Rare presentation of Rosai–Dorfman disease with severe lymphopenia: a pediatric case report and review of the literature

) T cells. B-cell subset analysis revealed reduced switched memory and marginal zone compartments with increased transitional B cells, suggesting immune dysregulation. Imaging confirmed extensive cervical and mediastinal lymphadenopathy. Lymph node excision biopsy showed characteristic sinus histiocytosis with emperipolesis, confirming the diagnosis of nodal RDD. No autoantibodies were detected, and bone marrow examination and genetic testing were unremarkable. Given the clinical stability and absence of organ dysfunction, the patient was conservatively managed with prophylactic antimicrobials and close surveillance, remaining stable at follow-up. A review of the literature was also conducted, identifying eight well-characterized RDD cases associated with cytopenia, involving only two cases reporting isolated lymphopenia, emphasizing the rarity of this presentation. Most cases required systemic immunosuppression due to autoimmune features or progressive disease. Detailed lymphocyte subset characterization was rarely reported. In conclusion, this case expands the immunologic spectrum of RDD and highlights isolated severe lymphopenia as a uniquely rare presentation. Comprehensive immunophenotyping is essential to distinguish RDD from primary immunodeficiency and lymphoproliferative disorders, as immune-dysregulated RDD may represent a biologically distinct subgroup with implications for precision management.