Consideration of Muscle Mass in Glabellar Line Treatment With Botulinum Toxin Type A
September 2012 | Volume 11 | Issue 9 | Original Article | 1041 | Copyright © 2012
The introduction of botulinum neurotoxin type A (BoNTA) for the treatment of glabellar lines marked a revolution in aesthetic medicine, allowing for noninvasive facial rejuvenation and sculpting. Treatment of the glabellar area requires a thorough understanding of facial anatomy and the interaction of adjacent muscle groups with respect to facial expression. Because the muscles underlying the glabella are among the larger muscles commonly treated with BoNTA, they may require higher doses than other facial sites. In addition, men typically have a greater glabellar muscle mass than women and require larger BoNTA doses. For optimal outcomes, it is necessary to account for individual variation in muscle mass, anatomy, and function to determine the proper dose, number, and location of injections. The validated Medicis Glabellar Muscle Mass Scale was developed to facilitate research on dose adjustment for muscle mass in the glabella and can be applied as a clinical tool. This review will discuss techniques for optimizing BoNTA treatment of the glabella, with emphasis on the need to assess muscle mass in individual patients and adjust BoNTA dosing and technique accordingly.
J Drugs Dermatol. 2012;11(9):1041-1045.
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The discovery of the aesthetic applications of botulinum neurotoxin type A (BoNTA) was a revolutionary change in aesthetic medical practice, providing a less invasive approach to facial rejuvenation and sculpting to achieve a more youthful appearance.1 Three BoNTA products are available for aesthetic use in the US: abobotulinumtoxinA (Dysport®, Medicis Aesthetics Inc., Scottsdale, AZ),2 incobotulinumtoxinA (Xeomin ®, Merz Pharmaceuticals, LLC, Greensboro, NC),3 and onabotulinumtoxinA (Botox® Cosmetic, Allergan, Inc., Irvine, CA)4 (Table 1). Doses of different BoNTA products are not interchangeable, or even directly comparable, due to differences in production and assay methods3,5,6; however, the techniques for treatment are otherwise generally similar. Although these products are widely used in aesthetic treatment of different facial areas, most research has focused on the temporary improvement of glabellar lines, for which multiple clinical studies have shown that BoNTA injections are effective and well tolerated.7-16
Achieving the desired outcome with BoNTA while minimizing the risk for adverse events requires proper dosing and accurate placement of injections to avoid migration of the product outside the target muscle. An optimal treatment plan takes into account facial anatomy, the interactions of adjacent muscle groups, and muscle mass. The muscles underlying the glabella are, in most patients, among the larger targets for BoNTA treatment of the face and require higher doses than most other facial muscles commonly treated with BoNTA.17 Furthermore, each of the muscles of the glabellar complex varies in mass and strength among individuals. Anatomic diagrams and bony landmarks such as the bony orbital ridge form an inadequate basis for placement of the injections; dynamic evaluation of the glabellar muscles via visualization and palpation at rest and at maximal contraction is needed to assess their location, bulk, contour, and symmetry.17 Clinical trials have typically evaluated standardized doses of BoNTA and a fixed number of injection sites for the treatment of glabellar lines. Formal grading scales for muscle mass may improve comparability of trial data and also find clinical applications.
This review will focus on the nuances of technique, including the need to judge muscle mass in individual patients and adjust dose based on muscle mass, when using BoNTA to treat glabellar lines.
Considerations for Optimal Treatment of Glabellar Lines
Muscular Anatomy of the Glabellar Complex
Muscles of the glabellar complex responsible for the formation of frown lines include the corrugator supercilii, depressor supercilii, procerus, and orbicularis oculi para frontalis muscles (Figure 1). The corrugator supercilii lies below the frontalis muscle and functions to draw the brow medially and downward, whereas the smaller depressor supercilii is located lower than the corrugator muscle and functions to draw the medial brow downward. The procerus is located between the eyebrows and also works to depress the glabellar medial brow region. The depressor function of the glabellar complex is opposed by the frontalis muscle. This muscle is merged with the superior portions of the glabellar complex, from which it extends upwards underneath the forehead. The frontalis is the sole brow elevator.17 Understanding of the anatomic location and interplay between elevator and depressor muscles is needed to guide injection technique in order to achieve a smooth, balanced, and aesthetically pleasing outcome with BoNTA.
The facial musculature of the individual patient (Figures 2 and 3) critically affects treatment decisions for several reasons. Gender-based differences may influence treatment decisions, and, in