Chronic Nonbacterial Osteomyelitis in Latvia from 2014 to 2025: Case Series.

Background and Objectives: Chronic nonbacterial osteomyelitis (CNO) is a rare pediatric autoinflammatory bone disease with variable presentation and frequent diagnostic delay. Data from Latvia are limited. This study aimed to evaluate demographic data, clinical manifestations, and treatment strategies of CNO in Latvia. Materials and Methods: This is a retrospective case series study of patients under 18 years of age diagnosed with chronic nonbacterial osteomyelitis (CNO) in the only pediatric tertiary hospital in Latvia between 2014 and 2025. Results: Thirteen patients were identified, 8 boys and 5 girls, with a median age at onset of 10 years. The pooled incidence was 0.31 per 100,000 children. The median time from symptom onset to diagnosis was 4.1 months. All patients had localized bone pain; most had fever, swelling, or a reduced range of motion. Multifocal disease occurred in all patients, with a median of 6 bones involved, and 61.5% had axial skeleton involvement. The most affected bones were the femur and tibia. Extraosseous manifestations included rash, central nervous system involvement, and lung granulomas. The most common comorbidities observed were inflammatory bowel disease and juvenile idiopathic arthritis (JIA). Inflammatory markers were moderately to markedly elevated. Whole body MRI with DWIBS was performed in all patients and showed bone marrow edema and STIR/T2 FS hyperintense lesions. All patients received NSAIDs, but only 15.4% had a complete response. Many required escalation to second-line treatment with methotrexate, TNF alpha inhibitors, or bisphosphonates. Conclusions: The incidence was similar to that reported in Europe. The cohort was characterized by multifocal, often severe disease with frequent fever and elevated inflammatory markers. Second-line treatment with methotrexate, TNF alpha inhibitors, or their combination showed a robust treatment response.