Photodynamic therapy - Lasers and Energy Devices for the Skin - page 254

corneum is a major barrier to the penetration of ALA (49,77).
Hyperkeratotic lesions must be treated with light curettage
prior to ALA application. Otherwise, ALA is preferentially
absorbed by the hyperkeratotic scale rather than the lesion
intended for treatment (48). Some physicians use occlusion to
improve delivery of ALA through thicker lesions. Tegaderm™,
opaque Mepore®, or Glad Press-N-Seal® may be used for these
purposes.
Methods of proper skin preparation to reduce stratum cor-
neum thickness also include light chemical peels, tape stripping,
microdermabrasion, and degreasing of the skin with acetone
(170,195-197). All of the above measures can improve the
absorption of ALA by the skin (49). We routinely use a vibrating
microdermabrasion system (Vibraderm, Great Plains, Texas,
USA) (Fig. 10.11) with subsequent acetone degreasing to pre-
pare the skin for ALA application (Fig. 10.12).

Incubation Time
ALA is FDA-approved for use with a 14- to 18-hour incuba-
tion and subsequent photoactivation with blue light (38).
However, longer incubation times often result in an increased
severity of adverse effects following ALA-PDT (Fig. 10.13)
(68), and furthermore, shorter incubation times (1-3 hours)
have demonstrated similar effi cacy in AK clearance (22,81).
We routinely use a 60-minute incubation time in the treat-
ment of AKs or for photorejuvenation. When treating thicker,
larger, or more invasive lesions, we extend the incubation time
to 3 hours and occlude the treated area with Glad Press'N
Seal®. Current FDA approval for MAL-PDT involves applying
a 16.8% cream under occlusive dressing for 3 hours followed
by illumination with a narrow spectrum red light lamp.

Light Sources
Blue, red, green, and broadband light sources may be used to
activate PpIX during ALA-PDT for AKs or photorejuvenation.
There is some evidence that blue light may be more effective
for superfi cial AKs due to the shorter wavelength and increased
potency during PDT of blue light (170). However, other
authors found no difference in effi cacy between blue and red
light for the treatment of AKs and photorejuvenation (106).
Green light was found to cause less pain than red light in the
treatment of AKs (80). Red light has a deeper depth of penetra-
tion, but is often used with MAL rather than ALA. Broadband
light sources, including IPL, have the advantage of improving
signs of photodamage. It is our practice, both in the treatment
of AKs and photorejuvenation, to use multiple light sources

Figure 10.11 Proper skin preparation prior to ALA application removes excess
layers of the stratum corneum and improves ALA penetration. We use a
vibrating microdermabrasion device for 5 minutes prior to acetone degreas-
ing. Abbreviation : ALA, aminolevulinic acid.

Figure 10.13 Moderate-to-severe phototoxic reaction due to extended ALA
incubation period. This woman had ALA-PDT with a 3-hour, unoccluded
incubation. The patient denied UV exposure for the 36 hours following PDT.
Abbreviations : ALA, aminolevulinic acid; PDT, photodynamic therapy; UV,
ultraviolet.

Figure 10.12 Acetone-soaked gauze following microdermabrasion enhances
aminolevulinic acid delivery. Firm pressure should be used during scrubbing
to remove excess skin lipids and keratinocytes.