What is the best way to describe an Actinic Keratosis (AK)?

Actinic Keratosis: Clinical Description and Characteristics

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

Definition and Key Features

• Clinical appearance:

  • Rough, scaly patches or papules on an erythematous base
  • Often better identified by palpation (rough texture) than by visual inspection in early stages
  • Typically 2-10mm in size
  • May be discrete or confluent

• Histological characteristics:

  • Cardinal feature is epithelial dysplasia
  • Dysplasia may be restricted to the basal layer or extend to full-thickness atypia
  • Disorderly arrangement and maturation of epithelial cells
  • Multiple buds of epithelial cells may occur at the membrane zone without invasion 1

• Histological variants include:

  • Hypertrophic
  • Bowenoid
  • Lichenoid
  • Acantholytic
  • Pigmented 1

Epidemiology and Risk Factors

• Primary cause: Chronic exposure to ultraviolet (UV) radiation 1

  • UVB-specific p53 mutations have been demonstrated in AKs 1

• Prevalence:

  • 19-24% of individuals aged >60 years in UK studies
  • 36% of men aged 40-49 years
  • 49% of men and 28% of women by age 72 in Dutch studies 1

• Risk factors:

  • Fair skin (Fitzpatrick phototypes I and II)
  • Chronic immunosuppression (organ transplant recipients, inflammatory bowel disease, rheumatological disease)
  • Arsenic exposure
  • Chronic sunbed use 1
  • Older age (linear increase with age from 60-80 years, especially in men) 1

Natural History

• Chronic disease pattern:

  • Lesions may regress and relapse over time (25-70% apparent resolution over 1-4 years)
  • Single lesion is a marker of excessive sun exposure and associated with development of further lesions 1

• Malignant transformation:

  • Low rate: less than one in 1000 AKs developing into SCC per annum
  • Risk increases with time: 0.6% of patients developed SCC in AK field within first year, rising to 2.57% at 4 years 1

Distribution and Location

• Common sites:
  • Head and neck (70% of lesions)
  • Dorsa of hands
  • Other chronically sun-exposed areas 1

Clinical Significance

• AKs represent a marker of excessive UV exposure and increased risk for developing skin cancer
• The presence of multiple AKs constitutes a "field cancerization" effect
• While individual lesion risk of progression to SCC is low, patients with multiple lesions have higher cumulative risk 1

Distinguishing Features

• AKs differ from SCC in situ (Bowen disease) primarily by the extent of dysplasia
• When dysplasia extends to full-thickness atypia, the lesion is classified as SCC in situ 1
• Palpable rough surface often precedes visible lesion 2

Understanding these characteristics is essential for proper identification, risk assessment, and management of actinic keratoses. Early recognition and appropriate treatment can prevent progression to invasive squamous cell carcinoma.