This study evaluates the inter-observer reliability of a standardized WB-MRI scoring system for CRMO and its consistency with the PedCNO clinical score. It also investigates whether changes in the radiologic score mirror therapeutic response, supporting a more objective clinical-radiological disease assessment.

This study seeks to investigate the reliability and clinical utility of a standardized WB-MRI scoring system for assessing disease activity in Chronic Recurrent Multifocal Osteomyelitis (CRMO), a rare pediatric autoinflammatory bone disorder. Although WB-MRI is the current reference technique for detecting both symptomatic and silent lesions, its interpretation remains highly dependent on the radiologist's experience, leading to variability in follow-up assessment. A structured radiologic score has recently been proposed, but its reproducibility and its relationship with clinical disease activity-measured through the PedCNO composite score-are still insufficiently defined.

The primary aim of this work is to determine the inter-observer reliability of the WB-MRI score when independently applied in a blinded manner by experienced pediatric radiologists. In parallel, the study explores how this radiologic score correlates with clinical indicators of disease activity and whether changes in WB-MRI findings over time accurately mirror therapeutic response. By examining the association between variations in the radiologic score and the treatments administered, the study ultimately seeks to clarify the potential role of WB-MRI scoring as an objective, reproducible tool for integrated clinical-radiological management of CRMO.

Inclusion Criteria:

• Patients with a diagnosis of CRMO according to the international Bristol clinical and radiologic criteria, followed at the Pediatric Rheumatology Clinic of the Pediatric Unit, IRCCS AOU Bologna, Sant'Orsola Hospital;
• Age under 18 years at the time of CRMO diagnosis;
• At least one WB-MRI performed as part of routine clinical follow-up between January 2015 and the start date of the study;
• Availability of complete clinical documentation (including reports, radiologic images, and clinical information) sufficient to apply both the WB-MRI score and the PedCNO score;
• Obtain informed consent.

Exclusion Criteria:

- Alternative diagnoses accounting for the bone lesions (e.g., infections, neoplasms).

Patients with a diagnosis of pediatric-onset CRMO and at least one WB-MRI performed between January 2015 and the start date of the study, followed at the Pediatric Rheumatology Clinic of the Pediatric Unit, IRCCS AOU Bologna, Sant'Orsola Hospital