Ultrasonographic observation of the masseter muscle after injection of different botulinum toxin type A

Botulinum toxin type A (BoNT-A) injection is a popular cosmetic procedure in East Asian countries, and there are multiple types of toxins on the market. Whether different toxin types induce different changes in the masseter has not been studied.We aimed to investigate and compare the changes induced by injection of different types of BoNT-A in the masseter.Upon retrospective review of clinical records and routine ultrasound examination results of patients who underwent BoNT-A injection, four groups were set for comparison: unapproved toxin, OnabotulinumtoxinA, LanbotulinumtoxinA, and non-injected. Clinical records and ultrasound images were collected. Ultrasound images were taken in both horizontal and coronal planes. Elasticity of the masseter muscle was also investigated by measuring the surface wave speed.A total of 24 patients were included (six patients per group). All patients were young females. For the non-injected group, the deep inferior tendon was clear and the muscle bundles were arranged, with little fibrous content. Patients who received unapproved toxin injection showed highly disarranged muscle and fiber bundles, with much fiber content present. The changes in OnabotulinumtoxinA and LanbotulinumtoxinA groups were in between those in the non-injected and unapproved toxin groups. Muscle rigidity was the highest in the unapproved toxin group, and generally higher in injected groups compared with the non-injected group.Different types of BoNT-A may induce different changes in the masseter.