Dermatofibroma

Introduction

Background

Dermatofibroma (DF) is a common cutaneous nodule of unknown etiology that occurs more often in women. The lesion frequently develops on the extremities (mostly the lower legs) and is usually asymptomatic, although pruritus and tenderness are not uncommon. The latter feature is seen in a sufficient number of patients to make DF the most prevalent of all painful skin tumors. A number of well-described, histologic subtypes have been reported. Removal of the tumor is not necessary unless diagnostic uncertainty exists or particularly troubling symptoms are present.

Pathophysiology

The precise mechanism for the development of DF is unknown. Rather than a reactive tissue change, DF seems more likely to be a neoplastic process because of the persistent nature of the lesion and the demonstration that it is a clonal proliferative growth.¹ Clonality, of course, by itself, is not necessarily synonymous with a neoplastic process; it has been demonstrated in inflammatory conditions, including atopic dermatitis, lichen sclerosis, and psoriasis.

Immunohistochemical testing with antibodies to factor XIIIa is frequently positive in DF, while antibodies to MAC 387 show less consistent results. The former antibody labels fibroblasts (dermal dendrocytes), while the latter labels monocyte-derived macrophages (histiocytes). Controversy exists as to whether the factor XIIIa positivity occurs within the actual tumor cells of DF or simply labels the reactive stromal cells; hence, the cell of origin for the spindle cell proliferation of DF is debatable. The cell surface proteoglycan, syndecan-1, may play a role in the growth of DF.² Transforming growth factor-beta signaling might be a trigger of the fibrosis seen in DF.³

Frequency

United States

DF is relatively common.

International

Incidence is probably similar to that in the United States.

Mortality/Morbidity

DF is regarded as a benign lesion; however, discomfort from pain or itching may be significant. The few case reports of metastatic DF are disputable from the standpoint of histologic diagnosis. Such reported lesions were highly cellular, of large size, and locally recurrent.⁴ Indolent pulmonary metastases also were observed.

Race

Frequency appears to be similar in all races.

Sex

Females are affected more commonly than males, with a male-to-female ratio of 1:4.

Age

DF can occur in patients of any age, but it usually develops in young adulthood. Approximately 20% of the lesions occur before age 17 years.

Clinical

History

Dermatofibromas typically arise slowly and most often occur as a solitary nodule on an extremity, particularly the lower leg, but any cutaneous site is possible. Several lesions may be present, but only rarely are multiple (ie, 15 or more) tumors found. This multiple variant is seen most frequently in the setting of autoimmune disease or altered immunity, such as systemic lupus erythematosus, HIV infection, or leukemia and may be indicative of worsening immunoreactivity. Mild regression has been reported with clinical improvement of the underlying disorder. Conversely, drugs to treat the underlying disorders have also been implicated in causation. Multiple clustered DFs also have been reported.⁵ Patients may describe a hard mole or unusual scar and may be concerned about the possibility of skin cancer.

DFs are characteristically asymptomatic, but itching and pain often are noted. They are the most common of all painful skin tumors.⁶ Women who shave their legs may be bothered by the razor traumatizing the lesion in that region, causing pain, bleeding, erosive changes, and ulceration. Although cases of unusually rapid growth exist, most DFs remain static for decades or persist indefinitely. Uncommon reports describe spontaneous regression,⁷ and this may yield postinflammatory hypopigmentation.

Physical

Typically, the clinical appearance is a solitary, 0.5- to 1-cm nodule. A sizable minority of patients may have several lesions, but rarely are more than 15 lesions present. The overlying skin can range from flesh to gray, yellow, orange, pink, red, purple, blue, brown, or black, or a combination of hues (see Media File 1). On palpation, the hard nodule may feel like a frozen pea or a small pebble fixed to the skin surface and is freely movable over the subcutis. Tenderness may be elicited with manipulation of the lesion.

The characteristic tethering of the overlying epidermis to the underlying lesion with lateral compression, called the dimple sign, may be a useful clinical sign for diagnosis.⁸ The dimple sign is not unique to DF, and dermatoscopy may be useful in supporting the clinical impression.⁹

The extremities are the most common sites of involvement, particularly the lower legs. Although any cutaneous site can be seen, palm and sole involvement is rare. Giant (>5 cm in diameter), atrophic, atypical polypoid and DF with satellitosis variants have been reported.

Causes

Historically attributed to some traumatic insult to the skin (eg, arthropod bite), the cause of DF is unknown. Because of its persistent nature, DF is probably better categorized as a neoplastic process rather than a reactive tissue change. A study of eruptive DFs in a kindred suggests that a genetic component may exist.¹⁰