The Increased Levels of Faecal Calprotectin in Children With Active Enthesitis Related Arthritis and Mri Signs of Sacroiliitis: the Results of A Single Centre Cross-Sectional Study in Juvenile Idiopathic Arthritis Patients

Background: Enthesitis related arthritis (ErA) is a specific subtype of juvenile idiopathic arthritis (JIA) which is often regarded as an undifferentiated form of juvenile spondyloarthritis (jSpA). Beside the arthritis of the peripheral joints, the crucial features of jSpA include enthesitis and/or arthritis of axial joints. Moreover, in adult onset spondyloarthritis gut is increasingly recognized as origin and/or target of inflammation, while the incidence of gut involvement in ErA patients is still largely unknown. The aim of this study was to assess the fCAL concentration, a surrogate marker of gut inflammation, in patients with various subtypes of JIA and non-inflammatory musculoskeletal conditions and to assess the correlation with various demographic, clinical, laboratory, imaging and treatment characteristics.Methods: This was a cross-sectional study involving 71 patients with various forms of JIA and other noninflammatory musculoskeletal diseases (NI-MSD). Along with detailed clinical and laboratory examination, fCAL and magnetic resonance imaging (MRI) of sacroiliac joints, thoracic and lumbar spine was routinely performed in all ErA patients, as well as in other patients who complained of abdominal and/or back pain, respectively. In all JIA patients, disease activity was measured using the juvenile arthritis (JADAS) or spondyloarthritis (jSpADA) disease activity score. Results: The median concentration of fCAL was highest in ErA subgroup (33.2 mg/kg, p=0.043), with a significant difference between patients with inactive and active disease (20.0 mg/kg vs 57.4 mg/kg, p=0.01), as well as between those with or without MRI signs of SIJ inflammation (22.6 mg/kg vs 54.3 mg/kg, p=0.048). In all patients, the fCAL concentration did not significantly differ among those receiving and not receiving NSAIDs (23 mg/kg vs 20 mg/kg, p=0.18), although weak correlation was found with the duration of the use (r=0.25, p=0.03).Conclusion: The (subclinical) gut inflammation might not be present only in adults with SpA, but also in children with undifferentiated forms of the jSpA, especially with active disease and/or MRI signs of SI inflammation.