Actinic Keratosis

Actinic keratosis (AK) is a common premalignant skin lesion resulting from chronic ultraviolet radiation exposure, representing focal abnormal proliferation of epidermal keratinocytes. The prevalence in the United States was estimated at approximately 58 million persons, with the condition commonly affecting men, persons with fair skin, those with a history of prolonged ultraviolet light exposure, and older individuals.

Causes

Chronic cumulative sun exposure is the primary cause of actinic keratosis in otherwise healthy Caucasians. Fair complexion (Fitzpatrick phototypes I and II), immunosuppression, and increased age contribute to increased risk of AK development.

Clinical Features

The lesions present with a characteristic rough, sandpaper-like surface texture, predominantly occurring on the face, ears, scalp, neck, arms, dorsal hands, and forearms—areas with chronic sun exposure. Patients often present with multiple lesions in one continuous area; a phenomenon termed "field change" or "field cancerization".

Complications

The primary concern is progression to invasive cutaneous squamous cell carcinoma (SCC), though the risk is variable. Earlier estimates suggested that up to 10% of AKs progress to cutaneous SCC within 2 years; other studies report progression rates ranging from 0.025% to 16% per actinic keratosis lesion per year.

Importantly, 60% to 65% of squamous cell carcinomas are documented to have arisen from lesions previously diagnosed as AKs. Of those rare AKs that progress to cutaneous SCCs, indirect evidence suggests that only 2% subsequently metastasize.

Diagnosis

Diagnosis is primarily clinical, based on the characteristic appearance of rough, scaly, erythematous plaques on sun-exposed skin. The diagnosis relies on recognizing the typical presentation in the appropriate clinical context of chronic sun exposure and patient risk factors.

Differential Diagnosis

This condition can resemble seborrheic keratosis, benign lichenoid keratosis, squamous cell carcinoma, or basal cell carcinoma.

Treatment

Treatment aims to clinically eradicate evident and subclinical lesions, prevent evolution into SCC, and reduce recurrence. The American Academy of Dermatology recommends early treatment with cryosurgery, topical imiquimod, or topical 5-fluorouracil. For multiple lesions and field cancerization, field-directed therapies are generally preferred because they treat both present AK and subclinical lesions, potentially preventing new lesion development and SCC progression: topical imiquimod, or topical 5-fluorouracil are appropriate in these cases.

Written by Dakota Olberding, PA

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