Introduction to laser treatment
of actinic keratoses
Actinic Keratoses or AK is a form of non-melanoma
skin cancer (NMSC). At present the chances of AK
becoming malignant ranges from 5% to 20%. There
is no way to predict which AK will become malignant.
Treatment of AK has been successful with traditional
therapies, such as, cryosurgery, topical cytotoxic
agents and surgical excision. Recently, laser and
PDT have met with equal success.
To date, no large-scale studies have been done
to assess the role of ablative laser therapy. However,
anecdotal studies have been conducted to examine
the role of CO2 and erbium: YAG laser in skin resurfacing,
in the prophylaxis and treatment of multiple facial
AK. These studies reported successful prophylaxis
against NMSCs after CO2 laser resurfacing. In another
study, thirty five patients with actinic involvement
were given full face laser resurfacing. At one
year of follow up, only five patients developed
AK or basal cell carcinoma (BCC).
Photodynamic therapy (PDT)
The combination therapy of a photosensitizer and
light, used in certain skin diseases and called
photochemo therapy, is very old dating back to
ancient Egypt, Greece and India. The modern photodynamic
therapy (PDT) is a take from this ancient therapy,
with the difference that the action here is an
oxygen dependent photosensitive reaction. Later,
for improved treatment, laser substituted ordinary
light. PDT, therefore, comprises mainly, three
components; light, photosensitizer and oxygen.
Traditionally, large complex lasers were used
for PDT. But now a wide range of coherent and non-coherent
light sources are available. These include dye
lasers pumped by argon or metal vapor lasers and
frequency doubled Nd: YAG lasers.
Topical photosensitizers, such as, 5-ALA and
the methyl ester of ALA, mALA, have been developed
for treating skin cancers, replacing systemic
photosensitizers without the significant photo
toxicity. The most common side effects of 5-ALA
and mALA are temporary irritation and edema,
during and immediately after treatment. Scarring
and dyschromia may also occur. One drawback of
these topical photosensitizers is their limited
depth of penetration, though extra penetration
depths are yet to be established.
Topical photosensitizers and their combination
with lasers have allowed PDT to be used in cutaneous
diseases. PDT is now a treatment option for actinic
keratoses (AK) and is rapidly becoming an established
option for treating non-hyperkeratonic AKs. Traditionally,
blue light of 430nm and red light of 630nm have
been used. The treatment effects of pulse dye laser,
at wave lengths of 580nm, 595nm and 600nm, and
incoherent light sources of wave lengths 580nm
to 740nm, on human keratinocytes treated with the
topical photosensitizer ALA was compared. It was
found that PDL at 585nm and incoherent light sources
produced the maximum cytotoxic effects. It was
inferred that PDL may be as effective as continuous
light at 28 days after treatment.
The safety and efficacy of 595nm PDL in AK treatment,
was evaluated on 41 patients, 3 hours and 14 to
18 hours after the incubation of 20% 5-ALA sensitizer.
On the average, lesion clearance per patient was
90%, which compared favorably with lesion clearance
by other treatments. In addition, treatment time
was less, discomfort was minimal and the post operative
erythema cured in five to six days. Importantly,
it was the first study to show that short incubation
period was as effective as a long one.
At present, several research groups are engaged
in evaluating differences between various light
sources and ALA-PDT in the treatment of AK. In
one study, treatment of AK by ALA-PDT was compared
with the treatment by 5-fluorouracil, in order
to assess the efficacy and tolerance of these
two therapies. The subjects in the study were
17 patients with dorsa of the hands. At six months
follow up, no statistically significant difference
was noted in the extent of clearance of the lesions
by these two treatments.
In another prospective randomized study, the results
of AK treatment by cryotherapy with two passes
were compared to red light- PDT using methyl ALA
as photosensitizer. It was found that patients
treated with cryotherapy gave, by and large, a
marginally better response. However, the cosmetic
appearance and patient satisfaction was significantly
higher in PDT patients. The inference drawn was
that a repeat PDT would improve on the results.
Investigation was also conducted on ALA-PDT treatment
of AK using a large field incoherent light. 78%
of the lesions remained clear at one year. The
side effects included pain, superficial ulceration,
infection and dyschromia.
A type of PDT is photodynamic rejuvenation where
the distinguishing feature is the use of intense
pulse laser (IPL). In one study, two treatments
of ALA-IPL gave 87% clearance in three months.
Other studies reported fewer clearances. So far,
this treatment has given variable results.