Chronic non-bacterial osteomyelitis: a retrospective international study on clinical manifestations and response to treatment.

Objectives Chronic non-bacterial osteomyelitis (CNO) is a rare non-infectious bone inflammatory disorder; when multifocal, it is referred to as Chronic Recurrent Multifocal Osteomyelitis (CRMO). This study evaluates the demographic, clinical and radiological characteristics of a multi-centre cohort of patients with CNO/CRMO. Methods Demographic and clinical data of patients with an established diagnosis of CNO/CRMO followed at paediatric rheumatology centres across Europe (Italy, France, Slovenia) and India were retrospectively collected. Results There were no demographic differences across countries, but time to diagnosis was significantly longer in India (p=0.041). Pain was almost invariably present at disease onset; functional impairment was more frequent among Italian and Slovenian patients (p=0.001). The number of sites of bone involvement was similar between genders and countries, with long bone metaphises being the most common site. Raised acute phase reactants, detected in >50% of patients, were not associated with clinical manifestations or response to treatment. Comorbidities, evinced in 37% of patients, were equally distributed between genders and nationalities. Imaging approach was similar across countries, without any association between radiological findings and clinical manifestations. NSAIDs were almost invariably used as first-line treatment, but response rate was significantly lower in Italy (p=0.02). Methotrexate was used in 28% of case, with an overall rate of response of 82%. Health conditions and rate of permanent deformities were similar across different countries. Conclusions The differences in clinical presentation, radiological features and response to treatment described in this multinational cohort of CNO/CRMO might provide novel insights into this still elusive disease.