Surface electromyography in the evaluation of temporomandibular involvement in Juvenile Idiopathic Arthritis

Introduction: Juvenile idiopathic arthritis (JIA) frequently affects also the temporomandibular joints (TMJ), potentially leading to condylar lesions. Condylar erosion can progress insidiously and alter the masticatory function and, in some cases. also the craniofacial profile. Even though bone alterations are best detected by Computed Tomography (CT), such investigation should be prescribed carefully, since it exposes the patient to ionizing radiation. In the last years, surface electromyography (SEMC) has been increasingly used to evaluate temporomandibular disorders. but its diagnostic accuracy is still questioned. Objectives: Our aim is to assess whether. in patients affected by JIA, SEMG findings of masticatory muscles correlate with condylar erosion as documented by cone beam CT scans of the TMJ. Methods: We retrospectively reviewed the medical records by JIA patients who were addressed to an orthodontist due to the presence of signs and symptoms of temporomandibular involvement. Patients who performed both a cone beam CT scan of the TMJ and a SE.MC of masseter and temporal muscles within a 6 month period were included in the study. Severity of TMJ condylar erosion was classified from grade 0 (absence of erosion) to grade 4 (extensive erosion). Each of the masseter and temporal muscles was classified as normotonic, hypotonic or hypertonic. Cone beam CT scan was considered pathologic if the grade of erosion was > 0. SEMG was considered pathologic If at least three of the examined muscles showed altered tone. Using CT as the gold standard to detect condylar lesions, we calculated sensitivity and specificity of SEMG examination. Results: Eighteen patients were included in the study, 13 females and 5 males. Mean age at onset of JIA was 5.9 + 3.8 years. The most represented. JIA category was polyarticular JIA (39%). Mean disease duration when CT scan was performed was 9.1 + 6.1 years; mean disease duration when SEMG was performed was 9.6 + 6,3 years. Cone beam CT scan of TMJ showed different grades of bone erosion in l4 patients out of I8. SEMG was completely normal only in one patient, while the other patients presented hypertonus or hypotonus in at least one of the masticatory muscles. Results are summarized in Table L Neither increased nor decreased muscle tone in any of the masticatory muscles examined showed a clear association with the severity of bone erosion of ipsilateral or contralateral condyle. Considering cone beam CT scan as the gold standard, SEMG showed low sensitivity (57%o) and specificity (25%). Conclusion: ln our study. SEMG findings of hypertonus or hypotonus did not show a clear correlation with the severity of condylar erosion as seen in CT scans. SEMG had poor sensitivity and specificity in detecting condylar damage. Nevertheless. it should be considered that our population is small and CT and SEMG were performed late in the disease course: further observations may better show the utility of SEMC for diagnosing and managing TMJ disease in JIA.