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A 19-year-old woman is referred for evaluation of a growth on her left leg. The lesion was first noted approximately 18 months ago and has slowly increased in size. She is an athlete and has on occasion traumatized the site, which has otherwise remained asymptomatic. Her family history is positive for skin cancer with basal cell carcinomas affecting 2 grandparents and a “pre-melanoma” diagnosed in her mother. Examination reveals a 0.5-cm deeply pigmented firm nodule on her left posterior leg.
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Dermatofibromas (DFs) are benign fibrohistiocytic tumors that occur most commonly on the lower extremities of women (2:1 female to male predominance).1 The lesions are usually asymptomatic, slightly elevated, dome-shaped, and range in size from 0.3 cm to more than 1.0 cm.1 Lateral palpation may result in increased depression, also known as a positive dimple or Fitzpatrick sign. Once considered pathognomonic for dermatofibromas, not all dermatofibromas dimple and other lesions may dimple as well.2
The color of tumors is variable although the majority are hyperpigmented. In fair-skinned individuals, dermatofibromas may take on a pinkish hue. Common dermoscopic findings include either a pigmented or whitish network often surrounding a zone of scarring.3 Histopathology reveals a dermal lesion containing spindle-shaped fibrous cells admixed with histiocytoid cells. Lesions arise spontaneously or following minor trauma such as an insect bite. Spontaneous resolution is uncommon.
The hemosiderotic variant is a less common subtype of dermatofibromas (2% of dermatofibromas) that reveals on histology a proliferation of macrophages containing hemosiderin.4 Similar looking lesions that need to be ruled out include melanoma, Kaposi sarcoma, and dermatofibrosarcoma protuberans.5 These conditions are ruled out by histologic evaluation and immunohistochemistry.
Brittany Spinosa-Weber, PA-C, is on staff at the DermDox Centers for Dermatology with offices in Bethlehem and Sugarloaf, Pennsylvania. Stephen Schleicher, MD, is director of the DermDox Dermatology Centers, associate professor of medicine at Geisinger Commonwealth Medical College, and clinical instructor of dermatology at Arcadia University and Kings College.
References
1. Myers DJ, Fillman EP. Dermatofibroma. StatPearls [Internet]. StatPearls Publishing: October 24, 2022.
2. Meffert JJ, Peake MF, Wilde JL. ‘Dimpling’ is not unique to dermatofibromas. Dermatology. 1997;195(4):384-386. doi: 0.1159/000245994
3. Zaballos P, Puig S, Llambrich A, Malvehy J. Dermoscopy of dermatofibromas: a prospective morphological study of 412 cases. Arch Dermatol. 2008;144(1):75-83. doi:10.1001/archdermatol.2007.8
4. Villarreal DJ, Luz AT, Buçard AM, Abreu L, Cuzzi T. Hemosiderotic dermatofibroma. An Bras Dermatol. 2017;92(1):92-94. doi:10.1590/abd1806-4841.20173563
5. Li C, Allen H, Loxas M, Sharma P. Hemosiderotic dermatofibroma mimicking melanoma: a case report and review of the literature. Clin Case Rep. 2021;9(3):1387-1392. doi:10.1002/ccr3.3780
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