Referred Pain in Temporomandibular Disorders: Prevalence, Associated Factors and Effects on TMD Prognosis

Abstract

When a stimulus is applied to one part of the body, pain sometimes occurs in a distant site. This distant pain is called referred pain. The aims of this project were: To describe the prevalence of referred pain in subjects with temporomandibular disorders (TMD) at baseline and 8-year follow-up and the prevalence of persistence of referred pain at follow-up. Another aim was to identify risk factors for having referred pain at baseline and for predicting its persistence at follow-up. Finally, we wanted to determine whether referred pain affects the prognosis of patients with a TMD diagnosis. For each objective, we explored demographics such as gender, age, income, education level, and race. Other factors investigated included facial pain duration, somatization, somatization without pain, depression, anxiety, characteristic pain intensity (CPI), graded chronic pain scale (GCPS), number of other pains (headache, chest, back or stomach), and TMD diagnosis (myofascial pain, disk displacement, arthralgia or degenerative joint disease DJD). Methods: This secondary analysis included the data sets from the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) Validation (baseline) and IMPACT (follow-up) studies. It focused on a subclassification pain diagnosis termed “myofascial pain with referral”. Subjects included in our analysis were TMD cases at baseline (n = 614) and TMD cases at follow-up (n = 286). Results. 26.4% of TMD cases had pain with referral at baseline and 36.4% at follow-up. The sites most likely to refer pain were extraoral sites (temporalis, masseter and mandible) at both baseline and follow-up. Female gender was associated with a higher prevalence of referred pain at baseline (p=.025). Other factors associated with referred pain included somatization (p<.0001 at baseline, p=.0195 at follow-up) and somatization without pain at baseline only (p<.0001), depression (p=.001 at baseline and p=.0002 at follow-up), CPI, GCPS and number of other bodily pains were also associated with referred pain at baseline and follow-up (p<.0001). Myofascial pain and arthralgia or DJD were TMD diagnoses associated with referred pain at baseline and follow-up (p<.0001). The rate of persistence from baseline to follow-up was 57.4%, with CPI being the only predictor of persistence (p=.02). On the impact on prognosis of TMD condition, regression analyses determined that referred pain was a predictor of CPI (p=.028) and moderate depression at follow-up (p=.028). Conclusion: Among individuals with TMD, referred pain was observed in around 30% at baseline and follow-up and persisted from baseline to follow-up in more than half of the individuals. It can be detected by following the protocol used by RDC/TMD and further revised by DC/TMD. It is associated with self-reported measures of both psychosocial factors and subjective pain measures that are associated with central sensitization process. Referred pain is an added and an independent factor for higher CPI and therefore may predict an overall higher intensity of pain and suffering. Referred pain is an important marker for assessment and management of any orofacial pain condition. In addition to indicating an increased central sensitivity, it may also reveal the true pain source in a pain condition that has otherwise been misdiagnosed.