# Seborrheic Keratoses (지루각화증) --- ## 1. Definition  - **Seborrheic Keratoses (지루각화증)** are **benign epidermal tumors** arising from keratinocytes. - Clinically: pigmented, verrucous, “stuck-on” plaques. - Pathologically: acanthosis, hyperkeratosis, and horn cysts without cytologic atypia. --- ## 2. Epidemiology & Prevalence - **Most common benign epithelial tumor in adults.** - **Prevalence**: - By age 40 → ~30% of population. - By age 60 → >80% have at least one lesion. - Nearly **universal in elderly**. - No gender predilection. - More common in **lighter phototypes (I–III)**, but dermatosis papulosa nigra variant is frequent in darker skin (particularly in African and Asian populations). - Rare in children and young adults → onset typically after 30s. --- ## 3. Pathophysiology ### A. Cellular Basis - Originates from **epidermal keratinocytes**. - Characterized by: - **Hyperproliferation** of basal keratinocytes. - **Accumulation of keratin** → hyperkeratosis and horn cysts. - **Basaloid cell nests** → proliferation without atypia. ### B. Molecular Mechanisms - **Genetic mutations** implicated: - **FGFR3** (fibroblast growth factor receptor 3) mutations. - **PIK3CA** mutations (PI3K-AKT pathway activation). - Lead to **increased keratinocyte proliferation** but no malignant transformation. - **UV radiation**: associated with solar-exposed SKs (solar lentigo-like). - **Aging process**: cumulative epidermal damage + senescent keratinocyte dysregulation. - **HPV**: controversial, but some evidence of low-risk HPV DNA in lesions. ### C. Systemic Association - **Leser-Trélat sign (레저-트렐라 증후군)**: sudden eruption of multiple seborrheic keratoses associated with internal malignancy (esp. GI adenocarcinoma). - Rare but clinically important → warrants systemic work-up if rapidly progressive SKs appear with systemic symptoms. --- ## 4. Clinical Presentation - **Morphology**: sharply demarcated, waxy, “stuck-on,” verrucous plaques. - **Colors**: light tan → dark brown → black. - **Variants**: - Dermatosis papulosa nigra (흑인·동양인에서 작은 다발성) - Stucco keratoses (작고 흰색, 각질성, 주로 하지) - Irritated seborrheic keratosis (홍반, 가려움, 딱지 동반) --- ## 5. Histopathology - **Acanthosis**: thickened epidermis. - **Hyperkeratosis**: excess keratin at surface. - **Horn cysts**: round keratin-filled cysts → pathognomonic. - **Basaloid cell proliferation** without atypia or dermal invasion. --- ## 6. Differential Diagnosis - **Melanoma (흑색종)** – irregular borders, color variegation, bleeding. - **Pigmented basal cell carcinoma (기저세포암)** – pearly papule with telangiectasia. - **Actinic keratosis (광선각화증)** – premalignant, scaly erythematous plaques. - **Solar lentigo (노인성 색소반)** – flat brown macules, no verrucous surface. --- ## 7. Treatment - Only if: cosmetic concern, irritation, or diagnostic uncertainty. - **Options**: - Cryotherapy (냉동치료) → thin lesions. - Curettage (소파술) → scraping off. - Electrocautery (고주파 소작술). - **CO₂ Laser (이산화탄소 레이저)** → gold standard for raised SK, precise ablation. --- ## 8. Prognosis & Patient Education - Benign, no malignant potential (except in Leser-Trélat sign context). - Lesions may recur or new ones appear with aging. - Patients should be reassured but educated about the **“ugly duckling sign”**—any lesion that looks different should be biopsied. --- ✅ **Key Pearls for Practice** - **Extremely common** in elderly, almost universal. - **Pathophysiology**: keratinocyte proliferation driven by **FGFR3 / PIK3CA mutations**. - **CO₂ laser** is the treatment of choice for cosmetic removal. - Watch for **Leser-Trélat sign** → possible paraneoplastic syndrome. ---