A Randomised, Cross-over, Double-blind, Sham-Controlled Superiority Trial of UltraSound-Guided Versus Non-Ultrasound-Guided Botulinum TOxin Injections in Cervical DYstonia

Cervical dystonia (CD) is the most common type of focal dystonia and is characterised by sustained or intermittent involuntary contractions of the neck muscles. These contractions lead to abnormal head postures and movements, frequently associated with pain and tremor, and have a major impact on quality of life.

The established treatment for CD is repeated intramuscular injections of botulinum toxin type A (BoNT-A), usually every 12 to 16 weeks. BoNT-A blocks acetylcholine release at the neuromuscular junction, producing a temporary and reversible chemodenervation of the target muscle. Clinical benefit generally appears within a few days, peaks after 2 to 4 weeks, and gradually wears off after 3 to 4 months, requiring repeated injections. Although this therapy is effective and safe, its clinical success largely depends on the accuracy of muscle targeting. Suboptimal precision in injections can lead to unsatisfactory outcomes, persistence of symptoms, or treatment discontinuation.

Several approaches are used in clinical practice to guide injections. The conventional method relies on palpation and anatomical landmarks, is widely available, and requires limited resources. However, it depends heavily on the injector's experience and may result in inaccurate targeting. Ultrasound (US) guidance, on the other hand, allows direct, real-time visualisation of the cervical muscles and adjacent structures. This technique may increase accuracy, optimise toxin distribution, and lower the risk of misplaced injections and adverse events.

Cadaveric studies have demonstrated higher accuracy of US-guided injections compared with landmark-based methods, and preliminary clinical studies suggest that US guidance may improve outcomes. However, these studies have been limited by small sample sizes, lack of randomisation, or non-blinded assessments. Robust evidence from randomised controlled trials is still lacking, and therefore the clinical superiority of US guided injectionsance remains uncertain.

US-guided injections also require additional equipment, time, and operator training. This may limit their widespread adoption in routine clinical practice unless a clear advantage over landmark-based injections is demonstrated. Addressing this knowledge gap is essential to inform clinical decisions and optimise the management of CD.