A several-year history of a pink and brown nodule after a mosquito bite


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A 44-year-old woman presents for her annual full skin examination. She has a specific concern regarding a lesion on her left lower leg. She recalls having a mosquito bite in that area a few years earlier, but it never went away. The lesion is bothersome only when she shaves her legs and nicks it; otherwise, there is no associated pain or tenderness. Physical examination reveals a firm, flat, pink and brown nodule located on the left anterior proximal shin. The lesion dimples inward when pressure is applied. 

Dermatofibroma, also known as a cutaneous fibrous histiocytoma, is a common benign lesion that was first described by Stout and Lattes in 1967.1 It was previously thought to have a reactive etiology, as lesions often present after trauma, such as...

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Dermatofibroma, also known as a cutaneous fibrous histiocytoma, is a common benign lesion that was first described by Stout and Lattes in 1967.1 It was previously thought to have a reactive etiology, as lesions often present after trauma, such as a shaving nick, insect bite, or thorn injury. Recent literature, however, points to a clonal neoplastic process.2

A dermatofibroma presents as a flat, firm nodule that appears tethered to the skin surface, although it is freely mobile over subcutaneous fat. Color varies from white to pink or brown, with a paler pigment in the center. Size generally ranges from 5 to 10 mm. A patient may present with more than one dermatofibroma. However, the presence of numerous dermatofibromas should raise suspicion of misdiagnosis or severe immunosuppression. A subcutaneous (deep) benign fibrous histiocytoma is a clinical subtype of the dermatofibroma and has a more aggressive nature, with a propensity for local recurrence.3

Dermatofibromas are seen in adults of all ages, are rarely seen in children, and occur equally across all ethnicities. Women appear to be affected at a slightly higher rate. Although dermatofibromas can occur anywhere, they frequently appear on the lower legs, particularly in women, as well as the upper arms and shoulders. Two recent reports presented unique cases of dermatofibroma occurring on a middle-aged woman’s finger4 and on a young woman’s nipple.5

Most dermatofibromas are asymptomatic. However, some patients may report itching or tenderness associated with the lesion. Lesions on the lower legs are often prone to trauma, particularly in patients who shave their legs.

There are several lesions that can look like a dermatofibroma. Basal cell carcinoma, both the nodular and superficial types, frequently appears on the legs and poses a diagnostic challenge. Keloids, neurofibromas, and dysplastic nevi are other common lesions to consider in the differential diagnosis. Dermatofibrosarcoma protuberans (DFSP) is a relatively uncommon spindle cell tumor of the skin that mimics dermatofibroma clinically. DFSP is locally aggressive and rarely can metastasize.

The diagnosis of dermatofibroma is often clinical. A positive dimple sign indicates that the lesion dimples inward and downward when peripheral pressure is applied. A dermoscope used by a trained clinician can further support the clinical diagnosis. A white central patch with a peripheral fine brown network is the classic stereotypical pattern seen on dermoscopy.6 Unfortunately, dermatofibromas may present with nonclassic patterns that can mimic other benign or malignant lesions. If the diagnosis is questionable or if the lesion has atypical features, such as ulceration or asymmetry, a shave biopsy sent for histopathologic examination can confirm the diagnosis.

Histology of a dermatofibroma reveals a poorly defined proliferation of fibrohistiocytic cells with excessive collagen entrapment in the dermis. There is often an overlying grenz zone of normal papillary dermis. Occasionally, the overlying epidermis shows acanthosis and pigmentation of the basal layer. The presence of Touton giant cells containing hemosiderin confirms the diagnosis.7 Lesions that microscopically display cellular, aneurysmal, epithelioid, palisading, or other atypical patterns predict a more aggressive nature.

A dermatofibroma is benign and does not require treatment unless the lesion is progressively changing. If the lesion is bothersome to a patient, it can be electively removed. Surgical excision is the preferred method for removal, although patients should be warned that there can be significant scarring. Cryosurgery, electrodessication, and laser have rarely been successful.

For the patient in our case, a skin biopsy confirmed the diagnosis of dermatofibroma. The patient was educated regarding the diagnosis and reassured regarding its benign nature. Due to the uncertain cosmetic outcome with local excision, the patient chose to leave the lesion alone. She was encouraged to return for annual full skin examinations.

Esther Stern, NP, is a family nurse practitioner at Advanced Dermatology & Skin Surgery, P.C., in Lakewood, N.J.


  1. Stout AP, Lattes R. Tumors of the Soft Tissues. Washington, DC: Armed Forces Institute of Pathology; 1967.
  2. Chen TC, Kuo T, Chan HL. Dermatofibroma is a clonal proliferative disease. J Cutan Pathol. 2000;27:36-39.
  3. Gleason BC, Fletcher CD. Deep “benign” fibrous histiocytoma: clinicopathologic analysis of 69 cases of a rare tumor indicating occasional metastatic potential. Am J Surg Pathol. 2008;32:354-362.
  4. Raghavendran RR, Jenkins R. Digital dermatofibroma: common lesion, uncommon site. J Am Acad Dermatol. 2013;68(suppl):AB48.
  5. Lee YB, Cho BK, Park HJ, Eun YS. Dermatofibroma on the nipple: a rare and interesting case. J Am Acad Dermatol. 2012;66(suppl 1):AB48.
  6. Espasandín-Arias M, Moscarella E, Mota-Buçard A, et al. The dermoscopic variability of dermatofibromas. J Am Acad Dermatol. 2015;72(1 suppl):S22-S24.
  7. James WD, Berger TG, Elston DM, Neuhaus IM. Andrews’ Diseases of the Skin: Clinical Dermatology. 11th ed. Philadelphia, PA: Saunders-Elsevier; 2011.
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