Significant clinical, histologic, and immunologic overlap between iMCD, malignancy, autoimmune, and infectious disorders. The exact location for iMCD on the spectrum from autoimmune, malignant, and infectious diseases is currently unknown and may vary from patient to patient. ALPS, autoimmune lymphoproliferative syndrome; AOSD, adult-onset Still disease; EBV, Epstein-Barr virus; FDC, follicular dendritic cell; HHV-8, human herpesvirus-8; HL, Hodgkin lymphoma; HLH-MAS, hemophagocytic lymphohistiocytosis- macrophage activation syndrome; IgG4, IgG4-related disease; JIA, juvenile idiopathic arthritis; M-HLH, malignancy-associated hemophagocytic lymphohistiocytosis; NHL, non-Hodgkin lymphoma; POEMS, polyneuropathy, organomegaly, endocrinopathy, monoclonal paraprotein, skin changes; RA, rheumatoid arthritis; SLE, systemic lupus erythematosus; V-HLH, viral hemophagocytic lymphohistiocytosis.