Introduction

Botulinum toxin type A has been found to be useful for many applications since its initial introduction, but one of its most popular uses has been for treatment of glabellar rhytides. In 1979, the Food and Drug Administration (FDA) gave limited approval for trials of botulinum toxin A for strabismus. In 1985 it was used for blepharospasm. Two years later, 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 & Carruthers and by Borodic in the early 1990s. However, it wasn’t until 2002 that botulinum toxin type A was granted its first approval for cosmetic use specifically for the treatment of glabellar rhytides.

The use of botulinum toxin type A over the last two decades for treatment of glabellar rhytides has revolutionized the field of cosmetic dermatology and plastic surgery. Several multicenter, double-blind, randomized, placebo-controlled studies have proven its efficacy (e.g. that by Carruthers et al in 2003). It is the first quick, less invasive and effective, non-surgical technique for both brow lift and rhytid treatment. The same group demonstrated in 2010 that botulinum toxin type A injection to the glabella has been shown to improve both dynamic glabellar rhytides and those in repose. Subsequent uses of botulinum toxin type A for cosmetic improvement of forehead, perioral area, chin, crow’s feet, and other rhytides have been successful, but its use in the glabella is the first and still the most widely used.

In this chapter, we will discuss the anatomy, injection technique, dosing, special considerations, and potential adverse events of botulinum toxin injection of the glabella.

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. 12.1). The corrugator supercilii are two sets of horizontally oriented muscle fibers that lie beneath the medial eyebrow to about the mid-pupillary line. In some patients, the corrugators extend beyond the mid-pupillary line (these muscles can be visualized at maximum contraction when ‘frowning’). 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 upon contraction. 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.

Figure 12.1 Muscles of the face.

Courtesy Dr Jean Carruthers, reproduced with permission.

Injection technique (see Video ‘Botulinum Toxin Glabella’)

The proper preparation, storage, and handling of botulinum toxin is discussed in Chapters 9 and 11. Insulin syringes or 1 mL syringes with 30–32 gauge needles are typically used for injection.

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 mid-pupillary line), and a single injection into the procerus (Fig. 12.2). 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 (a total of seven injections).

Figure 12.2 Five injection sites for botulinum toxin into the glabella: one at each medial corrugator, one at each lateral corrugator (1 cm above the orbital rim at the mid-pupillary line), and a single injection into the procerus.

Even without the lateral brow injection, injection of 20–40 units of botulinum toxin type 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 Huilgol et al and by Huang and co-workers found that the eyebrow elevation usually ranges from 1 to 3 mm (mean elevation 1 mm).

Dosing

Botox^® (onabotulinumtoxinA) (Fig. 12.3)

With standard dilutions of a 100-unit vial of Botox^® (Allergan Inc., Irvine, CA, USA) with 2.5 mL of 0.9% normal saline, a single injection of 0.1 mL yields 4 units. In women, 20–24 units of Botox^® via five injection points are typically injected into the glabellar complex; an additional 3 units may be injected into each lateral eyebrow to achieve brow lift. In our experience, in men, 20–40 or more units may be injected into the glabellar complex depending on the strength of muscle contraction. In a 2005 study by Carruthers and colleagues of 80 men randomized to receive 20, 40, 60, or 80 units of botulinum toxin type A (Botox^® or Vistabel^®, Allergan Inc., Irvine, CA), the 40, 60, and 80 U doses were consistently more effective than the 20-unit dose in reducing glabellar lines (duration, peak response rate, improvement from baseline).

Figure 12.3 (A) Pre-onabotulinumtoxinA injection, relaxed. (B) Pre-onabotulinumtoxinA in maximal glabellar contraction. (C) Pre-onabotulinumtoxinA in maximal frontalis contraction. (D) 1 week after 20 U onabotulinumtoxinA injection to the glabella, relaxed. (E) 1 week after 20 U onabotulinumtoxinA injection to the glabella, in maximal glabellar contraction. (F) 1 week after 20 U onabotulinumtoxinA injection to the glabella, in maximal frontalis contraction.

Onset of response is typically 1–14 days and results last for 3–4 months. In a 2011 study by Beer et al

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