Endogenous Pain Modulation Assessed with Offset Analgesia Is Not impaired in Chronic Temporomandibular Disorders Pain Patients

Background: Abnormal endogenous pain modulation (EPM) was suggested as a pathophysiological characteristic of chronic pain. EPM has been investigated using psychophysical tests for pain facilitation and inhibition such as temporal summation of pain and conditioned pain modulation, respectively. Another psychophysical test for pain inhibition is offset analgesia (OA), where small variations in noxious stimulus intensity over time elicit a disproportionately large analgesic response. OA has been investigated in patients with mixed pain conditions, but not in chronic temporomandibular disorder (TMD) patients. Objective: To compare OA responses in chronic TMD female cases to age-matched, pain-free female controls. Methods: Offset analgesia was assessed by applying noxious heat over the non-dominant forearm of chronic TMD cases (n = 22) and controls (n = 17), using a previously reported paradigm with individualised test temperatures (TT): T1(5 seconds) = TT, T2(5 seconds) = TT + 1°C and T3(20 seconds) = TT. Clinical and psychosocial characteristics were measured. Main outcomes for OA were delta computerised visual analogue scale (COVAS), per cent change (T2-T3/T2-T1) and area under the curve (AUC) ratio of pain ratings controlling for TT. Results: No statistically significant between-group differences were found for delta COVAS (TMD cases mean ± SD = 53.5 ± 22.0; controls = 51.6 ± 22.9, P = 0.876) and per cent change (T2-T3/T2-T1) (cases mean = 327.2 ± 375.1; controls = 226.9 ± 553.4, P = 0.515), with both groups presenting a robust OA response. TMD cases perceived more pain during OA trials than controls, as measured by AUC ratio (mean difference [95% CI] = −15.6 [−26.9, −3.5], P = 0.017). Conclusion: Chronic TMD cases presented with similar OA response over the forearm as controls; however, they experienced greater pain during testing. Future studies including this patient population should investigate OA responses over painful body sites, for example, jaw/face.