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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- Actinic keratoses are rough scaly lesions on sun-exposed skin caused by chronic UV-induced keratinocyte dysplasia
- They are premalignant precursors to cutaneous SCC and mark field cancerization
- Classic feel: sandpaper-like roughness on scalp, face, ears, dorsal hands, or forearms
- Treat isolated lesions with cryotherapy; treat field disease with topical 5-FU, imiquimod, diclofenac, tirbanibulin, or photodynamic therapy
- Biopsy lesions that are thick, tender, ulcerated, rapidly enlarging, indurated, bleeding, or treatment-resistant
Overview
Actinic keratosis is an intraepidermal proliferation of atypical keratinocytes caused by cumulative ultraviolet exposure. Lesions are common on sun-exposed sites and may be more easily felt than seen. Individual lesions have a low annual risk of progression, but the overall risk is clinically meaningful in patients with numerous lesions and field cancerization. AK is a common Step 2 CK lesion because it links UV exposure, premalignant dysplasia, and SCC prevention.
Epidemiology
AK is very common in older fair-skinned adults, outdoor workers, and immunosuppressed patients. Risk factors include cumulative UV exposure, bald scalp, fair skin, history of sunburns, tanning beds, advanced age, organ transplant immunosuppression, and prior keratinocyte cancer. Patients with AKs are at increased risk for SCC, BCC, and melanoma because AKs identify chronically UV-damaged skin.
Clinical Features
Symptoms
Rough or gritty spot on sun-exposed skin, often described as sandpaper-like
Mild tenderness, burning, or itching
Bleeding, ulceration, rapid growth, or pain suggests invasive SCC
Recurrent scaling lesion that improves then returns
Signs
Erythematous, skin-colored, or hyperpigmented rough scaly macule/papule
Common sites: bald scalp, forehead, ears, nose, cheeks, lower lip, dorsal hands, forearms
Field cancerization with multiple lesions and diffuse photodamage
Cutaneous horn may overlie AK or SCC and should be assessed carefully
Induration, ulceration, nodularity, or thick hyperkeratosis suggests transformation
Investigations
First-line
Clinical diagnosisUsually diagnosed by inspection and palpation in a patient with sun damage; feel may be more prominent than appearance
Full-skin examinationLook for concurrent SCC, BCC, melanoma, and extent of field cancerization
Second-line
BiopsyIndicated if lesion is thick, tender, ulcerated, bleeding, rapidly enlarging, indurated, recurrent, or fails appropriate therapy
DermoscopyMay help distinguish AK from SCC in situ, superficial BCC, or lentigo maligna but does not replace biopsy when concerning features exist
Specialist
HistopathologyAtypical keratinocytes limited to epidermis with parakeratosis and solar elastosis; invasion indicates SCC
Management
AAD Actinic Keratosis Guideline1
Lesion-directed therapy
- Cryotherapy with liquid nitrogen for isolated, clinically typical AKs
- Curettage or shave removal if lesion is thick or diagnosis is uncertain
- Biopsy before destructive therapy if SCC is possible
2
Field-directed therapy
- Topical 5-fluorouracil for diffuse field disease; causes expected inflammatory erosion/crusting during treatment
- Imiquimod as immune-response modifier for selected field therapy
- Photodynamic therapy for field disease, especially face/scalp where cosmetic outcome matters
- Tirbanibulin or diclofenac are alternatives in selected patients
3
Prevention
- Broad-spectrum sunscreen, protective clothing, hats, shade, and avoidance of tanning beds
- Regular self-skin examination and dermatology follow-up for extensive AKs, prior SCC, or immunosuppression
- Educate patient to return for lesions that grow, hurt, bleed, ulcerate, or fail treatment
Complications
- Progression to SCC: Risk per lesion is low but cumulative risk is meaningful with many AKs
- Field cancerization: Chronically damaged skin can develop multiple AKs and keratinocyte cancers
- Misdiagnosed invasive SCC: Thick, tender, indurated, or ulcerated lesions require biopsy
- Treatment inflammation: Field therapies such as 5-FU commonly cause erythema, crusting, and erosions during treatment
USMLE Step 2 CK Exam Tips
- 1Sandpaper-like rough lesions on sun-exposed skin = actinic keratoses
- 2AK is a precursor to squamous cell carcinoma, not basal cell carcinoma
- 3Isolated AK = cryotherapy; widespread field disease = topical 5-FU/imiquimod or photodynamic therapy
- 4Thick, ulcerated, painful, or nonresponsive AK = biopsy to rule out SCC
- 5Lower lip actinic cheilitis is premalignant for SCC
- 6Organ transplant recipients with AKs/SCCs are high-risk and need dermatology surveillance
practicetest your knowledge on actinic keratosisApply what you've learnt with USMLE Step 2 CK-style questions from the iatroX Q-Bank — dermatology and beyond.
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