Evoked pain in the motor endplate region of the brachial biceps muscle: an experimental study.
Spontaneous electrical activity, interpreted as motor endplate activity, has been reported at muscle trigger points. This study examined whether the motor endplate region, identified by electromyography, is more sensitive to noxious stimuli than other muscle sites. We induced pain in the brachial biceps muscles of 21 healthy subjects by injecting capsaicin (30 microg/0.1 ml) and NaCl (5%/0.2 ml) in the motor endplate region and at electrically silent muscle sites. Needle and evoked pain were measured by a visual analogue scale (VAS) (0-10) and the short form of the McGill Pain Questionnaire. The needle pain in the motor endplate region differed both in intensity and quality from that at other sites. The maximal pain after NaCl 5% was higher, and the VAS area-under-the-curve for NaCl 5% and capsaicin were larger, in the motor endplate region than in other sites. A higher density of muscle nociceptors in the vicinity of the motor endplate region may account for the observed differences in pain. These findings may have clinical implications for the treatment of musculoskeletal pain conditions.
Danish Pain Research Center, Aarhus University Hospital, Building 1A, Noerrebrogade 44, DK-8000 Aarhus, Denmark. erisela@akhphd.au.dk
Erisela
E
Qerama
Anders
A
Fuglsang-Frederiksen
Helge
H
Kasch
Flemming W
FW
Bach
Troels Staehelin
TS
Jensen
D000328:Adult; D002211:Capsaicin / Q000009:adverse effects; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000294:innervation* / Q000503:physiopathology*; D009209:Myofascial Pain Syndromes / Q000209:etiology / Q000473:pathology / Q000503:physiopathology; D009469:Neuromuscular Junction / Q000166:cytology / Q000502:physiology*; D009619:Nociceptors / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D010146:Pain / Q000209:etiology* / Q000473:pathology / Q000503:physiopathology*; D010147:Pain Measurement / Q000187:drug effects; D012016:Reference Values; D012462:Saline Solution, Hypertonic / Q000009:adverse effects; D011984:Sensory Receptor Cells / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D011795:Surveys and Questionnaires
D012462:Saline Solution, Hypertonic; D002211:Capsaicin