Spreading pigmented actinic keratosis (SPAK) is a common, but uncommonly reported or appreciated, variant of classic actinic keratosis (AK). It can mimic different pigmented lesions, which may be benign (eg, solar lentigo) or malignant (eg, lentigo maligna).

We sought to review current data and identify areas needing further research to establish diagnostic guidelines for SPAK and to increase awareness of this common entity.

A literature search was performed in both PubMed and MEDLINE databases using the search terms “spreading pigmented actinic keratosis,” “pigmented solar keratosis,” “pigmented actinic,” and “pigmented solar.” Each article was retrieved, reviewed, and summarized.

SPAK is a rarely reported lesion that can be difficult to distinguish from other benign and malignant pigmented lesions, including seborrheic keratosis, melanoma in situ (lentigo maligna type), and lentigo maligna melanoma. Located mainly on sun-exposed areas and with a size greater than 1.5 cm, the lesion typically spreads laterally. Pathologically, the lesion resembles classic AK with increased basal melanization. The malignancy potential has not yet been elucidated but destructive therapies such as cryotherapy are recommended.

Reports not yet published or not included in the comprehensive databases we used may exist that were not analyzed.

SPAK can be associated with adjacent melanoma in situ; therefore, its diagnosis merits increased suspicion for coexisting melanoma.