DermatofibromaD23.-

Common, solitary or multiple, completely harmless, 0.3-1.5 cm, tumor-like, brownish, reactive connective tissue proliferation, often occurring after an insect bite and characterized, on palpation, by a "surprising" firmness.

According to histological criteria, the following variants have been described in the past:

• neurothekeoma, cellular dermatofibroma
• Dermatofibroma with monster cells
• Dermatofibroma, xanthomatized
• Dermatofibroma, hemosiderin-storing
• Dermatofibroma with granular cells
• Epithelioid cell histiocytoma
• Dermatofibroma, ossifying
• Dermatofibroma, myxoid
• Dermatofibroma, keloidal
• Dermatofibroma, desmoplastic
• Dermatofibroma, sclerotic
• Dermatofibroma, deep infiltrating (deep dermatofibroma)
• Dermatofibroma in the facial area
• Aneurysmal dermatofibroma (characterized by rapid growth, high (20%) local recurrence rate after excision)
• Cell-rich der matofibroma (more common in young men in the lower extremities; local recurrence rate is increased (25%). Rare metastasis.
• Atypical (pseudosarcomatous) dermatofibroma (more common on the extremities, also on the head and neck. The term is sometimes used synonymously with fasciitis nodularis pseudosarcomatosa.
• Metastatic dermatofibroma

Prevalence not known; in larger dermatologic collectives > 60% of patients. f>m.

The nosological status of dermatofibroma is currently controversial.

Anamnestic evidence (previous) insect bites, folliculitis, microtrauma, localization (lower leg) and limited growth, indicate the changes as reactive proliferations (as "organged inflammations").

The significance of immunohistological findings (expression of MS-I-HMWP) pointing to a dermal dendritic cell as the tumor's population of origin, thus placing these "tumors" in the vicinity of cutaneous non-Langerhans cell histiocytoses, is debatable. Furthermore, clonal cytogenetic alterations have been demonstrated that identify the proliferations as "true neoplasms." This hypothesis is supported by the tendency of some variants to local recurrence.

Sporadically (extreme rarity), metastases and/or sarcomatous development have been observed (Mentzel). However, these observations have to be provided with a question mark!

Mostly adults in the 3rd-6th decade of life. Rarely also children.

Extremities, preferably lower leg, less frequently on the trunk. A rare "variant" in the facial region (dermatofibroma of the facial region) was described.

Solitary or multiple, occasionally pruritic or painful, coarse papules (or nodules) that do not protrude or slightly protrude above the surrounding skin level, sometimes sunken centrally, sharply demarcated. The color is reddish or yellow-brown, also dark brown. The surface is smooth, but more often wart-like rough. The "surprisingly" hard consistency of the neoplasm (fibroma durum) is remarkable. Dermatofibromas can be grasped between thumb and index finger like a hard pastille. With lateral pressure, the lesion sinks into depth (=Fitzpatrick sign or dimple sign), while melanocytic nevi bulge.

Some dermatofibromas tend to exophytic growth without any particular histologic architecture.

The so-called deep infiltrating dermatofibroma is primarily encountered on the trunk and extremities of younger individuals. At 1-2 cm in diameter, they are larger than the usual forms and should be separated from dermatofibrosarcoma protuberans.

Rare are dermatofibromas the size of a palm (giant dermatofibroma).

Rare are eruptive multiple dermatofibromas in the immunosuppressed organism.

• Circumscribed, but usually not sharply defined to the side and depth, dermal tumor with diffuse collections of spindle-like cells embedded in an eosinophilic connective tissue. Occasionally with lipid or hemosiderin storage. Giant cells of foreign body or Touton type, vascularization with endothelial swelling. Overlying epidermis is acanthotic; possibly basal cell carcinoma-like proliferation. Dermatofibromas may have a mat-like, intensely interwoven (storiform) pattern. Older dermatofibromas may transition to a cell-poor fibrous stage.
• Immunohistochemically, all involved cells express the nonspecific marker vimentin; phagocytosing dermal dendritic cells (dendrophages) are FXIIIa positive.
• Histologic variants of dermatofibroma:
  • Dermatofibroma with granular cells: appearance of large bright, S100 negative and PAS positive cells with granular cytoplasm, comparable to granular cell tumor).
  • Epithelioid cell histiocytoma: Tumor composed of large epithelioid cells with large eosinophilic cytoplasm and usually vesicular nuclei. Sporadic multinucleated giant cells also seen.
  • Neurothekeoma, cellular.
  • Dermatofibroma with monster cells
  • Ossifying dermatofibroma: with zones of ossification.
  • Xanthomatized der matofibroma: with fatty deposits
  • Dermatofibroma, hemosiderin-storing
  • Myxoid dermatofibroma: with myxoid degeneration zones
  • Desmoplastic dermatofibroma: markedly increased collagen production compared to classic dermatofibroma. Analogous for sclerotic and fibrosing dermatofibroma.
  • Deep penetrating dermatofibroma: Dermatofibroma with infiltration of subcutaneous adipose tissue. DD: dermatofibrosarcoma protuberans.
  • Facial der matofibroma (rare, often cell-rich tumors that infiltrate deeper structures at an early stage).
  • Aneurysmal dermatofibroma (characterized by rapid growth, the parenchyma is characterized by hemorrhage as well as large pseudovascular cavities; high (20%) local recurrence rate after excision).
  • Giant cell angiohistiocytoma with shot-like distribution of papules in a circumscribed region (usually thigh).
  • Cell-rich dermatofibroma (more common in young men in the lower extremity; increased proliferative actvity; tumors contain actin-positive myofibroblasts. Local recurrence rate is increased (25%). Rarely metastatic. Distinction from dermatofibrosarcoma protuberans necessary).
  • Atypical (pseuodsarcomatous) dermatofibroma (clustered on extremities, also on head and neck. Considerable cell and nuclear polymorphism, multinucleated giant cells, atypical mitoses; increased local recurrence rate, very rarely metastasis) - see also under Fasciitis nodularis pseudosarcomatosa .
  • Metastatic dermatofibroma (very rare metastasis involves cell-rich, atypical pseudosarcomatous, and aneurysmal dermatofibroma).

1. Alves FA et al (2003) Benign fibrous histiocytoma of the buccal mucosa: case report with immunohistochemical features. J Oral Maxillofac Surgery 61: 269-271
2. Hui P et al (2002) Clonal analysis of cutaneous fibrous histiocytoma (dermatofibroma). J Cutan Pathol 29: 385-389
3. Hill H (2006) Fibrohistiocytic skin tumors. J Dtsch Dermatol Ges 4: 544-555
4. Mentzel T (2016) Mesenchymal tumors of the skin. In: Cerroni L et al. histopathology of the skin. Springer-Verlag Berlin Heidelberg New-York S 742-744
5. Sellheyer K, Smoller BR (2003) Dermatofibroma: upregulation of syndecan-1 expression in mesenchymal tissue. At J Dermatopathol 25: 392-398
6. Yamamoto T et al (2003) Role of mast cells in dermatofibroma: recent viewpoints into the pathogenesis. Eur J Dermatol 13: 419-423
7. Zaccaria E et al (2008) Multiple eruptive dermatofibromas and immunosuppression: report of two cases and review of the literature. Int J Dermatol 47: 723-727