Unveiling the Dermoscopic Characteristics of Actinic Keratosis

Actinic keratosis, often referred to as AK or solar keratosis, is a precancerous skin condition characterized by its scaly texture and potential to evolve into squamous cell carcinoma. It typically manifests on areas of the skin that have experienced significant sun exposure, such as the scalp, ears, face, and the back of the hands.

Clinically, these lesions present as irregularly shaped, discolored papules or plaques that may be red or pigmented. They often appear in multiples and can be accompanied by a scaly, warty surface and tenderness to the touch.

Dermoscopic examination of actinic keratosis reveals several distinctive patterns. On facial skin, a 'strawberry pattern' is common,dermoscopy of actinic keratosis marked by a well-defined border and a pink, featureless backdrop. This is complemented by a network of pink to red vessels encircling hair follicles, and small, color-varied spots that correspond to the openings of these follicles. Additionally, one might observe skin-colored or white circles around a yellowish core, indicative of keratotic plugs, and under polarized light, four-dot clods known as rosettes, along with surface scaling.

When actinic keratosis affects nonfacial skin, the pattern is less distinct, with features such as irregular shapes, surface scale in white or yellow hues, and sometimes concentric yellow structures reminiscent of an oyster shell. Erythema with tiny red dots, known as dotted vessels, and rosettes visible only under polarized light, as well as short shiny streaks, may also be present.

Pigmented actinic keratosis shares similarities with its nonpigmented counterpart but includes pigmented structures. The most prevalent findings include hyperpigmented follicular openings, brown areas lacking distinct patterns, and annular-granular structures. Additional characteristics may include a brown background, angular brown lines on the surface, a grey halo around hair follicles, and grey rhomboidal structures.

Dermoscopic diagnosis of actinic keratosis is a clinical and visual endeavor, often challenging due to its resemblance to other skin conditions such as solar lentigo, squamous cell carcinoma, and lentigo maligna. Differentiating these requires attention to specific dermoscopic details, such as the presence of peripheral white areas around a central scaly core in squamous cell carcinoma, or the unique arrangement of dotted/coiled vessels in intraepidermal carcinoma.

Lentigo maligna, another condition in the differential, is associated with hyperpigmented follicular openings and pigmented rhomboids, which are more frequent in this condition than in pigmented actinic keratosis. The texture and border abruptness of lentigo maligna also differ from those of actinic keratosis, with the former often being smooth and having variable border definitions.

Psoriasis, known for its red, scaly plaques, can occasionally be mistaken for actinic keratosis. However, its regular structure and uniform, silvery scale distinguish it from the irregular, yellowish scale of AK. The distribution of dotted blood vessels in psoriasis is also uniform across the lesion, unlike in AK.

The correlation between the histological underpinnings of actinic keratosis and its dermoscopic appearance is not always clear. However, certain features like rosettes are thought to result from the interaction of polarized light with narrow, keratin-filled or fibrotic adnexal openings. The surface scale of AK is associated with alternating orthokeratosis and parakeratosis, while the 'strawberry pattern' is linked to vessels between hair follicles and white-haloded follicular openings. The circles observed in pigmented keratosis are due to the involvement of follicular infundibula.