Data from a multicentric international study unveils a neglected association between chronic non-bacterial osteomyelitis and inflammatory bowel diseases.

Objectives: We aimed to evaluate the clinical, serological, radiological characteristics and response to treatments of patients with chronic non-bacterial osteomyelitis (CNO) associated with inflammatory bowel diseases (C-IBD) in comparison to CNO patients without gastrointestinal disease.

Methods: Patients with C-IBD followed in the Rheumatology Department of the Istituto Gaslini, Genova, and Hacettepe Hospital, Ankara, were retrospectively enrolled in the Eurofever Registry and compared to a group of CNO patients. A literature review on paediatric C-IBD was also performed.

Results: 19 C-IBD patients were compared to 57 CNO. In C-IBD, disease onset was characterised by osteoarticular symptoms in 73.6%, by gastrointestinal symptoms in 10.5%, and was simultaneous in 15.8%. Spinal involvement was more frequent in CNO (p<0.05), while sacroiliac involvement was more frequent in C-IBD (p<0.005). 42% of C-IBD presented low-grade fever (p<0.05, 15% of CNO). All C-IBD presented a CRP elevation, present in only 45% of CNO (p<0.0001). In 68.4% of C-IBD, CRP remained elevated and became negative only after IBD treatment was started. Moreover, 58% of C-IBD patients presented microcytic anaemia (present in 17.6% CNO, p=0.0005). Fecal calprotectin resulted positive in 100% of C-IBD and 10% of CNO (p<0.0001).

Conclusions: This is the largest cohort of paediatric C-IBD reported in the literature. The persistence of inflammation and the presence of microcytic anaemia were associated with the development of an IBD. Given the frequent absence of intestinal symptoms, screening with fecal calprotectin is suggested in all CNO patients that present a persistent CRP elevation despite treatment, and have microcytic anaemia.