IL18 and rheumatoid arthritis: If serum IL-18 levels ˃ 1000 pg/mL, AOSD is highly suspected[7,8]; however, if it is ˂1000 pg/mL other systemic rheumatic diseases, such as rheumatoid arthritis, systemic lupus erythematosus, Sjögren syndrome, dermatomyositis/polymyositis, or systemic sclerosis should be suspected.[7,8] In our case, IL-18 was 170,000 pg/mL; thus, we strongly suspected the presence of elderly AOSD rather than rheumatic diseases or infection.