Brain functional networks adapt in response to surgery and Botox for facial palsy, reports study

For patients undergoing nerve transfer surgery for facial palsy, Botox injections can improve facial symmetry by reducing overactivity of the muscles on the unaffected side, suggests a study in the March issue of Plastic and Reconstructive Surgery®, the official medical journal of the American Society of Plastic Surgeons (ASPS). The journal is published in the Lippincott portfolio by Wolters Kluwer.

The added benefit of Botox reflects modifications in brain functional network connectivity, according to the new research, led by Ye-Chen Lu, MD, PhD, and Wei Wang, MD, PhD, of Shanghai Jiao Tong University School of Medicine, China. They write, "These findings imply that enhanced connectivity between brain functional networks play a vital role in the recovery process from neurological disorders."

BoNT-A improves outcomes of surgery for facial palsy

Facial nerve injury can cause paralysis on the affected side of the face, leading to functional and cosmetic impairments. For patients with this condition, nerve transfer surgery is recommended to restore facial nerve function and symmetry.

However, many patients have persistent impairment after surgery, especially drooping of the corner of the mouth (oral commissure) on the affected side. This condition has been linked to overactivity of the muscles on the opposite side, leading to facial asymmetry even at rest.

Such patients have been successfully treated using botulinum toxin-A (BoNT-A; best known by the brand name Botox) to produce temporary relaxation of overactive muscles on the unaffected side. Previous studies suggest lasting improvement, even after the effects of BoNT-A fade.

Benefits linked to changes in brain network connectivity

"We hypothesize that BoNT-A treatment triggers extensive cortical plasticity, offering a potential explanation for its long-lasting therapeutic impact on patients with facial asymmetry," the researchers write. They used functional magnetic resonance imaging (fMRI) scans to assess functional activity of brain networks before and after surgery and BoNT-A treatment.

The study included 38 patients with facial palsy and "severe oral commissure drooping" after surgery for benign tumors (acoustic neuromas). All underwent nerve transfer surgery followed by facial training and rehabilitation. In addition, patients were randomly assigned to a treatment group receiving a series of BoNT-A injections of the facial muscles on the unaffected side; or a control group receiving no BoNT-A.

Patients receiving BoNT-A had significant improvement in facial asymmetry. "BoNT-A injections improved facial static function without affecting smile function," the researchers write. As in previous studies, the benefits persisted beyond six months, after the effects of BoNT-A wore off.

Before surgery and one year later, patients underwent fMRI scans to assess changes in in brain functional network connectivity. Of nine resting state networks (RSNs) studied, five showed "significant differences of spatial distribution" between groups. Patients receiving BoNT-A "displayed an overall stronger interaction between several RSNs" – notably including the sensorimotor and visual networks.

"Our research provides evidence of long-term and widespread changes in cerebral networks among facial paralysis patients," Drs Lu and Wang and coauthors write. These effects may explain why the improvement persists even after the effects of BoNT-A dissipate.

BoNT-A injections "may create a "window of time for nerve reanimation, allowing the brain to learn and restore proper facial muscle activity." The researchers conclude: "These findings imply that enhanced connectivity between brain functional networks play a vital role in the recovery process from neurological disorders."

Reference:

Ma, Hao MD1; Zhou, Yu-lu MD1,3; Wang, Wen-jin PhD1; Chen, Gang MD1; Zhang, Chen-hao MD2; Lu, Ye-chen MD1,3; Wang, Wei MD2,3. Facial Symmetry Enhancement and Brain Network Modifications in Facial Palsy Patients after Botulinum Toxin Type A Treatment. Plastic and Reconstructive Surgery 155(3):p 586e-596e, March 2025. | DOI: 10.1097/PRS.0000000000011689