Ab0042 Non-Bacterial Osteitis (Nbo): A Single Center Experience

Background: NBO is a rare autoinflammatory disease with a very low prevalence, characterized by a slow onset of recurring sterile bone lesion(s). It has a variable presentation, ranging from asymptomatic or mild symptoms from a single focus, to severe localized pain from multiple foci [1,2]. It constitutes a clinical entity without validated diagnostic/classification criteria or disease biomarkers and is probably underdiagnosed. Treatment is largely based on expert opinion and small case series and it usually involves non-steroidal anti-inflammatory drugs (NSAIDs), corticosteroids, bisphosphonates or anti-TNF agents [3]. Objectives: Describe the clinical, analytical manifestations and treatment in a series of patients under follow-up in our unit. Methods: Retrospective cross-sectional observational study of patients with an NBO diagnosis under follow-up in a tertiary hospital. Clinical, radiological and therapeutic characteristics of patients diagnosed between 2002 and 2021 were collected. Results: 15 patients were included in the study, with a median age of 10 years (IQR 2), of which 80% were females. In the period studied, 0.8 diagnoses/year were made, with a delayed diagnosis median of 4 months (IQR 29). 80% of the patients presented multifocal involvement, the most frequent location being the lower limbs (87%), followed by the spine (47%), pelvis (33%) and thorax (33%). The guiding symptom was pain, present in 100% of patients, of which 53% debuted with bone swelling. Other recorded manifestations were skin involvement (40%, of which 33% included psoriasis), fever (33%) and inflammatory bowel disease (13%). Acute phase reactants presented mild-moderate elevation at the onset of the disease in approximately 50% of patients, which presented an average CRP of 2.1 ± 1,3 mg/dl and ESR of 69 ± 30 mm, with normalization after the start of the treatment. 80% of the patients provided a bone biopsy at the time of referral to Rheumatology. MRI was the diagnostic radiological test used in all cases (whole-body MRI since it became available). Regarding treatment, 67% were treated with antibiotics and 93% with NSAIDs without clinical response. Half received corticosteroids, achieving symptomatic control that only one patient managed to maintain after their suspension. 87% of the patients were treated with bisphosphonates, achieving remission of the disease in 3 patients. 73% of the patients received treatment with anti-TNF as a failure to Bisphosphonate except in 2 patients, one of whom had concomitant IBD. Currently, 63% are in clinical remission and 33% are in active treatment. Conclusion: In our study, the majority of patients with ONB were females, with multifocal involvement, of which approximately half started with acute phase reactants elevation. The majority of them received treatment with bisphosphonates and/or anti-TNF, with two thirds of patients achieving remission. Currently, a third continue with treatment. REFERENCES: [1] Buch K, Thuesen ACB, Brons C, Schwarz P. Chronic Non-bacterial Osteomyelitis: A Review. Calcified Tissue International. 2019;104(5):544-53. [2] Zhao Y, Ferguson PJ. Chronic Nonbacterial Osteomyelitis and Chronic Recurrent Multifocal Osteomyelitis in Children. Pediatr Clin North Am. 2018;65(4):783-800. [3] Hofmann SR, Kapplusch F, Girschick HJ, Morbach H, Pablik J, Ferguson PJ, Hedrich CM. Chronic Recurrent Multifocal Osteomyelitis (CRMO): Presentation, Pathogenesis, and Treatment. Curr Osteoporos Rep. 2017 Dec;15(6):542-554. Acknowledgements: NIL. Disclosure of Interests: None declared.