A possible mechanism for understanding the muscle pain and tenderness

Plain Language Summary of Fibromyalgia Study

Contexte

La cause exacte de la fibromyalgie (FM) est inconnue. On pense généralement qu'il s'agit d'une sensibilisation centrale, où le cerveau traite anormalement les signaux de douleur, ce qui provoque la douleur.

Why this study

This study challenges one theory of pain in FM, which is central sensitization and seeks to show that pain in the muscles is linked to elevated pressure in the muscles.

Qui a participé à l'étude ?

Patients seen in a Rheumatology Clinic in the United States were studied after approval from the University Review Board. 108 FM patients met criteria for diagnosis and were physically examined by a rheumatologist and have pain in their trapezius muscles. The trapezius muscle is a large muscle running from the upper back to the neck and shoulders.

The comparison group were 30 patients without FM but met the diagnosis of a rheumatic disease (most commonly rheumatoid arthritis, lupus, psoriatic arthritis and least commonly Sjogren’s syndrome).

Patients in both groups were 18-70 years old.

Comment l'étude a-t-elle été menée ?

Since the majority of FM patients experience pain in the trapezius muscle this muscle was used for testing. Pain intensity was measured with the Pain scale 0-10, muscle tenderness was graded by palpation and dolorimetry and pressure in the muscle was measured with a Stryker pressure gauge.

Statistics were done to indicate whether the results between the two groups were statistically different.

Résultats

The two groups were well matched for age; there were significantly more females in the FM group.

The FM group had a moderately high score that was significantly higher than the comparator group as expected. Tenderness of the muscle was significantly higher in the FM group. The pressure within the trapezius muscle was very much higher and significantly more than the other group. The higher the pain score and higher the muscle tenderness, the greater the pressure in the trapezius muscle. The authors wonder if the increased muscle pressure compresses the capillaries (very small blood vessels) in the muscle which then decreases the amount of oxygen getting to the muscle which would then lead to pain in the muscles of FM patients.

Limites de l'étude

The selection criteria for FM patients in the study required them to have pain specifically in the trapezius muscle. Consequently, it is possible that some FM patients who did not experience trapezius pain were excluded from the study. This potential bias in participant selection could have skewed the results and may lead to different interpretations. Unfortunately, the authors did not provide information on the number of FM patients without trapezius pain who were excluded from the study, which limits our understanding of the overall FM population included.

The groups of patients were selected from a large hospital rheumatology clinic and results might be different if a larger cross-section of patients were studied.

The non-FM group was much smaller than the FM group.

Measurement of muscle pressure and pain was studied in only one muscle and there may be different findings if other muscles were used. Since FM patients had to have pain in their trapezius muscle then the pain intensity was exaggerated in that group. It is crucial to note the statement directly quoted from the paper: "Sample size was not calculated for this study because the analyses are intended for hypothesis generation, rather than confirmation." This statement is of utmost significance as it highlights that the results merely support the hypothesis that FM patients may have increased pressure in the trapezius muscles. However, due to the lack of statistical relevance in the sample size, these results should not be seen as confirming the hypothesis.

Another limitation is how valid is the Research because there are 2 variables. The control group does not have fibromyalgia and it does not state if the control group has pain in the trapezius muscle. The question is would a person without fibromyalgia who happened to have pain in their trapezius muscles have increased muscle pressure?

Research Study Discussion

The pressure within the muscle was enough of a difference between the groups to consider muscle pressure as a possible diagnostic tool. The authors of the study thought that therapeutic attempts to educe muscle pressure might help fibromyalgia patients reduce their pain. There may be both a central cause (brain central sensitization) and a peripheral cause (found in the muscles themselves) for fibromyalgia pain.

To the researchers' knowledge, this is the first study to show increased muscle pressure in FM patients and suggests a target for evaluation and intervention.

Commentaires du comité de recherche de l’AFC :

In the Results section of the paper, the authors explicitly state, "The significantly higher pain score in the FM group (P < 0.001) was expected, as pain was an inclusion criterion for the FM group." This implies that the comparison was made between a group of FM patients with pain and a group of non-FM patients, regardless of their pain status. While this provides some insight into understanding FM, it weakens the strength of the evidence in favor of the study's results. Consequently, although it represents a step forward in comprehending FM, further study from other researchers that duplicate these results are needed to validate findings.

The FAC Research Committee thought that the title was misleading because people who don’t understand research would think that the researchers had found a way to test for
fibromyalgia.

The FAC Research Committee thought the research was a hypothesis and therefore expected a firmer conclusion.

Article summarized by FAC Research Committee, August 22, 2023.

For more information consult the original article at: The Journal of Rheumatology 2021;48:4; doi:10.3899/jrheum.191068
Intramuscular Pressure Is Almost Three Times Higher in Fibromyalgia Patients: A Possible Mechanism for Understanding the Muscle Pain and Tenderness (jrheum.org)