Chapter 51: Actinic Keratosis

INTRODUCTION

Actinic keratosis (AK) present as single or multiple discrete, scaly lesions, found most frequently in habitually sun-exposed skin of adults.

EPIDEMIOLOGY

Age: most commonly noted in middle age, occasionally occurs in patients under 30 years

Sex: more common in males

Incidence: very common; in Australia 1:1,000 persons

Race: skin phototypes I–III, rarely seen in skin phototypes IV–VI

Occupation: outdoor workers (eg, farmer, rancher, sailor) and outdoor sports (golf, tennis, sailing)

PATHOGENESIS

Prolonged and repeated sun exposure in susceptible persons results in cumulative keratinocyte damage. The principle sun damage is secondary to ultravoilet B (UVB) (290–320 nm) light.

PHYSICAL EXAMINATION

AKs present as single or multiple skin-colored, erythematous, or brown scaly patches. There is a predilection for sun-exposed areas including the face, ears, neck, forearms, and dorsal hands. AKs may become thickened, forming a cutaneous horn. More easily palpated than seen. They are generally asymptomatic but may be tender or pruritic. Actinic cheilitis develops on the vermilion border as diffuse scaling or dryness. Associated telangiectasia, solar elastosis, and lentigines are frequently observed.

DERMATOPATHOLOGY

Epidermal proliferation with mild-to-moderate basilar keratinocyte pleomorphism, parakeratosis, and dyskeratotic keratinocytes. Cytologically, atypical keratinocytes are usually confined to the epidermal basal layer.

DIFFERENTIAL DIAGNOSIS

• Eczematous dermatitis

• Extramammary Paget’s

• Squamous cell carcinoma

• Basal cell carcinoma

COURSE

AKs can self-resolve, but generally are persistent in nature. The progression to skin cancer within preexisting AKs is unknown but is estimated at less than 1% of individual lesions. Biopsy warranted for pigmented AKs (superficial pigmented actinic keratosis) or nodular keratosis.

KEY CONSULTATIVE QUESTIONS

• Duration of lesion(s)

• Lesional rate of growth

• Prior treatment for lesions and response

• Personal and family history of prior skin cancers

• History of prior radiation treatment to the area

• Current medical history

• Medication use

• Evidence of immunosuppression

• Predisposing syndromes

MANAGEMENT

Assessment of the number, size, location, frequency of development, and any underlying immunosuppressed state should be obtained. A biopsy should be obtained of any lesion that is suspicious for skin cancers. Consideration may then be given to treatment of individual or multiple lesions, prophylactic therapy, and determination of the need for clinical follow-up.

TREATMENT

• Prevention

  • – Application of daily sunscreen with UVA/UVB protection

  • – Topical tretinoin applied nightly

• Topical

  • – Once daily (Carac) or twice daily (Efudex) application of 5-fluorouracil for 3 to 4 weeks

  • – Twice weekly or every third day application of imiquinod (Aldara 3M St. Paul, MN) for 4 weeks (Fig. 51.1)