Background/purpose: Chronic non-bacterial osteomyelitis (CNO) is a rare bone disease spectrum with pediatric and adult presentations. Pediatric CNO is hypothesized to be auto-inflammatory in origin, mediated by pro-inflammatory cytokine dysregulation. In adult CNO, which mainly manifests in the sternocostoclavicular region (CNO/SCCH), inflammatory biochemical profiles are inconsistently detected. Similarly, elevated serum concentrations of interleukin (IL)-6, 8, 17A and TNF-a have been found in multiple pediatric CNO cohorts, whereas adult data are scarce and discrepant. We therefore provide a broad biochemical characterization of adult CNO/SCCH.

Methods: Cross-sectional study comparing adult CNO/SCCH patients with active disease to suspected (mimicking) CNO/SCCH controls not using immunomodulatory treatment (exempting NSAIDs) or bisphosphonates. Generic inflammation parameters and systemic inflammatory scores (SIBS) were compared between patients and controls and serum levels of Th1/2 and Th17-derived cytokines were determined in a subset of patients and controls by electrochemiluminescence immunoassays.

Results: ESR, CRP, platelet, leucocyte and neutrophil count were all significantly higher in patients (n=172) than in controls (n=82), but remained within absolute reference range. Neutrophil-derived SIBS (neutrophil/lymphocyte ratio (NLR) and systemic immune inflammation index (product of NLR and platelet count)) were also relatively elevated in patients. Cytokine analysis (40 patients, 8 controls) revealed a non-significant trend for higher IL-8 levels in patients and significantly lower IL-12p70 concentrations. No differences were found for IL-6, -10, -13, -17A, -22, -23, -27, TNF-a, IFN-γ, and MIP-3a.

Conclusions: In this adult CNO/SCCH cohort, generic inflammation markers were relatively increased compared to controls, but absolute values fell within reference range. In contrast to previous studies, we found no increased expression of pro-inflammato