Answer of Dermatopathology Case 16

Trichilemmoma

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Abstract:

Atypical clinical appearance and localization of trichilemmoma. a case report. Pathologica. 2009 Jun;101(3):133-4.
Trichilemmoma is a benign cutaneous tumor that shows characteristics of differentiation similar to the outer hair sheath. We report the case of a woman presenting with a nodular tender mass of the back that was diagnosed as anisolated trichilemmoma. Several lines of evidence suggest that trichilemmoma should be considered in the differential diagnosis of any indistinct facialpapule. This report documents a non-facial example of trichilemmoma. Atypical clinical appearance and localization of this neoplasm in our patient suggest thatonly histological findings are specific of this tumor.

Detection of Human Papillomavirus infection in trichilemmomas and verrucae using in situ hybridization. J Cutan Pathol. 2009
Background: It is hypothesized that trichilemmomas are 'burned out' verrucae. By performing in situ hybridization using HPV type-specific probes, we explored this concept. Methods: Verrucae vulgaris and plantaris were positive controls, andinverted follicular keratoses (IFKs) were negative controls. Additionally, all lesions were tested for HPV genital types (low and high risk). Results: We analyzed 9 trichilemmomas, 20 verrucae vulgaris, 8 verrucae plana, 3 verrucae plantaris and 6 IFKs. All trichilemmomas were negative for HPV types 1, 2 andgenital types. Conversely, 9/20 verrucae vulgaris, 2 verrucae plantaris, and 1verruca plana were positive for HPV type 2. Among HPV-2 positive lesions, 2/2verrucae plantaris and 1 verruca vulgaris (chin) were strongly positive forgenital-type HPV. One verruca plana (shin) was positive for genital-type HPVonly. All 6 IFKs were HPV negative. Conclusions: Using HPV type 1 and 2-specific probes and mixed genital-type probes, we were unable to detect HPV intrichilemmomas. This suggests that HPV-1, HPV-2 and low and high riskgenital-type HPVs are not involved in the histogenesis of trichilemmoma. We also showed that genital HPV types could be present in non-genital verrucae.

Trichilemmoma: an immunohistochemical study of cytokeratins. Br J Dermatol. 2003 Jul;149(1):99-104.
BACKGROUND: The histogenesis of trichilemmoma remains unclear. OBJECTIVES: To clarify the histogenesis of trichilemmoma by evaluating its cytokeratin (CK) expression. METHODS: In three cases of trichilemmoma, CK expression was studied immunohistochemically using seven antikeratin antibodies against CK1, 10, 14-17 and 19, respectively. RESULTS: CK1 and CK10 were present in keratinizing ductal epithelium. CK14 was present in the whole layer. CK15 was present in suprabasal layers in two cases. CK16 was present in the suprabasal layer, but was absent in keratinizing ductal epithelium. CK17 was present in suprabasal layers and the sebaceous duct-like structure. CK19 was totally absent. CONCLUSIONS: These results showed that trichilemmoma may differentiate mainly towards twodirections: infundibular keratinization and proliferation of the outer root sheath with undifferentiated and pluripotent characteristics.