Quantifying Temporomandibular Joint Synovitis in Children With Juvenile Idiopathic Arthritis

Abstract

Objective: Juvenile idiopathic arthritis (JIA) frequently affects the temporomandibular joints (TMJs) and is often undetected by history, examination, and plain imaging. Qualitative assessment of gadolinium-enhanced magnetic resonance images (MRIs) is currently the standard for diagnosis of TMJ synovitis associated with JIA. The purpose of this study is to apply a quantitative analysis of synovial enhancement to MRIs of patients with and without JIA to establish a disease threshold and sensitivity and specificity for the technique.

Methods: This is a retrospective case-control study of children (age ≤16 years) who had MRIs with gadolinium including the TMJs. Subjects were divided into a JIA group and a control group. From a coronal T1-weighted image, a ratio (enhancement ratio [ER]) of the average pixel intensity within three 0.2-mm² regions of interest (ROIs) in the TMJ synovium to that of a 50-mm² ROI of the longus capitis muscle was calculated. Receiver operating characteristic curves were used to determine the sensitivity and specificity. The inter- and intraexaminer reliability was evaluated with Bland-Altman plots and 2-way mixed, absolute agreement intraclass correlation coefficients.

Results: There were 187 and 142 TMJs included in the JIA and control groups, respectively. An ER threshold of 1.55 had a sensitivity and specificity for detecting synovitis of 91% and 96%, respectively. The inter- and intraexaminer reliability was excellent.

Conclusion: Calculating a ratio of pixel intensity between the TMJ synovium and the longus capitis muscle is a reliable way to quantify synovial enhancement. An ER of 1.55 differentiates normal TMJs from those affected by inflammatory arthritis.

Figure 1

T1‐weighted gadolinium‐enhanced magnetic resonance image (coronal view) of a healthy 10‐year‐old boy without temporomandibular joint (TMJ) pathology. The inferior (arrowheads) and superior (arrows) joint spaces are shown bilaterally. Regions of interest used to calculate the enhancement ratio (ER) are indicated at the right inferior TMJ space (circle) and left longus capitis muscle (ellipse). ER = 1.33 (left) and 1.21 (right).

Figure 2

T1‐weighted gadolinium‐enhanced magnetic resonance image (coronal view) of a 14‐year‐old boy with juvenile idiopathic arthritis and inflammatory temporomandibular joint (TMJ) arthritis. The superior (arrows) and inferior (arrowheads) joint spaces are shown bilaterally. Regions of interest used to calculate the enhancement ratio (ER) are indicated at the inferior right TMJ space (circle) and left longus capitis muscle (ellipse). Qualitative radiologist interpretation noted moderate to severe bilateral TMJ synovial enhancement. Quantitative analysis found ER = 2.48 (right) and 2.52 (left).

Figure 3

Receiver operating characteristic curve for synovial enhancement ratio (ER), indicating an area under the curve (AUC) of 0.959 (95% confidence interval [95% CI] 0.937, 0.980; P < 0.001), sensitivity of 91%, and specificity of 96%, for an optimal threshold value of ER = 1.55.

Figure 4

Probability curve derived from logistic regression analysis, demonstrating a high likelihood of juvenile idiopathic arthritis (JIA) for an enhancement ratio ≥1.55 (65%), 1.70 (85%), 1.90 (96%), and 2.00 (98%).