Expanding the Applications of Picosecond Lasers-Juniper Publishers
Authored
by Rawaa Almukhtar
Abstract
Picosecond laser technology has garnered much
interest since arriving on the dermatological scene. While its
effectiveness in removing tattoos has been well documented,
demonstrating its use in other skin lesions is an ongoing process.
Because quality switched nanosecond lasers and picosecond lasers share a
similar mechanism, clinicians hope that picosecond lasers will prove to
be useful for similar skin lesions. There has been a great focus in
particular on proving its effectiveness in treating pigmented lesions,
acne scarring, photodamage, and wrinkling. The early data and impressive
safety profile of picosecond lasers suggest that clinicians may have
another tool they can use to treat these troublesome skin conditions
particularly in patients with darker skin types.
Keywords: Picosecond; Laser; Hyperpigmentation; Acne; Scarring; Photodamage; Wrinkles
Abbrevations:
QS: Quality Switched; DLA: Diffractive Lens Array; CALM: Café-au-lait
Macule; Nd: YAG: Neodymium-doped Yttrium Aluminum Garnet; HQ:
Hydroquinone; VEN: Verrucous Epidermal Nevi; PIH: Post-Inflammatory
Hyperpigmentation
Introduction
Ever since lasers were invented in the 1960s,
dermatologists were among the first physicians who attempted to identify
possible applications in diseases [1]. This began a long tradition of
clinicians eagerly researching the various applications of each new
breakthrough in laser technology. Picosecond laser technology first
showed promise in the field of dermatology for its effectiveness in the
removal of tattoo pigment. Given its similarity to quality switched (QS)
nanosecond lasers, it has been hypothesized that picosecond technology
may be effective for treating many of the same lesions that show a
response to QS nanosecond lasers. By shortening the pulse duration to
the order of picoseconds, the thermal stress time of tissue can be
avoided as well as the thermal damage and pigmentary alterations
associated with it. Longer wavelengths correspond with deeper penetrance
into dermal layers. Higher fluences correspond with increased vacuole
formation necessary to stimulate release of factors that lead to dermal
remodeling. It has been demonstrated that tissue with a higher melanin
index correlates with an increase in intra-epidermal vacuole production
and less unintended vascular injury due to absorption by hemoglobin.
This implies that darker skin types are more likely to confine injury to
the epidermis and spare the vasculature [2]. This has been shown to be
of particular importance for the treatment of patients with Fitzpatrick
type IV to VI skin [3]. In these patients,
dyspigmentation is a common side effect of nanosecond laser treatment
due to microscopic thermal damage that follows melanosomal destruction.
Increased dermal collagen and elastin following picosecond laser
treatments has also been demonstrated [2]. This is likely due to the
release of chemokines, cytokines, and various growth factors by
keratinocytes in response to tissue injury [4]. This implies that
picosecond lasers may be effective for cosmetically improving
disfiguring scars and wrinkles. Alexandrite and neodymium-doped yttrium
aluminum garnet (Nd:YAG) are the two crystal mediums used for
solid-state lasers. The 755nm picosecond alexandrite laser (PicoSure,
Cynosure, Westford, MA) with diffractive lens array (DLA) and the dual
wavelength 1,064/532 nm fractionated picosecond Nd:YAG laser (PicoWay
Resolve, Synderon Candela, Irvine, CA) are the most commonly used laser
types. Identifying optimal wavelengths and laser settings for particular
lesion types can be challenging and clinicians are often guided by
professional judgement.
Effectiveness for Pigmented Lesions
Treatment of pigmented lesions with picosecond laser
technology has been shown to be an effective and safe method for
restoring natural skin tone and decreasing hyperpigmentation using both
subjective and objective measures. There are a wide variety of pigmented
skin lesions that have been treated with picosecond lasers. While these
early studies are limited by
patient numbers, the results have been promising and the safety
profile is maintained in all skin types.
Café-au-lait macules (CALMs) are very prevalent pigmented
lesions that have proven to be quite difficult to treat with laser
therapy. Inconsistent results have given clinicians a poor idea of
which treatment modalities are most effective. While considered
to be effective, the QS Nd: YAG 1064nm laser demonstrated near
complete to complete clearance in only one third of cases and
approximately one fourth of lesions recurred at 4 months on
average [5]. Picosecond laser treatments for these lesions may
be superior to the recommended QS Nd: YAG 1064nm laser [6].
In a series of 16 patients treated with a picosecond 532nm Nd:
YAG laser, 15 patients had pigmentation clearance ranging from
good to excellent with nine of these patients reporting nearcomplete
to complete clearance, and only one patient with no
response to treatment at all. Two patients in this series reported
partial recurrence [6]. Patients typically require 2 to 4 sessions
for adequate treatment response and recurrence of lesions was
very rare [6-9].
QS lasers have been shown to be an effective modality
for the treatment of nevus of Ota with a majority of patients
experiencing greater than 75% clearance after an average of
5.5 treatment sessions [8-10]. Patients treated with a 755nm
alexandrite picosecond laser required an average of 3.5 sessions
to achieve a comparable clinical satisfaction [8]. In one case
series, 3 patients with nevus of Ota who had either stopped
responding or had lesions resistant to QS laser treatment were
treated with a 755nm alexandrite picosecond laser. All patients
demonstrated significant cosmetic improvement and were well
pleased with their response [11]. Studies demonstrating the use
of picosecond lasers in the treatment of nevus of Ota are sparse
and limited by small patient numbers, yet the data suggest it is
highly effective.
Treatment of melasma is centered on reducing the severity of
hyperpigmentation to improve quality of life and limit recurrence
after successful treatment. Topical agents such as hydroquinone
(HQ) and azelaic acid are the current first-line treatment [12]. QS
lasers and ultrapulsed CO2 lasers are not recommended first line
agents in patients with melasma due to thermal damage and risk
of dyspigmentation [13]. Nonablative fractionated resurfacing
lasers have shown effectiveness yet recurrence occurs within 3 to
6 months after treatment in all cases [12]. Evidence for treatment
of melasma with a 755nm picosecond alexandrite laser was first
documented in a case report of two Korean women who had
previously reached a plateau in response to low-fluence QS laser
therapy. These patients exhibited modest but significant clearing
after 6 and 14 bimonthly treatment sessions [14]. A split-face
trial was conducted comparing a fractional picosecond 1064
nm laser with 4% HQ versus 4% HQ alone. In 30 patients the
mean melasma severity index was significantly decreased in the
laser treated side though patient satisfaction and quality of life
were similar [15]. Another split-face trial was conducted with
40 patients comparing a dual-wavelength (1064 and 595nm)
picosecond laser in combination with topical 2% hydroquinone
versus topical hydroquinone alone. It was found that weekly
laser treatments with hydroquinone achieved significantly
better clearance at 7 weeks compared to hydroquinone alone.
Recurrence of melasma at the 12-week evaluation did occur in
77% and 69% of patients treated with combination therapy and
hydroquinone respectively [16]. Melasma has proven to be a very
difficult lesion to treat with many patients often experiencing
resistance to treatments and recurrence after successful
treatment. Current data suggest that picosecond lasers may
not be an improvement over the standard of care in melasma
treatments.
Smaller studies have demonstrated the effectiveness of
picosecond lasers in the treatment of other hyperpigmented
skin lesions including verrucous epidermal nevi (VEN), Hori’s
nevus, solar lentigines, and even infraorbital dark circles. VEN
was successfully treated with a picosecond 532nm Nd:YAG laser
after up to 6 treatment sessions. The average patient had a rated
improvement of 3.7 in a 4-point scale and recurrence was not
seen in any patients after a 12 month follow up [17]. 10 patients
with infraorbital dark circles treated with a picosecond 755nm
alexandrite laser improved significantly after 3 treatment
sessions and clearance was sustained at a 132 day follow up [18].
This same study did however find that patients receiving a single
treatment with dual wavelength 532 and 1064nm picosecond
laser did not demonstrate any significant improvement. Solar
lentigines are known to be susceptible to treatment with QS
lasers but post-inflammatory dyspigmentation is a concerning
side effect especially in patients with darker skin types [19-
21]. Out of 43 solar lentigines treated with a dual-wavelength
532nm and 1064nm Nd:YAG picosecond laser, the average
improvement was 4.77 on a 5 point scale and post-inflammatory
hyperpigmentation (PIH) only occurred in 4.65% of lesions
[22]. For the treatment of Hori’s nevus, a 755nm picosecond
alexandrite laser demonstrated superior efficacy to the QS
alexandrite laser with a better side effect profile and a decreased
incidence of PIH [23].
Effectiveness in Acne Scarring
Due to the successful treatment of acne scarring with QS
nanosecond lasers, clinicians hoped picosecond lasers would
display a similar effectiveness with a better side effect profile
[24]. Clinical evidence on the efficacy for the treatment of rolling
and boxcar-type acne scars has been promising in the few
studies performed. Patients receiving 6 treatments with 755nm
picosecond alexandrite laser with DLA demonstrated significant
improvement in scarring at 1 and 3 months follow ups.
Histopathological examination at 3 months follow up revealed
an increase in dermal collagen III, elastic fiber density, and
mucin deposition in all layers [25]. A later study demonstrated
that treatment with a higher number of pulses from this same
laser had no statistical benefit compared to a standard number
of pulses in the treatment of acne scarring and wrinkling [26]. A head to head study comparing treatment response to 1,064
and 532nm wavelengths demonstrated improvement in acne
scarring with no observable difference between the wavelengths
[27]. While head to head trials have not yet been conducted
between treatment modalities, picosecond lasers may be a safe
alternative to skin types prone to pigment alterations and those
nonresponsive to other therapies.
Effectiveness in Wrinkles and Photodamage
Photodamage and wrinkling have been shown to be
responsive to QS lasers [26,28,29]. Picosecond laser treatment
causes increased dermal collagen and elastin and therefore
should be effective for treating sun damage and wrinkling [25]. A
small study investigating the efficacy for treating photodamaged
décolletage showed that treatment with the 755nm picosecond
alexandrite laser produced modest yet significant improvement
with a very favorable safety profile [29]. These results were
backed up by another study that showed very high patient
satisfaction rates for those receiving laser treatments for skin
rejuvenation on the dorsal hand and décolletage [30]. For the
treatment of wrinkles, the 755nm picosecond alexandrite laser
has been found to be incredibly effective. Weiss et al showed that
patients with a mean Fitzpatrick wrinkle score of 5.48 improved
to 3.47 on 6 month follow up after receiving 4 full-face monthly
treatments [28]. Biopsy results of specimens taken at 6 months
follow up showed significant increases in dermal collagen and
elastin fibers which correlated with improved appearance of
photodamage, wrinkles, and texture. Compressing this treatment
protocol to 2-3-week intervals resulted in expedited results with
no appreciable increase in side effects [31]. A split-face study was
conducted to better visualize the treatment effects of a 755nm
picosecond alexandrite laser when compared to a control side
receiving no intervention. These patients experienced significant
improvement in wrinkles and photoaging as well as improvement
in dyspigmentation limited to the treated side [32].
Safety
The safety of picosecond lasers has been well documented.
Occasionally patients requested topical anesthesia before
undergoing treatments, but generally treatments are only mildly
painful and well tolerated. The most common side effects across
all studies is transient erythema and edema. Clinicians often
regarded erythema as an end-treatment goal. A few studies have
described self-limited blistering and desquamation following
treatments with most cases resolving at one month follow up
[6,15]. Significant blistering was a desired end-treatment effect
in the treatment of verrucous epidermal nevi [33]. Crusting and
scabbing have also been described with one study documenting
a mean duration of 6.72 days [7,9,23,31]. A transient urticarial
reaction was noted immediately after treatment that resolved
acutely [29]. Interestingly, acneiform miliaras was observed on
both sides of the face in one patient of a split-face picosecond
alexandrite laser vs nanosecond alexandrite laser; it resolved
after 10 days [23]. PIH though rare was the most persistent
documented side effect of laser treatment. PIH was found to last
approximately 40 days in one study and all studies demonstrated
resolution of PIH at last follow up [3,18,23]. The transient nature
of PIH following picosecond laser treatments is especially
important in the management of patients with darker skin types
as other laser modalities are infrequently used in these patients.
Conclusion
The use of picosecond lasers in pigmentary lesions has
been characterized based on lesion type and extent with a
keen awareness of side effects particularly in darker skin types.
Histological examination of skin treated with picosecond lasers
revealed a marked increase in collagen and elastin fibers which
correlates with its effect in treating rhytides and photodamaged
skin. Though caused by a different underlying mechanism,
acne scarring has also been demonstrated to be responsive to
picosecond laser therapy. Identification of optimal laser settings
for specific lesion types has not yet been studied. Number of
treatment sessions and intervals between treatments are often
left to clinical judgement. The few studies examining shortened
interval times and higher pulse treatments have shown
comparable efficacy and safety to standard treatment regimens.
Moderate erythema was often a desired end-treatment effect
and number of passes and pulse count were based on the
amount needed to achieve this effect. While many of these
studies are limited by small patient numbers, the results have
been very promising. Patients tend to be well satisfied with
their improvement whether the outcome is evened skin tone or
improvement in texture.
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