Effect of intralesional botulinum toxin type A injection on keloid and hypertrophic scar

Abstract

Keloids and hypertrophic scars are dermal fibro proliferative disorders that usually develop after healing of a skin injury, although keloids sometimes occur spontaneously. Clinically, Keloids initially manifest as raised erythematous lesions that become pale as they age, extending beyond the original wound borders, do not usually regress spontaneously and tend to recur after excision. On the other hand, hypertrophic scars are raised erythematous fibrous lesions that remain within the confines of the original wound and usually undergo partial spontaneous resolution with time. In addition to the clinical differences between keloids and hypertrophic scars, each has unique histological appearance.Keloids are characterized by haphazard deposition of thick, hyalinized eosinophilic collagen bundles within the dermis with abundant mucinous mucopolysaccharide ground substance. The collagen bundles form nodules that contain an abundance of eosinophils, mast cells, plasma cells and lymphocytes. Hypertrophic scars also demonstrate increased collagen bundles but are less clearly demarcated and lack the hyalinized appearance noted with keloids. Moreover, they remain parallel to the epithelial surface as observed with normal skin. In addition, hypertrophic scars show myofibroblasts with α smooth muscle actin expression believed to be important in the pathogenesis of contractures. The aetiopathogenesis of keloids and hypertrophic scars is not completely understood.Predisposing factors include trauma, skin tension, foreign body, infection, immunological factors, hormonal factors, hypoxia and genetic predisposition. These result in increased fibroblasts proliferation; responsible for enhanced collagen production and excessive scarring. Keloids and hypertrophic scars represent a major therapeutic dilemma to the dermatologists. As enhanced collagen production represents the main frame for the pathogenesis of both conditions, the various treatment methods aim at breakage or removal of the overformed collagen. These methods include surgical, non-surgical as well as combined treatments. Surgical treatment includes surgical excision, cryotherapy and laser treatment. Non-surgical treatment includes intralesional steroid, radiation therapy, silicone gel sheeting and pharmacological treatment.Combined treatment represents combination of intralesional steroid with surgery, cryotherapy or laser treatment. BTXA could be used in controlling hypertrophic scars due to the temporary denervation of BTXA. As we all know, tension is one of the chief factors determining the degree of scar formation. Botulinum toxin (Botox) is a protease exotoxin produced from Clostridium botulinum. It works by blocking the release of acetylcholine from cholinergic nerve endings causing inactivity of muscles or glands. Its effects are transient and may be graded by varying the dose and frequency of administration. Botox is one of the most potent naturally occurring biological toxins and in the past has been responsible for many accidental deaths prior to its discovery in medicine. Pharmacologically, (Botox) acts by blocking cholinergic neuromuscular transmission or cholinergic autonomic innervation of exocrine glands and smooth muscles by inhibiting the action of the soluble N-ethylmaleimide sensitive factor attachment protein receptor protein, SNAP-25, which is involved in fusion of acetylcholine-containing synaptic vesicles with the plasma membrane49 In our study, we chose to treat keloids and hypertrophic scars by intralesional injection of botulinum toxin type A once a month for a total period of 3 months. Each lesion will be injected until slight blanching accurs. Our study enrolled 10 patients, 30% of whom were women. The mean age of the patients was 23.7 ±5.92 years, and the mean duration of the lesions was 1.9±0.84years.They were treated once monthly with intralesional BTX-A for a total of 3 month.