The injection prevents muscle movement from wrinkling the wound site by paralyzing the region thus creating a smooth surface for healing and leaving a smoother final scar.
The researchers have found that treating a facial wound in the early healing phase with the injection improves the appearance of a scar later. The findings of the research were published in the August issue of Mayo Clinic Proceedings.
"Our findings show that botulinum toxin offers an additional tool in preventing the formation of bad scars," says Holger Gassner, M.D., lead study researcher and former Mayo Clinic ear, nose and throat surgical resident who is now a fellow in Facial Plastic Surgery at the University of Washington in Seattle. "It will give us the option to optimize healing of forehead wounds in the first place and possibly allow us to avoid later surgeries to improve the scar's appearance."
Adds David Sherris, M.D., study investigator and former Mayo Clinic ear, nose and throat specialist who is now professor and chair of Otolaryngology at the University of New York at Buffalo, "This is the first medication found to minimize scarring. This is of substantial interest in the field of scar treatment. When a wound occurs, especially on the face, people are always worried about the scar. We can now try and improve scars with these injections."
The researchers found that an injection with botulinum toxin early after the occurrence of a wound -- such as trauma from a dog bite, motor vehicle accident or assault, or from a skin cancer biopsy or removal -- paralyzes the region, creating a smooth surface in which the wound can heal. This prevents muscle movement from wrinkling the wound site, allowing for a flat surface for healing and leaving a smoother final scar. The same process also could work if an unsightly older scar is surgically removed, and then botulinum toxin is injected into the wound at the time of the scar revision surgery, according to Dr. Gassner. "That's why our results with the botulinum toxin are so promising," says Dr. Gassner. "We can now for the first time eliminate the muscles' effect on healing for the first two to three months after the wound occurs."
Facial scarring can have a pronounced effect on patients' quality of life, according to Dr. Gassner.
"In general, we know that scars can cause functional problems -- they can interfere with eye closure, talking and eating," he says. "They also can have a deep psychological impact. For patients who have accidents that produce significant scarring, their lives can be profoundly changed. They can become depressed and withdraw socially."
Muscles may repeatedly distort wounds in the healing phase, which can result in inflammation that produces a thicker or wider scar. This is especially a problem with scars that cross muscle motion in the face, rather than lying parallel to muscle motion, a scenario common in cuts from dog bites or car accidents, says Anthony Brissett, M.D., study co-investigator and former clinician investigator at Mayo Clinic who is now director of Facial Plastic and Reconstructive Surgery at Baylor College of Medicine in Houston.
Scar reduction techniques designed to reduce the effects of muscle tension on a wound and to improve the final appearance of the scar include special stitches that pull the wound together and local flaps that bring additional skin into the wound bed. Injections of botulinum toxin in a wound differ in that they deter the muscle tension in the first place, says Clark Otley, M.D., study co-investigator and chair of the Division of Dermatologic Surgery at Mayo Clinic.
Side effects were minimal with the botulinum toxin injections, according to Dr. Sherris, including an occasional small bruise at the injection site or a headache. The largest potential risk in injecting this substance in the facial area would be transient paralysis of an important function. For example, he says a physician would not want to inject the eyelid, as this would impede its eye protection role. Patients in the trial also experienced positive side effects, such as a "good wrinkle benefit," according to Dr. Sherris, as the amount used to treat scarring is similar to that used to treat wrinkles.
The researchers undertook this trial after seeing significant results in wound healing with botulinum toxin in a basic research study. In the human trial, the researchers recruited patients with forehead wounds from trauma such as auto accidents, or from surgery, such as skin cancer excision. Forehead wounds were selected for study as they are a frequent site of facial scarring. Patients were randomly selected to receive injections with botulinum toxin or with saline, a benign substance used for comparison. All 31 patients' wounds were photographed at the time of the initial treatment and injection and again six months after initial treatment. Two experienced facial plastic surgeons rated the wounds' appearance on a scale in which 0 was the worst appearance and 10 was the best. These assessors were not informed about which patients received which treatment. The researchers averaged the ratings of the two surgeons for a final scar appearance score for each patient's wound. They found that the facial plastic surgeons rated the cosmetic results of the wounds injected with botulinum toxin more favorably than the wounds injected with saline. Median scores for wounds injected with botulinum toxin were 8.9, versus a median score of 7.1 for those injected with saline, a significant difference in appearance, according to the researchers.
Although injections with botulinum toxin would be available at local physicians' offices throughout the country, the injections are not yet approved for this use by the Food and Drug Administration (FDA).
The next step in this research, according to Dr. Sherris, would be to conduct a Phase III, multicenter trial with hundreds of patients to determine the appropriate dosage of the botulinum toxin; discover whether the injections are useful for better healing of scars elsewhere on the body, such as heart surgery wounds; and to provide more findings to present to the FDA to seek approval for this treatment.