Primary Cutaneous Rosai-Dorfman Disease Presenting as an Infiltrative Dorsal Nasal Mass With Deep Skeletal Muscle...

Rosai-Dorfman disease (RDD) is a rare non-Langerhans cell histiocytosis that most commonly presents with nodal disease but may involve extranodal sites, including the skin. Purely cutaneous Rosai-Dorfman disease (CRDD) is uncommon and demonstrates a wide range of clinical and histopathologic features, frequently resulting in diagnostic delay. We report a case of a 64-year-old woman with an 18-month history of a progressively enlarging, pruritic nasal mass encompassing the entire nasal dorsum and bilateral nasal sidewalls refractory to multiple therapies and repeatedly misdiagnosed as granulomatous rosacea. Deep biopsy revealed a dense lymphoplasmacytic infiltrate with storiform fibrosis involving the dermis, subcutis, and skeletal muscle. Scattered large histiocytes demonstrated emperipolesis and expressed S100, OCT2, and CD68, whereas CD1a was negative. Extensive ancillary studies excluded infection and hematolymphoid malignancy. This case highlights a rare and underrecognized presentation of CRDD with histopathologically confirmed skeletal muscle involvement and underscores key diagnostic pitfalls relevant to dermatologists and dermatopathologists.