Fibrofolliculoma/trichodiscoma and fibrous papule (perifollicular fibroma/angiofibroma): a revaluation of the histopathological and immunohistochemical features.

BACKGROUND: The multiple facial lesions of fibrofolliculoma (FF)/trichodiscoma (TD) and those of fibrous papule (FP; perifollicular fibroma/angiofibroma, AF) are characteristic of Birt-Hogg-Dubé (BHD) syndrome and tuberous sclerosis, respectively. However, there was a recently reported case of BHD syndrome with multiple facial FP lesions and a case of tuberous sclerosis, in which one FF lesion was included among the multiple facial FPs.

METHODS: The histopathological and immunohistochemical features of FF/TD and FP lesions were revaluated to study the relationship between the two. This investigation evaluated 20 FF/TD lesions including two cases of BHD syndrome and 35 FP lesions including three cases of tuberous sclerosis.

RESULTS: There are common histopathological features in the two lesions, such as the follicular and perifollicular elements, an angiofibromatous element and stellate fibrocytes. The similar immunohistochemical features between the two lesions included the expression patterns of CD34, factor XIIIa, nestin and c-kit in the stromal cells as well as abnormal CK15 expression in the hair follicles.

CONCLUSIONS: Both FF/TD and FP are hamartomas composed of perifollicular or interfollicular connective tissue and a hair follicular epithelial component, which may be caused by an abnormal functioning of the hair follicle bulge cells.