Botulinum Toxin Injection for the Treatment of Upper Esophageal Sphincter Dysfunction

Abstract

Dysphagia associated with upper esophageal sphincter (UES) dysfunction remarkably affects the quality of life of patients. UES injection of botulinum toxin is an effective treatment for dysphagia. In comparison with skeletal muscles of the limb and trunk, the UES is a special therapeutic target of botulinum toxin injection, owing to its several anatomical, physiological, and pathophysiological features. This review focuses on (1) the anatomy and function of the UES and the pathophysiology of UES dysfunction in dysphagia and why the entire UES rather than the cricopharyngeal muscle before/during botulinum toxin injection should be examined and targeted; (2) the therapeutic mechanisms of botulinum toxin for UES dysfunction, including the choice of injection sites, dose, and volume; (3) the strengths and weaknesses of guiding techniques, including electromyography, ultrasound, computed tomography, and balloon catheter dilation for botulinum toxin injection of the UES.

Keywords: botulinum toxin; cricopharyngeal muscle; dysphagia; electromyography; injection; ultrasound; upper esophageal sphincter.

Figure 1

Schematic diagram of inferior pharyngeal constrictor. Anatomical structures are displayed in the sagittal plane (i.e., lateral view). The approximate location of the vocal folds is indicated.

Figure 2

Schematic diagram of cervical esophagus muscle layers. The esophagus lumen is enclosed by the mucosa of the cervical esophagus. The inner circular layer (in grass green) and outer longitudinal muscle fibers (in pink) are presented. The adventitia of the cervical esophagus is not shown. The inner circular layer is the injection target.

Figure 3

Structures under direct view by flexible endoscopy. The red circle indicates the approximate location of the postcricoid region, where botulinum toxin injection can be administrated into the UES wall under direct view by flexible endoscopy.

Figure 4

Transcutaneous injection approach. A cervical spine magnetic resonance image (MRI) of a young, healthy individual is presented. The UES slightly deviates from the midline to the left. The MRI of the (right) panel is the same as the (left) one and demonstrates three injection approaches as follows: 1, the needle route passes through the thyroid gland; 2 and 3, the needle route passes through the lateral side of the neck to bypass the thyroid gland and big blood vessels.

Figure 5

UES and inflated balloon viewed by ultrasound. The inflated balloon dilation procedure is monitored by ultrasound. The (left) panel is a cross-sectional demonstration. Note that the hypoechoic interface (dark zone) between the thyroid gland and the UES is not the UES wall. The (right) panel presents the balloon moving along the long axis of the UES. See Supplementary Video S1 (corresponding to the (left) panel) and Video S2 (corresponding to the (right) panel) for dynamic display.