EMG-Guided Versus Endoscopic-Catheter Botulinum Toxin Injection for Spasmodic Dysphonia

This randomized, controlled non-inferiority trial will compare two established botulinum toxin injection techniques for adductor spasmodic dysphonia: percutaneous electromyography-guided injection and transnasal endoscopic catheter-guided injection. The study will evaluate whether the endoscopic technique provides voice outcomes that are not inferior to the standard EMG-guided approach, while also assessing treatment-related adverse effects, procedural tolerability, and practical advantages such as direct visualization and suitability for patients with challenging neck anatomy.

Inclusion Criteria: * Age 18 years or older * Known diagnosis of adductor spasmodic dysphonia (AdSD), who has previously received ≥1 course of BTX injection for AdSD with symptomatic benefit * Able to independently provide informed consent * Able to tolerate flexible laryngoscopy Exclusion Criteria: 1. Age under 18 years 2. Inability to provide independent informed consent 3. Known hypersensitivity or allergy to botulinum toxin preparation or to local anaesthetics 4. Documented neuromuscular junction disease (e.g. myasthenia gravis, Eaton-Lambert syndrome) 5. Unable to tolerate flexible laryngoscopy 6. Active laryngeal pathologies other than AdSD requiring concurrent treatment 7. Uncorrected coagulopathy or bleeding tendency