Tender Points Are Not Sites of Ongoing Inflammation - In Vivo Evidence in Patients with Chronic Tension-Type Headache

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Abstract
Increased muscle tenderness is the most prominent finding in patients with tension-type headache, and it has recently been shown that muscle blood flow is diminished in response to static exercise in tender points in these patients. Although tenderness has been ascribed to local inflammation and release of inflammatory mediators, the interstitial concentration of inflammatory mediators has not previously been studied in tender muscles of patients with tension-type headache. The aim of the present study was to investigate in vivo concentrations of prostaglandin E2 (PGE2), adenosine 5'-triphosphate (ATP), glutamate, bradykinin and other metabolites in a tender point of patients with chronic tension-type headache, in the resting state as well as in response to static exercise, and to compare findings with measurements in a matched non-tender point of healthy controls. We recruited 16 patients with chronic tension-type headache and 17 healthy control subjects. Two microdialysis catheters were inserted into the trapezius muscle and dialysates were collected at rest, 15 and 30 min after start of static exercise (10% of maximal force) and 15 and 30 min after end of exercise. All samples were coded and analysed blindly. There was no difference in resting concentration of any inflammatory mediators or metabolites between tender patients and non-tender controls ( P > 0.05). We also found no difference in change in interstitial concentration of ATP, PGE2, glutamate, glucose, pyruvate and urea from baseline to exercise and post-exercise periods between patients and controls ( P > 0.05). The present study provides in vivo evidence of normal interstitial levels of inflammatory mediators and metabolites in tender trapezius muscle in patients with chronic tension-type headache during both rest and static exercise. Thus, our data suggest that tender points in these patients are not sites of ongoing inflammation.