Dermatofibroma or benign fibrous histiocytoma is a common cutaneous nodule that may be superficial or deep. It is the most common painful skin tumour, affecting women more commonly. Although, the precise underlying etiology and mechanism for the development of this skin pathology is not well known, it is believed to be a neoplastic process owing to its clonal proliferation growth. While the patients may usually be asymptomatic, the tumour growth may exhibit rapid growth or may remain static for several years. An intervention is not called for unless the patient is symptomatic.
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dermatofibroma

Image: “Fibrous histiocytoma (dermatofibroma).” by LWozniak&KWZielinski – Own work. License: CC BY-SA 3.0


Definition and Epidemiology of Dermatofibroma

Dermatofibroma are a common mesenchymal growth of the skin where skin fibroblasts are the major cell constituents. It is also known as cutaneous benign fibrous histiocytoma or sclerosing haemangioma.

A common mesenchymal tumour of the skin, dermatofibroma are known to have a similar occurrence across all races. They have a predilection for women, mostly in the lower legs, and in their early adulthood from 20-30 years of age. It can, however, occur in any age.

Pathophysiology of Dermatofibroma

The exact mechanism for the development of dermatofibroma is not known with clinicians divided on whether it is a reactive process or a neoplastic one. Association with trauma and insect bites have led some to believe a reparative or reactive process being the underlying pathology. However, recent demonstrations on chromosomal abnormalities and clonal proliferation have hinted more towards a neoplastic mechanism.

But more likely, it is said to arise from a distortion of protein kinase C activity. Immunohistochemical testing results have been found to be more consistent with presence of factor XIIIa and fascin (dendritic cell markers) than with MAC – 387,  a histocyte marker.

Mast cells are found in abnormally high numbers that release fibrogenic factors like transforming growth factor beta (TGF beta) and trigger the fibrosis seen in dermatofibroma. In the epitheloid and atypical dermatofibroma variants specifically, ALK gene rearrangement and over-expression have been implicated.

Clinical Features of Dermatofibroma

  • Measuring about 0.5-1cm in size, dermatofibroma are characteristically firm, indurated and mobile.
  • The lesions may be solitary or multiple (defined as at least 15 but most commonly benign finding), generalised or neoplastic. Multiple lesions are usually associated with an immunosuppressive condition like HIV, myasthenia gravis, systemic lupus erythematosus, diabetes etc.
  • When neoplastic, they are usually confined to soles and palms and may grow rapidly within weeks. However, some have been found to remain static for years.
  • Lateral compression produces a dimple like depression in the overlying skin and it disappears with release of pressure. This is called button-holing but is not specific to dermatofibroma. Positive button hole sign is also seen in type 1 neurofibromatosis (Von-Recklinghausen’s disease), and anetoderma.
  • Regression of these lesions may leave hypopigmented spots.
  • Dermatofibroma arising on the face are quite uncommon but distinct from lesions seen at other sites. More commonly of the cellular type, they may extend into subcutaneous fat or muscle and recur frequently. This is why a wider initial excision is warranted in this case.
  • Local recurrence is a feature of the atypical variant as well along with distant metastasis seen here.

Differential Diagnosis

Storiform pattern in dermatofibrosarcoma protuberans

Image: “Very high magnification micrograph of the storiform pattern in a case of dermatofibrosarcoma protuberans. H&E stain.” by Nephron – Own work. License: CC BY-SA 3.0

The deep variant of dermatofibroma may be confused with an entity called dermatofibrosarcoma protuberans, which is rather typically found on the trunk in younger adults. The size of this lesion is much larger – about 1-2cm.

In ambiguous cases, where the histological picture of the cellular variant closely resembles that of dermatofibrosarcoma protuberans, immunolabelling can be useful in distinguishing the factor XIIIa and fascin positive dermatofibroma from the latter (found to be negative for these markers).

However, the following skin pathologies are also to be considered in the differential:

Investigations for Dermatofibroma

While the diagnosis of dermatofibroma is usually made clinically, confirmation can be undertaken by histological analysis on biopsy.

Biopsy

Histological picture obtained on punch biopsy of the lesion reveals information on not just the type of variant but also helps in making crucial decisions regarding management.

A typical picture that is most often encountered is:

Dermatofibroma

Image: “Histopathology of dermatofibroma.” by Ed Uthman from Houston, TX, USA. Uploaded by CFCF. License: CC BY 2.0

  • Epidermis: usually hyperplastic and hyperpigmented known as the dirty finger nail sign
  • Dermis: haphazardly arranged fascicles of plump spindle shaped cells that typically lack atypia
  • Edges of lesion: not well defined with individual cells infiltrating between thickened and hylanized collagen bundles (typical keloidal picture), also known as “collagen trapping”.
  • Mitotic figures may be present but atypia is characteristically not seen.

A cellular variant shows a storiform arrangement embedded in the deep dermis, with a much larger size and increased cellularity. It may often extend into the superficial subcutaneous tissue making it difficult to distinguish from an entity called dermatofibrosarcoma protuberans.

A rare form of atypical variant shows atypical features against a background of a classic picture of dermatofibroma. Pleomorphic, spindle shaped, plump or polyhedral shaped cells are seen with keloidal collagen and storiform arrangement.

Dermatoscopy

Visualising under a dermatoscope usually presents a peripheral pigment network with a central white area.

Serology

Indicated in cases where immunosuppressive conditions are suspected.

Management of Dermatofibroma

An intervention is usually not indicated in asymptomatic cases that constitute the majority. Watchful waiting and reassurance suffice.

For symptomatic cases:

  • Medical management: This is for patients who do not desire to undergo a surgical procedure. Topical or intralesional corticosteroids may help relieve symptoms.
  • Cryosurgery is another option to flatten out the dermatofibroma but is usually not curative.
  • Surgical management: This includes cutaneous shaving, excisional surgery and ablative laser surgery. This is usually indicated for cases where repeated trauma is suffered due to shaving on the lower legs. 20% of the cellular variant are known to recur after a simple biopsy and thus warrant a fusiform excision into the superficial subcutaneous tissue. For deeper variants, excision to the deeper subcutaneous tissue is done to decrease the risk for recurrence.

Lesions that continue to increase in size, become symptomatic or bleed or change size or symmetry are to be biopsied before establishing a management protocol.

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