Clinical characteristics and outcomes of paediatric CNO: a retrospective cohort study with focus on zoledronic acid.

OBJECTIVES: Chronic non-bacterial osteomyelitis is a rare autoinflammatory bone disease of childhood. Non-steroidal anti-inflammatory drugs are often used first-line, while conventional and biologic disease-modifying antirheumatic drugs and bisphosphonates are reserved for severe or refractory disease. Zoledronic acid is used off-label, but robust data on its role remain limited. This study aimed to describe the clinical characteristics, management, and outcomes of children with Chronic non-bacterial osteomyelitis, with primary focus on the effectiveness and tolerability of Zoledronic acid. METHOD: A retrospective review was conducted of children diagnosed with chronic non-bacterial osteomyelitis between 2014 and 2024 at the Royal Children's Hospital, Melbourne. Clinical and magnetic resonance imaging responses to ZA, as well as adverse effects, were evaluated. RESULTS: Fifty-seven patients were included (mean age 10.3 years; 70% female; median follow-up 3.7 years [range 1.4-8.9]). Multifocal disease was present in 86%, and 63% underwent biopsy. All received non-steroidal anti-inflammatory drugs initially. Twenty-two patients (37%) received zoledronic acid (mean 2.6 doses); 77% showed significant clinical improvement. Three later required tumour necrosis factor inhibitors, and two received tumour necrosis factor inhibitors without prior zoledronic acid. Among 10 patients with pre- and post-zoledronic acid whole body magnetic resonance imaging, 80% demonstrated significant radiological improvement. Mild, transient flu-like symptoms were reported in 54% of patients treated with zoledronic acid; no serious adverse events occurred. CONCLUSION: Zoledronic acid was associated with high clinical and radiological response rates and was well tolerated. Its infrequent dosing schedule, typically one infusion every six months, offers a practical alternative to other bisphosphonates.