Cutaneous Rosai-Dorfman-Destombes disease: the diagnostic value of the yellow island sign.

Rosai-Dorfman-Destombes (RDD) disease is a rare non-Langerhans cell histiocytosis typically characterized by massive lymphadenopathy. The purely cutaneous subtype (CRDD) is clinically polymorphic, mimicking various inflammatory or neoplastic conditions, making its diagnosis challenging. We present a case of a young phototype 4 Moroccan female with a 2-year history of a progressively enlarging violaceous tumor on her posterior thigh. Dermoscopy revealed structureless yellow areas with fine telangiectasias. Histological along with immunohistochemical examination showed a dense dermal infiltrate with large histiocytes exhibiting prominent emperipolesis confirming the diagnosis of CRDD. A comprehensive systemic workup was negative. No recurrence was detected after a 6 month follow up after surgical excision. This case highlights the importance of dermoscopic clues which correlates with the histological findings. In patients with higher phototypes, these findings are essential to guide the clinician toward a histiocytic disorder. Differential diagnoses such as Langerhans cell histiocytosis, juvenile xanthogranuloma, and sarcoidosis must be ruled out through immunohistopathology.