Botulinum toxin

1 - INTRODUCTION

Botulinum toxin is a neurotoxic protein produced by the bacterium Clostridium botulinum, an anaerobic, gram-positive, spore-forming rod whose natural habitat is soil. It induces muscle paralysis by blocking the release of acetylcholine at the neuromuscular junction of striated muscle, thereby inhibiting the transmission of nerve impulses across the synaptic junction to the motor end plate. Botulinum toxin A (BoNT-A) is the most potent of seven distinct toxin serotypes that have been assigned the letters A through G (A, B, C [C1, C2], D, E, F and G) [1]. The different subtypes are structurally and functionally similar but they differ in important features, such as their efficacy in muscle paralysis, duration of effects, specific affinity to the target, and location of the toxin complex in the chain of amino acids [2]. However, only the A and B serotypes are commercially available for clinical use in humans.

The A toxin was first used clinically in the treatment of strabismus, blepharospasm and hemifacial spasm and dystonia [3, 4]. A few years later Dr. Jean Carruthers, an oculoplastic surgeon in Toronto, noted that patients treated with botulinum toxin for facial dystonia exhibit an improvement in glabellar rhytids [5]. The rejuvenating effects of botulinum toxin led to its introduction and development as a keystone in the treatment of hyperfunctional lines of the face.

In 2002, the U.S. Food and Drug Administration (FDA) approved uses of BoNT-A for the treatment of facial rhytids, and since then has proven to be a simple, effective and widely used therapeutic modality, which has revolutionized the cosmetic treatment of the aging face in the last decades.

BoNT-A use for treating rhytids on the upper third of the face is unmatched, and presents well-described, noticeable, and predictable results. Forehead, glabellar, and periocular rhytids are the most frequently treated facial regions [6, 7]. In recent years, BoNT-A has been used gradually in the lower face and neck, not exclusively by its demonstrated efficacy and safety for indications in the upper face, but also because of awareness that muscular hyperactivity (in addition to volume depletion) contributes to the aesthetic appearance of the mid- and lower face and neck.

In facial aesthetics, botulinum toxin injection has firmly established as an independent nonsurgical modality for facial rejuvenation and rehabilitation, but it can also be combined safely with a series of other invasive and minimally invasive procedures such as fillers and lasers, to optimize the cosmetic results.