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Chronic nonbacterial osteomyelitis (CNO) is an autoinflammatory bone disorder, covering a clinical spectrum with asymptomatic inflammation of single bones at the one end, and chronic recurrent multifocal osteomyelitis (CRMO) at the other end. The exact molecular pathophysiology of CNO remains largely unknown. Provided familial clusters and the association with inflammatory disorders of the skin and intestine suggest a genetic predisposition. Recently, profound dysregulation of cytokine responses was demonstrated in CRMO. Failure to produce antiinflammatory cytokines interleukin (IL)-10 and IL-19 contributes to activation of inflammasomes and subsequent IL-1β release. In IL-10-deficient and in CNO-prone chronic multifocal osteomyelitis mice, IL-1β was linked to bone inflammation. Further, alterations to the gut microbiome were suggested in contributing to IL-1β release from innate immune cells in mice, offering an interesting target in the search for molecular mechanisms in CNO. Here, we summarize clinical presentation and treatment options in CNO/CRMO, current pathophysiological concepts, available mouse models, and promising future scientific directions.

Objective: Evolving inflammatory bowel disease (IBD) is a matter of interest in patients with juvenile idiopathic arthritis (JIA) and might be associated with JIA therapy., Methods: Data from the German biologics registry (Biologika in der Kinderrheumatologie; BiKeR) from 2001 to 2013 were analyzed., Results: There were 3071 patients with 8389 patient-years (PY) of observation followed. IBD was diagnosed in 11 patients, 8 with Crohn disease and 3 with ulcerative colitis. IBD incidence in patients with JIA was 1.31/1000 PY and higher than published IBD incidences in pediatric populations. Compared with the total BiKeR cohort, patients with IBD more commonly had enthesitis-related arthritis, extended oligoarthritis, psoriatic arthritis, and also rheumatoid factor (RF)-negative polyarthritis. No IBD occurred in patients with systemic JIA or RF-positive polyarthritis. In patients treated with methotrexate (MTX), the IBD incidence was significantly lower compared with patients not treated with MTX. Etanercept (ETN) monotherapy, but not the combination of ETN and MTX, was associated with an increased incidence of IBD., Conclusion: Incidence of IBD in patients with JIA is higher than in the population. MTX turned out to be protective, even in combination with ETN.