Comparing Injection Methods of Botulinum Toxin A for Cervical Dystonia: A Systematic Review.

[BACKGROUND] Cervical dystonia (CD) is a chronic neurological disorder characterized by involuntary neck muscle contractions, leading to abnormal head postures, pain, and functional impairment. Botulinum toxin type A (BoNT-A) remains the treatment of choice, but its efficacy is highly dependent on injection accuracy. Various techniques, including palpation-guided, ultrasound-guided, and electromyography-guided (EMG), have been developed to optimize delivery, each with distinct advantages and limitations.

[METHODS] A systematic search of PubMed and Scopus was conducted up until 30 December 2024, using defined keywords related to BoNT-A, CD, and injection techniques. Studies were included if they reported clinical outcomes of BoNT-A injection methods in adult CD patients. Data on efficacy, safety, accuracy, and muscle targeting were extracted and synthesized.

[RESULTS] Seven studies comprising 239 patients were included: two randomized controlled trials, one retrospective study, one cohort study, one systematic review, one literature review, and one cadaveric study. The most common CD subtype was torticollis/torticaput (49.79%). Frequently targeted muscles included the trapezius (56.9%), levator scapulae (51.7%), and splenius capitis (48.3%). Ultrasound guidance consistently demonstrated superior injection accuracy and reduced adverse effects due to real-time anatomical visualization. EMG-guided techniques showed advantages in identifying dystonic muscles, especially when anatomy was unclear. In contrast, palpation-guided injections were less accurate and suitable only for superficial muscles. Dosing varied by product, with mean doses of 117-118 units for onabotulinumtoxinA and incobotulinumtoxinA, and 405 units for abobotulinumtoxinA. Adverse events were generally mild, including local discomfort, dysphagia, and transient muscle weakness.

[CONCLUSIONS] Ultrasound- and EMG-guided injections enhance the precision, safety, and efficacy of BoNT-A therapy for CD compared to anatomy-guided techniques. While ultrasound guidance improves anatomical accuracy, EMG remains valuable for functionally identifying dystonic muscles. Integration of both may offer optimal outcomes. However, further high-quality, standardized trials are needed to definitively establish best practices.