Intramuscular Pressure is Almost Three Times Higher in Fibromyalgia Patients..., 2020, Katz et al

Apologises if this has been posted - I searched and could not find it.

Intramuscular Pressure is Almost Three Times Higher in Fibromyalgia Patients: A Possible Mechanism for Understanding the Muscle Pain and Tenderness

https://www.jrheum.org/content/early/2020/09/10/jrheum.191068

Robert S. Katz, Frank Leavitt, Alexandra Katz Small and Ben J. Small
The Journal of Rheumatology September 2020, jrheum.191068; DOI: https://doi.org/10.3899/jrheum.191068

Abstract
Objective Widespread pain in the fibromyalgia syndrome (FMS) is conventionally viewed as arising from disordered central processing. This study examines intramuscular pressure in the trapezius as an alternative mechanism for understanding FMS pain.

Methods 108 patients who satisfied the ACR criteria for FMS and 30 patients who met the ACR criteria for another rheumatic disease comprised the study groups. Muscle pressure was measured in mmHg using a pressure gauge attached to a No. 22 needle inserted into the mid portion of the trapezius muscle. In addition, FMS patients and rheumatic disease controls had dolorimetry testing, digital palpation, and reported pain scores.

Results Muscle pressure was substantially higher in patients with FMS with a mean value of 33.48± 5.90 mmHg. Only 2 of 108 patients had muscle pressure of <23 mmHg. The mean pressure in rheumatic disease controls was 12.23±3.75 mmHg, with a range from 3-22 mmHg. FMS patients were more tender than controls based on both dolorimetry (p<0.001) and digital palpation (p<0.001). The mean pain score in patients with FMS and controls was 6.68±1.91 and 1.43±1.79 (p<0.001).

Conclusion Pressure in the trapezius muscle of patients with FMS is remarkably elevated and may be an intrinsic feature of FMS that could be monitored as part of the diagnostic evaluation. The burden of the pressure abnormality may help explain the diffuse muscle pain of FMS. Therefore, FMS as a disorder of exclusively central pain processing should be revisited. Therapeutically, the reduction of muscle pressure may change the clinical picture significantly.

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Any thoughts on this as a finding? Reliable testing method use? Easy to carry out in routine clinical practice? Value clinically?

 

The relatively high sensitivity and specificity is rather curious. I'd like this to be replicated by blind examiners before getting too excited. The FMS pain score vs muscle pressure plot suggests the association is weak, but that could be due to too much variation in the anchoring of the pain rating scores themselves.

Proposed mechanism:

 

Sounds interesting because the differences between groups are enormous, especially since they didn't use healthy controls but patients with other rheumatic conditions.

Looks like more than a weak correlation to me:

Agree

 

Hydrostatic pressure in relaxed muscle should be slightly below atmospheric. That suggests to me that the pressures here are indications of muscle contraction. It would not be surprising if people with a diagnosis of fibromyalgia contracted the trapezius harder when a needle was stuck in.

 

Interesting but like @Trish indicates it looks like three individuals are contributing a lot to the heavy lifting.

Also it would be interesting to have data from other comparator groups, as even if the association is robust, it would be good to have more confirmation about the possible direction of any causality.

 

@Hutan,
It would take a few thousand words to fully explain the problem here. But in simple terms human tissues are solids. Hydrostatic pressures are properties of liquids. If you try to ascribe hydrostatic pressures to solids you have to be very very careful and know exactly what you are doing. Whole careers have been wasted measuring 'hydrostatic pressures' in tissues, particularly hyaline cartilage.

To illustrate, it has been said that the hydrostatic pressure in cartilage is three atmospheres - that is why the tissue is so firm, despite being mostly just a fishnet of collagen. But if you cut it no water comes out. The response is that this is because of counteracting oncotic pressure. But it doesn't actually make sense. There is no 'hydrostatic pressure' as normally defined.

So if you are going to measure pressure in muscle you have tome very sure you know what that means.

There is no way that pressure in a relaxed muscle is going to obstruct capillaries. Muscles function under persistent tension which creates high. compressive (not hydrostatic) forces on blood vessels normally and blood flows fine. Muscle gets into trouble when compressive forces on vessels compete with arteriolar pressures. You can apply a hydrostatic analysis in the case of acute ischaemic compartment syndrome when a muscle swells to the limit of its sheath and effectively becomes a closed fluid compartment, but not otherwise.

In the 1970s and 1980s eminent research groups thought they were studying hydrostatic pressures like this and had big grants and published lots of papers - until they finally realised that they weren't measuring what they thought. I would bet this reinventing the same wheel.