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Endogenous Pain Facilitation Rather Than Inhibition Differs between CFS, MS, and Controls

hixxy

Senior Member
Messages
1,229
Location
Australia
Pain Physician. 2017 May;20(4):E489-E497.

Endogenous Pain Facilitation Rather Than Inhibition Differs Between People with Chronic Fatigue Syndrome, Multiple Sclerosis, and Controls: An Observational Study.

Collin SM, Nijs J, Meeus M, Polli A, Willekens B, Ickmans K.

Abstract

BACKGROUND:
Commonalities in the core symptoms of fatigue and cognitive dysfunction experienced by chronic fatigue syndrome (CFS, also known as ME) and multiple sclerosis (MS) patients have been described. Many CFS and MS patients also experience chronic pain, which has been attributed to central sensitization in both groups of patients. However, the characteristics of pain in CFS and MS patients have not been compared.

OBJECTIVES:
To compare experimental pain measurements in patients with CFS or MS and healthy controls.

STUDY DESIGN:
Observational study.

SETTING:
This study took place in Belgium at Vrije Universiteit Brussel and the University of Antwerp.

METHODS:
Pressure pain thresholds, temporal summation, conditioned pain modulation, and occlusion cuff pressure thresholds rated as painful (1st cuff pressure threshold) and as 3/10 on a verbal numerical scale (2nd cuff pressure threshold) were measured in patients with CFS (n = 48), MS (n = 19) and healthy pain-free controls (n = 30). Adjusted between-group differences were estimated using linear regression models.

RESULTS:
Finger pain pressure thresholds of patients with CFS, compared with patients with MS, were 25% lower (difference ratio 0.75 [95% CI 0.59, 0.95], P = 0.02) and shoulder pain pressure thresholds were 26% lower (difference ratio 0.74 [0.52, 1.04], P = 0.08). Compared with patients with MS, patients with CFS had 29% lower first cuff pressure threshold (difference ratio 0.71 [0.53, 0.94], P = 0.02) and 41% lower 2nd cuff pressure threshold (0.59 [0.41, 0.86], P = 0.006). Finger temporal summation was higher in patients with CFS than in patients with MS (mean difference 1.15 [0.33, 1.97], P = 0.006), but there were no differences in shoulder temporal summation or conditioned pain modulation at either site. Differences between patients with CFS and MS tended to be greater than between either patient group and healthy controls. Pain pressure thresholds and cuff pressure thresholds tended to be positively correlated, and temporal summation negatively correlated, with higher physical function and lower fatigue in both groups of patients. Subjective pain in patients with CFS but not in patients with MS was strongly negatively correlated with pain pressure thresholds and cuff pressure thresholds, and positively correlated with temporal summation.

LIMITATIONS:
The main limitations of our study are the relatively small sample sizes, its cross-sectional design, and its exploratory nature.

CONCLUSIONS:
We found differences in the characteristics of pain symptoms reported by patients with CFS and patients with MS, which suggest different underlying mechanisms. Specifically, overactive endogenous pain facilitation was characteristic of pain in patients with CFS but not in patients with MS, suggesting a greater role for central sensitization in CFS.

PMID: 28535557

https://www.ncbi.nlm.nih.gov/pubmed/28535557
 

Hutan

Senior Member
Messages
1,099
Location
New Zealand
I haven't seen the full paper.

Differences between patients with CFS and MS tended to be greater than between either patient group and healthy controls.

So, they presumably didn't find significant differences in pain thresholds and the like between people with CFS and healthy controls (and between people with MS and healthy controls). Why don't they say that in their conclusion? (rhetorical question).

The differences found between people with CFS and people with MS that they make so much of could easily be an artefact of the small sample size (especially the MS sample).

Adjusted between-group differences were estimated using linear regression models.

The adjustment process provides scope for fudging stuff. Maybe there were differences in the ages or gender mix of the samples.
 

Snow Leopard

Hibernating
Messages
5,902
Location
South Australia
This study was poorly matched with regards to gender 64.1% (HC n=39) 68.4% (MS n=19) 95.8% (CFS n=48). Specifically the CFS group only had two men out of 48, vs fourteen out of thirty-nine for HC.

The results attempted to statistically control for gender, but I wonder how this could have effected the results?

Comparing the CFS group to healthy controls (HC), the following measurements were not significant:
Pain pressure threshold finger
1st cuff pressure threshold
2nd cuff pressure threshold was not significant when correcting for multiple comparisons
Temporal summation finger
Temporal summation shoulder
Conditioned pain modulation finger
Conditioned pain modulation shoulder

Comparing the CFS group to healthy controls (HC), the following measurements were significant:
Pain pressure threshold shoulder.

Of the Pairwise correlations between experimental pain measurements and patient-reported characteristics, only a few were significant (P < 0.007 (Bonferroni-adjusted P < 0.05)):
CIS reduced physical activity was associated with Temporal summation finger for CFS patients
Visual analogue pain (VAS) rating was associated with Temporal summation finger, Temporal summation shoulder, 2nd cuff pressure threshold. Keeping in mind that self reported pain on the VAS was one of the biggest symptomatic differences reported between MS and CFS - MS reported the same as healthy controls.

Pain pressure method:
Pressure pain thresholds were measured at the middle of the right trapezius belly (shoulder pain pressure
threshold) and at the dorsal surface of the right hand middle finger midway between the first and second distal joint (finger pain pressure threshold) with an analog Fisher algometer (Force Dial, Wagner Instruments, Greenwich CT) (24). Participants’ pain pressure thresholds were determined by increasing the pressure provided by the algometer (at a rate of one kg/s) until the point the sensation first became painful (participants were instructed to say “stop” at this point). This was performed twice (30 seconds apart) at the shoulder and at the finger in order to calculate the
mean pain pressure threshold for each site.

Given that only one of the eight measurements was statistically significant and there were substantial gender differences, this is a fairly weak result that doesn't provide much confidence for the "central sensitization of pain" theory.
 

A.B.

Senior Member
Messages
3,780
Specifically, overactive endogenous pain facilitation was characteristic of pain in patients with CFS but not in patients with MS, suggesting a greater role for central sensitization in CFS.

Haven't read the paper, but they did not appear to have measured central sensitization and therefore do not know whether the increased pain reflects a central or local problem.

This tendency to interpret findings that are not particularly specific as consistent with a specific explanatory model while not considering alternatives is indicative of bias. We've seen the same behaviour by the BPS model proponents and it's a good recipe to end up with a wrong model. It's not difficult to collect data in favor of an explanatory model. One could theorize that increased pain sensitivity is characteristic of demonic possession and that therefore any finding of increased pain sensitivity is consistent with demonic possession.
 

Effi

Senior Member
Messages
1,496
Location
Europe
I wish this team would stop conflating CFS with chronic pain conditions. Tbh I wish this team would stop working on CFS altogether. Pretty much every single one of their papers I have read so far was written clearly for the sole purpose of making people believe central sensitization is a thing. (Many researchers have tried to prove this hypothesis over the years, so far all have failed. It's time to move on from this!) Also, they need a reason for their association 'Pain in Motion' to exist. Their samples are always so ridiculously small, their illness criteria are warped at best, and their conclusions are always the same: central sensitization and/or gentle movement as a tool towards rehabilitation. :cautious: