Assessing Joint Damage in Children with Arthritis

A study in Pediatric Rheumatology suggests a possible method for differentiating mild synovitis from normal temporomandibular joints (TMJ) in children with juvenile idiopathic arthritis (JIA).

JIA is the most common rheumatologic disease of childhood. The TMJ is particularly susceptible to damage in JIA patients, but early detection and treatment of that damage is complicated due to the often asymptomatic nature of TMJ arthritis. Typically, detection of synovitis is made through magnetic resonance imaging with contrast enhancement and graded as absent, mild, or moderate/severe. But there are lingering clinical questions regarding what level of synovial enhancement defines mild TMJ arthritis as compared to normal enhancement in children.

The current retrospective study used the non-affected TMJs of non-rheumatologic subjects as controls, alongside an examination of the TMJs of JIA patients without any evidence of active inflammation on MRI, in an effort to distinguish between the various degrees of TMJ inflammation using quantitative measurements of synovial and condylar enhancement.

The researchers retrospectively assessed TMJ MRI examinations in 67 children with JIA and in 24 non-rheumatologic children who underwent MRI for neurologic/orbit indications. The signal intensity (SI) of the synovial tissue around each condyle and of the bone marrow was measured to calculate the enhancement ratio (ER) and relative SI change. The ER was calculated using signal to noise ratios, while relative SI change was calculated using signal intensities alone. Mean ER values were significantly different between the TMJs without active disease and those with mild and moderate/severe synovial enhancement, with highest values in the moderate/severe group (P&thinsp;<&thinsp;0.0001).

“Our results [suggest] that specific ER values may be useful as cutoffs to aid in distinguishing TMJs with mild involvement (in terms of synovial and condylar enhancement) from those without evidence of active disease on MRI,” the researchers noted. “We propose that the synovial ER threshold of 0.6 with a sensitivity of 80% and specificity of 75% may be a reliable predictor of the presence of active synovitis. This method of quantitative TMJ assessment had excellent inter- and intra-reader reproducibility. There is currently a controversy regarding whether any synovial or condylar enhancement is pathologic or physiologic in children. Although previous studies have regarded any enhancement to be pathological in children and adults, in our study TMJs without active arthritis were found to have some degree of synovial enhancement on signal to noise and signal intensity measurements.”

Although TMJs with a greater degree of synovial enhancement were associated with higher mean condylar enhancement ratios, a significant portion of the study population (36%) with synovial enhancement did not demonstrate any condylar enhancement on qualitative assessment, suggesting that the absence of condylar enhancement does not necessarily exclude the presence of active TMJ inflammation.

The researchers hope the findings will lead to greater use of quantitative signal to noise ratios of the degree of temporomandibular joint synovial and condylar marrow enhancement using static MRI in the coronal plane generate thresholds and tendencies alongside subjective visual assessment to aid in the diagnosis of mild active temporomandibular joint involvement. “Such quantitative measures may also allow us to more accurately compare imaging findings to assess responses to treatments and help us to direct further interventions, as needed, for children and adolescents with juvenile idiopathic arthritis,” the authors conclude.