Ab1454 diagnostic and therapeutic practices in adult chronic nonbacterial osteomyelitis (cno)/sapho syndrome: an international landscape

Background Chronic nonbacterial osteomyelitis (CNO) is a rare auto-inflammatory bone disease. CNO, especially the adult variant, may occur in the broader spectrum of Synovitis, Acne, Pustulosis, Hyperostosis, Osteitis (SAPHO) syndrome. Adult CNO lacks diagnostic or management guidelines in contrast to pediatric disease (1, 2). Objectives We mapped current diagnostic and therapeutic practices for CNO/SAPHO in adults. Methods A primary survey was spread among global rheumatological/bone networks and 57 experts as identified from literature (May 2022), covering terminology, diagnostic tools (clinical, radiological, biochemical) and treatment steps. A secondary survey (sent to primary survey responders in August 2022) further queried diagnostic features, treatment motivations, disease activity and treatment response monitoring. Results 36 and 23 physicians completed the primary and secondary survey respectively. Diagnosis was mainly based on individual physician assessment, in which the combination of chronic relapsing-remitting bone pain with radiologically-proven osteitis/osteomyelitis, sclerosis, hyperostosis and increased isotope uptake on bone scintigraphy were reported indicative of CNO. Physicians appeared more likely to refer to the condition as SAPHO syndrome in the presence of joint and skin pathology. MRI was most frequently performed as imaging diagnostic, and the preferred diagnostic test for 47%. X-rays were second-most frequently used, while considered least informative. Typical imaging features reported were hyperostosis, osteitis, osteosclerosis, bone marrow edema, while degeneration, soft tissue calcification, and ankylosis were not regarded characteristic. Inflammation markers and bone markers were generally regarded unhelpful for diagnostic and monitoring purposes, and physicians infrequently performed bone biopsies. Management strategies diverged, including indications for treatment, response monitoring and declaration of remission. Step-1 treatment generally consisted of non-steroidal anti-inflammatory drugs/COX-2 inhibitors (installed by 83%). Common step 2-3 treatment were pamidronate, methotrexate, and TNF-a-inhibition (anti-TNFα), the latter two regarded especially convenient to co-target extra-skeletal inflammation as often seen in SAPHO syndrome. Pamidronate and anti-TNFα and were considered as most effective treatments overall. Conclusion Adult CNO appears to be a condition embedded within a broad and insufficiently characterized disease spectrum, likely including SAPHO syndrome. MRI is the favoured imaging diagnostic, while biochemical and histopathological investigations are rated less useful. Management strategies for CNO/SAPHO vary but pamidronate and anti-TNFα are commonly regarded most successful treatments. The survey results lay out current practices for adult CNO/SAPHO, which may serve as backbone for a future consensus clinical guideline. References [1]Leerling et al. Clinical and therapeutic diversity in adult chronic nonbacterial osteomyelitis (CNO) of the sternocostoclavicular region: a meta-analysis. Rheumatology (Oxford) 2022. [2]Buch et al. Chronic Non-bacterial Osteomyelitis: A Review. Calcified Tissue International 2019. Acknowledgements: NIL. Disclosure of Interests None Declared.