Solar Keratosis (Actinic
keratosis) is a common premalignant skin lesion seen
on areas of the body that have been exposed to sun.
Premalignant means that the lesions have the potential
to become skin cancer.
The Solar Keratosis is the
earliest identifiable lesion that can eventually
develop into an invasive squamous cell carcinoma (SCC).
These Solar Keratosis lesions are diagnosed in 14
percent of all visits to dermatologists, following
only acne and dermatitis in frequency. Debate swirls
around the nomenclature for these Solar Keratosis
lesions because some consider them to be pre-cancerous
and others consider Solar Keratosis to be a SCC
confined to the lower portion of the epidermis. Solar
Keratosis typically occur in fair-skinned individuals.
In various northern hemisphere populations, 11 percent
to 25 percent of adults have at least one Solar
Keratosis lesion, compared to 40 percent to 60 percent
of adult Australians who live closer to the equator.
One prospective study estimates that one Solar
Keratosis/1,000/year transforms into SCC, whereas
retrospective studies predict that from 5 percent to
20 percent of all untreated Solar Keratosis lesions
will progress to SCC. Solar Keratosis are typically
produced by ultraviolet radiation, but ionizing
radiation, arsenic, or polycyclic hydrocarbon exposure
might also cause them. At least two prospective
studies have demonstrated that sunscreen reduces the
likelihood of developing more Solar Keratosis.
On physical examination, the
typical Solar Keratosis is a poorly demarcated,
slightly erythematous papule or plaque found on
sun-exposed areas such as the face, balding scalp,
posterior neck, and dorsal upper extremity.
Characteristically, Solar Keratosis feel rough or
gritty and might be difficult to see. Therefore,
palpation of high-risk areas under an intense light
source is essential to accurate diagnosis.
Microscopically, one sees large keratinocytes with
atypical nuclei in the lower portion of the epidermis.
Liquid nitrogen, 5-fluorouracil cream, trichloroacetic
acid, electrodesiccation and curettage, and CO2 laser
all can eradicate Solar Keratosis. Two newer treatment
modalities include photodynamic therapy and the
topical immunomodulator, imiquimod.
A single Solar Keratosis may
appear at first, but most people with one Solar
Keratosis will develop other Solar Keratosis lesions.
Solar Keratosis can appear in groups and may
occasionally itch or become tender, especially after
sun exposure.
