Dermatofibromas

Lauren L. Levy

Amanda Zubek

Macrene Alexiades

BACKGROUND

Dermatofibromas (DFs), also called benign fibrous histiocytomas, are benign connective tissue neoplasms that have a predilection for the lower extremities. DFs are extremely common and have multiple histologic and clinical variants. They occur more commonly in females than in males at a 2:1 ratio and are slow growing, and in 20% of cases development of a DF correlates to a site of mild trauma such as an injection or insect bite.

PRESENTATION

Patients present with a complaint of a long-standing dark pimple, bump, or mark on the extremities that does not fade but can be pruritic or tender.

DIAGNOSIS

Clinical Diagnosis

DFs are firm 0.5- to 1.0-cm papules that are often hyperpigmented that dimple when the lesion is pinched (“dimple sign”). Most commonly, they are solitary and asymptomatic, but they can be associated with pruritus, pain, or tenderness when pressure is applied and can be multiple (Figure 11.7.1). DFs are most commonly found on the extremities, but they can also be found on the trunk (especially buttocks and shoulders) or rarely other areas.

Dermoscopy may be helpful in making the diagnosis. In the majority of lesions a central white patch is observed and a pigment network may be present.¹

Several lesions may be found; rarely (<1%), numerous nodules are present in the eruptive subtype. Eruptive DF is associated with underlying diseases, most often systemic lupus erythematosus and human immunodeficiency virus (HIV), and in case reports also linked to thyroid disorders, inflammatory bowel disease, dermatomyositis, and lymphoproliferative disorders.

Histopathology

A classic DF is characterized by acanthotic epithelium and basilar hyperpigmentation, a superficial dermal
Grenz zone overlying a dermal spindle cell proliferation with collagen trapping by the dermal fibrohistiocytes. Pseudoepitheliomatous hyperplasia may be seen. On superficial shave biopsies where the dermal proliferation is not captured, these lesions can be mistaken for seborrheic keratosis, basal cell carcinoma, trichoblastoma, or even Bowen disease.²

FIGURE 11.7.1 The clinical appearance of dermatofibromas.

Subtypes

Histological Subtypes

Multiple histologic subtypes of DFs exist, many of which are not discernible clinically. Among DFs, 80% are common type and 5.7% are aneurysmal (hemosiderotic); other less common variants include epithelioid, cellular, lipidized, atrophic, and clear cell.³

Cellular DF. Clinically cellular DFs are larger than common DFs and have a more aggressive behavior with high local recurrence rates and rare metastasis. They are often found on limbs and head/neck in young men. On histology, these lesions have a dense dermal cellular component that can involve deeper dermis or subcutaneous fat. These lesions must be differentiated from dermatofibrosarcoma protuberans and leiomyosarcoma.²

Aneurysmal (Hemosiderotic) DF. Aneurysmal DFs tend to be darker than common DFs, with hemorrhagic appearance. On histology there are multiple irregular large cystic spaces within the dermal component surrounded at the periphery by typical fibrohistiocytic pattern of common DF. There is significant interstitial hemosiderin and hemorrhage within the lesion.²

Epithelioid DF (Epithelioid Fibrous Histiocytoma). Clinically, epithelioid DFs are more nodular and redder than common DFs. They may have a collarette of scale and appear polypoid. On histology, these have more rounded epithelioid histiocytes with eosinophilic cytoplasm, and dermal fibrohistiocytic infiltrate tends to be more superficial than in common DFs. These must be differentiated histologically from Spitz nevi.²

Atrophic DF. Atrophic DF is thought to represent a progression of DFs with reduced dermal cellularity and more sclerotic or hyalinized dermal collagen. Clinically they appear depressed relative to surrounding skin or are anetodermic.²

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