A Recurrent Indurated Plaque on the Thigh

A 57-year-old woman with chronic thyroiditis, dermatitis and rosacea presented with an indurated plaque on her left thigh that had evolved intermittently over several years. The lesion, which began as discrete papules, enlarged and coalesced into a plaque over time, with increasing firmness. Topical corticosteroids offered transient relief, but the plaque persisted. Physical examination revealed a brownish-red, 5 × 4 cm indurated plaque composed of grouped papules (Figure 1). Punch biopsy was obtained (Figures 2 and 3). Rosai−Dorfman disease (RDD). These clinical and histologic features were consistent with RDD. The punch biopsy was notable for a collection of histiocytes showing emperipolesis (the presence of intact cells within the cytoplasm of another cell) accompanied by plasma cells and lymphocytes (Figures 2 and 3). The histiocytes stained positive for CD68, CD163 and S100, and negative for CD30, and special stains for infectious organisms were negative. RDD, also known as sinus histiocytosis with massive lymphadenopathy, is a benign disorder of histiocyte proliferation often presenting with painless, bilateral lymphadenopathy 1. While cutaneous manifestations of systemic RDD are not entirely uncommon, purely cutaneous RDD (CRDD) without systemic involvement is a rare, distinct clinical diagnosis affecting only 3 in 200 million, with a marked female predominance (2:1) 1. RDD is characterized by the presence of large histiocytes with emperipolesis and positive immunohistochemistry staining for CD68, CD163 and S100 2. This patient's punch biopsy demonstrated these findings (Figures 2 and 3). CRDD may present as singular or numerous papules, nodules, plaques or any combination of these 1. This rather nonspecific presentation necessitates the consideration of other differential diagnoses that may present similarly, such as granuloma annulare, morphea, sarcoidosis or cutaneous B-cell lymphoma. Our patient's initial physical examination revealed a brownish-red, indurated plaque composed of grouped papules (Figure 1). In isolation, this clinical description is associated with various diagnoses. However, histology showed the presence of emperipolesis (Figure 3) and positive IHC staining for CD68, CD163 and S100, which confirmed the diagnosis of RDD. Histological examination of granuloma annulare would show a palisaded or interstitial histiocytic infiltrate with altered collagen. Morphea would exhibit increased collagen deposition, without a histiocytic infiltrate. Sarcoidosis would reveal discrete, non-caseating granulomas, distinct from the histiocytes with emperipolesis observed in this case. Excluding systemic involvement with additional imaging and laboratory studies is essential, as CRDD is managed differently from systemic RDD. Further CT and laboratory studies conducted by our patient's primary care physician ruled out lymphadenopathy and systemic involvement. While most cases of RDD are self-limiting and do not require treatment, CRDD is a difficult entity to treat, with an overall cure rate of 28.6% 3. Therapeutic options for CRDD include localized treatment with corticosteroids or systemic therapies in cases of extensive or symptomatic lesions 2. In this case, intralesional corticosteroid injections achieved partial improvement, with reduced induration but residual discoloration. Other therapeutic modalities, such as localized radiotherapy, cryotherapy, laser therapy or surgical excision, may be considered depending on lesion location and patient preferences 4, 5. Tram T. Tran: participated in the performance of research, data analysis and writing of the paper. Sabine L. Abukhadra: participated in data analysis, writing of the paper and editing of the paper. Samuel T. Hwang: participated in research design and performance of research. Maija Kiuru: participated in research design, performance of research and editing of the paper. The authors have nothing to report. The authors obtained written consent from patients for their photographs and medical information to be published in print and online, and with the understanding that this information may be publicly available. Ethical Approval: not applicable. The authors declare no conflicts of interest. Data sharing is not applicable to this article as no data sets were generated or analyzed during the current study.