Fibromyalgia (FM) is defined by widespread chronic musculoskeletal pain [
The temporal summation paradigm is the experimental model the most frequently used in humans to study endogenous excitatory pain mechanisms (e.g., central sensitization). Temporal summation results in an amplification of pain perception following repeated or continuous administration of constant noxious stimuli [
In human experimental settings, temporal summation is usually elicited using phasic repetitive pain stimuli administered at short interstimulus intervals (≥0.3 Hz) [
Seventy-two women suffering from FM and 39 healthy women participated in this study aged between 18 and 65 years old. Patients were diagnosed with FM using
Clinical and psychophysical differences between fibromyalgia patients and healthy controls.
Variable | FM | <45°C | >45°C | HC | Statistics | Statistics |
---|---|---|---|---|---|---|
Age | 47.6 | 44.8 | ||||
Menstrual cycle | Yes, 27; | Yes, 18; | ||||
Antidepressants | Yes, 12; | Yes, 15; | ||||
Anticonvulsants | Yes, 9; | Yes, 8; | ||||
FIQ total score | ||||||
FIQ pain item | ||||||
Pain rating at time 0 (%) | ||||||
TPTs (°C) | ||||||
Experimental temperature (°C) | ||||||
Temporal summation (Δ) |
Δ: delta, FIQ: Fibromyalgia Impact Questionnaire, FM: fibromyalgia, HC: healthy controls, TPTs: thermal pain thresholds, ± refers to standard deviations.
*missing data for a few subjects; **FM lower than 45°C < 2 other groups (Bonferroni correction).
The symptoms of FM were assessed using the French version of the self-administered
In a pretest at the beginning of the session, thermal pain thresholds (TPTs) were measured by applying a thermode on the left forearm of participants. The Peltier thermode used (TSA II, Medoc, Advanced medical systems, Minneapolis, MN 55435) was a heating plate connected to a computer, which allowed a precise setting of experimental temperature. Subjects were advised that the thermode temperature would gradually increase from 32°C to 51°C (maximum) by a rate of 0.3°C per seconds until it reached their thermal pain tolerance. During the full thermal stimulation, pain intensity was continuously measured (at 1 Hz) using a computerized visual analog scale (COVAS), which ranged from 0 (no pain) to 100 (most intense pain tolerable). Subjects were also instructed to start displacing the COVAS’ cursor when their sensations changed from heat to pain (TPTs). For each subject, the procedure was repeated twice to ensure the stability of measurement of the TPTs and the experimental temperature.
The temporal summation test was completed after the pretest and consisted of a continuous heat pulse administered with a thermode for 2 minutes on the left forearm of participants. Experimental temperature reached a predetermined fixed value and remained constant during the 2-minute testing period (Time 0 to Time 120). It was set at a value corresponding to a temperature individually predetermined to induce a 50/100 pain rating during the 2 pretesting sessions used to determine the individual’s TPT. That is, during the pretests, the experimenter noted the temperature associated with a 50/100 pain rating, as displayed on the Medoc software (laptop), for each subject. For the temporal summation stimulation, participants were not told that the temperature remains constant throughout testing, after reaching the individualized experimental temperature (Time 0). During the thermal temporal summation stimulation, pain intensity was also measured using the COVAS. Research in our laboratory has shown that pain perception scores increase through the 2 minutes of testing, most prominently during the last 15 seconds, even if the thermode temperature remains constant [
For statistical purposes, we used 3 dependent variables, namely, (i) TPTs, (ii) experimental temperature, and (iii) temporal summation (Mean COVAS
Relative to healthy controls, FM patients (as a whole) had lower TPTs and lower experimental temperature (Table
Temporal summation of heat pain fibromyalgia patients and healthy controls. This figure depicts the time course of pain perception during the tonic thermal noxious stimulation in fibromyalgia (FM) patients (open circles) and healthy controls (HCs) (black lines). We can clearly see that HCs have more pain at the end of the curve (temporal summation) when compared to FM patients; error bars refer to standard errors.
Given that FM patients required lower experimental temperatures to achieve 50/100 pain ratings, and that it has been shown that low-intensity nociceptive stimuli elicit less (or even no) temporal summation than high-intensity stimuli in healthy subjects [
Temporal summation of heat pain in fibromyalgia subgroups. This figure depicts the time course of pain perception during the tonic thermal noxious stimulation in fibromyalgia (FM) patients receiving experimental temperatures lower and higher than 45°C. We can clearly see a temporal summation effect in the
As shown previously by our group and others, TPTs were lower in FM relative to HC [
One possible explanation for the lack of increased or even lack of temporal summation of pain in FM is that we only included female patients in our study, whereas most previous studies on the topic included both male and female participants [
We acknowledge that these methodological differences (continuous stimuli, individualized temperatures) between our procedure and the procedures used previously by other labs may explain the discrepancy of the results obtained in the
Intriguingly, both FM subgroups did not differ in FIQ total and FIQ pain scores. Although the exact meaning of this result remains elusive, it may suggest that thermal pain hypersensitivity, as displayed by the
Overall, our results strikingly cast some doubt on the whole idea that endogenous excitatory pain mechanisms are overactive in the great majority of FM patients. However, it is important to be cautious when interpreting our results, since we cannot rule out that temporal summation may have emerged as significantly increased in the
Although the temporal summation results of the
This paper was funded by the Canadian Institutes of Health Research (S. Marchand) and the American Fibromyalgia Syndrome Association (S. Marchand, S. Potvin). S. Marchand is a supported member of the