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Dermatofibroma

Synonyms: benignes fibröses Histiozytom, Histiozytom

By Dr. Pascal Bafteh · last updated 09/2026

Dermatofibroma: pigmented, firm nodule on the leg of a 34-year-old man. — Jmarchn, „Pigmented and tenderness dermatofibroma", CC BY-SA 3.0, via Wikimedia Commons · CC BY-SA 3.0 · Source

Definition & Classification

Dermatofibroma (synonyms: benign fibrous histiocytoma, in everyday practice simply "histiocytoma") = benign fibrohistiocytic proliferation of the dermis.
Pathogenesis: predominantly interpreted as a reactive fibroblast proliferation after minor trauma (insect bite, thorn injury, shaving); a subset of lesions is nevertheless clonal.
Epidemiology: peak incidence 20–50 years of age, women more often; one of the most common benign skin tumours overall.
Dignity: benign, no risk of malignant transformation, no metastasis — its whole importance lies in the distinction from malignant spindle cell tumours.

Clinical Features

Site: preferentially the lower extremity, especially the lower leg — about two thirds of lesions; women are affected considerably more often.
Morphology: usually a solitary papule or flat nodule of 0.5–1 cm, firm like a lentil, skin-coloured to reddish-brown, often with a peripheral pigmented rim.
Palpation: the lesion feels firm and button-like and sits within the dermis — it is tethered to the epidermis but mobile over the subcutis.
Dimple sign (Fitzpatrick sign): on lateral compression between thumb and index finger the lesion dimples inward — a consequence of its anchoring in the fibrosed corium.
Symptoms: usually asymptomatic, occasionally itching or tenderness; shaving injuries on the lower leg are a frequent reason for presentation.

Dermoscopy

Classic basic pattern (the most frequent of the described patterns): central whitish scar-like patch with a delicate peripheral pigment network.
The central white zone corresponds histologically to dermal fibrosis with thickened collagen bundles and is the decisive feature separating it from a melanocytic nevus.
The peripheral network is fine, light brown and fades out gradually — in the prospective series of 412 lesions by Zaballos the most constant single feature.
Variants (Zaballos described ten dermoscopic patterns): total or partial pigmentation, vessel-dominated forms with dotted vessels within the white area; atypical patterns do occur and justify excision in case of doubt.

Histology & Immunohistochemistry

Architecture: an ill-defined dermal proliferation of spindle cells in a storiform-fascicular arrangement, unencapsulated, without tentacular permeation of the subcutaneous fat.
Collagen trapping: at the periphery the spindle cells surround thick, eosinophilic collagen bundles — a marginal finding typical of dermatofibroma.
Overlying epidermis: acanthosis with basal hyperpigmentation; follicular and basaloid induction phenomena are also seen.
Immunohistochemistry: dermatofibroma is factor XIIIa positive, CD34 negative.
Counter-check dermatofibrosarcoma: dermatofibrosarcoma protuberans (DFSP) shows the mirror image, CD34 positive, factor XIIIa negative, and carries the COL1A1-PDGFB fusion.

Differential diagnoses

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