The temporomandibular joint in juvenile idiopathic arthritis: frequently used and frequently arthritic

Initial estimates of the prevalence of TMJ involvement in JIA varied widely, ranging from 25–70%, and were based on cross-sectional analyses primarily using orthopantomograms (OPTs) for diagnosis [4, 9, 10]. The large variation in estimates likely resulted from differences in inclusion criteria, including variable types of JIA, and differences in disease duration (Table 1). Measurement of the prevalence of TMJ disease has been further complicated by the observation that TMJ symptoms and physical examination are not reliable for the assessment of TMJ arthritis and a large proportion of children may be asymptomatic and/or have a normal TMJ examination despite radiographic evidence of TMJ damage. In a prior series, as many as 69% of children with evidence of TMJ damage on OPT have been found to be asymptomatic [11, 12]. Although longer disease duration, younger age at disease onset, decreased mouth opening, decreased or absent translation, pain with mandibular excursion, and crepitus have all been associated with the presence of TMJ damage, the heterogeneity of prior studies makes interpretation of these results difficult [10, 12, 13]. Given the high prevalence of TMJ involvement in JIA, and because many children are asymptomatic despite TMJ damage, investigations have sought to identify specific patient and laboratory characteristics associated with the development of TMJ arthritis. Such patient and laboratory characteristics may help to identify patients at highest risk of TMJ involvement and those most likely to benefit from screening or early intervention.

Data from recent reports have confirmed the relatively high prevalence of radiographic evidence of TMJ involvement in JIA and the low prevalence of patient-reported TMJ symptoms and/or physical exam abnormalities. A recent cross-sectional report of 100 children with multiple JIA types and different disease durations reported condylar damage on the OPTs of 78% of the 46 children who had OPTs performed [6]. In this cohort, 78% of the children who had OPTs performed had evidence of bilateral TMJ involvement. Furthermore, although a relatively large proportion of the entire cohort (70%) reported TMJ symptoms, there was no association between patient-reported symptoms and the presence of damage on OPT. There was also no association found between disease activity (dichotomized as active disease versus inactive disease based on the criteria published by Wallace and colleagues [14]), disease duration, or JIA subtype and the presence of unilateral or bilateral damage. In a similar series of 66 children with polyarticular or oligoarticular JIA, condylar damage on OPT was reported in 50% of the cohort and 35% of this group had bilateral disease [15]. Seventy-five percent of the children with polyarticular JIA had evidence of TMJ damage and 20% of the children with oligoarticular JIA had damage. There was no association between RF, ANA, or HLA-B27 positivity and the presence of TMJ damage. While girls in this cohort tended to have a higher prevalence of TMJ damage, this finding was not statistically significant. Children with polyarticular JIA and children with longer disease duration in this cohort were more likely to have bilateral disease. In contrast, Pederson and colleagues reported that, in a cohort of children with JIA referred for orthodontic evaluation, children with longer disease duration and polyarticular course were more likely to have extensive damage on OPT, while those children who were ANA positive or HLA-B27 positive tended to have less TMJ damage visible on OPT [4]. Although these OPT-based studies reflect a degree of selection bias, they also likely under-represent the extent of TMJ arthritis, as OPT detects evidence of arthritis only after bone damage has already occurred [8].

Studies using magnetic resonance imaging (MRI) with gadolinium enhancement have provided even higher prevalence estimates. A prospective cohort study of 15 children with JIA followed with MRI over 2 years reported that, although the MRI findings tended to fluctuate over time, 14 of the children had evidence of synovial enhancement during the study period [16]. Twenty-five percent of the children in this cohort had normal TMJ exams throughout the follow-up period and 70% of children were asymptomatic. Detailed TMJ exams were performed by the same orthodontist at 6–8 weeks and included assessment of tenderness, swelling, loss of range of motion, and asymmetry. In a more recent, cross-sectional report of 46 children with JIA and widely varying ages (2–37 years) and disease durations (0.3–24.8 years), 32% of participants were reported to have abnormal condyles, 10% had intra-articular fluid, and 45% had enhancing pannus [17]. In this cohort, systemic JIA with a polyarticular course, younger age at onset, and longer disease duration were independent predictors of condylar damage. In a separate report, Weiss and colleagues prospectively screened a cohort of 32 children with newly diagnosed JIA by MRI with gadolinium within 8 weeks of their diagnosis. Seventy-five percent of this cohort had evidence of active TMJ arthritis, defined as effusion and/or synovial thickening, and 69% of this cohort had evidence of chronic TMJ arthritis, defined as abnormal condyles or condylar erosions [18]. Despite the high prevalence of TMJ disease in this cohort, 81% of the children had no TMJ symptoms and 59% had a normal TMJ examination performed by a pediatric rheumatologist, which included assessment of mouth opening, pain, asymmetry, translation, and micrognathia. The positive predictive value (PPV) for TMJ symptoms was 100% whereas the negative predictive value was only 32%. Similarly, the PPV of a normal TMJ exam was 69% and the negative predictive value was only 21%. Eighty-one percent of children with acute TMJ arthritis had bilateral involvement and 68% of children with evidence of chronic TMJ arthritis had bilateral disease. These results were supported by a recent report by Muller and colleagues in which 30 consecutive JIA patients were evaluated by physical exam, orthodontic exam, TMJ ultrasound (US), and TMJ MRI [19]. Sixty-three percent of children in this cohort were determined to have active TMJ disease by MRI. Using MRI as the gold-standard for detection of TMJ disease, the authors reported rheumatological exam had a PPV of 0.85 (0.54–0.97) for the detection of active TMJ disease, orthodontic exam had a PPV of 0.56 (0.31–0.79), and US had a PPV of 0.75 (0.36–0.96). The highest predictive value was for abnormal maximal incisal opening (MIO), and an MIO of < 40 mm had a PPV of 1 (0.56–1.0).

Given the challenges of identifying children with TMJ involvement and those at highest risk of developing TMJ disease, it has been difficult to estimate the incidence of TMJ disease in JIA and very few reports have specifically addressed this question. Recently, Twilt and colleagues screened a series of 89 JIA patients with yearly OPTs and reported the incidence of condylar damage to be 0.071 per patient year in the subgroup of 48 patients who had no evidence of TMJ damage by OPT at baseline [20]. However, screening by MRI with contrast or ultrasound, as discussed below, may yield notably higher incidence rates of TMJ disease in children with JIA than those generated by screening by OPT.

Because the signs and symptoms of TMJ arthritis have been found to be unreliable, radiographic imaging plays a central role in the diagnosis and follow-up of TMJ arthritis. OPT and computed tomography (CT) scanning are both useful in delineating the extent of condylar damage. Computed tomography is generally preferred to OPT because of the shorter exam time and lower radiation dose. However, these modalities cannot distinguish damage due to past disease activity from that associated with ongoing, active disease. Nor can these modalities detect early changes, such as synovial inflammation. To date, scoring systems for condylar damage have been proposed for US, CT, and MRI in TMJ disease [21‐23]. Conversely, although it's detection of condylar damage is limited, MRI performed with gadolinium and ultrasound (US) can detect joint effusion and pannus formation, and therefore can be used to determine whether the arthritis is active [24]. The primary disadvantages to MRI are that younger children may require sedation for the exam and cost is higher than other imaging modalities. Moreover, optimal MRI exams require MRI machines equipped with TMJ-specific surface coils.

Several prior reports have directly compared US and MRI and have reported varying sensitivities and specificities, likely reflecting the operator-dependent nature of US as the high sensitivities for US were reported in studies from Europe where there is more experience with this modality [25, 26]. The use of US in this case is also limited by the anatomy of the TMJ, which allows for probe placement only on the most lateral aspect of the joint. Most recently, US and MRI were directly compared in the series of 32 children with newly diagnosed JIA (described above) [18]. While 75% of children had evidence of active disease by MRI, no children were diagnosed with active TMJ arthritis by US (kappa = 0). Likewise, 69% of participants were found to have evidence of chronic TMJ arthritis on MRI, but only 28% were diagnosed by US (kappa = 0.12). Thus, for most centers, MRI seems to be far more sensitive than US at detecting TMJ arthritis in children with JIA.

Additional studies have attempted to correlate particular physical exam findings and disease characteristics with specific radiographic abnormalities. The series by Billiau and colleagues described above reported that decreased MIOs were more common in children with active disease [6]. One study of 15 children with JIA and minimum disease duration of 3 years followed with MRI and/or OPT for 2 years reported that decreased translation (lateral movement of the mandible at maximal opening) was associated with condylar resorption visible on both OPT and MRI [8]. Furthermore, in this small study, decreased mouth opening was significantly associated with condylar resorption on both MRI and OPT at baseline, but only with OPT at the end of the study. Interestingly, overall TMJ function improved in this cohort over the 2 year follow-up. Mouth opening in this cohort was similar to healthy controls by the end of the 2 years of follow-up, even though the majority of children (80%) had condylar changes on MRI by the end of the study. Based on these observations, the authors proposed the use of translation and mouth opening as a screening technique for early TMJ disease. Argyropoulou and colleagues also reported a significant association between decreased mouth opening and condylar damage on MRI in their series of patients described above [17]. One study of 48 children screened by US reported that children with ≥ 5 active joints were more likely to have US evidence of TMJ arthritis, children with disease duration more than 23 months were more likely to have disc dislocation and/or condylar damage, and children with disease duration more than 60 months were most likely to have condylar damage [27]. Moreover, since three-quarters of the children with JIA were found to have active TMJ disease at onset by MRI, the vast majority of which were asymptomatic, it could be argued that perhaps all children with newly diagnosed JIA should be screened by this approach [18]. In the few patients with follow-up MRIs post-IAS treatment, improvement in the TMJ arthritis was frequently noted [18].

There are to date few descriptions of the evolution of the radiographic findings over time. Twilt and colleagues reported improvement in 27 out of the 89 patients who were followed up for a mean of 14 months [20]. Nineteen patients had normal OPTs at the end of the study and 4 patients had evidence of worsening changes. Disease activity, as measured by physician-reported visual analog scale, was lower in the patients who demonstrated improvement. Systemic medication use in this cohort was not reported; however, a substantial number of patients had splinting and none of these patients underwent IAS during the study period. After 5 years of follow-up of this same cohort, 83% of patients had evidence of improvement of their condyles on OPT, and the overall prevalence of abnormal condyles in the study cohort decreased from 49 to 40%, again indicating a trend towards improvement in previously visualized damage [28]. Although children with TMJ damage were more likely to receive immunosuppressive medications and biological agents, treatment effects could not be assessed in this study. Moreover, the response of TMJ arthritis to systemic TNF inhibitory therapy in children with JIA is unknown at present.

Recently, cone-beam CT has been proposed as a novel way of delineating the extent of condylar damage. This technique uses specialized CT to create detailed images of the condyle and estimates of condylar volume and results in lower radiation exposure to the patient than conventional CT [29]. Twenty children were evaluated with this technique. JIA subtype and disease history were not detailed for the patients. The investigators reported significant asymmetry, defined as differences in shape or volume, of the condyles of these children. At present, this degree of detail may be more useful for research rather than for routine clinical care [30].

Historically, TMJ arthritis in children has been treated with splinting and/or surgical techniques intended to compensate for the poor mandibular growth, with variable outcomes [31].