Solar keratosis, also known as actinic keratosis or keratosis senilis, primarily occurs in fair-skinned middle-aged and elderly individuals who are frequently exposed to sunlight. In addition to sunlight, factors such as ionizing radiation, radiant heat, and products like asphalt and coal tar can also trigger the condition. The incidence rate is higher in men than in women.

bubble_chart Pathological Changes

Extensive hyperkeratosis of the epidermis with well-demarcated areas of parakeratosis. The granular layer is often absent beneath the parakeratotic areas, where the epidermal cells appear markedly atypical with disordered arrangement. Some nuclei are irregular, large, and hyperchromatic, while others show premature keratinization. The atypical cells frequently exhibit budding proliferation extending into the upper dermis. The abnormal epidermis is sharply demarcated from adjacent normal epidermis and normal glandular epithelium. This alternating pattern of normal and dysplastic epidermis is a characteristic histopathological feature of this condition. The dermis shows marked actinic degeneration and often exhibits grade III lymphocytic infiltration.

bubble_chart Clinical Manifestations

The skin lesions are red to light brown or grayish-white round or irregular keratotic papules with well-defined borders. The surface is covered with dry, adherent scales of varying thickness and extent, which are difficult to remove, and surrounded by erythema. Occasionally, the lesions may exhibit significant hyperkeratosis, forming cutaneous horns. The size varies, ranging from one or several millimeters to 1 cm or larger. The affected areas typically show prior significant sun damage, manifesting as dryness, wrinkling, atrophy, and telangiectasia, often accompanied by senile freckle-like nevi. These lesions commonly occur on sun-exposed areas such as the face, lower lip, dorsum of the hands, forearms, neck, and bald scalp. They may be multiple or solitary. Patients usually experience no symptoms or mild itching. Without treatment, approximately 20% of patients may develop squamous cell carcinoma in one or more lesions, though metastasis is rare, with a metastatic rate ranging from 0.5% to 3%.

Isolated lesions can be treated with liquid nitrogen or CO₂ snow cryotherapy or by curettage and electrodesiccation under local anesthesia. For multiple or extensive lesions, topical application of 1-5% 5-fluorouracil ointment or solution may be used.