Muscular Pressure Pain Withdrawal Reflex Threshold

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(Author’s term.)

Definition[edit]

This is the minimum force needed for application to a muscle in order to induce a nociceptive withdrawal reflex.

Potential to use mechanical pain withdrawal reflex testing on tender points in fibromyalgia[edit]

Author’s opinion:

There may be a clinical opportunity to begin doing routine mechanical pressure thresholds for the induction of withdrawal reflexes in fibromyalgia patients. My experience is that there seems to be separate withdrawal reactions for many or most of the 18 fibromyalgia tender points. It is difficult for me to say at this time if they are all stereotyped reflexes. Currently, in our clinic we generally stop pressing as soon as the patient says they feel pain. Under these conditions, my impression is that healthy controls never have withdrawal reflexes at low levels of force. Since we never press harder than 4kgs we don’t know what the normal values are.

Another consideration is that when testing tender points, it is sometimes necessary to stabilize the limb. This can be done, for example, by holding the arm or placing it on a desk when testing the epicondylar tender points. This tends to block the ability to withdraw the body part away from the pressure. This means that not all tender points are practical for testing withdrawal. I suspect that withdrawing is a generally tendency and that it may not be important to test more than one or two of the reflexes. This requires further research, but my inclination is to focus on the trapezius tender point because it is a substantial muscle that is easily located, and in most cases it can be safely palpated. My inclination is to avoid the tender points in the neck, especially those near the carotid artery. My suspicion is that it is almost always safe to press on the trapezius of most people at forces well above 4 kg. but this requires further study. If this is the case then it would be a good candidate site for muscular pressure withdrawal reflex threshold testing. I have tested several severe fibromyalgia by applying firm downward force to their trapezius muscles with the tip of a hand-held algometer. They dropped their shoulder involuntarily when their pressure pain threshold was reached to withdraw it from the force. This was expected. However they also unexpectedly and suddenly demonstrated involuntarily flexion of their knee on the same side. This caused their whole body to drop down. I had the impression that this was a stereotyped reaction. Perhaps it is related to the RIII reflex.

My current thinking is that what is needed is a study aimed at establishing the normal values for the minimum force needed for application to tender points (such as the trapezius tender points) to induce a withdrawal reflex. If this is done for a muscle then it could be called the “muscular tenderpoint withdrawal reflex threshold”. If the study were to be successful, then perhaps this approach could evolve to part of the basic physical exam of pain patients. Perhaps it could become a semi-objective test for fibromyalgia.