actinic (solar) keratosis (AK)

Introduction

Single or multiple, dry, rough, scaly lesions that occur on sun-exposed skin of adults.

Etiology

• prolonged & repeated sun exposure in sensitive individuals
• damage to keratinocytes by UVB radiation

Epidemiology

• middle aged individuals
• incidence 50% of white Australians > 40 years of age
• fair-skinned individuals, almost never in blacks or East Indians
• more common in males
• common in individuals who work outdoors

Pathology

• precursor lesion to cutaneous squamous cell carcinoma
• abnormal cells confined to epithelium
• spontaneous regression occurs in up to 25% of lesions
• 1:1000 lesions/year convert to squamous cell carcinoma

Clinical manifestations

• adherent hyperkeratotic scale, but may be papular
• color: yellow-brown to brown, often with reddish tinge
• rough like coarse sandpaper; may easier to palpate than visualize
• generally round or oval < 1.0 cm, ~ 2-3 mm
• lesions bleed easily when picked off, but recur
• distribution: sun-exposed skin, sparing of nasolabial folds
• generally asymptomatic, but slight tenderness may occur

* images

Complications

• precursor lesion to cutaneous squamous cell carcinoma

Differential diagnosis

• discoid lupus erythematosus
• keratoacanthoma
• squamous cell carcinoma

Management

• prevention
  • UVA/UVB sun screens applied daily to sun exposed skin
  • sunblocks (zinc oxide) applied to highly exposed areas, i.e. nose, ears
  • clothing & hats
• cryotherapy with liquid nitrogen
  • may be followed with topical 5-fluorouracil
  • useful for a few individual lesions (use 5-FU for many lesions)
• topical 5-fluorouracil (5-FU) (5%) for several days to weeks
  • for many lesions (> 10-15) within a confined area, topical 5% fluorouracil better than imiquimod, photodynamic therapy, ingenol mebutate or cryotherapy
  • may leave patient extremely uncomfortable with > 4 week recovery period
  • pulse dose therapy: BID application 2 consecutive days per week for 3 months produces less inflammatory response
• imiquimod (Aldara)
  • apply twice a week for 4 months
  • apply at night, wash off after 8 hours
  • 50% complete clearance of 4-8 AKs
  • clearance correlates with erythema
• tirbanibulin (Klisyri) 1%: apply once daily for 3-5 days to face or scalp
• masoprocol (Actinex)
• Solaraze (topical diclofenac 5%)
• ingenol mebutate (Picato)
• excisional biopsy of lesions:
  • > 5 mm in size
  • nodular lesions
  • thick, indurated papules
  • rapidly growing lesions
  • bleeding lesion
  • itching or painful lesions

More general terms

• keratosis
• premalignant skin lesion

Additional terms

• keratoacanthoma (KA)