Effect of local glucocorticoid injection on masseter muscle level of serotonin in patients with chronic myalgia

The aim of this study was to compare the effects on the level
of serotonin (5-HT) in the masseter muscle by intramuscular
glucocorticoid (GC) administration in patients with
fibromyalgia (FM) and localized myalgia (LM), as well as to
determine associated changes in pain, tenderness, and
microcirculation. The study comprised 22 patients with pain
and tenderness in the masseter muscle region. Ten patients
(all women) had FNI, and 12 (1 man and 11 women) had LM
involving the temporomandibular system. The patients were
examined clinically and by microdialysis at 2 visits 2-3 weeks
apart and received local glucocorticoid treatment at the first
visit. The ratio (S1/S2) between the initial level of 5-HT
(S1) and steady state level (S2) was used as a relative
measure of the intramuscular release of 5-HT. This ratio
decreased significantly after treatment in the FM group. In
the FM group there was also a negative correlation regarding
changes between visits of 5-HT and changes of intramuscular
temperature. In the LM group there was a negative correlation
regarding changes between visits of 5-HT and changes of
pressure pain threshold and pressure pain tolerance level.
This study indicates that there is a reduction of the ratio
between initial 5-HT and steady state level in the painful
masseter muscle after intramuscular GC administration to FM
patients, a reduction not present in the LM patients. In
addition, 5-HT seems to be involved in the modulation of local
muscle microcirculation in FM patients and in hyperalgesia in
LM patients.

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