Search

Background: Fibrofolliculomas and trichodiscomas are benign dermal neoplasms that likely derive from the mantle of the hair follicle and can occur sporadically or in association with Birt–Hogg–Dube syndrome (BHDS). Little is known about the pathogenesis and immunophenotypic properties of these entities. Methods: We investigated the histomorphologic and immnophenotypic properties of 15 fibrofolliculomas and trichodiscomas in two patients with BHDS and eight with sporadic disease. Results: We found the following: (1) fibrofolliculomas and trichodiscomas occurring in the setting of BHDS show microscopically contiguous histomorphologic features as compared to those occurring sporadically; (2) the immunophenotypic characteristics of syndromic-associated and sporadic types are identical and consist of (3) perifollicular vimentin (+), CD34 (+) and Factor XIII (–) spindle cells. Conclusions: Despite subtle histomorphologic differences, trichodiscomas and fibrofolliculomas are immunophenotypically similar, and are thus likely derived from a similar histogenic precursor. Given the previously reported CD34 (+) immunophenotype of the hair mantle, our findings would support an origin of these lesions from the mantle of the hair follicle. The proliferation of CD34 (+) spindle cells seen in conjunction with these lesions should not be confused with other CD34 (+) dermal entities.

Background: Trichodiscomas are rare hamartomas of the dermal portion of the hair disc, a specialized component of the perifollicular mesenchyme. They are usually found as asymptomatic multiple skin-colored papules on the face and extremities and may have an autosomal dominant inheritance pattern. However, a solitary variant has been described. Case report: A 78-year-old woman presented with a single, non-pigmented, firm papule on the left tip of the nose, measuring 3.5 mm in diameter. Results: The histological examination revealed the previously described features of a trichodiscoma. The immunohistochemical analysis showed strong immunoreactivity for CD34 in the spindle cell component. Spindle cells were negative for S-100, HMB-45, Melan-A, EMA, neurofilament, desmin, and Factor XIIIa by immunohistochemistry. Conclusions: We report strong reactivity for CD34 in the spindle cell component of a trichodiscoma. We suggest that this lesion be considered in the differential diagnosis of any CD34+ dermal spindle cell proliferation, in which an adjacent epithelial component cannot be entirely excluded.

Background: Mutation in the folliculin gene in Birt–Hogg–Dube (BHD) syndrome leads to a spectrum of benign tumors of the hair follicle, classically including both fibrofolliculoma and trichodiscoma. In addition, lesions clinically indistinguishable from fibrofolliculoma/ trichodiscoma may show histopathologic findings of perifollicular fibroma or angiofibroma. Although some consider perifollicular fibroma to be a variant of angiofibroma, the specific histopathologic findings of perifollicular fibroma are uncommon. Methods: This is a case series. Results: In 4 patients with multiple facial lesions, recognizing perifollicular fibroma would have been helpful in leading to the diagnosis of BHD syndrome. Conclusion: Perifollicular fibroma is on a spectrum with fibrofolliculoma and trichodiscoma; in a patient with multiple lesions, the diagnosis of perifollicular fibroma is suggestive of BHD syndrome.

The autosomal dominant inherited syndromes of Hornstein and Knickenberg (HKS), and Birt, Hogg and Dube (BHDS) are both characterized clinically by the overall spread of multiple flesh coloured papules of the skin. However, it is a matter of debate if colonic neoplasms (adenomas as well as adenocarcinomas) are associated findings in the HKS or rather in the BHDS. Furthermore, histological differences are said to exist between the skin lesions in the two syndromes: whereas perifollicular fibromas were described in the HKS, fibrofolliculomas and trichodiscomas were found in the BHDS. In the present study, we report on a father and his daughter in whom we initially diagnosed a BHDS. We then examined a greater number of the papular lesions in histologic sections cut vertically as well as horizontally to the epidermis. Our results indicate that the histologic differences between the skin lesions in the two syndromes are artificial ones, caused by interpretation of different sectioning planes, and that consequently HKS and BHDS are the same. Therefore, it is necessary to look for colonic polyps in the syndrome in question, regardless if one prefers the name HKS or BHDS for it.