Relationship between faecal calprotectin and inflammation in peripheral joints and entheses in axial spondyloarthritis.

Objectives: To compare faecal calprotectin levels according to the type of manifestation and to investigate factors associated with increases in faecal calprotectin in patients with axial spondyloarthritis (axSpA). Method: The study enrolled 190 patients fulfilling the imaging arm of the Assessment of SpondyloArthritis international Society axSpA criteria. Faecal calprotectin levels were measured in an enzyme-linked immunosorbent assay. Systemic inflammatory markers and the Ankylosing Spondylitis Disease Activity Score (ASDAS) were also assessed. Peripheral joint involvement was assessed using the 44-joint examination and Spondyloarthritis Research Consortium of Canada Enthesitis Index. Results: Of 190 patients, 34 (18%) had increased faecal calprotectin levels. These patients were more likely to have ongoing peripheral arthritis and enthesitis (p = 0.016 and 0.001, respectively). A history of psoriasis and uveitis, or current uveitis symptoms, had no bearing on faecal calprotectin levels. Faecal calprotectin levels increased along with ASDAS-C-reactive protein (CRP), and correlated with ASDAS-erythrocyte sedimentation rate (ESR) (r = 0.240, p = 0.001), ASDAS-CRP (r = 0.162, p = 0.025), ESR (r = 0.228, p = 0.002), and CRP levels (0.258, p < 0.001). Tender joint and swollen joint counts also correlated with faecal calprotectin levels (r = 0.252 and 0.205, p < 0.001 and p = 0.005, respectively). Faecal calprotectin levels were higher in patients with current peripheral symptoms (p = 0.003). Peripheral symptoms were independently associated with increased faecal calprotectin levels (odds ratio = 4.083; 95% confidence interval 1.580-10.556). Conclusions: Faecal calprotectin levels in axSpA patients were associated with disease activity. Subclinical gut inflammation (assessed by measuring faecal calprotectin) in axSpA is more closely related to peripheral joint inflammation than to axial joint inflammation.