Actinic Keratosis (Solar Keratosis)

Definition: Actinic keratosis is a precancerous scaly spot found on sun-damaged skin, also known as solar keratosis.

Significance: Considered an early form of cutaneous squamous cell carcinoma (keratinocyte cancer).

• Prevalence: Common in individuals over 65 years old; affects 50% of New Zealanders in this age group.
• Common Locations: Develops on face, shoulders, neck, hands, and arms due to years of sun exposure.
• Age Group: Typically affects people aged 40 or older.
• Potential for Cancer: Lesions may become cancerous.
• Predisposing Factors:
  • Other signs of photoaging skin
  • Fair skin with a history of sunburn
  • Long hours spent outdoors (work or recreation)
  • Defective immune system

Clinical Presentation

• Appearance:
  • Adherent scaly patches on lips, forearms, neck, ears, forehead, scalp, and hands.
  • Difficult to pick off.
  • Not well circumscribed.
  • Erythematous base.
  • Hard and wart-like surface possible.
  • Color variations include pink, brown, or red.
• Histology:
  • Large, irregular nuclei.
  • Overgrowth of epidermis.
  • Hyperkeratosis and parakeratosis.

Complications

• Risk of Squamous Cell Carcinoma (SCC):
  • Increased risk with more than 10 actinic keratoses
  • Tender, thickened, ulcerated, or enlarging actinic keratosis may indicate evolution to SCC
• Other Skin Cancers:
  • Actinic cheilitis, basal cell carcinoma (BCC), melanoma, Merkel cell carcinoma
• Cutaneous Horn: May arise from an underlying actinic keratosis or SCC.

Diagnosis

• Clinical Diagnosis: Usually straightforward based on appearance.
• Dermoscopy: Useful for confirming diagnosis.
• Biopsy: Sometimes necessary to exclude SCC or if treatment fails.

Treatment

• General Approach: Removal of defective skin cells; some actinic keratoses may resolve with regular sunscreen use.
• Physical Treatments:
  • Cryotherapy: Liquid nitrogen spray, healing time varies by location.
  • Shave, Curettage, and Electrocautery: For thicker lesions, healing takes several weeks.
  • Excision: Ensures complete removal, confirmed by pathology, leaves a permanent scar.
• Field Treatments:
  • Diclofenac Gel: Applied twice daily for 3 months.
  • 5-Fluorouracil Cream: Applied once or twice daily for 2 to 8 weeks.
  • Imiquimod Cream: Applied 2 or 3 times weekly for 4 to 16 weeks.
  • Photodynamic Therapy (PDT): Photosensitizer applied before light exposure.
  • Tirbanibulin: Topical treatment, licensed in 2021.
  • Oral Retinoids: For organ transplant recipients to reduce SCC risk.

Prevention

• Sun Protection: Strict sun protection measures, high SPF (50+) broad-spectrum sunscreen applied daily.
• Nicotinamide (Vitamin B3): 500 mg twice daily can reduce number and severity.

Outlook

• Recurrence: Actinic keratoses may recur months or years after treatment; repeat or alternative treatments may be necessary.
• Increased Risk: Patients with actinic keratoses are at increased risk of new keratoses and other skin cancers, including intraepidermal SCC, invasive cutaneous SCC, BCC, and melanoma. Regular skin checks and monitoring are recommended.

Feature	Actinic Keratosis	Seborrheic Keratosis
Nature	Precancerous	Benign
Risk	Can progress to SCC	Non-cancerous
Common Age Group	40 years or older	50 years or older
Cause	Sun exposure (UV radiation)	Unknown, not related to sun exposure
Common Locations	Face, shoulders, neck, hands, arms	Anywhere except palms and soles
Appearance	Adherent, scaly patches, not well circumscribed, erythematous base, color variations	Waxy, wart-like, well-circumscribed, stuck-on appearance, various colors
Histology	Large, irregular nuclei, hyperkeratosis	Benign basal cell proliferation, horn cysts
Treatment	Sun protection, lesion removal if needed	Usually unnecessary, cosmetic if desired