Quantifying Synovial Enhancement of Temporomandibular Joints From MRIs of Patients With Juvenile Idiopathic Arthritis

Juvenile Idiopathic Arthritis (JIA) is the most common pediatric rheumatic disease and often affects the temporomandibular joints (TMJ). The TMJ may be asymptomatic until irreversible changes occur. Synovitis is the most common early finding of inflammatory arthritis, and magnetic resonance imaging (MRI) with gadolinium is the most sensitive and specific diagnostic tool ¹. While synovitis is a good indicator of disease, some authors are hesitant to rely on this measure because of absence of a standardized method to differentiate MRIs of normal joints with synovial enhancement from those with synovitis due to inflammatory arthritis. Determining the presence of synovitis from an MRI is also subjective and severity is typically reported qualitatively, resulting in inter-examiner variability in the assessment of disease. We recently developed a method to quantify TMJ synovial enhancement as a ratio of signal enhancement to the longus capitus muscle in the normal TMJ² . The purposes of this study were to apply this technique to MRIs of TMJs affected by JIA and to controls in order to establish a disease threshold, sensitivity and specificity for synovial enhancement.

This is a multicenter case-control study of children (≤16 years) who had MRIs with gadolinium that included the TMJs from 2006-2014. Subjects were included in the ‘JIA group’ if had a diagnosis of JIA and their TMJ MRI subjectively demonstrated synovitis on at least one side. The ‘control group’ included subjects without JIA who had an MRI for other reasons. Coronal slices of a T1-weighted, gadolinium-enhanced MRI containing the TMJ were used to assess the ratio of signal intensity of a 0.2mm² region of interest (ROI) within the upper and lower joint space to a 50mm² ROI within the longus-capitus mucle, which controls for time after gadolinium infusion. A receiver operating characteristic (ROC) curve was used to determine the sensitivity and specificity of the ratio of enhancement. Independent 2-sample t test (2-tailed) was performed for each group with unequal variance assumed. Statistical significance was set at p<0.05.

Seventy-four subjects with JIA (82% female, mean age 13.19 ± 3.78) with 114 MRIs with clear visualization of 211 TMJs were included in the JIA group. The control group consisted of 71 subjects (54% female, mean age 11.4 ± 3.5) with 71 MRIs with clear visualization of 142 TMJs. The mean signal intensity ratio in the JIA group was 2.52 ± 0.79 compared to 1.28 ± 0.16 in the control group (p<0.001). The ROC analysis indicated a sensitivity of 91% and specificity of 94% in detecting synovitis with a signal intensity ratio cutoff value of 1.55.

Comparing signal intensity of TMJ synovium to the longus capitis muscle is a reliable method for assessment of synovial enhancement. A signal intensity ratio of 1.55 discriminates TMJs affected by JIA from unaffected controls with high sensitivity and specificity.

References:

1. Abramowicz S, Cheon JE, Kim S, Bacic J, Lee EY: Magnetic resonance imaging of temporomandibular joints in children with arthritis. J Oral Maxillofac Surg 2011, 69(9):2321-2328.
2. Peacock ZS, Vakilian P, Caruso P, Resnick CM, Vangel M, Kaban LB: Quantifying synovial enhancement of the pediatric temporomandibular joint. J Oral Maxillofac Surg (Accepted for publication March 14, 2016)