# Actinic Keratoses (광선각화증) --- ## 1. Definition - **Actinic keratoses (광선각화증)** are **premalignant lesions** of keratinocytes caused by chronic ultraviolet (UV) exposure. - Represent early stages of **cutaneous squamous cell carcinoma (SCC, 편평세포암)** in situ. - Sometimes called “solar keratoses.” --- ## 2. Epidemiology - Very common in **older, fair-skinned individuals (Fitzpatrick I–III)** with cumulative UV exposure. - Prevalence: up to **40–60% in adults >60 years** living in sunny climates. - Male > Female (due to more outdoor exposure). - In Korea/Asia: incidence rising with aging population and tanning habits. --- ## 3. Pathophysiology - **UVB radiation** → induces **DNA damage** (pyrimidine dimers) in keratinocytes. - Mutations in **p53 tumor suppressor gene** → clonal expansion of atypical keratinocytes. - Histologic continuum: **normal → actinic keratosis → SCC in situ → invasive SCC**. --- ## 4. Clinical Features - **Appearance**: - Rough, scaly, erythematous or brown papules/plaques. - Often described as “sandpaper-like.” - **Location**: Sun-exposed areas — face, scalp (balding men), ears, dorsal hands, forearms, lower legs. - **Symptoms**: Usually asymptomatic, may cause pruritus or tenderness. - **Number**: Often multiple, field cancerization (광범위 병변). --- ## 5. Histopathology - Atypical keratinocytes confined to **lower epidermis**. - **Parakeratosis, dyskeratosis, nuclear pleomorphism.** - Solar elastosis in dermis (from UV damage). - If atypia extends full thickness → Bowen’s disease (SCC in situ). --- ## 6. Risk of Malignancy - Each lesion: ~0.1–10% risk/year of progressing to invasive SCC. - Patients with multiple AKs → increased overall risk of non-melanoma skin cancer. - Thus, **clinical management recommended** even for asymptomatic lesions. --- ## 7. Differential Diagnosis - Seborrheic keratosis (지루각화증) → stuck-on, waxy, not scaly. - Psoriasis → symmetric, thicker plaques. - Squamous cell carcinoma → thicker, indurated, tender, ulcerated. - Basal cell carcinoma → pearly papules, telangiectasia. --- ## 8. Management ### A. Lesion-Directed Therapies (for isolated AKs) - **Cryotherapy (액화질소 냉동치료)** → most common, effective for single lesions. - **Curettage & electrocautery (소파술+소작술)**. - **CO₂ laser (이산화탄소 레이저)** for resistant lesions. ### B. Field-Directed Therapies (for multiple AKs / field cancerization) - **Topical 5-fluorouracil (5-FU)** cream (Efudix): cytotoxic to atypical keratinocytes. - **Imiquimod** (Aldara): immune response modifier. - **Ingenol mebutate** (not available everywhere). - **Photodynamic therapy (PDT, 광역학치료)**: ALA/MAL cream + red/blue light activation. ### C. General Measures - Lifelong photoprotection (sunscreen, protective clothing). - Regular skin exams (higher risk of SCC, BCC, melanoma). --- ## 9. Prognosis - Many AKs remain stable or regress. - Some progress to SCC, which can metastasize if untreated. - With proper treatment, prognosis is excellent. --- ## 10. Clinical Pearls 1. **“Rough, scaly spot on sun-exposed skin in elderly = Actinic Keratosis until proven otherwise.”** 2. AK is not just cosmetic; it is a **precancerous lesion**. 3. Field therapy is important → treating clinically invisible atypia. 4. Dermoscopy: red pseudonetwork, surface scale, targetoid hair follicles. 5. Biopsy if lesion is thickened, indurated, ulcerated (rule out SCC). --- ✅ **Summary for practice**: Actinic keratoses (광선각화증) are common UV-induced premalignant lesions of keratinocytes, representing early squamous cell carcinoma in situ. Clinically they are rough, scaly patches on sun-exposed skin. Management includes lesion-directed therapies (cryotherapy, CO₂ laser) and field-directed therapies (5-FU, imiquimod, PDT). Because of their potential to progress to invasive SCC, **all AKs warrant treatment and follow-up**. ---