Despite the distinction between autoimmune and autoinflammatory diseases, NOMID shares features with many autoimmune diseases, particularly systemic juvenile rheumatoid arthritis (JRA), which is often a major consideration in the differential diagnosis. Both NOMID and JRA exhibit signs of systemic inflammation, such as high intermittent fevers, arthralgias, deforming arthropathy, and rash. Patients with JRA also show a great heterogeneity of disease severity, from Still systemic-onset disease to pauciarticular or polyarticular disease. Some patients with JRA, especially those with Still disease, may lack serologic markers of autoantibody formation, which further complicates the diagnostic distinction.10 Despite these similarities, there are important features that differentiate the two diseases. The onset of skin disease in the newborn period, as well as a fluctuating but persistent rash, is characteristic of NOMID. In addition, joint signs and symptoms differ: NOMID shows nonspecific arthralgias and characteristic patellar bony enlargement, while true arthritis in JRA manifests as synovial hypertrophy, increased synovial fluid production, and warm, swollen, stiff joints. The common features suggest that effector pathways may be similar despite differences in pathogenesis. At the same time, their differences may also ultimately yield important information regarding the pathogenesis of both disorders.