Dermatology · Pre-malignant Skin Lesions
The facts most likely to be tested
Actinic keratosis is a pre-malignant lesion caused by cumulative ultraviolet (UV) light exposure that serves as a direct precursor to squamous cell carcinoma (SCC).
The classic physical exam finding is a rough, sandpaper-like texture on an erythematous base located on sun-exposed areas such as the face, scalp, or dorsal hands.
Diagnosis is primarily clinical, but a skin biopsy is indicated if the lesion is indurated, ulcerated, or rapidly growing to rule out invasive squamous cell carcinoma.
Histopathology reveals atypical keratinocytes confined to the basal layer of the epidermis with parakeratosis and solar elastosis in the dermis.
First-line treatment for isolated or few lesions is cryotherapy with liquid nitrogen.
Field cancerization, characterized by multiple lesions in a single area, is best managed with topical 5-fluorouracil (5-FU), imiquimod, or ingenol mebutate.
Patients with actinic keratosis are at high risk for developing other non-melanoma skin cancers and require annual full-body skin examinations.
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A 68-year-old male presents for an annual physical exam. He has a history of working as a construction foreman for 40 years. On physical examination, you note several ill-defined, erythematous macules with a rough, sandpaper-like scale on his forehead and the dorsal aspect of his forearms. The lesions are not tender, and there is no evidence of ulceration or significant induration. He has no personal history of skin cancer.
What is the most appropriate initial management for these lesions?
Cryotherapy
The patient presents with classic actinic keratosis, which is a pre-malignant lesion. For isolated or limited lesions, cryotherapy is the standard first-line treatment.
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High yield triage
Etiology / Epidemiology
Pre-malignant lesion caused by cumulative UV exposure in fair-skinned individuals.
Clinical Manifestations
Small, rough, sandpaper-like papules on sun-exposed areas.
Diagnosis
Punch biopsy is the gold standard to rule out progression to SCC.
Treatment
5-fluorouracil is first-line; teratogenic.
Prognosis
Precursor to Squamous Cell Carcinoma; monitor for rapid growth.
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Epidemiology & Etiology
Primarily affects older adults with a history of chronic sun exposure. High-risk groups include those with Fitzpatrick skin types I and II. Incidence increases significantly with age and cumulative ultraviolet radiation dose.
Pertinent Anatomy
Lesions occur on sun-exposed surfaces, most commonly the face, scalp, ears, and dorsal hands. The pathology is restricted to the epidermis.
Pathophysiology
Chronic UV radiation induces p53 tumor suppressor gene mutations in keratinocytes. This leads to clonal expansion of atypical cells. If left untreated, these lesions may progress to invasive squamous cell carcinoma.
Clinical Manifestations
Lesions present as erythematous, scaly macules or papules that feel like sandpaper upon palpation. They are often easier to feel than to see. Rapid enlargement, ulceration, or bleeding are red flags for malignant transformation into Squamous Cell Carcinoma.
Diagnosis
Clinical diagnosis is often sufficient for classic lesions. A punch biopsy is the gold standard if the diagnosis is uncertain or if the lesion is thick/indurated to rule out invasive SCC.
Treatment
Localized lesions are treated with cryotherapy (liquid nitrogen). For widespread field cancerization, topical 5-fluorouracil or imiquimod is indicated. 5-fluorouracil is strictly contraindicated in pregnancy due to teratogenicity.
Prognosis
While most lesions remain stable, they are considered a marker for increased risk of non-melanoma skin cancer. Patients require regular skin exams to monitor for malignant transformation.
Differential Diagnosis
Seborrheic Keratosis: 'Stuck-on' appearance with waxy texture
Squamous Cell Carcinoma: Indurated, ulcerated, or rapidly growing nodule
Lichen Planus: Violaceous, polygonal, pruritic papules
Tinea Corporis: Annular, scaly patch with central clearing
Bowen Disease: Persistent, well-demarcated erythematous plaque (SCC in situ)