Acute phase reactants in pediatric chronic nonbacterial osteomyelitis: ımplications for diagnosis and correlation with disease phenotype

Abstract Objectives The role of acute phase reactants (APRs) in the diagnosis of chronic nonbacterial osteomyelitis (CNO) is controversial. Many patients have moderate elevation and some have normal levels. Markedly elevated APRs are more likely to have CNO mimickers that cause lower classification scores. This study aims to investigate how elevated APRs affect the classification of CNO at the diagnosis and their relationship with patient and disease characteristics. Methods This retrospective single-center study included patients diagnosed with CNO who were grouped according to APRs at diagnosis: markedly elevated APRs (CRP ≥30 mg/L and/or ESR ≥60 mm/hour as proposed by classification criteria) and normal-to-moderately elevated APRs. Clinical and imaging findings, and treatment modalities were compared between groups. Results Fifty one patients with CNO were included into the study, 31% of them (n = 16) were classified in markedly elevated APRs group. They exhibited lower classification scores and hemoglobin, higher platelet and ferritin concentrations, more extensive involvement of CNO, and a higher likelihood for CNO-associated diseases. Median total number of bone lesions was significantly higher in this group and a moderate correlation was observed between number of bone lesions and CRP. Pelvic bone, clavicle, and sacroiliac joint involvement were significantly more common in patients with markedly elevated APRs. Conclusion Markedly elevated APRs are observed in a substantial subset of CNO patients that may cause classification limitations. These patients show more severe systemic inflammation, more extensive involvement, particularly in clavicle, pelvis, and sacroiliac joints, and a higher likelihood of CNO-associated diseases.