Actinic Keratosis: Definition and Management
Actinic keratoses (AKs) are premalignant keratotic lesions occurring on chronically sun-exposed skin that represent focal areas of abnormal keratinocyte proliferation and differentiation, carrying a low risk of progression to invasive squamous cell carcinoma (SCC). 1
Definition and Clinical Characteristics
Actinic keratoses present as:
- Discrete, sometimes confluent, patches of erythema and scaling
- Predominantly on sun-exposed skin (face, scalp, ears, dorsa of hands)
- Usually affecting middle-aged and elderly individuals
- Often asymptomatic but may occasionally be sore or itch
- Can be single or multiple lesions 1
Histologically, AKs are characterized by:
- Epithelial dysplasia (cardinal feature)
- Disorderly arrangement and maturation of epithelial cells
- Multiple buds of epithelial cells at the membrane zone (without invasion)
- Various subtypes: hypertrophic, bowenoid, lichenoid, acantholytic, and pigmented 1
Epidemiology and Risk Factors
AKs result from chronic exposure to ultraviolet (UV) radiation, as evidenced by:
- Predominant occurrence on chronically sun-exposed skin
- Higher prevalence in fair-skinned individuals
- Presence of UVB-specific p53 mutations in AK lesions
- Increased prevalence in immunosuppressed individuals 1
Clinical Significance
AKs are significant because:
- They represent in-situ squamous cell carcinomas of the skin 2
- They have potential for progression to invasive SCC, though individual lesion risk is low 1
- They have potential for spontaneous regression 1
- The risk of SCC increases for those with more than 5 AKs 3
- They indicate field cancerization, where surrounding skin contains subclinical lesions with similar genetic changes 4
Diagnosis
Diagnosis is primarily clinical, based on:
- Visual inspection and palpation (rough surface often precedes visible lesion)
- Dermoscopy for additional information
- Biopsy and histopathologic evaluation when diagnosis is uncertain or invasion is suspected 2
Treatment Approach
Treatment is mandatory due to potential progression to invasive SCC. The approach depends on:
1. Lesion Characteristics
| Characteristic | Preferred Treatment |
|---|---|
| Low number of AKs | Cryosurgery, 5-FU [1] |
| High number of AKs | 5-FU, imiquimod, PDT [1] |
| Thin AKs | 5-FU, imiquimod, diclofenac [1] |
| Hypertrophic AKs | Curettage, cryosurgery with prolonged freezing [1,2] |
| Isolated resistant lesions | Curettage, biopsy [1] |
2. Location
| Location | Preferred Treatment |
|---|---|
| Face, scalp, ears | Cryosurgery, 5-FU, imiquimod [1,5] |
| Periorbital | Cryosurgery, curettage (avoid topicals) [1] |
| Confluent scalp | 5-FU, imiquimod (consider pre-treatment with 5% salicylic acid) [1] |
| Below knee | Curettage, cryosurgery, diclofenac [1] |
| Hands | Cryosurgery, 5-FU [1] |
3. Treatment Options
Field-directed therapies (for multiple lesions or field cancerization):
5-Fluorouracil (5-FU): Strong recommendation for use 6
- Efficacy: High clearance rates for multiple AKs
- Application: Typically once daily for 1-4 weeks
- Best for: Multiple thin lesions, especially on scalp, face, hands 1
Diclofenac: Conditional recommendation 6
- Best for: Lesions below the knee, patients preferring milder side effects 1
Photodynamic therapy (PDT): Conditional recommendation 6
- Best for: Multiple, non-hypertrophic and hypertrophic AKs 2
Lesion-directed therapies (for isolated lesions):
Cryosurgery: Strong recommendation 6
- Best for: Low numbers of lesions, particularly on face, scalp, ears 1
Curettage:
- Best for: Hypertrophic AKs, isolated lesions failing other therapies 1
Prevention
Prevention strategies include:
- UV protection (strong recommendation) 6
- Regular application of sunscreen with high SPF 2
- Regular clinical checkups for early recognition 2
Treatment Selection Algorithm
Assess number of lesions:
- Few isolated lesions → Cryosurgery
- Multiple lesions → Field-directed therapy
Assess lesion thickness:
- Thin lesions → 5-FU, imiquimod, diclofenac
- Hypertrophic lesions → Pretreatment with salicylic acid followed by cryotherapy or curettage
Consider location:
- Face/scalp → Cryosurgery, 5-FU, imiquimod
- Near eyes/mouth → Avoid topicals, use cryosurgery
- Below knee → Diclofenac, curettage, cryosurgery
Consider patient factors:
- Self-reliant → Topical therapies
- Medically dependent → Cryosurgery, diclofenac (fewer side effects)
- Distance from healthcare → Prefer treatments monitored in primary care
For resistant lesions:
- Consider biopsy to rule out progression to SCC
- Consider combination or sequential therapy approaches