Introduction

Botulinum toxin has been employed for clinical cosmetic use for over twenty years. Currently it is the most commonly performed non-surgical facial cosmetic procedure and is also widely used for non-cosmetic purposes. Botulinum toxin type A (BoNT-A) is produced from Clostridium botulinum and acts on presynaptic neurons to block acetylcholine release by cleavage of the SNAP-25 protein. There are three formulations of BoNT-A that are currently approved cosmetically by the Food and Drug Administration (FDA) for the treatment of moderate to severe glabellar rhytides: (Botox^® – Allergan, US), (Dysport^® – Medicis / Ipsen, Arizona, US and France), (Xeomin^® – Germany). Following cosmetic botulinum toxin A injections, the effects begin to be noticeable within 1 to 3 days and will typically last for 3 to 4 months.

Although these botulinum toxin A formulations are FDA approved only for treating glabellar rhytides, they are also commonly used cosmetically in other areas on the face and neck. The frontalis is a large forehead muscle responsible for the development of horizontal forehead lines (HFLs) due to contraction – which raises the eyebrows and upper eyelids, and over time results in these contraction lines etching into the forehead. The forehead is thus a major target area for botulinum toxin treatment owing to the vertical movement of the underlying frontalis muscle to lift the eyebrows during animation. The inferior frontalis fibers insert into periocular muscles including: the procerus, corrugator supercilii, orbicularis oculi, and depressor supercilii. Superiorly, the fibers course horizontally and insert into the galea of the scalp, often with no fibers in the midline between the hairline and the middle of the forehead.

Side effects

Potential side effects from botulinum toxin use in the forehead include injection site pain, swelling, and bruising, as well as headache, eyebrow ptosis, eyelid ptosis, diplopia, and the development of new rhytides. New rhytides may appear as a result of overcompensation of untreated adjacent muscles. A case series by Kang et al (2011) of four patients receiving BoNT-A for HFLs reported the development of lower frontalis and glabellar protrusions as well as new unilateral forehead rhytides above the eyebrow. In all patients, most of the new rhytides were almost completely resolved within 4 weeks without further treatment. Indeed, the majority of side effects resulting from cosmetic use of botulinum toxin in the forehead as well as in other aesthetic regions resolve spontaneously without treatment.

Other possible side effects from botulinum toxin treatment of HFLs include eyebrow and eyelid ptosis and periorbital edema, which are also self-limited. BoNT-A agents have been shown to spread up to 3 cm from the site of injection, but this may depend on the actual agent used and the method of dilution. Certain predisposing factors for eyebrow ptosis include age greater than 50 years and patients with mild eyebrow ptosis at baseline. Patients with pre-existing low eyelid platforms (i.e. the upper eyelid itself hangs down to or near the level of eyelashes) and dermatochalasis (Fig. 14.1; redundant skin at the eyebrow that hangs down toward the eyelid) should also be carefully evaluated to decide whether or not to proceed with treatment of the HFLs. Techniques that may help to prevent eyebrow ptosis include simultaneous treatment of brow depressors (especially the superior–lateral aspect of the orbicularis oculi) and to avoid eyelid ptosis by choosing injection points sufficiently superior to the orbital rim.

Figure 14.1 Dermatochalasis: redundant skin at the eyebrow that hangs down toward the eyelid, with eyes (A) closed and (B) open.

Pearl 2

Evaluate forehead and brow position prior to treatment by studying the frontalis at rest and with animation, and document each of these appearances with a photograph prior to treatment (Fig. 14.2).

Figure 14.2 Clinical photograph of horizontal forehead lines at rest and with brows raised: (A, B) before and (C, D) after treatment with botulinum toxin type A.

Injection techniques

Numerous different injection points and total units have been suggested for treating the forehead rhytides. The difficulty associated with treating this region is related to individual differences in frontalis muscle and forehead structure, as well as how the muscle is used functionally for facial expression. Individualized injection techniques are typically required, especially for patients with tall (wide) and short (narrow) foreheads, in order to achieve effective results and prevent complications such as eyebrow depression. For example, some physicians will perform two or more horizontal lines of injection for patients with tall foreheads while administering only one horizontal line of injection for those with short foreheads. However, these lines are not usually absolutely straight and typically we employ a higher injection point above the mid-brow in women, to avoid flattening an arched feminine brow.

In a study reported by Ozsoy et al in 2005, 90 patients with short and tall foreheads were treated with BoNT-A using different injection techniques. In the study, a glabella–frontal hairline distance greater than 70 mm was considered to be a tall forehead, while a distance less than 60 mm was classified as a short forehead. For tall foreheads, three vertical lines of injections were performed; for short foreheads, three horizontal lines of injections were given. The authors reported effective results in all patients without any instances of ptosis or brow asymmetry. In this study, the average age of male and female participants ranged from 41.5 to 42.3 years. In an older population, brow repositioning may develop and become problematic, especially for those with dermatochalasis who depend on the lower lateral frontalis muscle to hoist up the affected brow.

In addition to the physical variability of each patient, there are also differences in the properties of the botulinum toxin products currently available on the market. The different formulations of BoNT-A are made from different bacterial strains and processing methods. The commonly used formulations in the United States include onabotulinumtoxinA (Botox Cosmetic^®; Allergan Inc., Irvine, CA, USA) and abobotulinumtoxinA (Dysport^®