Actinic Keratosis: Definition, Clinical Characteristics, and Risk Factors

Pathological Features

Actinic keratoses (AKs) are characterized by epithelial dysplasia, which may be restricted to the basal layer or extend to full-thickness atypia, with a disorderly arrangement and maturation of epithelial cells 2
The cardinal histological feature of AKs is the presence of multiple buds of epithelial cells at the membrane zone, but without invasion, and several histological variants exist, including hypertrophic, bowenoid, lichenoid, acantholytic, and pigmented types 1, 3

AKs present as discrete, sometimes confluent, patches of erythema and scaling on predominantly sun-exposed skin, typically appearing on the face, scalp, ears, dorsa of hands, and other chronically sun-exposed areas 1, 3
Lesions are often asymptomatic but may occasionally be sore or itch, and they most commonly affect middle-aged and elderly individuals, particularly those with fair skin (Fitzpatrick skin types I and II) 1, 4, 3

AKs are primarily caused by chronic exposure to ultraviolet (UV) radiation, with UVB-specific p53 mutations demonstrated in AKs, providing molecular evidence for the role of sunlight in their development 3
Immunosuppressed patients, particularly organ transplant recipients, and individuals with chronic sunbed use are at higher risk of developing AKs 3

Prevalence of AKs increases with age, with 19-24% of individuals over 60 years having at least one AK in UK studies, and AKs are found in 49% of men and 28% of women in the Rotterdam study of individuals with mean age 72 years 3
The condition is often underestimated due to difficulties in measuring the burden reliably 3

AKs represent a chronic disease with lesions that may regress and relapse over time, with 25-70% of lesions may spontaneously resolve over 1-4 years 3
The risk of progression to invasive squamous cell carcinoma is low, with less than one in 1000 AKs developing into SCC per annum, but the presence of AKs is a marker of excessive sun exposure and is associated with the development of further lesions 3