## Diagnosis: Keratoacanthoma ### Clinical Presentation **Key Point:** Keratoacanthoma is a rapidly growing, self-limited tumor of the pilosebaceous unit that presents as a solitary, firm nodule with a central keratin-filled crater, typically on sun-exposed areas (dorsal hands, face, forearms). The clinical vignette provides multiple diagnostic clues: - **Central keratin plug** — pathognomonic feature - **Starburst pattern of telangiectasia** — characteristic dermoscopic finding - **Rapid growth** (implied by presentation) — typical for KA - **Sun-exposed site** — common location - **Age and sun exposure history** — risk factors ### Histopathology **High-Yield:** The cup-shaped (crater-like) lesion with: - Central keratin-filled crater - Intact overlying epidermis - Surrounding chronic inflammation - Well-demarcated borders This is the **gold standard** for diagnosis. The intact epidermis overlying the crater distinguishes KA from SCC. ### Biological Behavior **Clinical Pearl:** Keratoacanthoma is a **self-limited tumor** that typically: 1. Grows rapidly over 4–6 weeks 2. Stabilizes for 2–3 months 3. Involutes spontaneously over 6–12 months, often leaving a depressed scar This natural history is unique and helps differentiate KA from malignant alternatives. ### Dermoscopic Features | Feature | Keratoacanthoma | SCC | BCC | | --- | --- | --- | --- | | Central plug | Present (keratin) | Variable | Absent | | Starburst telangiectasia | Yes (radiating) | Irregular | Arborizing | | Border | Well-demarcated | Ill-defined | Rolled, pearly | | Crater | Cup-shaped, intact epidermis | Ulcerated | Absent | ### Controversy: KA vs. Well-Differentiated SCC **Warning:** There is ongoing debate in dermatopathology regarding whether KA is a **distinct entity** or a **variant of SCC**. However, for NEET PG purposes, the **clinical and histologic criteria** provided in the question (cup-shaped crater, intact epidermis, self-limited course) define **keratoacanthoma**. The WHO (2016) recognizes KA as a distinct entity based on these morphologic features and natural history. ### Management - **Observation** — many regress spontaneously - **Surgical excision** — if diagnosis uncertain or cosmetic concern - **Intralesional 5-FU or methotrexate** — for rapid involution - **Topical imiquimod** — emerging option **Key Point:** Excision is curative; recurrence is rare (~5%). [cite:Robbins 10e Ch 25; Harrison 21e Ch 409]
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