Response to a Letter by M. Slouma Et Al

A letter by Slouma et al highlights several important matters regarding the recently reported association of serum levels of interleukin (IL)-22 with the clinical diagnosis of axial spondyloarthritis (AxSpA).1 While the full spectrum of action and pathological significance of IL-22 has not been fully elaborated, the involvement of this cytokine in the pathogenesis of various systemic disorders has been demonstrated or suggested. Thus, the potential diagnostic utility of this test should be limited to the differentiation of AxSpA from non-inflammatory conditions, such as osteitis condensans ilii, fibromyalgia and myofascial pain, enthesopathy, facet joint disease, and diffuse idiopathic systemic hyperostosis, which were diagnosed in this study in the group of patients with an alternative to AxSpA diagnosis. We completely agree with Slouma et al that the presence of some chronic systemic disorders can cause a bias in the interpretation of the test. Thus, it is important to mention that none of the enrolled patients was diagnosed with any malignant or chronic disease with possible inflammatory pathogenesis, excluding 3 smokers with mild chronic obstructive pulmonary disease; serum levels of IL-22 were at the low end in these patients. The IL-22 levels did not depend on the presence of peripheral arthritis, uveitis, psoriasis, or inflammatory bowel disease in our study; however, the numbers of patients with the extra-spinal manifestations were too low to make statistical calculations. The total sample size of the study was also judged to be insufficient for making final recommendations on the practical utilization of IL-22 test for AxSpA diagnosis, and as it was advocated by Slouma et al, and also acknowledged in the manuscript, further prospective studies examining the diagnostic utility of IL-22 testing in patients with suspected AxSpA are warranted. The authors declare no conflict of interest.