Botulinum Neurotoxin Therapy in the Clinical Management of Laryngeal Dystonia

Abstract

Laryngeal dystonia (LD), or spasmodic dysphonia (SD), is a chronic, task-specific, focal movement disorder affecting the larynx. It interferes primarily with the essential functions of phonation and speech. LD affects patients' ability to communicate effectively and significantly diminishes their quality of life. Botulinum neurotoxin was first used as a therapeutic agent in the treatment of LD four decades ago and remains the standard of care for the treatment of LD. This article provides an overview of the clinical application of botulinum neurotoxin in the management of LD, focusing on the classification for this disorder, its pathophysiology, clinical assessment and diagnosis, the role of laryngeal electromyography and a summary of therapeutic injection techniques, including a comprehensive description of various procedural approaches, recommendations for injection sites and dosage considerations.

Keywords: botulinum neurotoxin; electromyography; injection; laryngeal dystonia; spasmodic dysphonia.

Figure 1

Schematic diagram of the larynx depicting the intrinsic laryngeal muscles, highlighting the thyroarytenoid (TA) and lateral crico-arytenoid (LCA) from the adductor muscle group (left) and the posterior crico-arytenoid (PCA) abductor muscle (right).

Figure 2

Clinical photograph depicting the ground and negative transcutaneous leads required for laryngeal EMG setup and the landmarks for the cricothyroid membrane approach to the adductor muscle complex. The surface landmarks for the thyroid and cricoid cartilages are delineated in black. The entry points for the injection needle are marked by ‘X’.

Figure 3

Schematic diagram illustrating the cricothyroid membrane injection approach to TA muscle in the treatment of ADLD.

Figure 4

Schematic diagram illustrating transthyrohyoid injection approach to the TA. The supraglottic structures can also be approached in this way.

Figure 5

Schematic diagram illustrating lateral rotational injection approach to the PCA.

Figure 6

Schematic diagram illustrating anterior trans airway approach to the PCA muscle.

Figure 7

Schematic diagram illustrating technique for injection into the cricothyroid muscle.