To the Editor:
Dermatofibromas (DFs) are banal lesions of the skin predominantly developing on the legs of middle-aged women. Several histopathological varieties of DFs have been described, including fibrocollagenous, storiform, cellular histiocytoma, lipidized, angiomatous, aneurysmal, clear cell, granular cell, Halo, DF with ‘monster’ cells, osteoclastic, myofibroblastic, myxoid, palisading, atrophic, subcutaneous, and combined DF.1 Keloidal DF (KDF) is a rare variant characterized by the presence of keloidal collagen within an otherwise typical DF; it was first described in 19982 and has so far been reported mostly in Asian patients, in whom it represents 0.8%–2.4% of all DFs.2,3 A new case of KDF is reported here; it seems identical to the originally reported cases,2 except that it occurred in a white patient.
The patient was a 17-year-old white French woman who presented with a lesion of the right hip that caused discomfort because of rubbing with the clothes; it was therefore excised under local anesthesia and submitted for microscopic examination with the clinical diagnosis of DF. Microscopic examination of routinely stained sections showed an otherwise typical DF overlaid by an acanthotic, hyperpigmented epidermis. The dermis contained a proliferation of mesenchymal, spindle-shaped, and occasionally polygonal cells, some of which had a slightly foamy cytoplasm. In the papillary dermis, a well-circumscribed mass of thick, hyalinized, keloidal collagen bundles was seen (Figs. 1A, B); it was partially refractile under polarized light and stained blue green with Masson trichrome (Fig. 2A). The keloidal collagen bundles were intermingled with some stellate and multinucleated cells and some Perls-positive siderophages (Fig. 2B). Immunohistochemistry showed DF cells (including those intermingled with keloidal collagen) to express factor XIIIa (Fig. 2C), and more weakly the monocytic–macrophagic CD68 and CD163 antigens (Fig. 2D).
Keloidal collagen may be found within various epithelial and mesenchymal skin tumors including basal cell carcinomas,4 Kaposi sarcoma,5 indeterminate fibrohistiocytic tumors,6 and atypical fibroxanthoma (AFX). Keloidal AFX are not exceptional, accounting for 5%–19% of all cases.7–9 However, the presence of keloidal collagen within DF, at least in white patients, is exceedingly rare.10 The reason why keloidal collagen may develop within otherwise typical DF remains speculative. One explanation is that of collision lesions; indeed, DF may develop secondary to trauma (such as mosquito bites and folliculitis), and it can be speculated that the trauma may trigger simultaneously the development of a keloid and a DF. Another possibility is that the keloidal collagen is produced by DF cells, either as such ab initio or as ordinary collagen that subsequently undergoes “aging” and hyalinization. It has also been hypothesized (in the case of AFX) that the collagen represents a host response to the tumor.9 This hypothesis seems unlikely in the case of KDF, because the keloidal collagen is present in the center of the lesion and not at the periphery, as would happen in the case of a reactive process directed against the original lesion.
The reason why KDF has so far been observed mostly in Asians is unknown; one possible explanation is that Asians have a greater propensity to develop keloids.2 The case presented here shows that KDF may also, although exceptionally, develop in white patients.
1. Weedon D: Skin Pathology. 3rd ed. London: Churchill-Livingston Elsevier; 2010.
2. Kuo TT, Hu S, Chan HL. Keloidal dermatofibroma: report of 10 cases of a new variant. Am J Surg Pathol. 1998;22:564–568.
3. Han TY, Chang HS, Lee JH, et al.. A clinical and histopathological study of 122 cases of dermatofibroma (benign fibrous histiocytoma). Ann Dermatol. 2011;23:185–192.
4. Jones M, Bresch M, Alvarez D, et al.. Keloidal basal cell carcinoma: not a distinctive clinicopathological entity. Br J Dermatol. 2009;160:127–131.
5. Grayson W, Pantanowitz L. Histological variants of cutaneous Kaposi sarcoma. Diagn Pathol. 2008;3:31.
6. Horenstein M, Prieto VG, Nuckols JD, et al.. Indeterminate fibrohistiocytic lesions of the skin: is there a spectrum between dermatofibroma and dermatofibrosarcoma protuberans? Am J Surg Pathol. 2000;24:996–1003.
7. Beer TW, Drury P, Heenan PJ. Atypical fibroxanthoma: a histological and immunohistochemical review of 171 cases. Am J Dermatopathol. 2010;32:533–540.
8. Fussell JN, Cooke ER, Florentino F, et al.. Atypical fibroxanthoma with keloidal collagen. Am J Dermatopathol. 2010;32:713–715.
9. Offman S, Pasternak S, Walsh N. Keloidal and other collagen patterns in atypical fibroxanthomas. Am J Dermatopathol. 2010;32:326–332.
10. Kovach BT, Boyd AS. Melanoma associated with a dermatofibroma. J Cutan Pathol. 2007;34:420–422.