Variable extent of emperipolesis in the evolution of Rosai Dorfman disease: Diagnostic and pathogenetic implications

This study examines variation of morphologic features, including emperipolesis, during the evolution of a case of Rosai Dorfman Disease (RDD). A 44-year-old male patient with RDD affecting the salivary glands, cervical lymph nodes, nasal and maxillary sinus mucosa had a waxing and waning course over two and a half years, with episodic sudden increase in size followed by involution and then a static course with moderate sized swellings. Multiple aspirations and biopsies were performed, which form the basis of this study. Four classical cases of RDD on aspirates and another four on biopsy were analyzed for comparison, with quantification of the number of lymphocytes engulfed by histiocytes (emperipolesis). Three nasal biopsies and one salivary gland excision of the index case, performed during acute exacerbation, showed chronic inflammation and foamy histiocytes without emperipolesis, the aspirate showing emperipolesis nil in 45%, 1-3 lymphocytes in 15%, 4-10 in 36% and > 10 in 4%. Two aspirations and one lymph node biopsy done from static phase showed classical features of RDD with extensive emperipolesis, the aspirate from left cervical lymph node showing emperipolesis nil in 2%, 1-3 in 5%, 4-10 in 35% and > 10 in 58% while right cervical lymph node aspirate showed emperipolesis nil in 9%, 1-3 in 21%, 4-10 in 29% and > 10 in 41%. A biopsy performed from involuting cervical lymph node showed extensive apoptosis and vasculitis without foamy histiocytes or emperipolesis. For comparison, eight classical RDD cases showed abundant emperipolesis with mild variation. Emperipolesis is variable in RDD depending on disease activity, which has differential diagnostic relevance and demonstrates the natural history of this rare disease.