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Actinic keratosis
Actinic keratosis (also called "solar keratosis"〔 and "senile keratosis"; abbreviated as "AK") is a pre-cancerous patch of thick, scaly, or crusty skin.〔Freedberg, et al. (2003). ''Fitzpatrick's Dermatology in General Medicine''. (6th ed.). McGraw-Hill. ISBN 0-07-138076-0.〕 These growths are more common in fair-skinned people and those who are frequently in the sun. They usually form when skin gets damaged by ultraviolet (UV) radiation from the sun or indoor tanning beds. AKs are considered potentially pre-cancerous; left untreated, they may turn into a type of cancer called squamous cell carcinoma.〔 Untreated lesions have up to a 20% risk of progression to squamous cell carcinoma, so treatment by a dermatologist is recommended.
Development of these growths occurs when skin is constantly exposed to the sun over time. They usually appear as thick, scaly, or crusty areas that often feel dry or rough. In fact, AKs are often felt before they are seen, and the texture is often compared to sandpaper. They may be dark, light, tan, pink, red, a combination of all these, or have the same color as the surrounding skin. An actinic keratosis lesion commonly ranges between 2 and 6 millimeters in size but can grow to be a few centimeters in diameter.〔 They often appear on sun-exposed areas of the skin, such as the face, ears, neck, scalp, chest, backs of hands, forearms, or lips. Because they are related to sun-damage on the skin, most people who have an AK have more than one.
Diagnosis is suspected clinically on physical exam, but can be confirmed by looking at cells from the lesion under a microscope. There are various options for treatment, but 5-fluorouracil cream seems to be popular and effective. A significantly faster treatment is ingenol mebutate which is effective after a 3-day treatment as opposed to 21 days. By following up with a dermatologist, AKs can be treated before they turn into skin cancer. If skin cancer does develop from an AK lesion, it can be caught early with close monitoring, at a time when treatment can be curative.
== Signs and symptoms ==
Actinic keratoses ("AKs") most commonly present as a white, scaly plaque of variable thickness with surrounding redness; they are most notable for having a sandpaper-like texture when felt with a gloved hand. Skin nearby the lesion often shows evidence of solar damage characterized by notable pigmentary alterations, being yellow or pale in color with areas of hyperpigmentation; deep wrinkles, coarse texture, purpura and ecchymoses, dry skin, and scattered telangiectasias are also characteristic. Photoaging leads to an accumulation of oncogenic changes, resulting in a proliferation of mutated keratinocytes that can manifest as AKs or other neoplastic growths. With years of sun damage, it is possible to develop multiple AKs in a single area on the skin. The lesions are usually asymptomatic, but can be tender, itch, bleed, or produce a stinging or burning sensation. AKs are typically graded in accordance with their clinical presentation: Grade I (easily visible, slightly palpable), Grade II (easily visible, palpable), and Grade III (frankly visible and hyperkeratotic).
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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