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Author: Dr Amanda Oakley, Dermatologist, Hamilton, New Zealand, 1997. Updated December 2015.
Actinic keratosis is a scaly spot found on sun-damaged skin. It is also known as solar keratosis. It is considered precancerous or an early form of cutaneous squamous cell carcinoma (a keratinocyte cancer).
Actinic keratoses affect people that have often lived in the tropics or subtropics and have predisposing factors such as:
Actinic keratoses are a reflection of abnormal skin cell development due to DNA damage by short wavelength UVB.
Actinic keratosis may be solitary but there are often multiple keratoses. The appearance varies.
Actinic keratoses are very common on sites repeatedly exposed to the sun, especially the backs of the hands and the face, most often affecting the ears, nose, cheeks, upper lip, vermilion of the lower lip, temples, forehead and balding scalp. In severely chronically sun-damaged individuals, they may also be found on the upper trunk, upper and lower limbs, and dorsum of feet.
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The main concern is that actinic keratoses predispose to squamous cell carcinoma. It is rare for a solitary actinic keratosis to evolve to squamous cell carcinoma (SCC), but the risk of SCC occurring at some stage in a patient with more than 10 actinic keratoses is thought to be about 10 to 15%. A tender, thickened, ulcerated or enlarging actinic keratosis is suspicious of SCC.
Cutaneous horn may arise from an underlying actinic keratosis or SCC.
Because they are sun damaged, people with actinic keratoses are also at risk of developing actinic cheilitis, basal cell carcinoma (BCC, which is more common than SCC), melanoma and rare forms of skin cancer such as Merkel cell carcinoma.
Actinic keratoses are usually removed because they are unsightly or uncomfortable, or because of the risk that skin cancer may develop in them.
Treatment of an actinic keratosis requires removal of the defective skin cells. Epidermis regenerates from surrounding or follicular keratinocytes that have escaped sun damage.
Tender, thickened, ulcerated or enlarging actinic keratoses should be treated aggressively. Asymptomatic flat keratoses may not require active treatment but should be kept under observation.
Physical treatments are used to destroy individual keratoses that are generally symptomatic or have a thick hard surface scale. The lesions may recur in time, in which case they may be retreated by the same or a different method.
Liquid nitrogen spray is required to ensure adequate depth and duration of the freeze. This varies according to lesion location, width and thickness. Healing varies from 5–10 days on the face, 3–4 weeks on the hands, and 6 weeks or longer on the legs. A light freeze for a superficial actinic keratosis usually leaves no mark, but longer freeze times result in hypopigmentation or scar.
Shave, curettage (scraping with a sharp instrument) and electrocautery (burning) may be necessary to remove a cutaneous horn or hypertrophic actinic keratosis. Healing of the wound takes several weeks or longer, depending on the body site. A specimen is sent for pathological examination.
Excision ensures the actinic keratosis has been completely removed, which should be confirmed by pathology. The surgical wound is sutured (stitched). The sutures are removed after a few days, the time depending on the size and location of the lesion. The procedure leaves a permanent scar.
Creams are used to treat areas of sun damage and flat actinic keratoses, sometimes after physical treatments have been carried out. Field treatments are most effective on facial skin. Pretreatment with keratolytics (such as urea cream, salicylic acid ointment or topical retinoid), and thorough skin cleansing improves response rates. Results are variable and the course of treatment may need repeating from time to time. With the exception of diclofenac gel, field treatments all result in local inflammatory reactions such as redness, blistering and discomfort for a varying length of time.
Actinic keratoses are prevented by strict sun protection. If already present, keratoses may improve with a very high sun protection factor (50+) broad-spectrum sunscreen applied at least daily to affected areas, year-round.
The number and severity of actinic keratoses can also be reduced by taking nicotinamide (vitamin B3) 500 mg twice daily.
Actinic keratoses may recur months or years after treatment. The same treatment can be repeated or another method used. Patients who have been treated for actinic keratoses are at risk of developing new keratoses. They are also at increased risk of other skin cancers, especially intraepidermal squamous cell carcinoma, invasive cutaneous squamous cell carcinoma, basal cell carcinoma and melanoma.
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