Who is the patient with resistant myofascial temporomandibular disorders pain? A somatosensory, psychosocial, and genetic characterization

Background: Resistance to treatments have been assessed in chronic conditions such as migraine, but not in temporomandibular disorders (TMD). This study aimed to identify factors that influence treatment outcome in patients with myofascial TMD pain. Methods: Seventy-two females were divided into three groups: TMD successfully treated (TMD-S, n = 24), TMD resistant to treatment (TMD-R, n = 24) and Controls without TMD (n = 24). Criteria for resistance included: less than 30% pain reduction after three months of conservative treatment and an average pain intensity > 50 mm (VAS) during the last month. Quantitative sensory testing (QST), psychosocial status and genetic polymorphisms were examined. ANOVA on ranks (psychosocial variables) with Dunn’s test as post-hoc or ANOVA (age and somatosensory variables) with Tukey test as post-hoc test, and Dwass-Steel-Critchlow-Fligner test (genetic variables) were used for univariate groups comparisons. Multivariate statistics were used to identify outcomes that separated the groups. Results: QST assessment revealed lower baseline pressure pain threshold and higher wind-up ratio in the trigeminally and spinally innervated areas in the TMD-R group compared with the other groups (p = 0.01). Also, the TMD-R group presented higher values in all assessed psychosocial variables (p < 0.01) and higher prevalence of the HTR1A polymorphism rs6295 (p = 0.02) compared with the other groups at baseline. Multivariate analysis showed that the three variables that distinguished the best between TMD-R and TMD-S were sleeping quality, central sensitization, and depressive symptoms. Conclusion: Psychosocial, somatosensory, and genetic alterations are related to unsuccessful treatment response in myofascial TMD patients.