Dermatology — USMLE Step 3 Practice
Dermatology on USMLE Step 3 focuses on recognizing skin manifestations of systemic diseases, managing common inflammatory conditions, and identifying malignant lesions. Clinical photo interpretation is commonly tested.
Frequently Asked Questions
What are the ABCDE criteria for melanoma on USMLE Step 3?
Asymmetry, Border irregularity, Color variation, Diameter >6mm, Evolution/change over time. Suspicious lesions require excisional biopsy with 1-2 mm margins. Stage determines management: sentinel lymph node biopsy for tumors >1 mm Breslow thickness. BRAF inhibitors (vemurafenib) for metastatic BRAF-mutated melanoma.
How do you differentiate Stevens-Johnson syndrome from TEN?
Both are severe mucocutaneous reactions (most commonly drug-induced: sulfonamides, allopurinol, anticonvulsants). Stevens-Johnson syndrome: <10% body surface area involved. TEN (toxic epidermal necrolysis): >30% BSA. 10-30% BSA = overlap. Both require stopping causative drug, ICU burn unit care, supportive therapy. IV immunoglobulin is used in some centers.
What systemic diseases present with skin findings on Step 3?
Key associations: psoriasis (psoriatic arthritis), necrobiosis lipoidica (diabetes), erythema nodosum (sarcoidosis, IBD, streptococcal infection, drugs), dermatitis herpetiformis (celiac disease), acanthosis nigricans (insulin resistance, diabetes, GI malignancy), pyoderma gangrenosum (IBD, rheumatoid arthritis).
What is the first-line treatment for atopic dermatitis on Step 3?
Mild-moderate: topical corticosteroids (low-potency on face/intertriginous areas, medium-potency elsewhere) + emollients. Topical calcineurin inhibitors (tacrolimus, pimecrolimus) as steroid-sparing alternatives. Severe: dupilumab (IL-4/IL-13 inhibitor) is FDA-approved biologic. Avoid triggers, short fingernails, gentle skin care.
How do you manage squamous cell carcinoma vs. basal cell carcinoma?
Both arise from UV exposure on sun-damaged skin. BCC: pearly papule with rolled borders, rarely metastasizes; treat with Mohs surgery, excision, or topical therapies. SCC: hyperkeratotic papule/ulcer on sun-exposed areas, can arise from actinic keratosis; higher metastatic risk, requires excision with clear margins ± sentinel lymph node biopsy.
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Master dermatology for USMLE Step 3 — melanoma staging, Stevens-Johnson syndrome, drug eruptions, and systemic disease skin findings.
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