Evolution of bone lesions in adults with chronic nonbacterial osteitis (CNO): A long-term follow-up study.

Objectives: Chronic nonbacterial osteitis (CNO) is a rare disease characterised by sterile bone inflammation. Little is known about the evolution of bone lesions, especially for the adult variant of the disease (adult CNO). We therefore aimed to characterize the radiologic course of adult CNO.

Methods: We conducted a cohort study among confirmed adults with CNO, treated at the Dutch national CNO referral centre between 1992 and 2023. Imaging reports from the first-performed radiological scan (baseline) to the last available scan (end of follow-up) were systematically reviewed for lesion location and radiologic features (sclerosis, hyperostosis, erosions, ankylosis). Incidence rates (IRs) for new lesions, progression, and regression of existing lesions were estimated using the Poisson method. Kaplan-Meier curves were used to visualize cumulative incidence, and Poisson regression models assessed associations between patient characteristics and the outcomes.

Results: The study included 182 adult CNO patients with a mean follow-up of 6.1 ± 5.2 years, treated with nonsteroidal anti-inflammatory drugs or cyclooxygenase-inhibitors and/or intravenous bisphosphonates or tumour necrosis factor alpha inhibitors. The most common pattern was sole involvement of the anterior chest wall (84 %). IRs per 100 person-years were 4 (95 % CI 3-5) (new lesions), 7 (6-9) (progression), and 1 (0.3.-1) (regression). Among patients with anterior chest wall involvement only (n = 147), one person developed a lesion outside this area (IR 0.3 (0.06-1)). At 2 years, cumulative incidence of new lesion development and progression were 2 % (0-5) and 7 % (3-10), increasing to 11 % (5-17) and 29 % (20-36) at 5 years, and 36 % (23-48) and 56 % (43-64) at 10 years. No associations were found between clinical characteristics at baseline and these outcomes.

Conclusions: The development of new bone lesions in treated adult CNO patients is typically confined to previously affected regions, primarily the anterior chest wall. Progression of structural changes occurs in the majority of patients after longer follow-up. These findings can be used for prognostic counselling, and suggest that routine whole-body imaging may not be necessary for most patients during follow-up.