OA02 Validation of newly proposed ACR/EULAR classification criteria for pediatric chronic nonbacterial osteomyelitis
Authors: Patel Aarat M , Lee Kelley , Kim Ashley 
Published: August 2023

Abstract

Background
Chronic nonbacterial osteomyelitis (CNO) is an aseptic autoinflammatory bone disease of unknown aetiology. This diagnosis can be delayed due to the non-specific nature of symptoms, referral patterns to non-rheumatology specialists and normal imaging studies. New ACR/EULAR classification criteria have been proposed for CNO and were presented at the American College of Rheumatology scientific meeting in 2022. This study seeks to validate these new classification criteria.

Methods
This is a retrospective case-series of paediatric patients diagnosed with CNO (n = 34). They were diagnosed and managed between 2012 and 2022 at the University of Virginia in Charlottesville, Virginia and Bon Secours Mercy Health in Richmond, Virginia. The entry criteria of chronic bone pain, age &lt; 18 years, abnormal radiograph and/or MRI were used prior to applying the newly proposed ACR/EULAR classification criteria. Ten domains were evaluated to indicate whether a patient has CNO; those who scored 55 points or higher qualified (see table). The clinical manifestations, laboratory results, and imaging studies that lead to a diagnosis of CNO were reviewed in detail. We applied and validated the newly proposed classification criteria for CNO to this Virginia cohort of previously diagnosed paediatric CNO patients. We also reviewed the characteristics of those that did not fulfill these classification criteria.

Result
Upon application of the newly proposed ACR/EULAR classification criteria for CNO, 31 out of 34 patients (91%) were found to meet these classification criteria. Of the three patients diagnosed with CNO that did not fulfill the criteria, none had ‘least specific sites’ such as hands or neurocranium, all had elevated ESR and two out of three had an initial response to antibiotics. Their scores were 49, 51 and 53 with classification criteria being met with 55 or higher. The average age at diagnosis was 10 (range 2–17) years-old with the average time between onset of symptoms to confirmed radiographic evidence being 25 (range 1–120) months. The most common presenting symptoms were bone pain (100%) and arthritis (52%) with fever (23%) and rash (3%) being less common. Elevated ESR (39%) and CRP (39%) were found at initial visit with rheumatology. Evidence of commonly seen radiographic abnormalities leading to CNO diagnosis was found with regional MRI (65%), bone scan (42%) with some requiring full body MRI (26%) to confirm other lesions. Some patients did have multiple imaging studies including X-ray, CT, bone scan, MRI and bone biopsy in their workup.

Conclusion
This retrospective chart review validates the newly proposed ACR/EULAR classification criteria for CNO. We conclude that these criteria are easy to apply even in the absence of a bone biopsy or advanced imaging studies. This will aid in the development of a homogeneous cohort for future studies in CNO.

Implication
The newly proposed ACR/EULAR classification criteria can be easily applied to a cohort of CNO patients. These criteria have taken into account the lack of advanced imaging availability in certain institutions and lack of availability of a bone biopsy.
Our work is ethically approved.