What is actinic keratosis?

Actinic Keratosis: Definition and Clinical Characteristics

Actinic keratoses (AKs) are premalignant keratotic lesions occurring on chronically ultraviolet-exposed adult skin that represent focal areas of abnormal keratinocyte proliferation and differentiation, carrying a low risk of progression to invasive squamous cell carcinoma. 1

Pathological Features

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

Clinical Presentation

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

Etiology and Risk Factors

• AKs are primarily caused by chronic exposure to ultraviolet (UV) radiation 1
• UVB-specific p53 mutations have been demonstrated in AKs, providing molecular evidence for the role of sunlight in their development 1
• Higher prevalence is observed in:
  • Fair-skinned individuals (Fitzpatrick phototypes I and II) 2
  • Elderly populations, especially men 2
  • Immunosuppressed patients, particularly organ transplant recipients 1
  • Individuals with chronic sunbed use 1

Epidemiology

• Prevalence increases with age, with 19-24% of individuals over 60 years having at least one AK in UK studies 1
• In the Rotterdam study of individuals with mean age 72 years, AKs were found in 49% of men and 28% of women 1
• The condition is often underestimated due to difficulties in measuring the burden reliably 1

Natural History and Malignant Potential

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

Field Cancerization Concept

• Subclinical skin alterations in the periphery of visible AK lesions contain the same genetic changes as those found in the AK lesions themselves 3
• This concept of "field cancerization" has important implications for treatment approaches, as guidelines now recognize the importance of treating the entire field in patients with multiple AKs 3

Clinical Significance

• Due to their potential for progression to invasive squamous cell carcinoma, all AKs warrant therapeutic intervention 4
• Early treatment may prevent progression to invasive disease 5
• Regular clinical checkups aid in early recognition of AKs 4

Understanding the nature of actinic keratoses is essential for appropriate management and prevention of potential progression to invasive squamous cell carcinoma, particularly in high-risk populations.