CHAPTER 158
Aesthetic Uses of Botulinum Toxins

Nicholas J. Lowe

The Cranley Clinic, London, UK

Introduction

Botulinum neurotoxins, sometimes referred to as neuromodulators, have proven efficacy for a variety of clinical indications arising from neuromuscular hyperactivity, and other conditions caused by acetylcholine (ACh) release. The approved indications include the aesthetic use of botulinum toxin to reduce hyperfunctional facial muscles which cause facial lines and the treatment of focal hyperhidrosis.

In 1992, the seminal observation that botulinum toxin type A (BTX-A) was effective in reducing muscle-induced forehead lines was reported [1]. This was followed by double-blind, placebo-­controlled, evidence-based studies confirming the efficacy of BTX-A for the reduction of dynamic facial lines [2, 3, 4, 5]. Botox™, now designated onabotulinumtoxinA (BTX-A Ona), was developed in the USA as the first BTX-A for aesthetic treatments. It rapidly gained popularity during the 1990s and the early 21st century [1–3, 4, 5] as a paradigm shift in the treatment of facial rejuvenation. In the UK, an alternative type of BTX-A known as Dysport™, now designated abobotulinumtoxinA (BTX-A Abo), was developed for similar indications. Controlled clinical trials followed with publications in 2004 and 2006 [6, 7].

Another approved indication for BTX-A Ona is the management of severe axillary sweating. The treatment of gustatory sweating was reported by Naumann et al. [8] and was followed by studies treating severe axillary hyperhidrosis with BTX-A Ona [9]. BTX-A is now a recognized treatment option for severe localized hyperhidrosis and is discussed in more detail in Chapter 94.

Three types of BTX-A currently exist and are approved in Europe and in the USA for aesthetic indications (Table 158.1). In addition, a botulinum toxin type B (BTX-B) has been developed with ­distinct pharmacological mechanisms but similar clinical indications to that of type A toxins.

Table 158.1  Pharmaceutical terminology of neurotoxins

Trade name Pharmaceutical name
Botox Ona botulinum toxin type A
Dysport Abo botulinum toxin type A
Xeomin Inco botulinum toxin type A
Myobloc/NeuroBloc Rima botulinum toxin type B

History and early research

Botulism was first described by a German physician, Justinus Kerner, in the early 19th century when he observed outbreaks of food poisoning from contaminated sausages [10]. He noted neurological effects resulting in muscle paralysis and then death secondary to respiratory depression. In the late 19th century, van Ermengem identified the bacterium causing botulism which he named the botulinum bacterium. This terminology was later changed to Clostridium botulinum [10].

In the 1940s, the USA and UK developed botulinum toxins as potential biological agents to be used during the Second World War. As a corollary, vaccines were also developed in order to prevent troops from succumbing to reciprocal biological warfare from the enemy. BTX-A toxin was purified and developed by Dr Edward J. Schantz at the US biological warfare centre in Fort Detrick, ­Maryland [1]. This strain later became known as Occulinum™ and then Botox™, or Ona BTX-A. In the UK, at the Porton Down biological warfare centre on Salisbury Plain, research was conducted with a different serotype of BTX-A with similar ­characteristics to the Fort Detrick toxin, which became known as Dysport after Porton, now called Abo BTX-A.

Medical use of Ona BTX-A was pioneered by ophthalmologist Dr Alan Scott in an attempt to discover a non-surgical treatment for strabismus. Scott had obtained the toxin from Fort Detrick and initially studied the effects of this toxin in the ocular muscle of monkeys [11].

In the 1980s, Scott and colleagues proved that it was possible to improve strabismus by injecting BTX-A into the appropriate periocular muscles. The trade name of this injectable toxin became Occulinum and was utilized for the treatment of strabismus, blepharospasm and hemifacial spasm [12, 13]. Another pharmaceutical company subsequently acquired Occulinum and renamed it Botox.

History of clinical applications

It was noted during the treatment of strabismus that BTX-A could reduce wrinkles in the glabellar region of the face. These seminal observations were reported initially by an ophthalmologist and a dermatologist in 1992 [1]. Other researchers confirmed these findings in double-blind placebo-controlled studies, demonstrating the ability of BTX-A to reduce what were essentially hyperfunctional muscle-induced facial lines [2, 3, 4, 5], or so-called dynamic wrinkles. In 2002, the US regulatory body, the Food and Drug Adminstration (FDA), approved Ona BTX-A for the treatment of glabellar lines, and regulatory body approval in a variety of other countries including the UK followed shortly thereafter. An additional approved indication, the treatment of severe ­axillary ­hyperhidrosis, has been confirmed as safe and effective in ­evidence-based multicentre studies [9].

In addition to the reduction of facial lines and hyperhidrosis, there are many other approved and non-approved indications for botulinum toxins in medicine. These include conditions relating to muscle hyperactivity such as focal dystonia, blepharospasm, cervical dystonia, spasmodic dysphonia, writer's cramp, occupational cramps, hemifacial spasm, spasticity of the limbs in adults and children, strabismus, nystagmus, brow ptosis, facial tics, rigidity syndromes and bruxism. Autonomic nervous system indications include focal hyperhidrosis, gustatory sweating, hyperlacrimation and sialorrhoea, and span various organ systems including urological indications such as overactive bladder, vaginismus, urethrism, gastrointestinal indications such as anal fissure, outlet constipation, sphincter of Oddi dysfunction, and neurological applications for treatment of essential tremor, parkinsonian tremor and spasticity, pain control in migraine and focal muscle pain [14].

Pharmacology and action of neurotoxins

The clinical effects of BTX-A and BTX-B result from pharmacological action at the neuromuscular junction blocking release of ACh at the neuronal endplate [15, 16], with subsequent inhibition of muscular contraction (Figure 158.1). The core molecule in all botulinum toxins is a 150 kDa protein with three distinct domains, and various accessory or neurotoxin-associated proteins (NAPs) according to serotype.

Image described by caption.

Figure 158.1 Different botulinum toxins block acetylcholine release via different synaptic proteins, BTX-A – SNAP25 and BTX-B – synaptobrevin. VAMP, vesicle-associated membrane protein.

The three domains of the core molecule are the binding domain, translocation domain and catalytic domain. The binding domain docks with specific receptors on the neuronal surface and the translocation domain allows for entry of the catalytic domain into the cell. Once inside the neuron, the catalytic domain binds to specific intracellular proteins resulting in blockade of neurotransmitter release. The catalytic domain of BTX-A binds to intracellular SNAP-25 proteins [15] which prevent exocytosis of ACh from the synaptic vesicle, thus inhibiting muscular contraction. BTX-B binds the intracellular synaptic protein synaptobrevin [16], also referred to as vesicle-associated membrane protein (VAMP), likewise preventing ACh transportation across the neuronal cell membrane into the neuromuscular junction and blockading muscular contraction. It is thought that the limited duration of the clinical effect of botulinum toxins results from the synthesis of new synaptic proteins over time, re-establishment of ACh release and subsequent muscular activity.

Variation and equivalence

Manufacture of botulinum toxins utilizes similar processes of anaerobic fermentation to produce Clostridium botulinum. The toxin produced by the bacteria is then separated and purified by a variety of proprietary methods. It is likely that the active light chain toxin in all proprietary BTX-A products is identical, but variations in subsequent manufacturing processes result in pharmacological differences between final products. These include differences in molecular weight, amongst other formulation variations (Table 158.2).

Table 158.2 Some characteristics of the botulinum neurotoxins

Product Toxin type Molecular weight (kDa) pH Approved for forehead lines Approved for hyperhydrosis Approved for medical indications, e.g. cervical dystonia, blepharospasm
Botoxa A 900 7 Yes Yes Yes
Dysport A 500–900 7 Yes No Yes
Xeomin A 150 7 Yes No Yes
Myobloc/NeuroBloc B 300–500 5.6 No No Yes

aBotox also approved for crow's feet by the US FDA, October 2013.

Botulinum toxin potency is estimated as units of activity. These vary amongst the different type A toxins and have been the subject of numerous comparative studies [5, 6, 7, 17–19]. The following summary of the comparative per unit therapeutic efficacy is based on such studies, and on anecdotal and extensive personal experience:

Ona BTX-A 1 unit equivalent to Inco BTX-A 1–1.25 units equivalent to Abo BTX-A 2.5–3 units

It must be stressed that it is best practice to consider each as a different drug, the dose of which is to be individually determined.

Clinical applications of botulinum toxins in aesthetic dermatology

Upper face

Applications for the aesthetic use of botulinum toxin have become well documented over the last two decades. The main target muscles for botulinum toxin in the face are shown in Figure 158.2.

Image described by caption.

Figure 158.2 Idealized diagram of the facial muscles that create lines and can be injected with botulinum toxin for aesthetic changes to the face.

There are many variations in the selection of injection site, and treatment must be tailored according to the muscular dynamics of the patient; what is considered to be optimum placement ­continues to evolve over time. Industry-sponsored research studies involving botulinum toxin injections into the lower forehead utilized different injection sites in order to gain relevant regulatory approval (see Figure 158.2) [4, 5, 6, 18]. Idealized diagrams can be helpful but are not necessarily relevant or optimal for individual patients, due to the frequency of facial asymmetry, or imbalance in baseline muscular action.

In reality, the first and most critical aspect of cosmetic facial use of botulinum toxin injection is to learn how to accurately examine the patient. Assessment should be made at rest and at maximum muscle contraction. It is this author's practice to take facial photographs at rest and at maximum muscle contraction. Many cases of facial asymmetry are found and as a result require a change from the ‘standard’ patterns of injection sites for botulinum toxin that are recommended in many articles.

Most of the clinical research studies addressing the cosmetic use of botulinum toxin have focused on dividing varying doses of BTX-A over five to seven injection sites [1–3, 4, 5]. In general, one or two injection sites into the procerus and usually two each into the corrugator are the ideal injection sites frequently cited in education and training for the cosmetic use of botulinuim toxin. The relevant injection sites and doses of various BTX-A serotypes must be based on a detailed knowledge of facial anatomy. The desired aesthetic outcome requires appropriate training and experience, underpinned by a fundamental knowledge of the evidence-based research and literature [1–3, 4, 5].

The muscles producing the frown or ‘knitting of the brow’ were those first studied for regulatory approval of the cosmetic use of BTX-A. All three commercially available BTX-A products were first approved for injection at this site. Figure 158.3 shows the injection sites from an early study on Ona BTX-A [3]. The corrugator and procerus are the most important muscles that lead to lower and central vertical forehead lines. These muscles are also responsible for eyebrow depression and ptosis (Figures 158.3, 158.4 and 158.5). It must be noted that m. frontalis is the main brow elevator which lifts the forehead and brows, and is responsible for horizontal forehead lines. Understanding the brow depressor/elevator muscle balance is key to successful upper face botulinum toxin rejuvenation strategies.

Image described by caption.

Figure 158.3 (a) Usual injection sites for a symmetrical forehead with vertical glabella lines before treatment and to correct brow ptosis. 4 Ona BTX-A units per site. (b) Patient photographed again at maximum frown 7 days after injection of BTX-A.

Image described by caption.

Figure 158.4 Forehead facial asymmetry. Stronger right corrugator and procerus muscles. Results in right brow ptosis compared to left.

Image described by caption.

Figure 158.5 Forehead facial asymmetry. BTX-A 2 and 4 Ona BTX-A units or equivalent. Aesthetic goal: (1) reduce right brow depressors and give brow elevation; and (2) maintain left brow height and shape.

Glabella

Muscles that give vertical forehead lines in the glabellar area and act as brow depressors are as follows:

Brow elevation is produced mainly by the frontalis (see Figure 158.3b). When the m. corrugator and m. procerus muscles contract, the facial expression is that of anger or concern. Contracting the corrugator muscles also results in ‘narrowing of the eyes’. Contracting the procerus muscle will induce further medial brow depression and create horizontal lines between the eyebrows and the base of the nose [20].

Forehead

The frontalis muscle is employed to raise the eyebrows and to prevent eyebrow ptosis. It also creates forehead expression lines that are horizontal and can express surprise or fear. Botulinum toxin treatment to the mid and lateral forehead should be performed with relatively small amounts of toxin and placed more superficially as compared to the glabellar area. Overdose of total toxin across the frontalis muscle inevitably results in undesirable brow ptosis.

Individual injection site doses and the number of sites used will vary between the different proprietary brands of botulinum toxin. Complications in this area of injection are relatively rare, but occur as a result of the wrong placement of the toxin, e.g. too large a dose of BTX-A can result in either eyelid or eyebrow ptosis or both if placed in the lateral forehead. In some patients, there is already relative ptosis of one brow compared to the other and appropriate adjustment to the standard injection site and dose is required to achieve brow lift of the lower brow side. Examples of idealized injection sites are in a ‘symmetrical’ forehead shown in Figure 158.3. Examples of forehead facial asymmetry are shown in Figure 158.4 and 158.5.

The differences between male and female eyebrow shape should be noted. Many males prefer a flatter, more masculine brow, whereas the ideal feminine brow is slightly arched mediolaterally. In men, additional injection sites and higher units can be used in the lateral forehead to achieve a more masculine brow appearance. Facial musculature also varies between genders, with increased strength and bulk in men. Therefore, higher doses and increased number of injection sites are generally required in men in all regions of the face (Figure 158.6).

Image described by caption.

Figure 158.6 Higher total doses of BTX- A often required in the male forehead: 36 total Ona BTX-A units. (a) Male forehead with the corrugator and procerus muscles creating multiple vertical and horizontal lines and brow points. Before Ona A toxin units as indicated. (b) Seven days after (a); smooth forehead at frown plus brow elevator.

Elevation of brows with botulinum toxin

The corrugator and procerus are the primary muscles used for brow depression. There is a further contribution from the superolateral orbicularis oculi muscle. Selective reduction in the activity of these muscles with botulinum toxin can result in the ­elevation of the lateral and to a lesser degree the medial brow. This is often the desired aesthetic outcome in women. Over-elevation of the brow resulting in unnaturally arched or pointed eyebrows is usually undesirable, but can be corrected with injections of small doses of BTX into the lateral lower frontalis muscle.

Crow's feet or lateral periocular lines

Commonly known as crow's feet, the lateral periocular lines radiate outwards from the lateral canthal area (Figures 158.7, 158.8 and 158.9). They are caused by the contraction of the orbicularis oculi muscle; wrinkles are exacerbated by squinting and smiling. In addition, both intrinsic and extrinsic skin ageing will add to their persistence and severity [21].

Image described by caption.

Figure 158.7 Crow's feet: wrinkles extending laterally from the periorbital area produced by contraction of the orbicularis oculi muscle.

Image described by caption.

Figure 158.8 Crow's feet: BTX-A injection sites. Wrinkles extending laterally from the periorbital area produced by contraction of the orbicularis oculi muscle. ona BTX-A, 2 units; 4 units.

Image described by caption.

Figure 158.9 Crow's feet: combination of BTX-A followed by ultrapulsed carbon dioxide laser. (a) Before: crow's feet plus multiple lentigo. (b) Six months postoperation.

In order to reduce these lines, the target muscle for botulinum toxin is the lateral orbicularis oculi. The ideal site is determined by examination of the patient at both smiling and at rest. Typically, two to four injections are placed around the lateral canthal area on each side, 1–2 cm lateral to the ocular bony rim [21] (Figure 158.7 and 158.8). If there is coexistent cutaneous photodamage exacerbating periocular lines in the crow's feet region, combination treatment with laser resurfacing can be used [22] (Figure 158.9). Infraorbital lines can also be reduced by very small and carefully placed doses of botulinum toxin (Figure 158.10).

Image described by caption.

Figure 158.10 BTX-A: infraorbital lines (a) before 2 units BTX-A; and (b) 7 days after (a).

Mid face

The mid face area can be also selected as a site for cosmetic botulinum toxin injections. Undesirable lines on the lateral nose also known as ‘bunny lines’ can be softened by treating the nasalis muscle [20]. Drooping of the nasal tip occurs with age and slight elevation can be achieved with very small doses of botulinum toxin into the depressor septi nasi muscle. Exaggerated gum show with smiling, also referred to as ‘gummy smile’, is undesirable to some patients, where the central upper lip is elevated excessively with smiling. This can be improved with injection into the levator labii superioris alaeque nasi muscle.

Lower face

There are several muscles targeted for aesthetic botulinum toxin treatment in the lower face. These include the depressor anguli oris muscle that depresses the angles of the mouth often leading to a ‘sad’ appearance. This muscle is shown in Figure 158.2. Injection is at the very lower point of this muscle where it is inserted into the mandibular area. This is found by teeth clenching, and injecting just anteriorly to the anterior border of the masseter on the mandible (Figure 158.11).

Image described by caption.

Figure 158.11 Perioral wrinkling due to contraction of the orbicularis muscle and dermal actinic elastosis. 1 unit per wrinkle site. 2 ona BTX-A units maximum per lip quarter per session.

The orbicularis oris muscle is responsible in part for lines between the lip and the medial nasal area, so-called ‘smoker's’ lip lines. They are caused by lip pursing and contraction and with time these lines will become more severe and visible even at rest. Very small doses of botulinum toxin can be injected into the relevant part of the upper lip (see Figure 158.11). Additionally, if the upper lip is atrophic, combination with lip filler has been described [23].

The primary chin or mentalis muscle is m. mentalis. Activity can lead to puckering of the chin, known as a ‘peau d'orange’ appearance. It can also lead to additional depression of the angles of the mouth. This pebbling or puckering of the chin can be corrected by a single injection of a relatively small dose of BTX into the centre of the mentalis muscle (Figure 158.12).

Image described by caption.

Figure 158.12 Mentalis muscle ‘creases’ treated with BTX-A. (a) Before ona BTX-A, 2 units; and (b) 7 days after (a).

Neck

The main muscles of the neck appropriate for aesthetic injections of botulinum toxin are the bands of the platysma muscle. Platysmal vertical bands tend to become more notable with age because of the loss of subcutaneous fat, exposing the platysma muscle [23]. The platysma tightens the skin of the neck and in addition can produce depression of the lateral face. In some patients, activation of the platysma can produce downward pull of the perioral lateral area and the medial and lateral cheek. Injection of small doses of BTX-A into the platysma can reduce the ‘bands’ produced by the platysma as well as reduce downward traction of the lateral face [23].

Though there have been anecdotal claims for the value of botulinum toxin injections to reduce horizontal superficial neck lines, the impact is minimal, though some effect may be achieved by reduction of the platysma muscle action.

Figure 158.13 shows some common sites for facial botulinum toxin injections. These will vary with the individual patient and tailored treatment after careful assessment is key to an optimal outcome.

Image described by caption.

Figure 158.13 Some frequent sites for injection of BTX into facial muscles for aesthetic indications.

Adverse events

Serious side effects from botulinum toxin for aesthetic indications are uncommon because the total doses utilized are low. The main causes for adverse events are poor injection technique, inappropriate dose selection and incorrect injection site. Resultant side effects are listed in Box 158.1. Undesirable results and complications are usually mild and transient. Poor results may be improved by further injection, e.g. into compensatory muscles, in order to correct or minimize the unsatisfactory response. It is imperative that the practitioner understands the complexities of the relevant muscle vectors for a satisfactory and natural outcome.

Bruising from needle injections is probably the most common side effect, occurring most frequently in the periorbital region, e.g. the lateral periocular crow's feet area. The forehead is the second most common site. Bruising can usually be avoided by close examination of the patient's cutaneous vascular network. Further mitigation of bruising risk involves avoidance of injection in those patients taking medications or supplements which increase predisposition, such as those taking aspirin, non-steroidal anti-inflammatory agents, anticoagulant drugs, oral omega-3 and omega-6 fish oil supplements, excessive ingestion of oily fish or alcohol. Local tissue oedema at the injection site can usually be more visible on the forehead skin, but will clear within an hour or less.

Another common side effect is pain on injection. Rarely, patients may have persistent headache and pain lasting several days. The mechanisms for this are not known, but may possibly be due to injection close to a subcutaneous nerve. This pain is paradoxical, as one of the medical indications for botulinum toxin is reduction in frequency and severity of migraine headaches.

Other site-specific side effects relating to botulinum toxin for aesthetic treatments are eyebrow and lower eyelid ptosis. Again, this usually results from inaccurate placement of botulinum toxin, commonly the result of injection of too high a dose into the lower lateral or mediolateral forehead. The resultant diffusion of the toxin into the elevator muscles of the eye or lower fibres of the frontalis results in ptosis. Lower facial and lateral lip ptosis can also result when injections in the lower periocular area are too lateral and too low to the infraorbital areas, encroaching on the zygomatus areas. The effect of the toxin on the levator muscles of the lower face causes ptosis and lateral lip drooping. Facial asymmetry resulting from an unequal effect of the toxin is another complication which can be of considerable concern.

Less common side effects include paraesthesia, diplopia, dry eyes, dysphagia and dysarthria. These are all due generally to inappropriately high doses of toxin injection, with diffusion into either the periocular muscles, or the muscles of the larynx and pharynx. Practitioners must remember the therapeutic window for a cosmetic patient is even narrower than that of one receiving medical therapy, therefore a cautious conservative approach is best, particularly for inexperienced practitioners.

Special considerations

The incidence of undesirable side effects are generally higher in older patients possibly because of increased spread of the toxin into atrophic muscles, as well as increased likelihood of weaker baseline facial musculature. Furthermore, in the older patient with more severe extrinsic and intrinsic facial ageing, it is unlikely that the use of botulinum toxin alone will be sufficient to result in an acceptable outcome, and consideration must be given to ageing changes associated with other anatomical structures such as subcutaneous fat and underlying bone and dentition.

Botulinum toxin use in the perioral area should be used with caution for professional wind musicians or others where subtle alterations in fine muscular activity will have significant impact. The same theoretical risk exists for the treatment of palmar hyperhidrosis in those who require very fine muscular control in the hands, e.g. jewellers.

Contraindications to botulinum toxin injections include patients with a history of myasthenia gravis or other neuromuscular disorder. Pregnancy and breastfeeding are also contraindications (manufacturers advise avoidance unless essential for medical treatment). Some oral medication and supplements, e.g. oral erythromycin and zinc supplements, can also increase the therapeutic response to BTX. A careful medical history and examination are mandatory prior to botulinum toxin injection.

Acquired resistance to botulinum toxins

A rare problem is the development of acquired resistance to BTX-A. This does not appear to be related in all cases to the presence of antibodies, as resistance has been noted in patients where antibodies remain undetected. In addition, studies have demonstrated instances where antibodies to BTX-A are present, but a therapeutic response to the toxin persists. If BTX-A resistance occurs, BTX-B can be effective as it acts via a different synaptic protein [15, 16].

Combination treatment and future trends

The various serotypes of botulinum toxin may be combined with selected treatments for aesthetic indications in relevant patients [20]. Combination treatments with improved outcomes include concomitant use with dermal fillers to address facial folds and volumising [20], with radiofrequency skin tightening and laser skin rejuvenation procedures [22].

The development of a topical application of BTX-A is anticipated. Preliminary research shows efficacy against hyperhydrosis and superficial facial lines [24]. Further research on new injectable toxins continues. Modified formulations of the existing toxins may be developed to improve therapeutic efficacy.

References

  1. Carruthers JD, Carruthers JA. Treatment of glabellar frown lines with C. botulinim-A toxin. J Dermatol Surg Oncol 1992;18:17–22.
  2. Keen M, Blitzer A, Aviv J, et al. Botulinum toxin A for hyperkinetic facial lines: results of a double-blind, placebo-controlled study. Plast Reconstr Surg 1994;94:94–9.
  3. Lowe NJ, Maxwell A, Harper H. Botulinum A exotoxin for glabellar folds: a double-blind, placebo-controlled study with an electromyographic injection technique. J Am Acad Dermatol 1996;35:569–72.
  4. Carruthers JD, Lowe NJ, Menter MA, et al., for the BOTOX Glabellar Lines I Study Group. A multicenter, double-blind, randomized, placebo-controlled study of the efficacy and safety of Botulinum toxin type A in the treatment of glabellar lines. J Am Acad Dermatol 2002;46:840–9.
  5. Carruthers JD, Lowe NJ, Menter MA, et al., for the BOTOX Glabellar Lines II Study Group. Double-blind, placebo-controlled study of the safety and efficacy of Botulinum toxin type A for patients with glabellar lines. Plast Reconstr Surg 2003;112:1089–98.
  6. Ascher B, Zakine B, Kestemont P, et al. A multicenter, randomized, double-blind, placebo-controlled study of efficacy and safety of 3 doses of Botulinum toxin A in the treatment of glabellar lines. J Am Acad Dermatol 2004;51:223–33.
  7. Lowe P, Patnaik R, Lowe N. Comparison of two formulations of Botulinum type A for the treatment of glabellar lines: a double-blind randomized study. J Am Acad Dermatol 2006;55:975–80.
  8. Naumann M, Jost W, Toyka KV. Treatment of disorders of the autonomic nervous system with botulinum Toxin A. Arch Neurol 1999;56:914–16.
  9. Naumann M, Lowe NJ. Botulinum toxin type A in treatment of bilateral primary axillary hyperhydrosis; randomised parallel group, double blind, placebo controlled trial. BMJ 2001;323:1–4.
  10. Erbgurth F, Nauman M. Historical aspect of botulinum toxin; Justinus Kerner (1786–1862) and the “sausage poison”. J Hist Neurol 2000;9:218–20.
  11. Scott AB. Development of Botulinum toxin therapy. Dermatol Clin 2004;22:131–3.
  12. Scott AB, Rosenbaum A, Collins CC. Pharmacologic weakening of extraocular muscles. Invest Ophthalmol 1973;12:924–7.
  13. Scott AB. Botulinum toxin injection into extraocular muscles as an alternative to strabismus surgery. Ophthalmology 1980;87:1044–9.
  14. Naumann M, Jost W, Toyka KV, Moore P. History and current application of botulinum toxin from poison to remedy. In: Moore P, Naumann M, eds. Handbook of Botulinum Toxin Treatment, 2nd edn, Chapter 1.3–8. Oxford: Blackwell Science, 2003.
  15. Blasi J, Chapman ER, Link E, et al. Botulinum neurotoxin A selectively cleaves the synaptic protein SNAP. Nature 1993;365;160–3.
  16. Schiavo G, Banfanti F, Poulain B, et al. Tatarus and botulinum B neurotoxins block neuromuscular transmitter release by proteoytic cleavage of synaptobrevin. Nature 1992;359:832–5.
  17. Lowe NJ, Shah A, Lowe PL. Dosing, efficacy, safety and computerized photography of botulinum toxins. J Cosmet Laser Therapy 2010;12.2:106–11.
  18. Sattler G, Callander MJ, Grablowitz D, et al. Non inferiority of Incobotulimun toxin-A, compared with another botulinum. Toxin type A. J Dermatol Surg 2010;36:2146–54.
  19. Maas C. One Botulinum Toxin slightly better than another for crow's feet. Arch Facial Plast Surg 2011;Dec 19.
  20. Lowe NJ. When and how to combine treatments. In: Lowe NJ, et al., ed. Textbook of Facial Rejuvenation, Chapter 28. London: Martin Dunitz/Taylor & Francis, 2002:322–5.
  21. Lowe NJ, Ascher B, Heckmann M, et al., for the Botox Facial Aesthetics Study Team. Double-blind, randomized, placebo-controlled, dose-response study of the safety and efficacy of Botulinum toxin type A in subjects with crow's feet. Dermatol Surg 2005;31:257–62.
  22. Yamauchi P, Lowe NJ, Lask GL. Botulinum toxin plus Erb Yag Laser for periorbital lines. J Cosmet Laser Ther 2004;6.3:145–8.
  23. Carruthers J, Carruthers A, Maberly D. Deep resting glabellar rhytides respond to BTX-A and Hylan BD. Dermatol Surg 2003;29:539–44.
  24. Brandt F. Efficacy and safety evaluation of novel Botulinum toxin topical gel for the treatment of lateral canthal lines. J Dermatol Surg 2010;36:211–18.