Rheumatoid arthritis (RA) is an intricate autoimmune inflammatory disease of the joints. The varied effects of RA may exhaust patients and challenge clinicians. RA occurring in children below the age of 16 is referred to as juvenile idiopathic arthritis (JIA). The temporomandibular joint (TMJ) is one of the most frequently affected joints in RA. However, the prevalence of TMJ involvement has been reported to range between 17% and 90% [1-3]. Activated inflammatory pathways lead to the overproduction of pro-inflammatory cytokines, inducing joint destruction [4]. Long-term accumulated joint damage is closely related to permanent bony changes and joint dysfunction. This damage decreases patients’ responsiveness to treatments, such as medication [5]. Thus, early therapeutic intervention is critical to improve clinical outcomes and prevent further progression to late-stage RA with joint disability.

For patients with JIA, a proper approach in the early stage of the disease is especially important. The common symptoms of TMJ osteoarthritis (OA), such as joint pain, sound, swelling, and progressive joint destruction, can significantly affect growing children, leading to psychological distress, malocclusion, and growth disturbances of the maxilla and mandible [2,5,6]. Clinically, the RA symptoms affecting the TMJ are similar to the OA symptoms in the TMJ. However, RA is a systemic disease that can affect other joints. Progressed and polyarticular RA can have more adverse effects on the systemic conditions of growing children than those in adults. Conversely, early detection and monoarticular RA are relatively reactive to treatments and demonstrated better prognoses [6]. Thus, early detection and JIA management may determine the success and failure of subsequent treatments, and clinicians must consider the possibility of JIA when managing children with clinical symptoms of arthritis.

Despite its importance, early detection of JIA is challenging and is even more complicated because structural changes in the early stages of RA (ERA) are not apparent in radiological images [7]. For the differential diagnosis of ERA, clinical symptoms such as joint pain, stiffness, and swelling are considered. However, the clinical symptoms of ERA are usually insidious and do not always correlate with radiological bony changes. This increases the difficulty of differential diagnosis between RA and other joint diseases. The confirmation of RA diagnosis requires laboratory tests to check for RA inflammatory markers, and additional imaging such as bone scintigraphy is useful for determining the active inflammatory state of the TMJ [8]. This study reports a case in which the TMJ had no pathologic findings on cone-beam computed tomography (CBCT) images; however, JIA was later diagnosed based on bone scan and blood tests.

A 14-year-old male visited the Department of Orofacial Pain and Oral Medicine at the affiliation hospital with chief complaints of bilateral TMJ pain and sound. The symptoms began 1 year prior to the initial visit. The patient had no significant past medical history, and no family history of RA was observed on either his maternal or paternal side. The patient experienced bilateral TMJ pain and slight malocclusion, especially in the morning and after mastication. Pain was ranked as 5 on the Visual Analog Scale (VAS=0-10). Radiological examination of bilateral TMJs was unremarkable without morphological changes (Fig. 1). Oral and clinical examinations showed stable occlusion (Fig. 2). The patient complained of bilateral TMJ and masseter muscle pain during mouth opening, but the TMJ sound was not reproduced. The mouth opening pathway and range of motion/extent were within normal ranges. Palpation provoked pain in the bilateral masseter muscle and TMJ capsular areas. Considering that the TMJ sound reported by the patient was not reproduced during the examination, a differential diagnosis between simple arthralgia and degenerative joint diseases was necessary.

During the initial visit, a symptom checklist-90-revised (SCL-90-R) instrument was used, and bone scan, CBCT, and blood tests were conducted for further evaluation. Baclofen (10 mg, twice daily), aceclofenac (100 mg, twice daily), and prednisolone (5 mg, once per day) were prescribed for 5 days to manage pain and muscle stiffness. The psychological profile of the SCL-90-R result was unremarkable; all nine dimensions were in the normal range. The CBCT images revealed no significant bony changes in either TMJ (Fig. 3). However, the bone scan showed increased radiotracer uptake in both TMJs, which was indicative of bilateral TMJ OA (Fig. 4). Furthermore, blood tests showed an RA factor of 82.4 IU/mL, which is more than four times the normal range (Table 1). Considering these results, the final diagnosis was JIA (more specifically, bilateral TMJ ERA).

For JIA management, a mixture of 2% lidocaine and dexamethasone was administered via injection to both TMJs. In addition, a stabilization splint was created. The patient was referred to the Department of Rheumatology for further evaluation of ERA, which included additional laboratory tests for autoimmune antibodies and radiological images of other joints, including the foot and ankle. The additional radiographs showed no bony changes in other joints, and autoimmune antibodies were not detected; thus, the patient was scheduled for routine follow-up appointments to monitor the ERA. After fitting of the stabilization splint and giving instruction regarding its use, the patient was scheduled for monthly follow-up appointments to evaluate the symptoms, and regular blood tests were scheduled every 3 months. Early in the follow-up, the patient’s symptoms varied at every visit. Therefore, intra-articular injection and physical therapy were performed on an as-needed basis for pain. A bruxofacet was observed on the stabilization splint, which led to the suspicion of night clenching or bruxism as a contributor to symptoms. The serial blood test results revealed a temporary increase in the RA factor to 119 IU/mL. However, the RA factor decreased to 66.6 IU/mL at the 1-year follow up. The vitamin D levels (7.42-13.74 ng/mL) were lower than the normal range (30-100 ng/mL) in all four blood test results. About 14 months after the initial visit, the patient had no pain in the TMJs; however, the masseter muscle pain has persisted. Therefore, even with improved symptoms and laboratory test results, we will continue regular follow-up checks. This case study was approved by the Institutional Review Board of the Kyung Hee University Dental Hospital (IRB no. KH-DT22032). Informed consent was obtained from the patient.

This report presents the case of a 14-year-old patient with bilateral TMJ RA. The TMJs exhibited no morphological changes on CBCT images; therefore, bone scan and laboratory tests played a crucial role in distinguishing RA from simple arthralgia. To manage RA, intra-articular injections and and co-evaluation with the Department of Rheumatology were performed, and stabilization splints were created. After 14 months of treatment, the patient’s symptoms and laboratory test results improved.

Among pediatric rheumatologic diseases, JIA is the most common autoimmune disease occurring before the age of 16. The global prevalence of JIA is estimated at between 3.8 to 400 patients for every 100,000 children [9]. The effect of JIA on the TMJ widely varies; reports have indicated that the TMJ is involved in 17% to 87% of patients with JIA [10-12]. Because the TMJ is one of the most frequently affected joints in patients with JIA, clinicians should be mindful of the possibility of JIA when treating young patients with TMD. Incipient arthritis does not often lead to bony changes in the joints; thus, clinical symptoms are key to diagnosing JIA. Symptoms may include joint and palpation pain, TMJ sounds, limited jaw opening, swelling, and warmth in the TMJ area [4,5,8]. If clinical symptoms are observed and RA is suspected, blood tests need to be conducted to confirm RA. The most common diagnostic blood test is evaluation of the RA factor. However, because RA can be detected in healthy older adults or in patients with other diseases, such as hepatitis C, additional blood tests, including anti-nuclear antibody, anti-cyclic citrullinated peptide antibodies, and C-reactive protein, are recommended after RA factor detection [2].

Furthermore, radiological examination is necessary to confirm JIA. In conventional radiological imaging studies, such as panoramic views and CBCT, patients with TMJ OA often demonstrate bony changes of the condyle and articular fossa, including flattening, erosion, osteophytes, and sclerosis. Previous studies have demonstrated that these typical radiological findings have also been observed in patients with JIA [4,5,7,12]. However, patients with early-stage JIA often show no morphological changes in the bone, as in our case. CBCT can only reveal progressive bony changes, which are not always proportional to the progression and symptoms of OA [13]. Similar to our case, in a suspected diagnosis of OA due to clinical symptoms, but with unremarkable radiological findings, a bone scan is recommended. Bone scans are useful for evaluating the real-time inflammatory state of joints, which is a clear sign of arthritis [8]. In OA, bone scan can detects subchondral bony changes, which is the initial pathogenesis of OA and is often not seen in conservative radiographs, such as panoramic images [14]. In JIA, only 40% to 85% of patients have rheumatoid biomarkers in blood tests, and often in the early stage, there are no morphological changes in the joints [10]. Bone scan was proven to be useful in ERA cases, in which patients do not satisfy the diagnosis criteria of the 2010 American College of Rheumatology/European League Against Rheumatism due to insufficient clinical symptoms [15]. Thus, bone scans enable a clear differential diagnosis of arthritis, particularly in cases without bony changes or serous rheumatoid biomarkers.

When JIA of the TMJ is confirmed, the first-line treatment plan is conservative, considering the patients’ young age. Non-steroidal anti-inflammatory drugs and corticosteroids are commonly recommended, and additional disease-modifying anti-rheumatic drugs, such as methotrexate, interleukin inhibitors, and tumor necrosis factor inhibitors, can be considered [12,16]. Furthermore, concomitant with oral administration, intra-articular corticosteroid injection has been reported to effectively reduce the inflammatory state of the TMJ and prevent mandibular condyle growth alterations in patients with JIA [12,17]. Intra-articular injections can improve arthritis and increase mouth opening without complications, such as chondrolysis and ankylosis. Vitamin D is a secosteroid hormone essential for calcium absorption and bone mineralization, and the vitamin D level in the blood is positively related to bone mineral density [18]. Deficient vitamin D levels are reportedly unfavorable in patients with TMD, and vitamin D supplementation is effective in pain reduction [19]. In the present case report, the VAS score and subjective pain level decreased; however, the vitamin D level decreased from baseline more than 1 year later. Further studies are required to elucidate the relationship between vitamin D levels and TMJ pain.

Occlusal stabilization splints are effective in patients with JIA of the TMJ. Although the definite mechanism and extent to which the splint is effective remain controversial, many reports indicate that stabilization splints can alleviate arthritis-related orofacial pain and symptoms [17]. In fact, only a limited correlation exists between improved clinical symptoms with a stabilization splint and improved image-verified signs of TMJ inflammation [7,17].Considering this, the use of stabilization splint can be much more effective when combined with anti-inflammatory therapies, such as oral medications and intra-articular injections.

The final goal of JIA management is to prevent progression to joint destruction, which can lead to serious complications, such as malocclusion and growth disturbance. Clinicians must consider the necessary treatment to achieve this goal. However, early-stage JIA is easily overlooked due to often unremarkable radiological images. For early detection, clinicians must always be mindful of the clinical symptoms, such as pain, and signs, such as blood test results, of JIA. Furthermore, additional diagnostic tests such as bone scans and autoimmune antibody tests should be conducted as needed. Even if JIA is confirmed and symptoms improve after accurate diagnosis and treatment, it is an idiopathic disease that can worsen at any time. Thus, clinicians practicing in the pediatric population must be vigilant and schedule regular follow-up appointments until the patient has reached the end of growth. The clinician, patients, and parents all play a role in monitoring JIA. Along with medical treatment, clinicians should instruct patients and parents regarding JIA precautions. The intimate cooperation between clinicians and patients/patients’ families can lead to the complete management of JIA.

No potential conflict of interest relevant to this article was reported.

This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (No. NRF-2020R1F1A1070072).

The authors extend their special thanks to Jung-Pyo Hong of the Department of Orofacial Pain and Oral Medicine, Kyung Hee University Dental Hospital.

Conceptualization: YHL. Data curation: TSK, YHL. Formal analysis: TSK, YHL. Funding acquisition: YHL. Methodology: YHL. Project administration: YHL. Visualization: TSK, YHL. Writing original draft: TSK, YHL. Writing review & editing: YHL.