Temporal summation of painful heat stimulation is facilitated in trigeminal and extratrigeminal regions in painful myofascial temporomandibular disorders:Evidence from a case-control study

Aims: To determine whether patients with painful myofascial temporomandibular disorders (TMD) demonstrate facilitated temporal summation (TS) responses to painful heat stimuli applied to the painful trigeminal and extratrigeminal regions and whether there is a side difference in the trigeminal region for myofascial TMD pain patients compared to healthy controls. Methods: Twenty female Chinese myofascial TMD pain patients and 20 age-matched female volunteers participated in this case-control study. Thermal detection thresholds, thermal pain thresholds, and TS of 20 repetitive noxious thermal stimuli were measured on the skin above the masseter muscle on both sides and the thenar eminence of the less painful side/dominant hand. Numeric rating scale (NRS) scores of pain were provided after the 1st, 5th, 10th, 15th, and 20th stimuli, and TS was calculated as the highest NRS score minus the first NRS score in each test. Results: Evidence of TS was found in the trigeminal and extratrigeminal regions for both groups, but with facilitated TS responses in myofascial TMD pain patients (P < .001). Within the myofascial TMD group and control group, there were no side-to-side differences (P > .289). Interestingly, the repetition of the TS test was associated with facilitated responses in myofascial TMD pain patients (P < .001). Conclusion: The current findings suggest TS of painful heat stimulation is facilitated in myofascial TMD pain patients with no side difference in the trigeminal region.