Actinic Keratosis

Actinic keratoses (AKs) are also known as "solar keratoses" because of their relationship to chronic sun exposure. These lesions are most common on the dorsal surfaces of the hands and arms, neck, ears, bald scalp, and face, areas that are not covered by clothing on a daily basis (Fig. 33-78). AKs are usually scaly, pink to flesh-colored macules or papules and are often easier to feel than see. They have a rough texture as

Figure 33-77 Dermatofibroma undergoing pinch test, in which lesion dimples downward. © Richard P. Usatine.)

Figure 33-78 Extensive actinic keratoses on forearms and dorsum of hands.

Figure 33-78 Extensive actinic keratoses on forearms and dorsum of hands.

a bare finger slides over the skin. The lesions have malignant potential and can transform into squamous cell carcinoma at a rate of about 0.1% per lesion per year.

Cryotherapy with liquid nitrogen is the most effective and practical method for treating AKs when a limited number of lesions are present. For more extensive lesions, topical 5-FU (Efudex 5%, Carac 0.5%), diclofenac (Solaraze), or imiqui-mod (Aldara) is recommended. This treatment can be temporarily disfiguring with erythema, crusting, or ulcerations, but if the skin is kept lubricated with petroleum jelly during treatment, the process usually looks worse than it feels. Both 5-FU and diclofenac are applied daily for 4 weeks. Patients often will not tolerate the 4-week duration, but if erythema or crusting is achieved in 2 to 3 weeks, treatment may still be successful. Lesions will take another 2 to 4 weeks to heal. Treatment with imiquimod is once daily for 3 to 5 days of the week (depending on irritation) and is continued for 12 to 16 weeks. Imiquimod is supplied in small, expensive packets, so it is less practical for treating larger surface areas. Lesions that are hyperkeratotic should be biopsied because they often recur with cryotherapy and may not be penetrated by topical therapies.

Treating AKs with liquid nitrogen using a 1-mm halo freeze demonstrated complete response of 39% for freeze times less than 5 seconds, 69% for times over 5 seconds, and 83% for more than 20 seconds (Thai et al., 2004). More hypopig-mentation is caused by 20 seconds of freeze time. The physician should base duration of freeze time on the size and thickness of the lesion, using sufficient time for clearance while attempting to avoid hypopigmentation and scarring.

All patients with actinic keratosis or skin cancer should be educated on daily sun protection and sun avoidance. This includes sunscreen with a sun protection factor (SPF) of 30 or greater, wide-brimmed hats, long sleeves and pants, and avoiding peak hours of sunlight (10 am to 4 pm).

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