Bilateral thermal hyperalgesia in trigeminal and extra-trigeminal regions in patients with myofascial temporomandibular disorders.

Our aim was to assess thermal sensitivity in both trigeminal and extra-trigeminal regions in patients with myofascial temporomandibular disorder (TMD) but without comorbid conditions as compared to age-matched controls. Twenty women (age 24 +/- 3 years) diagnosed with myofascial TMD according to the research diagnostic criteria for TMD and 20 healthy women (age 24 +/- 4 years) were included. Warm and cold detection thresholds (WDT and CDT, respectively) and heat and cold pain thresholds (HPT and CPT, respectively) were bilaterally assessed over the masseter and frontalis muscles (trigeminal regions) and the wrist (extra-trigeminal region). The mean of three determinations at each site was calculated and used for analysis. The order of the test sites was randomized. A two-way ANOVA was used to test for differences between groups and sides (most painful/contra-lateral side; dominant/non-dominant). No significant differences between groups for WDT or CDT in trigeminal and extra-trigeminal regions (ANOVA, P > 0.389) were found. There were significant differences between groups, but not between sides, for HPT and CPT in both trigeminal and extra-trigeminal areas (ANOVA, P < 0.001). CPT (P < 0.001) over the trigeminal area was positively correlated with both pain intensity and duration of pain symptoms: the longer the history of pain or the greater the pain intensity, the higher the CPT (i.e., the greater cold hyperalgesia) over the trigeminal region. Our findings revealed bilateral thermal hyperalgesia (lower HPT and higher CPT) but normal WDT and CDT in trigeminal and extra-trigeminal regions in women with myofascial TMD as compared to healthy controls. Bilateral heat/cold hyperalgesia in trigeminal and extra-trigeminal areas may reflect a dysfunction of thermal channels in myofascial TMD patients as result of some combination of peripheral sensitization, facilitation of central nociceptive processing and/or decreased descending inhibition.