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Surgery and Cosmetics

James M. Spencer, MD, MS

PMMA for the Treatment of Acne Scars

James M. Spencer, MD, MS

Wednesday, October 01, 2014

Acne scars can be one of the most distressing facial lesions for patients and remain a challenge for dermatologists to treat. In general, acne scars are atrophic, and the deeper the atrophy the more challenging these scars are to treat. True icepick scars, are deep pits that are usually less than 2 mm across. They extend into the skin, giving the skin an appearance of having been punctured by an ice pick. Treatment usually begins with acne scar surgery (excision and punch-replacement grafting). Sometimes it can be combined with laser resurfacing as it removes layers of skin, which allows the body to produce new skin cells to help the skin look its best. Boxcar scars are angular scars with sharp vertical edges, and resemble the scars left by chicken pox. They may be shallow or deep, and are most often found on the cheeks and temples. Rolling scars are caused by damage under the surface of the skin. They give the skin a wave-like appearance and tend to be wide and shallow. Hypertrophic scars are raised and lumpy. They tend to appear on the back and chest, but can also appear on the neck and face. Often the result of severe acne (cysts or nodules), they generally stay within the boundary of the original wound, and may decrease in size over time.1

PMMA jpeg

A number of fillers benefit acne scars, but carry the drawback of being temporary. Permanent fillers are available, and since one is treating a scar anyway, these become an attractive choice for permanent correction. Two permanent fillers are currently available: liquid silicone and polymethylmethacrylate (PMMA) beads.

Liquid silicone has a long and somewhat controversial history in dermatology. Liquid silicone is actually a polymer based on elemental silicone: dimethylsiloxane polymer. The viscosity of the fluid is dependent on the degree of polymerization, which in turn affects its usefulness for cosmetic use. Currently, liquid silicone is U.S. Food and Drug Administration (FDA) approved for ophthalmic use for retinal tamponade. Therefore, skin injection is an off-label use. This product has a viscosity of 1000 centistokes, which is more viscous than the 350 centistoke preparation considered ideal for skin injection by most experts. Current advocates of liquid silicone suggest the microdroplet technique wherein microdroplets are injected under the scar. A fibrotic reaction ensues, which traps the droplets of silicone in place. It is imperative to avoid overcorrection but rather inject in more than one session until the desired effect is reached. Controversy has arisen over two possible side effects of silicone: granulomas and migration. The formation of silicone granulomas is well documented, but the point has been made that these may be due to the use of non-medical grade silicone with adulterants included. The other complication, migration, is generally ascribed to overinjection and possibly may be avoided with the microdroplet technique in which the silicone droplets become enmeshed and trapped in a fibrotic response. However, both granuloma formation and migration with silicone remains controversial.

PMMA represents the newest choice in permanent scar correction. PMMA refers to microspheres of PMMA suspended in bovine collagen for dermal injection. The bovine collagen is absorbed leaving the non-resorbable microspheres of PMMA behind. These microspheres in turn become enmeshed in a fibrotic response holding them in place. This material is FDA approved as Artefill for the correction of nasolabial folds. Recently, a multicenter trial was completed in order to obtain FDA approval for acne scar correction.2 One hundred and forty seven patients were enrolled and treated in this study. Subjects were required to have at least four facial acne scars that were soft-contoured rolling type scars that were distensible with skin stretching and thus amenable to correction with a filler. The scars needed to be moderate to severe, which corresponds to a 3 or 4 on the validated 4-point acne scar scale. Subjects were seen every 2 weeks for the first two visits and allowed injections of either active material or control saline at each of these visits. An optional touch-up treatment was administered 4 weeks after the first treatment. Subjects were then seen at 3, 6, 9, and 12 months for evaluation. A positive response was considered to be that 50% of their scars or more showed at least a 2-point improvement on the validated 4-point scar scale. At Month 6, those who had received saline were allowed to cross over and receive active PMMA-collagen.

Of the 147 subjects treated, 64.4% of the PMMA-collagen patients demonstrated a positive response at 6 months compared to 32.6% of the control subjects (p=0.0005) (Figure 1). The improvement with PMMA-collagen was durable over time with a response rate of 61.5% at 9 months and 70.7% at 12 months. Crossover patients showed similar results out to 12 months.

 

Acne

Figure 1. Acne scars at baseline (left-hand images) and 6 months following treatment initiation with PMMA (right-hand images).Six rolling acne scars (indicated by yellow circles) received initial treatment of 0.75 mL PMMA, with two scars receiving subsequent touch up of 0.70 mL PMMA. At 6 months post-treatment, a notable improvement is observed.

 

Treatment with PMMA-collagen was also associated with high satisfaction levels. Ninety eight percent of treated subjects were rated as improved on a Physician Global Aesthetic Improvement Scale while 83% of subjects rated themselves as improved on a Subject Global Aesthetic Improvement Scale. In addition, 90% of subjects expressed satisfaction specifically with the amount of scar correction. Safety data showed events that one would expect with injection. No serious adverse events were seen in the PMMA group and it was well tolerated.

In summary, this study showed PMMA-collagen provides excellent correction in the majority of patients with an excellent safety profile, and persistence of correction at 1 year follow-up.

 

References

  1. www.acne.org
  2. Karnik J, Baumann L, Bruce S, et al. A double-blind, randomized, multicenter, controlled trial of suspended polymethylmethacrylate microspheres for the correction of atrophic facial acne scars. J Am Acad Dermatol 2014;71:77-83.

 

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