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BACKGROUND. Multiple treatment modalities
have been used for the revision of acne scarring with varying degrees of success.
Nonablative laser resurfacing has recently been shown to improve the appearance
of atrophic acne scars.
OBJECTIVE. The objective was to determine
the efficacy of a 1320-nm Nd:YAG laser for the treatment of acne scars.
METHODS. Eight patients with facial acne
scars received six monthly treatments with a 1320-nm Nd:YAG laser with built-in
cryogen cooling. Results were evaluated by objective and patient assessment using
a 6-point improvement scale: 1 no improvement, 6 = 80% to 100% improvement.
RESULTS. Acne scar improvement was statistically
significant at both the 5-month and 1-year marks. Mean improvement by objective
assessment was 3.9 points (p = 0.002) at 5 months and 4.3 points (p = 0.011) at
1 years. The mean acne scar improvement by patient assessment was 3.6 points (p
= 0.002) at 5 months.
CONCLUSION. The 1320-nm Nd:YAG laser with
cryogen cooling significantly improves the appearance of acne scarring.
ACNE IS a common condition that affects
up to 80% of people between the ages of 11 and 30 years and up to 5% of older adults.
In approximately 95% of patients with the disease, acne scarring ensues.
The etiology of acne is multifactorial; however, the primary inciting factors include
colonization by Pro-pionihacterium acnes, overproduction of sebum, and
hyperkeratinization of follicular epithelium. Follicular hyperkeratosis promotes
retention of comedone plugs, which in turn creates an environment conducive to overgrowth
of P. acnes. P. acnes colonization triggers a lymphocytic and neutrophilic
inflammatory response.
This inflammatory response functions to both protect the environment from further
injury and repair the damaged tissue. Nevertheless, the dermal inflammatory response
to P. acnes may lead to destruction of collagen and, in turn, dermal
atrophy. The final step in the healing process is fibrosis, giving rise to acne
scars of varying gross morphology.
Acne scars contract as they mature, giving rise ro a "bound-down" appearance. With
age, acne scars may
become more prominent as the sagging facial skin appears
to be tethered by the resulting areas of dermal fibrosis. It is often at this stage
when patients seek corrective treatment.
Dermatologic surgeons have tried a variety of treatment modalities for revision
of acne scarring; these include dermabrasion techniques, chemical peels, punch grafting,
scar excision, intradermal filler injection, and ablative laser resurfacing.
Traditional laser resurfacing has been used to treat rhytids and atrophic scars
by removing the epidermis and inducing dermal injury, which in turn leads to collagen
shrinkage and remodeling. Although this technique has also been used to improve
the appearance of atrophic acne scars, it is associated with lengthy cosmetic downtime
in addition to significant postoperative complications.
Recently, nonablative lasers have been introduced for facial resurfacing. Nonablative
techniques leave the epidermis intact, which makes the process safer and eliminates
the extended recovery period associated with epidermal ablation. Lasers have been
developed with longer wavelengths, in the midinfrared range, enabling deeper penetration
into the dermis. When paired with surface cooling methods, these laser systems
were designed to induce controlled injury to the dermis without removing the epidermis.
The thermal injury damages dermal collagen and, in turn, triggers the local release
of inflammatory mediators. These mediators activate fibroblasts and stimulate collagen
remodeling. Because acne scarring involves atrophy and fibrosis, new collagen production and remodeling are thought to improve the appearance of atrophic acne scars.
The CoolTouch II is a nonablative 1320-nm Nd:YAG laser with thermal feedback and
a built-in cryogen spray cooling system. This laser was designed to induce
thermal injury to the dermis while protecting the epidermis with the cryogen cooling
mechanism. By cooling the epidermis, the epidermal chromophores are effectively
shielded from the effects of the incident light. The long 1320-nm wavelength penetrates
to the papillary and midreticular dermis and is nonspecifically absorbed by dermal
water. In addition, the large scattering coefficient of the 1320-nm Nd:YAG laser
causes the thermal energy to disperse laterally, inducing thermal injury to the
surrounding dermis, which may be beneficial in producing more uniform results. The
CoolTouch II differs from its predecessor, the CoolTouch I, with the incorporation
of a dynamic thermal sensing device that provides negative feedback of epidermal
temperatures that fall outside the desired range of 32 to 34 "C.
The goal of this study was to evaluate the Cool-Touch II laser system for the treatment
of acne scarring. Acne scarring was assessed before and after a series of six
monthly laser treatments.
Methods
Laser Settings
A 1320-nm Nd:YAG laser (CoolTouch II, New Star Lasers, Roseville, CA) with a 10-mm
fixed spot size was used to deliver fluences of 13 to 18 J/cm2 (Table 1). The laser
delivered six stacked 350-usec micro-pulses at a rate of 1 Hz, which combined to
form a 50-msec macropulse.
Three continuous passes of the CoolTouch laser were delivered to the entire affected
area. The first two passes were performed in precooling mode, which
Table 1. 1320-nm Nd:YAG Laser Settings
Wavelength
1320 nm
Spot size
10 mm
Precooling mode
Cooling duration
30 msec
Delay
10 msec
Laser fluence
14-18 J/cm2
Pulse duration*
50 msec*
Postcooling mode
Laser fluence
13-17 J/cm2
Pulse duration*
50 msec*
Delay
10 msec
Cooling duration
30 msec
.Three stacked 350 usec micropulses form a 50-msec macropulse.
delivered a 30-msec cryogen spray burst 10 msec before introduction of the laser
energy beam. The third pass of the laser was applied in postcooling mode, in which
a 30-msec cryogen burst was delivered 10 msec after the laser beam.
Patient Selection
Eight subjects (seven female patients and one male patient) who had facial acne
with acne scarring were enrolled in the study. The subjects had a mean age of 36
years (range 30-39 years). Informed consent was obtained from all subjects.
The study protocol conformed to the guidelines of the 1975 Declaration of Helsinki
and was approved by our institutional review board.
Subjects were excluded from the study for pregnancy or lactation, history of
laser resurfacing or dermabrasion of the face in the previous year, or predisposition
for keloids.
Protocol
Six laser treatments were performed at 4-week intervals. Each treatment consisted
of three consecutive passes of the laser beam. Each pass was delivered to the entire
acne scar treatment area in uniform nonoverlapping pulses. The first two passes
delivered precooling cryogen spray followed by fluences of 14 to 18 J/cm2.
The third pass delivered fluences of 13 to 17 J/cm2, followed by postcooling cryogen
spray. The fluences delivered in precooling mode were adjusted to achieve a peak
surface temperature of 44°C. The fluences used in the postcooling mode were determined
by the manufacturer's guidelines according to starting skin temperature (above 35°C,
13 J/cm2; 33-34°C, 15 J/cm2; 30-32°C, 17 J/cm2; less than 30°C, prewarm patient).
At baseline patients were classified according to acne scar severity using the following
system: Class I (mild), punched out scars without fibrous tracts; Class II (moderate),
ice pick-type scars without fibrous tracts; and Class III (severe); ice pick scars
with fibrous tracts. Patient evaluations were performed at each monthly visit during
visits 1
through - 6. Photographs were taken at baseline, at 5 months (1 month after
treatment 5), and again at 1 year (7 months after the treatment 6). Objective assessments
were performed by comparing the baseline photographs to those taken at 5 months
and at 1 year. The photographs were independently evaluated and scored by two nontreating
physicians in a nonblind fashion.
Both objective and patient assessments were made using a 6-point scale of improvement:
1, no improvement; 2, 1% to 19% improvement; 3, 20% to 39%, improvement; 4,
40% to 59% improvement; 5, 60% to 79%, improvement; and 6, 80% to 100% improvement.
The percentage scale reference range was also provided. The photography was performed
using a Nikon s70 camera (Canfield Clinical Systems, Fairfield, NJ). Complications
were to be noted at each visit.
Statistics
Paired t tests were used to analyze the acne scar improvement scores at 5 months
and at 1 year for both objective and patient ratings. Because the t test requires
a baseline value for comparison, improvement at baseline was defined by a score
of 1 (no improvement), in adherence to the 6-point rating scale. A p value
of less than 0.05 was considered significant. One-tailed p values are presented.
All statistics were computed using Analyze-It computer software.
Results
Eight patients were enrolled in the study. The patients were classified at baseline
as having primarily Class I scars (n = 3), Class II scars (n = 3), or Class III
scars (n = 2). All eight patients were followed for at least 5 months, and four
patients were followed for 1 year.
Mean acne scar improvement was statistically significant at both the 5-month
and the 1-year objective assessments. Assessments were made by comparing baseline
to postreatment photographs (Figures 1-4). Improvement was reported by seven of
the eight patients at the 5-month follow-up. Mean acne scar improvement
by objective assessment was 3.9 points (p = 0.002) at 5 months and 4.3 points (p
= 0.011) at 1 year (Table 2). These scores are equivalent to improvement of
20% to 39% and 40% to 59% at 5 months and 1 year, respectively. By objective
assessment, only one patient was determined not to have shown improvement by
the 5-month mark. Class II acne scars (ice pick type scars without fibrous tracts)
appeared to respond better to treatment than Class I and III scars in this study.
There was no difference in response to treatment by anatomic location or Fitzpa-trick
skin type.
Patients reported continued improvement following each consecutive treatment. Mean
patient assessment scores demonstrate a linear pattern of improvement following
each monthly treatment (Figure 5). The mean acne scar improvement at 5 months by
patient assessment was statistically significant at 3.6 points or 20% to 39% (p
= 0.002) (Table 2). By the third treatment follow-up, improvement was reported
by all seven patients who ultimately noticed an improvement during the study.
There were no complications reported during the study. There were no reports of
acne scar worsening by patient or objective assessment.
Discussion
Nonablative laser treatment of acne scars began after the discovery that laser irradiation
promotes collagen remodeling. Ablative lasers have been found to produce variable
results and are associated with a prolonged postoperative recovery period. Neocollagenesis
has been demonstrated histologically following nonablative treatment with a 1320-nm
Nd:YAG laser an intense pulsed light source, a 585-nm pulsed dye laser, and a 1450-nm
erbium glass laser. In 1994, Alster reported the improvement of hypertrophic scars
associated with dermal collagen remodeling following treatment with a 585-nm flashlamp-pumped
pulsed dye laser.
Soon thereafter, Alster and McMeekin used the 585-nm pulsed dye laser for the treatment
of 22 patients with facial acne scarring. They demonstrated significant improvement
in facial acne scars following one to two treatments with a fluency of 6 to 7 J/cm2.
The 1320-nm Nd:YAG laser was compared to the 1450-nm diode laser for the treatment
of 20 patients with mild to moderate atrophic facial scars. Patients received three
successive monthly treatments with the 1320-nm Nd:YAG laser on one side of the face
and the 1450-nm diode laser on the contralateral side of the face. Mild to moderate
clinical improvement in the facial scars was reported following treatment with both
nonablative lasers.
Recently, Rogachefsky et al. studied a 1320-nm Nd:YAG laser with cryogen cooling
for the treatment of atrophic and "mixed-pattern" acne scars in 12 patients. Each
patient received three monthly laser treatments, each consisting of three passes.
The first two passes delivered fluences of 16 to 22 J/cm2, and the third pass delivered
fluences of 13 to 17 J/cm . They reported statistically significant acne scar improvement
of 15% by physician ratings and 22% by patient ratings 6 months after the final
treatment.
Our study demonstrates that the 1320-nm Nd:YAG laser with thermal sensing and built-in
cryogen cooling significantly improves facial acne scarring. Improvement was
noted in seven of eight patients by both physician and patient evaluation. Mean
acne scar improvement was statistically significant at 3.9 points (20%-39%)
and 4.4 points (40%-59%) by objective assessment at 5 months and 1 years, respectively.
By patient assessment at 5 months, there was statistically significant improvement
of 3.6 points (20%-39%). Although this study is limited by the small sample size
(N = 8), the posttreatment improvement that was observed exceeded the minimum t
score values needed to reach statistical significance.
We found that five treatments produces superior improvement in acne scarring compared
to prior studies using only three treatments. It is difficult to assess the
effect of the sixth laser treatment because assessments were not performed
the following month. Nevertheless, further improvement in acne scarring was
evident at the 1-year mark (7 months after the sixth treatment).
The authors clinical experience has shown six treatments with three passes at each
treatment session to be effective in treatment of acne scarring. The exact protocol
for number of treatments remains to be proven in a definitive double-armed
study; however, the 40%-59% physician improvement with six treatments is greater
than that noted (15%) in the three-treatment study previously described. Both methods
are associated with minimal complication profiles.
In conclusion, the 1320-nm Nd:YAG laser with cryogen cooling significantly improves
the appearance of acne scarring. We recommend performing at least five monthly laser
treatments to optimize the laser performance. Using the laser settings described
above, patients may begin to notice improvement as early as 2 months after commencement.
Multiple modalities may be used to improve acne scarring. The authors combine
this modality with
superficial chemical peeling, microdermabrasion, and fat transfer
in this clinical setting.
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