EffectofLocalAnestheticVersusBotulinumToxin-AInjectionsforMyofascialPainDisorders:ASystematicReviewandMeta-Analysis

Myofascial pain is a chronic pain disorder characterized by painful localized regions of stiff muscle and myofascial trigger points (MTrPs). It is highly prevalent, affecting approximately 30% of general clinic patients and 85% of pain clinic patients. Intramuscular trigger point injections are considered first-line treatments, with local anesthetics and botulinum toxin-A (BTX-A) being the most common injectates. However, previous studies have reported heterogeneous results regarding their effectiveness, and no prior review had directly compared these two injectates for myofascial pain.

This gap in knowledge is clinically significant because both treatments are widely used, yet clinicians lack robust evidence to guide their choice of injectate.

The researchers conducted a comprehensive systematic review and meta-analysis following PRISMA guidelines. They searched three major databases (EMBASE, Cochrane CENTRAL, and Medline) from inception through May 2017, using broad search terms for myofascial pain and various injectates. After screening 2,301 records, 33 studies met eligibility criteria: 18 studies assessed local anesthetic injections, 16 assessed BTX-A injections, and one study evaluated both. The included studies were randomized controlled trials, controlled trials, or randomized trials with adult patients having myofascial pain confirmed by expert assessment.

The primary outcome was patient-reported pain intensity, measured using visual analog scales (VAS) or the Neck Pain and Disability Scale (NPAD). The researchers performed meta-analyses using standardized mean differences (SMD) with random-effects models, comparing local anesthetic and BTX-A injections across multiple follow-up periods: immediately after injection (0 weeks), and at 1-2, 3-4, 5-6, 7-8, 9-10, 11-12, 16, 18, and 24 weeks. They also conducted subgroup analyses comparing single versus multiple injection sessions and different body regions (cervical/shoulder, temporomandibular joint, and widespread muscles). Risk of bias was assessed using Cochrane Collaboration criteria.

The qualitative analysis revealed inconsistent effectiveness of both local anesthetic and BTX-A injections across follow-up periods. The meta-analyses showed that local anesthetic injections were more effective than BTX-A at reducing pain intensity. Specifically, local anesthetics demonstrated large effect sizes favoring the experimental intervention at 1-2 weeks (SMD = -0.96, 95% CI: -1.80 to -0.13, P<0.05), 3-4 weeks (SMD = -1.01, 95% CI: -1.76 to -0.27, P<0.05), and 16 weeks (SMD = -1.33, 95% CI: -2.11 to -0.55, P<0.001). At 7-8 weeks, the effect size was also large (SMD = -1.27) though the confidence interval was wide (-3.50 to 0.96).

In contrast, BTX-A injections showed negligible or small effect sizes favoring the control intervention at most follow-up periods, with only small to moderate effects at 18 weeks (SMD = -0.59) and 24 weeks (SMD = -0.33). The overall meta-analysis across all injectates showed a significant effect only at 3-4 weeks (SMD = -0.37, 95% CI: -0.69 to -0.06, P=0.02). Multiple injection sessions of local anesthetics showed a larger effect size (SMD = -0.86, 95% CI: -1.45 to -0.26, P=0.005) compared to single sessions (SMD = -0.51, 95% CI: -0.94 to -0.08, P<0.05). For BTX-A, only single-session data were available, showing negligible effect (SMD = 0.02).

Regarding body region, local anesthetics showed large effects at temporomandibular joint muscles (SMD = -1.01, 95% CI: -1.35 to -0.67, P<0.001) and widespread muscles (SMD = -1.41, 95% CI: -2.45 to -0.38, P<0.001), with smaller but significant effects at cervical and shoulder muscles (SMD = -0.44, 95% CI: -0.82 to -0.07, P<0.05). BTX-A showed only a marginally small significant effect at temporomandibular muscles (SMD = -0.19, 95% CI: -0.35 to -0.03, P<0.05) and no effect at cervical/shoulder muscles (SMD = 0.01). Heterogeneity was high across most analyses (I2 values frequently >75%), particularly for local anesthetic studies. Eighteen of 33 studies had low risk of bias on 4-6 of 6 assessed items.

Adverse events were generally transient for both injectates, including subcutaneous hemorrhage, dizziness, muscle soreness with local anesthetics, and transient pain, weakness, and muscle soreness with BTX-A.

For clinicians treating myofascial pain, this systematic review suggests that local anesthetic injections are generally more effective than BTX-A injections for reducing patient-reported pain intensity, with benefits persisting up to 16 weeks post-treatment. Multiple sessions of local anesthetic injections appear more beneficial than single sessions. The effectiveness of both injectates may depend on injection location, with temporomandibular muscles responding better than cervical and shoulder muscles. The mechanism of action may explain these differences: local anesthetics block both afferent and efferent signals at the MTrP and motor endplate region, potentially disrupting the spinal facilitation mechanism maintaining trigger points, while BTX-A primarily inhibits acetylcholine release at neuromuscular junctions and may be more effective when injected at motor endplates rather than within trigger points themselves.

However, the high heterogeneity across studies limits the certainty of these conclusions. The variability in local anesthetic types (lidocaine, bupivacaine, prilocaine), concentrations (0.3% to 2.0%), quantities, and diverse comparison groups contributed to this heterogeneity. For patients, this means that if offered trigger point injections for myofascial pain, local anesthetic injections may provide better pain relief than BTX-A, though individual responses vary. The authors recommend ultrasound guidance for injections and emphasize that comprehensive management should include nonpharmacological treatments such as physical therapy before considering injections.

Future research should standardize injection protocols, compare MTrP versus motor endplate injection sites, assess optimal dosing, and investigate which patient characteristics predict better response to each injectate type.