Consideration of Muscle Mass in Glabellar Line Treatment With Botulinum Toxin Type A

September 2012 | Volume 11 | Issue 9 | Original Article | 1041 | Copyright © September 2012

table 3
ed using weighted kappa coefficients (separately for men and women; Table 2). Although a somewhat lower overall weighted kappa coefficient was found in the evaluation of men (within-observer, 0.719; between-observer, 0.557-0.607) compared with women (within-observer, 0.872; between-observer, 0.625-0.718), the results are consistent with substantial within-observer agreement (ie, kappa 0.60-0.79). Despite its robust validation and direct applicability to glabellar muscle mass, the MGMMS has several potential limitations. First, assessment is based on static 2-dimensional images, rather than on live assessments of patients. Additionally, a standard relationship between MGMMS results and a proper starting BoNTA dose has not yet been established.

Dosing of BoNTA to Treat Glabellar Lines

The prescribing information for each BoNTA product specifies a standard, fixed total dose for the glabellar complex (50 U of abobotulinumtoxinA, 20 U of onabotulinumtoxinA, or 20 U of incobotulinumtoxinA), but states that the location, size, and use of muscles vary significantly among individuals.2-4Some studies have shown that variable dosing of BoNTA can facilitate more effective treatment of glabellar lines when comparing women versus men or patients with smaller versus larger glabellar muscle mass.12,21 Moreover, BoNTA was shown to be safe when dosage was adjusted for small, medium, or large muscle mass (ie, 50, 60, or 70 U in women, and 60, 70, or 80 U in men, respectively) in a large clinical trial.12 Statements by consensus groups and experienced clinicians further support individualization of BoNTA dosing for achieving optimal improvement of glabellar lines (Table 1).17,18
A starting dose should be chosen based on a standard dose from the prescribing information or recommendations of consensus groups and experienced clinicians17,22 and then adjusted based on individual assessment of muscle mass. Individual dose adjustment is based on clinician judgment, aided by a thorough understanding of facial anatomy (as noted previously), assessment of glabellar muscle mass, appearance at presentation (eg, presence of facial asymmetry or ptosis), and previous experience with the individual patient if he or she has received BoNTA treatment before. For new patients, it is advisable to estimate the initial dose conservatively and follow up in 2 to 4 weeks for a touch-up dose if needed. This approach requires careful clinical judgment because definitive data are lacking on how to adjust the dose and about potential risks associated with administering doses higher than those approved in the prescribing information.

Localization and Technique for Injections of BoNTA to Treat Glabellar Lines

Variation in muscle bulk, length, angle, and symmetry are particularly common for the corrugator supercilii.23,24 Injections of BoNTA should be kept >1 cm superior to the bony supraorbital ridge (Figure 1)2-4 if visualization and palpation clearly indicate that the belly of the corrugator supercilii lies at least 1 cm superior to the orbital ridge. In individuals whose corrugator supercilii is less than 1 cm superior to the orbital ridge, care must be taken to avoid missing the corrugator and injecting the lower margin of the frontalis, which will likely result in brow ptosis. Overdosing of the glabella can lead to excessive widening of the inter-brow space, distortion of brow contour, and loss of normal facial expression. Thus, ensuring proper placement and adjusting the dose in individuals according to muscle mass reduces the risk for adverse events associated with overdosing of smaller muscles.2-4
When injecting, the following points are helpful to keep in mind: grasp the target muscle (corrugator supercilii) and simultaneously press the frontalis upward to avoid injecting it.17 Aim the needle away from the eye in order to reduce the chance of injecting behind the septum into the orbicularis oculi, thus causing upper lid ptosis (ie, eyelid droop). Although some authorities advise injecting perpendicular to the muscles,22 angling the needle parallel to the body of the corrugator can improve the likelihood of injecting directly into the belly of the muscle. To help prevent bruising, avoid visible blood vessels while injecting and immediately apply pressure if bleeding