Musculotendinous pain is the main symptom.
Thought to be due to nociception from an abnormally sensitive tight band of soft tissue known as a myofascial trigger point (MTrP)
It is spontaneously painful, has a lower pressure pain threshold than surrounding muscle
Likely form due to movement or postural inefficiencies causing low grade eccentric load in some part of the muscle. Acetylcholine receptors may play a part.
When they have persisted for some time, central and peripheral sensitisation can then occur
Cause
Local and referred pain develop, modulated by adrenergic activity.1
There are measureable elevations in the concentrations of substance P, CGRP, bradykinin, and assorted cytokines, in the trigger point area, indicating that there is a chemical inflammatory response.1
The pH is low in the trigger point, consistent with the region being hypoxic and ischaemic.1
Once the peripheral nociceptive focus is established, it is subject to the usual phenomena of peripheral and central sensitisation, like any other somatic nociception.
Examination
Has been shown to have good inter examiner reliability
Exquisite tenderness at the site ('jump sign' ) and response to trigger point injection are the most clinically robust signs
Reference:
1. Gerwin RD. Myofascial pain syndrome. In Muscle Pain: Diagnosis and Treatment. S. Mense & RD Gerwin (eds). Springer-Verlag Berlin Heidelberg 2010.
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