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Excimer Laser Therapy for the Treatment of Psoriasis
power of 1–2W and the newer XTRAC Velocity is 300–400% more Figure 1: Patient at Baseline and Following 12 Weeks of
powerful than XTRAC Ultra, with faster delivery. This allows physicians to
Twice-weekly Excimer Laser Treatment, Demonstrating a
Decrease in Induration, Erythema and Scale
consider laser therapy for patients with 10–20% BSA involvement.
Furthermore, in clinical practice, excimer laser can be used in
combination with topical therapies or acitretin (Soriatane
®
) to achieve
more rapid results.
Dosage and Administration
Several companies manufacture 308nm excimer laser machines;
however, the authors are most familiar with the XTRAC Ultra by
PhotoMedex and thus use it for illustration (see Figure 2). This machine
delivers monochromatic 308nm light as a uniform square beam
measuring 4cm
2
, which can be used in either paint or tile mode. In paint
mode, monochromatic UV light is delivered continuously as the
handpiece is moved over the plaques. In clinical practice, physicians
prefer the more rapid and convenient paint mode. In tile mode, the
handpiece is held in place, a pre-determined amount of UV light is
administered and the handpiece is then moved to an adjacent area of
Figure 2: Use of the XTRAC
®
Ultra 308nm Excimer
the plaque. The tile mode is generally preferred in the research setting Laser for the Treatment of Psoriasis
as it is more reproducible.
Administration of excimer laser therapy is conducted bi-weekly, initially
for 10 treatments. Treatment times vary depending on the number,
induration and size of psoriatic plaques. There should be a minimum of
48 hours between treatments. Patients are encouraged to comply with
the treatment schedule as closely as possible. Patients may see a
response following only four to six treatment sessions, and some
patients notice marked reduction in pruritus after 24 hours. In clinical
practice, the outer boundary of a plaque tends to be one of the last
areas to clear compared with the centre of the plaque.
Most of the aforementioned clinical studies utilised dosage protocols
based on multiples of MED determined by non-psoriatic skin. However,
psoriatic tissue has a much higher tolerance for UV irradiation compared
with non-involved tissue, withstanding much higher doses without
burning or blistering. Therefore, a standard protocol has recently been
Table 1: XTRAC
®
Ultra Induration-based Protocol
established in which dosage is determined by plaque thickness (mild,
moderate or severe). This induration-based protocol uses the actual
Determining Dose for First Treatment of Psoriasis
dose of light therapy as measured in milliJoules, rather than adjusting
dosimetry by multiples of MED. Table 1 is an example of an induration-
Fitzpatrick Skin Type
Plaque Thickness Induration Score 1–3 (mJ/cm
2
) 4–6 (mJ/cm
2
)
based dosing protocol established by PhotoMedex, which was validated
Mild 1 300 400
by results from over 30 clinical trials testing localised laser therapy for
Moderate 2 500 600
psoriasis. Notably, other laser machines may have differing protocols;
Severe 3 700 900
the table included here is simply an example of a protocol used for the
XTRAC
®
Clinical Reference Guide. Dosing guideline for targeted UVB phototherapy of
XTRAC Ultra machine. psoriasis. XTRAC treatment guidelines 12-95359-01 rev. C.
As patients are treated, psoriatic plaques become acclimatised to A misconception is that patients with high MED thresholds are not
previous dosages, requiring higher UV dosages for further improvement necessarily good candidates for laser treatment. However, patients with
in the plaque.
14
Additionally, physicians must be careful to ensure that higher Fitzpatrick skin types and higher MED thresholds can still be good
thinning lesions do not receive an excessively high dose resulting in treatment candidates; clinicians just have to adjust the dosimetry
blistering or erythema, even though the same dose was previously upwards according to skin type. Conversely, patients who have very low
tolerated when the plaques were thicker. The standard induration-based MED thresholds (e.g. Fitzpatrick skin type 1) may have trouble tolerating
protocol takes these factors into account when determining incremental very aggressive UVB phototherapy such as excimer laser because of
dosing changes (see Table 2). Another advantage of excimer laser is that their tendency to blister more easily. Clearly, skin type and sensitivity are
therapy can be tailored to the needs of patients, with higher doses important in determination of dosage; therefore, skin type is factored
targeted at thicker plaques. However, in the opinion of the authors, the into the induration-based protocol (see Table 1).
major advantage of excimer laser treatment is in making phototherapy
more convenient for patients by greatly improving or possibly clearing Safety
psoriasis in ~10 treatment sessions, rather than in the ~30 treatment The most common side effects of treatment with excimer laser, in
sessions typically needed for traditional UVB phototherapy. decreasing order of frequency, are erythema, blistering and
EUROPEAN DERMATOLOGY 13
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