Dermatofibroma simulating seborrheic keratosis dermoscopically

Abstract

Dermatofibroma is a frequent benign tumor of easy clinical diagnosis in most cases, but that can mimic other dermatoses. Dermoscopy may help to define the diagnosis and its classical pattern is a central white area, similar to a scar, surrounded by a discrete pigment network. However, dermoscopic findings are not always typical. We describe here a case of dermatofibroma exhibiting ridges, furrows and pseudocomedos, a pattern which is typical of seborrheic keratosis, in dermoscopy.

INTRODUCTION

Dermatofibroma is a frequent benign cutaneous neoplasm that fits the group of fibrohistiocytic skin tumors.¹ Most of the time the diagnosis is clinical, although it may simulate other dermatoses.¹

Dermoscopy is an auxiliary method with diagnostic criteria described for several skin lesions.² In its classical forms, the dermoscopic differentiation between seborrheic keratosis and dermatofibroma is not difficult: the former shows the pattern of ridges and furrows³ and the latter, the white scar surrounded by discrete pigment network.^2,3 Nevertheless, the findings may also be atypical and, in these cases, histopathological confirmation is required.¹ A case of dermatofibroma simulating seborrheic keratosis dermoscopically is here presented.

CASE REPORT

A female patient mentioned a pruritic lesion on right calf. On physical examination, a hardened tumor measuring 1.5 x 1 cm with hyperchromic surface was found (Figure 1). Clinically, the hypotheses of simple chronic lichen and dermatofibroma were suggested. The dermoscopy revealed a pattern of ridges and furrows accompanied by pseudocomedos, compatible with seborrheic keratosis (Figure 2). Histopathologic examination showed a dermal tumor composed of fusiform cells, blood vessels and foamy histiocytes. The upper dermis was not affected by cellular proliferation (Figures 3 and 4). The epidermis was acanthotic, hyperkeratotic and with keratin-filled invaginations (Figure 3).

Figure 1.

Elevated lesion measuring 1.5 x 1 cm on right calf

Figure 2.

Dermoscopy showing pattern of ridges, furrows and pseudocomedos (arrow points)

Figure 3.

Presence of fusocelular skin tumor sparing the upper dermis. The epidermis shows acanthosis, hyperkeratosis and kera tin-filled invaginations (asterisk) (hematoxylin-eosin, x40)

Figure 4.

Many of the neoplastic cells present cytoplasm of foamy aspect (arrow points). Hematoxylin-eosin, x400

DISCUSSION

Typically, the dermatofibroma is an erythematous-brownish tumor of less than 1 cm and, most of the time, with a clinical diagnosis.¹ However, it may be confused with Spitz nevus, melanocytic composed nevus, melanoma and hemangioma.¹ In the described case, after macroscopic evaluation, the diagnoses of dermatofibroma and simple chronic lichen were suggested.

Even with the use of dermoscopy, diagnosis of dermatofibroma may be a challenge. Its classical dermoscopic appearance is that of a white area similar to a scar surrounded by a discrete pigment network.² Zaballos et al., in a large series of cases, described ten dermoscopic patterns associated with this diagnosis.⁴ The classical pattern is the most common, present in 34% of the cases.⁴ Other common patterns are the discrete pigment network in all the lesion (14%) and the discrete pigment network with a white central area (9%). Nevertheless, in 6% of the cases, the dermatofibroma presents an atypical pattern⁴ and may simulate lentigo, blue nevus, melanoma and non-melanocytic lesions.²

Dermoscopy of the lesion presented a pattern of ridges and furrows, classical of pigmented seborrheic keratosis², despite its low specificity (43%)³ ; it may be observed in other dermatoses, like dermatofibroma.² In addition, pseudocomedos could be found, which have 91% specificity for the diagnosis of seborrheic keratosis.³ Such dermoscopic findings associated with the absence of a classical dermatofibroma pattern would be sufficient to define the diagnosis of seborrheic keratosis. However, from a clinical point of view, the lesion was not compatible with this diagnosis and consequently our option was to withdraw it.

The histopathologic examination revealed a dermal tumor of fusiform cells and histiocytes, consistent with dermatofibroma.¹ The epidermis was acanthotic, hyperkeratotic and with keratin-filled invaginations. These findings of epidermis hyperplasia may also be found in dermatofibroma, and their presence may explain the dermoscopic aspect of ridges and furrows.^1,4 This association between dermoscopic and pathologic findings is corroborated by the case herein described. Although dermoscopy is an important tool in the diagnosis of melanocytic and non-melanocytic skin lesions, the histopathologic examination is important when there is disagreement between clinical and dermoscopic diagnosis.