Effect of Electrical Stimulation on Botulinum Toxin A Therapy in Patients With Chronic Myofascial Pain Syndrome: A 16-Week Randomized Double-Blinded Study

ObjectiveTo evaluate the effect of different intensities of electrical stimulation on botulinum toxin A (BTX-A) injection at trigger points (TrPs) in patients with chronic myofascial pain syndrome (MPS).DesignDouble-blind randomized trial.SettingOutpatient rehabilitation clinic.ParticipantsPatients (N=76) with chronic MPS of the neck and shoulder regions.InterventionsPatients were randomly assigned to 1 of 2 intervention groups: BTX-A injection followed by (1) electrical stimulation that induces visible muscle contraction (MOTOR group); or (2) electrical stimulation with an intensity just above the sensory threshold (SENSORY group). Electrical stimulation was administered for 30 minutes a day for 3 consecutive days after injection.Main Outcome MeasuresThe primary outcome was the visual analog scale (VAS) for pain. Secondary outcomes included the Neck Pain and Disability Scale (NPAD), Global Assessment of Improvement Scale (GAS), and pressure pain threshold (PPT).ResultsThe VAS scores decreased significantly at 4, 8, 12, and 16 weeks from the baseline in both groups. Significant changes in the NPAD score over time were noted only in the SENSORY group at 8, 12, and 16 weeks. The SENSORY group showed lower VAS and NPAD scores at 16 weeks (P=.043 and P=.041, respectively), and higher treatment success rates at 12 and 16 weeks (P=.039 and P=.024, respectively) than the MOTOR group. There was no significant result in the GAS and PPT.ConclusionsShort-term electrical stimulation may affect the reduction in pain after BTX-A injection at TrPs in patients with chronic MPS of the neck and shoulder regions. Based on the results, it seems that sensory electrical stimulation was superior to motor electrical stimulation as an adjuvant therapy to BTX-A injection in patients with chronic MPS. Further studies are warranted to investigate the method facilitating the effect of BTX-A on MPS.