Dermatofibromas (benign fibrous histiocytomas) are most likely fibrous reactions to minor trauma, insect bites, viral infections, ruptured cysts, or folliculitis. The nodules can be found anywhere on the body, but most often appear on the legs and arms. Dermatofibromas are firm, raised papules, plaques, or nodules that vary from 3 to 10 mm in diameter (Fig. 33-76). Dermatofibromas have a central fibrous scar and often have a hyperpigmented or pink halo around the central hypopigmented area. This has a characteristic pattern on dermoscopy.

Dermatofibromas dimple downward when compressed laterally, caused by tethering of the overlying epidermis to the underlying nodule (Fig. 33-77). Dermatofibromas are usually asymptomatic but may be tender or pruritic. Dermatofibromas can be confused with melanomas, and if growing rapidly, they could be a malignancy called a "dermatofibro-sarcoma protuberans." An excisional biopsy can be used to determine the diagnosis. Because of the dermal location of the nodules, excision is superior to shave biopsy to ensure clear histology and complete removal. A punch biopsy can be used for smaller lesions. Dermatofibromas that are stable in size and asymptomatic can be left alone without treatment.

Figure 33-76 Dermatofibroma on leg with hyperpigmented halo. © Richard P. Usatine.)

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