Rosai-Dorfman disease presenting as isolated cervical lymphadenopathy in a young adult: A case report.

Rosai-Dorfman disease, also known as sinus histiocytosis with massive lymphadenopathy, is a rare non-Langerhans cell histiocytic disorder most commonly involving the cervical lymph nodes, which are affected in approximately 80%-90% of cases. It predominantly affects children and young adults but may occur at any age, typically presenting with painless, bilateral, and sometimes bulky cervical lymphadenopathy, occasionally associated with systemic inflammatory symptoms and laboratory abnormalities such as elevated inflammatory markers and polyclonal hypergammaglobulinemia. Histopathological examination is essential for diagnosis and demonstrates marked sinus expansion by large histiocytes with abundant pale cytoplasm and characteristic emperipolesis, set within a lymphoplasmacytic background. Immunohistochemically, these histiocytes express CD68, CD163, and S100 protein, while lacking CD1a and langerin expression, allowing distinction from other histiocytic disorders. Although historically considered a benign reactive condition, recent molecular studies have identified activating mutations in the MAPK/ERK signaling pathway, including