Treatment of glabellar lines with neuromodulators

Introduction

Botulinum toxin type A (BoNT-A) has been useful for many applications, but its most popular use is for treatment of glabellar rhytides. In 1979, the US Food and Drug Administration (FDA) gave limited approval for trials of BoNT-A for strabismus. In 1985, it was used for blepharospasm and, in 1987, Dr. Jean Carruthers made an observation that patients who received botulinum toxin treatment for blepharospasm also had improvement of dynamic glabellar rhytides. The first published reports of the use of botulinum toxin for the treatment of facial lines were those by Carruthers and Carruthers and by Borodic in the early 1990s. However, it was not until 2002 that BoNT-A was granted its first approval for cosmetic use, specifically for the treatment of glabellar rhytides.

The use of BoNT-A for treatment of glabellar rhytides has revolutionized the field of cosmetic dermatology and plastic surgery. Several multicenter, double-blind, randomized, placebo-controlled studies have demonstrated its efficacy. It is the first effective nonsurgical technique for both brow lift and rhytid treatment. Carruthers et al. demonstrated in 2010 that BoNT-A injection to the glabella has been shown to improve both dynamic glabellar rhytides and those in repose. In 2015, Carruthers et al. presented data demonstrating that patients repeatedly treated with BoNT-A over the long term (three treatment cycles with 4-month intervals) show progressive improvement in static glabellar lines.

Anatomy

The glabellar complex consists of the two corrugator supercilii muscles and the procerus muscle that collectively serve upon contraction to pull the brow medially and downward ( Fig. 15.1 ). The corrugator supercilii are two sets of horizontally oriented muscle fibers that lie beneath the medial eyebrow to the midpupillary line. In some patients, the corrugators extend beyond the midpupillary line. (These muscles can be visualized at maximum contraction when “frowning,” or asking the patient to “concentrate very hard” or “furrow the eyebrows.”) The procerus is a vertically oriented muscle that lies in between the eyebrows. The frontalis muscle of the forehead is vertically oriented, and the medial belly interpolates with the glabellar complex, and its lateral portion interpolates with the lateral orbicularis oculi. Its main function is to elevate the brow. The orbicularis oculi is a thin circular muscle around the eyes that lies on top of the lateral portion of the corrugator supercilli. The lateral portion of the orbicularis oculi under the tail of the brow is a powerful brow depressor. The levator palpebrae muscle lies beneath the orbicularis oculi, underneath the bony orbital rim, and its function is eyelid opening. Rhytides are typically perpendicular to the orientation of muscle fibers, thus contraction of the glabellar muscles typically produces vertically oriented lines between the brows.

Injection technique (see Videos 15.1A – C “Botulinum Toxin Glabella”)

In the glabella, there are typically five injection sites: one at each medial corrugator, one at each lateral corrugator (1 cm above orbital rim at the midpupillary line), and a single injection into the procerus ( Fig. 15.2 ). For some patients with particularly long or stronger corrugator muscles, an additional injection site may be given midway between the medial and lateral corrugator injection sites. For those who desire more movement of their glabellar complex after injection, three injection sites may be preferred, skipping the lateral corrugator injections, or keeping all five injection sites and lowering the dose. Insulin syringes or 1-mL syringes with 30- to 32-gauge needles are typically used for injection. See the “Botulinum Toxin Glabella” video for further illustration of the injection technique.

Even without the lateral brow injection, injection of 20 to 40 U of BoNT-A into the glabellar muscles alone leads to eyebrow elevation. This is due to relaxation of the depressor actions of the corrugator procerus muscles, as well as inactivation of the medial muscles of the frontalis, with resultant increased muscle tone of the lateral and superior muscles of the frontalis. Studies by Huang et al. found that the eyebrow elevation usually ranges from 1 to 3 mm.

Dosing