The specific study objectives are to determine if:
* the neck circumference is decreased at 4 weeks after botulinum toxin (prabotulinumtoxinA-xvfs) injection.
* patients can appreciate a difference in their neck contour, self-confidence, and the way they perceive themselves post-injection via an aesthetics outcome and a neck perception survey.
* injection of the botulinum toxin into the sternocleidomastoid muscle is safe to perform based on adverse events.
