Poster Session II - A253 CLINICAL CHARACTERISTICS OF INFLAMMATORY BOWEL DISEASE IN PATIENTS WITH CHRONIC NONBACTERIAL OSTEOMYELITIS: A CASE SERIES

Abstract Background Chronic nonbacterial osteomyelitis (CNO) is a rare pediatric autoinflammatory bone disorder characterized by relapsing aseptic inflammation. CNO is increasingly recognized as an extraintestinal manifestation of inflammatory bowel disease (IBD), most commonly Crohn’s disease (CD) Aims To describe the clinical features, management and outcomes of patients with concomitant CNO and IBD at the Montreal Children’s Hospital. Methods We conducted a retrospective chart review of patients <18 years of age at our centre diagnosed with CNO between 2019-2025 and identified those with co-existing IBD. Data was collected on time of diagnosis, clinical and laboratory characteristics and treatment Results We identified 31 patients with CNO and among these 4 (13%) had both CNO and IBD. The cohort included 2 males and 2 females. The mean age at CNO diagnosis was 10.5 years (range 9–13), and the mean age at IBD diagnosis was 12.3 years (range 11–14). The interval between both diagnoses ranged from 2 months to 5 years (mean 2.3 years). CD was the predominant phenotype (3/4 patients), while one case was classified as IBD-U. Paris classification among CD patients included L3 and L4b phenotypes. Three out of 4 patients were asymptomatic at the time of diagnosis of IBD, while one had symptoms of abdominal pain and diarrhea. The number of CNO lesions per patient ranged from 3 to 14 (mean 7.75, SD 4.6). Lesions most frequently involved the pelvic girdle and lower extremities. Laboratory data showed mild anemia in half of the patients (mean Hb 120.5 g/L, range 111–133), with elevated inflammatory markers (ESR, CRP) in only 2 patients. Fecal calprotectin levels were markedly elevated in all tested patients (range 507–2100 µg/g). Initial CNO therapy consisted of nonsteroidal anti-inflammatory drugs (naproxen) in three patients, and infliximab (as part of IBD management) in one. Three of 4 patients were started directly on a biologic (adalimumab or infliximab) for treatment of their IBD while one patient was treated initially with mesalamine and methotrexate and was subsequently escalated to an anti-TNF. One patient required a change to ustekinumab due to refractory GI tract inflammation in the absence of clinical symptoms. At last follow-up, 3/4 (75%) achieved CNO remission, whereas IBD remained active in 3/4 (75%) Conclusions This study illustrates the importance of considering a diagnosis of IBD in patients with CNO even in the absence of clinical symptoms. Furthermore, therapeutic responses differ, with anti-TNF agents more consistently achieving bone remission than intestinal control in this cohort. Larger studies are needed to better understand the links between these conditions and to optimize therapeutic strategies Funding Agencies None