies against type IV collagen was observed, thus providing evidence that the collagen eliminated in RPC may be derived from the basement membrane zone.