Extra-osseous manifestations in chronic recurrent multifocal osteomyelitis: a retrospective study

Objectives: Extra-osseous (EO) manifestations are poorly characterized in chronic recurrent multifocal osteomyelitis (CRMO). This study aimed to further define the frequency, characteristics and treatment of EO events in CRMO and whether different phenotypes can be distinguished and benefit from special management.Methods: This multicentre retrospective study included CRMO patients followed in several paediatric rheumatology departments in France between 2015 and 2022. EO manifestations were defined as skin lesions, gastrointestinal manifestations, arthritis, enthesitis, sacroiliitis, uveitis, vasculitis and fever. At the last visit, the physician defined CRMO as active in the presence of clinical manifestations including both osseous and EO symptoms.Results: We included 133 patients; 87 (65.4%) were girls and the median age at first symptoms was 9.0 years (interquartile range 7.0-10.0). EO manifestations were described in 90 (67.7%) patients, with a predominance of skin lesions [n = 51/90 (56.7%)], followed by sacroiliitis [n = 38/90 (42.2%)], enthesitis [n = 21/90 (23.3%)], arthritis [n = 14/90 (15.6%)] and gastrointestinal manifestations [n = 6/90 (6.7%)]. The use of non-steroidal anti-inflammatory drugs and bisphosphonates did not differ by the presence or not of EO manifestations. Biologics were taken more frequently by patients with than without EO manifestations (P < 0.001); TNF inhibitors were used in 33 (36.7%) EO-positive patients. Under this treatment, 18 (54.5%) patients achieved complete remission of osseous and EO manifestations. At the last visit, more EO+ than EO- patients were on treatment (P = 0.009), with active disease in 58 (64.4%) patients.Conclusion: The analysis of EO manifestations in CRMO delineates two groups of patients in terms of severity and treatments used. Our study opens up new pathophysiological leads that may underlie the wide range of CRMO phenotypes.