Pain modulation profiles in temporomandibular disorders with migraine and fibromyalgia

Background: Temporomandibular disorders (TMD) frequently occur with other pain conditions, and existing research has yielded mixed results regarding the presence or absence of endogenous pain modulation (EPM). This study aimed to investigate EPM in TMD patients with comorbid migraine and fibromyalgia (FM) in the non-trigeminal innervated area. Methods: Conditioned pain modulation (CPM) and temporal summation (TS) were assessed in healthy controls (n = 30), TMD without comorbidity (n = 30), migraine (n = 30), TMD with migraine (n = 30), and TMD with migraine + FM (n = 19). Based on the TS and CPM responses, participants were categorized into pain modulation profiles (PMP, I–IV). Results: In serial stimulation, patients with migraine, TMD + migraine, and TMDs + migraine + FM showed significantly reduced pain inhibition compared with controls (p = 0.003, p < 0.001, and p = 0.001, respectively), while TMD patients without comorbidity exhibited intact modulation. Increasing comorbidities were also linked to weaker CPM (single stimulation: R = −0.312, p < 0.001; serial stimulation: R = −0.344, p < 0.001). The PMP categorization demonstrated distinctions among the study population, although further subgroup analysis proved challenging. Conclusions: TMD patients without comorbid pain exhibited intact EPM in non-painful areas. However, when these individuals experience comorbid pain conditions, their ability to modulate pain may be compromised due to the pain amplification and central sensitization associated with multiple comorbid pain conditions.