A double-blind, controlled study of botulinum toxin A in chronic myofascial pain.
BACKGROUND
Recent studies have reported a potential analgesic effect of botulinum toxin A (BTXA) in musculoskeletal pain. The present double-blind, randomized, placebo-controlled, parallel clinical trial studied the effect of BTXA on pain from muscle trigger points and on EMG activity at rest and during voluntary contraction.


METHODS
Thirty patients with trigger points in the infraspinatus muscles received either 50 units/0.25 mL of BTXA or 0.25 mL of isotonic saline. Baseline measures were determined during a run-in period of 1 week. Outcome measures including local and referred spontaneous pain, pain detection and tolerance thresholds to mechanical pressure, and shoulder movement were assessed at 3 and 28 days after injection. The interference pattern of the EMG during maximal voluntary effort of infraspinatus muscle was recorded and a standardized search for spontaneous electrical motor endplate activity at the trigger points was performed before and 28 days after BTXA or saline injection.


RESULTS
BTXA reduced motor endplate activity and the interference pattern of EMG significantly but had no effect on either pain (spontaneous or referred) or pain thresholds compared with isotonic saline.


CONCLUSIONS
The results do not support a specific antinociceptive and analgesic effect of botulinum toxin A.
Qerama
E
E
Danish Pain Research Center, Aarhus University Hospital, Denmark. erisela@akhphd.au.dk
Fuglsang-Frederiksen
A
A
Kasch
H
H
Bach
F W
FW
Jensen
T S
TS
D000700:Analgesics / Q000627:therapeutic use; D019274:Botulinum Toxins, Type A / Q000627:therapeutic use*; D002908:Chronic Disease; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009209:Myofascial Pain Syndromes / Q000175:diagnosis* / Q000188:drug therapy*; D010147:Pain Measurement / Q000187:drug effects*; D017288:Pain Threshold / Q000187:drug effects*; D015990:Placebo Effect; D016896:Treatment Outcome
D000700:Analgesics; D019274:Botulinum Toxins, Type A