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

## TL;DR

This study shows that measuring salivary interleukin-17A can accurately detect joint issues in spondyloarthritis patients, even when symptoms are not present.

## Contribution

The study introduces salivary IL-17A as a novel diagnostic biomarker for temporomandibular joint derangements in spondyloarthritis patients.

## Key findings

- Salivary IL-17A levels were higher in patients with TMJ internal derangements compared to controls.
- IL-17A demonstrated diagnostic accuracy for both symptomatic and asymptomatic TMJ-IDs with specific cutoffs.
- Higher IL-17A levels correlated with increased disease activity and pain in spondyloarthritis patients.

## Abstract

Objective: 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). Methods: 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 (n = 64) and asymptomatic TMJ-ID group without intracapsular arthralgia (n = 50), regardless of joint sounds, were compared with controls (healthy TMJs, n = 86). Results: 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. Conclusions: 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.