Depth of Botulinum Neurotoxin Injection for Treatment of Glabellar Lines

STUDY AIM, BACKGROUND, AND DESIGN ABSTRACT

Botulinum neurotoxin (BoNT) is a safe and effective treatment for numerous conditions in neurology, ophthalmology, dermatology, gastroenterology, psychiatry, and urology. In dermatology, BoNT is commonly used for treatment of facial rhytides and is by far the most frequently performed cosmetic procedure in recent years. In 2002, the US Food and Drug Administration (FDA) approved the use of BoNT for the treatment of glabellar lines. Although, BoNT has shown excellent safety profile for the treatment of glabellar lines, injection methods vary widely between practitioners and no standardized method for the depth of injection has been established.

The most common treatment area is the glabellar complex, which consists of bilateral corrugator supercilii, depressor supercilii, procerus, and the orbital portion of the orbicularis oculi. With increasing age and repetitive contraction of the glabellar complex, particularly the bilateral corrugator supercilii and procerus, the formation of prominent dynamic glabellar lines and static, etched-in glabellar lines can form and lead to the appearance a more severe frown. In a study using ultrasonographic imaging and the three-dimensional scanning Cho et al. determined that the procerus was located at a depth of 3.8 ± 0.7 mm at the glabella and 2.7 ± 0.6 mm at the sellion while the intercanthal vein was located 3.0 ± 0.6 mm below the skin's surface superior to the sellion. Careful consideration of depth of injection and facial anatomy must be taken to avoid bruising and intravascular injection of BoTN. Additionally, in a cadaveric study looking at depth of corrugator supercilii of 32 Korean hemifaces using 3D scanning, Lee et al. found that the corrugator supercilii muscle rested at a depth of 5.7 +/-1.4 mm medially and 6.6 +/-1.4mm laterally and recommended BoTN injections at the depth of 4mm. However, no in vivo studies have been performed to validate this as the optimal depth of injection. In a split face study evaluating the depth of botulinum injection into the corrugator supercilii muscle no difference in brow height between injecting periosteally versus in superficial dermis. The investigators previously studied the ability of botulinum toxin to diffuse in crow's feet through laser pores into the target muscle. (8)

In our randomized study, the investigators will evaluate the efficacy of BoTN for the treatment of glabellar lines when injected at a depth of 2mm (superficial dermis) versus 4mm (intramuscularly). The investigators hypothesize that no difference exists between the two depths as the 150kD botulinum toxin molecules can easily diffuse to the target at the muscle. If this is validated, patients can be treated with more superficial depths, which will result in less pain and bruising.

STUDY HYPOTHESIS: Depth of injection of onabotulinumtoxinA neurotoxin in the glabellar complex does not affect efficacy of the BoTN for the improvement of glabellar lines.