Diagnostic Accuracy of Interleukin-17A for Internal Derangements of Temporomandibular Joints in Patients with Spondyloarthritis

<b>Objective</b>: The oral cavity is the beginning of the digestive tract and the composition of saliva could indicate immune events in the gut and joints. The objective of this research was to evaluate the diagnostic accuracy of salivary interleukin (IL)-17A for temporomandibular joint (TMJ) internal derangements (IDs) in patients with spondyloarthritis (SpA). <b>Methods</b>: SpA disease activity was assessed using the Bath Ankylosing Disease Activity Index (BASDAI), Ankylosing Spondylitis Disease Activity Score (ASDAS) and Disease Activity Index for Psoriatic Arthritis (DAPSA). Salivary cytokines were analyzed using enzyme-linked immunosorbent assay. TMJ conditions were evaluated using The Diagnostic Criteria for Temporomandibular Disorder (DC/TMD) protocol. A symptomatic TMJ-ID group with intracapsular arthralgia (<i>n</i> = 64) and asymptomatic TMJ-ID group without intracapsular arthralgia (<i>n</i> = 50), regardless of joint sounds, were compared with controls (healthy TMJs, <i>n</i> = 86). <b>Results</b>: Women were more prevalent and salivary IL-17A concentration was higher in both ID groups than in controls. Salivary IL-17A levels positively correlated with erythrocyte sedimentation rate, anti-streptolysin-O titer, salivary IL-12/23 p40 and matrix metalloproteinase-3 levels, sore and swollen joint counts, BASDAI, chronic TMJ pain and anxiety. IL-17A demonstrated diagnostic accuracy for currently symptomatic (cutoff, 11 pg/mL) and asymptomatic (cutoff, 11.6 pg/mL) TMJ-ID vs. controls. Patients with IL-17A levels above these cutoffs more frequently exhibited disc displacement with reduction and degenerative TMJ disease, higher self-reported spinal pain and higher SpA activity, as assessed by ASDAS, than patients with IL-17A levels ≤ cutoffs. TMJ-related headache and somatization contributed to greater TMJ pain in those with IL-17A > cutoffs, when compared with dichotomous controls. <b>Conclusions</b>: Salivary IL-17A concentration provides an accurate laboratory marker of SpA activity and enables the diagnosis of both currently symptomatic and asymptomatic TMJ-IDs in patients with SpA.