Abstract

Cutaneous Rosai-Dorfman disease, a rare form of non-Langerhans cell histiocytosis, typically presents with multiple skin nodules and often involves extremities, contrasting conventional Rosai-Dorfman disease which primarily involves lymph nodes. Diagnosis is based on biopsy revealing characteristic histopathologic features. We present a 55-year-old female who initially presented at an outside institution with multiple cutaneous nodules of the left leg, back, chest, and right arm. An initial outside biopsy reportedly demonstrated a dense infiltrate composed of histiocytes which contained small, round GMS-positive forms, favored to represent cryptococcal organisms, with a differential diagnosis including other disorders of “parasitized histiocytes”. Several lesion were excised completely without evidence of recurrent disease. Additionally, some of the larger lesions had shown marked regression following antibiotic and steroid therapies. However, due to incomplete resolution of her lesions, the patient presented to an academic dermatology department, whereupon a repeat biopsy showed a diffuse infiltrate of histiocytes with voluminous pale cytoplasm with emperipolesis of inflammatory cells and S100 positivity by immunohistochemistry. A next generation sequencing panel (oncogenomic solid tumor v2.0) found a MAP2K1 mutation on chromosome 15, exon 2 [c.169A>C, p.Lys57Gln, g.66727453A>C], which has been described in a subset of Rosai-Dorfman disease and offered further support for a clonal neoplastic process. Following her diagnosis, therapy with doxycycline and prednisone was continued with some additional improvement, however, one larger lesion on her right back required wide-local excision surgery followed by radiation therapy. This case illustrates a challenging diagnostic pitfall and also demonstrates the utility of genetic analysis for supporting a diagnosis of cutaneous Rosai-Dorfman disease.

Financial Disclosure:
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