Purpose: Deoxycholic acid (Kybella) is a drug commonly injected in non-surgical aesthetic procedures to locally reduce subcutaneous fat. Kybella treatment has been reported to have adverse effects, one of which can cause marginal mandibular nerve injury with noticeable functional deficits when injected to target submental fat. As an adipocytolytic agent, Kybella may damage the lipid-rich myelin surrounding peripheral nerves. Given that limited basic science studies investigating this agent have been performed to date, this study seeks to characterize the nerve injury associated with Kybella.
Methods: Using a sciatic nerve injection model in rats, intrafascicular and extrafascicular injections of deoxycholic acid (Kybella) were compared to intrafascicular lidocaine (positive control) and intrafascicular saline (negative control) injections. All agents were administered in a 50 µL volume to the sciatic nerve proximal to its trifurcation. Injection sites were delineated with 10-0 nylon suture 1mm proximal and distal to the injection. Nerves were harvested at a 2-week endpoint for histomorphometric analysis and electron microscopy.
Results: Intrafascicular saline injection caused minimal injury to sciatic nerve. Comparing the area of healthy nerve with injured nerve fibers marked by scarring and fibrosis, the percent area of injured sciatic nerve was 78% in the intrafascicular Kybella group, 49% in the extrafascicular Kybella group, and 40% for the intrafascicular lidocaine group. There was a significant difference between the intrafascicular lidocaine and Kybella groups (p=0.003), as well as the intrafascicular and extrafascicular Kybella groups (p=0.045). The g-ratio assessing axonal myelination was not significantly different between the lidocaine (0.58), Kybella (0.58 and 0.56), and saline (0.56) injection groups.
Conclusion: Initial results suggest deoxycholic acid (Kybella) is capable of extensive nerve injury. Although Kybella is a known adipocytolytic agent, its mechanism of damage does not seem to involve myelin. Physicians administering Kybella for non-surgical aesthetic treatment of excess fat should be aware of these potential side effects, and further translational studies are needed. Appropriate knowledge of surgical anatomy is recommended for those practitioners providing Kybella injections.