Continuous pain report demonstrates time delay of pain ratings in Fibromyalgia

Background: Enhanced temporal summation (TS), measured through self-reported pain ratings, has been interpreted as indicative of central sensitisation in fibromyalgia. Greater TS in patients, however, has not been universally observed. It is also unclear whether increased pain report maintains beyond the TS period. Methods: In this study, we measured TS through continuously reported pain ratings. Fibromyalgia-diagnosed patients (n = 17) and matched pain-free controls (n = 13) rated painful transcutaneous electrical stimulation of various intensity levels in 18 one-minute-long blocks. Pain was rated on a 101-point visual analogue scale. The resulting continuous response was divided into TS (< 15s) and adaptation (15 - 60s) periods. Average pain values were extracted for each period alongside the timing of key events such as maximal pain ratings. The difference in temporal summation and adaptation measures between fibromyalgia and control participants was analysed using mixed-effects modelling. Results: The average pain ratings for TS and adaptation periods were not significantly associated with fibromyalgia diagnosis but were with stimulation intensity. The same was true for the magnitude of the maximal rating during TS and the slope leading to that peak rating. The presence of fibromyalgia, however, did predict the time of the maximal TS rating, as well as the value and the time of the maximal adaptation rating. Conclusions: Our study did not find homogeneously increased TS pain ratings. Instead, by utilising continuous pain data we demonstrate for the first time that the time of TS peak rating, as well as the magnitude and time of adaptation peak rating are linked to fibromyalgia diagnosis.