Clinical Findings: The patient is a 36 year-old African American female with a single 6 x 6.5 cm purple plaque in the left anterior thigh, which has shown an increase in size as time passed. She first developed a dark pinpoint spot-like pimple on her left thigh 5 years ago. Since then, multiple biopsies were performed, but inconclusive. One year ago, another biopsy had been interpreted as a cutaneous Rosai-Dorfman disease. The recent patient’s physical examination was uneventful and there were no lymphadenopathy and oral mucosa lesions detected. Clinical work-up was negative for systemic involvement. The patient is a sickle cell trait.
Pathological Findings: Histological sections showed a dense cellular infiltrate involving the full thickness of dermis and extending into the subcutis. The epidermis showed mild hyperkeratosis, otherwise unremarkable. No clear Grenz zone was noted. The infiltrate was composed of sheets of histiocytes admixed with numerous plasma cells, lymphocytes, and rare eosinophils. A few emperipolesis was also noted. The histiocytes showed round vesicular nuclei with prominent nucleoli in some of those. Immunohistochemical studies showed that the infiltrating histiocytes are intensely positive for S100 and CD68. Infiltrating plasma cells showed a normal ratio of kappa and lambda light chains. Findings supported a diagnosis of Rosai-Dorfman disease.
Treatment and Follow up: She received an injection of Kanalog in the center and peripheries of plaque several times for one year that caused some central clearing. However, no significant improvement was noted. Alternatively, the application of Aldara and every other day application of clobetasol ointment to the affected area had been recommended but no further follow-up record was available.