Dermatology — high-yield patterns

Tinea, scabies, eczema herpeticum, skin cancers, SJS/TEN, drug eruptions, vitiligo, burns.

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◆Superficial infections

•Tinea corporis: annular scaly plaque with central clearing, KOH-positive hyphae — TOPICAL antifungal (terbinafine, clotrimazole)
•Tinea capitis: scaly alopecic patch with black dots in children — ORAL griseofulvin or terbinafine (topical doesn't penetrate hair shaft)
•Pityriasis versicolor: hypo/hyperpigmented trunk patches, KOH 'spaghetti and meatballs' — topical selenium sulfide or topical antifungal
•Scabies: severe nocturnal itch, web spaces / flexor wrists / waist papules — topical permethrin for patient AND household, wash linens
•Impetigo: honey-colored crusts in children — topical mupirocin (or oral cephalexin for extensive); Group A Strep / S. aureus

•Atopic dermatitis: chronic itchy flexural rash; associated with asthma, allergic rhinitis (atopic triad)
•Treatment: emollients, topical steroids (low potency face/folds), topical calcineurin inhibitors (tacrolimus, pimecrolimus), dupilumab for severe
•Eczema herpeticum: sudden vesicular eruption with punched-out erosions on eczema — IV acyclovir; ophthalmology if periocular
•Contact dermatitis (type IV): linear/geometric pattern matching exposure (nickel, poison ivy) — avoid trigger, topical steroids

•Basal cell carcinoma: pearly papule, telangiectasias, rolled borders, slow growing, rare metastasis — Mohs surgery for face/recurrent
•Squamous cell carcinoma: hyperkeratotic, ulcerated; sun-exposed; transplant patients — surgical excision; can metastasize
•Actinic keratosis: rough scaly precursor to SCC — cryotherapy or topical 5-FU/imiquimod
•Melanoma: ABCDE — Asymmetry, Border irregular, Color varied, Diameter >6 mm, Evolution; thickness (Breslow depth) determines prognosis
•Melanoma: wide local excision + sentinel lymph node biopsy if depth ≥0.8 mm; immunotherapy for metastatic (anti-PD1, anti-CTLA4)

•SJS / TEN: lamotrigine, allopurinol, sulfa, anticonvulsants, NSAIDs — stop drug, burn unit, supportive care
•DRESS: drug rash + eosinophilia + systemic sx (fever, LFTs, kidney) — 2–8 weeks after drug; stop drug, steroids
•Erythema multiforme: target lesions, HSV-triggered most common — supportive; treat HSV trigger
•AGEP: acute generalized exanthematous pustulosis — antibiotics; self-limited

•Vitiligo: sharply demarcated depigmented patches, Wood lamp accentuation, autoimmune associations (thyroid, T1DM) — topical steroids, calcineurin inhibitors, UV phototherapy
•Erythema nodosum: tender red nodules on shins; sarcoidosis, IBD, strep, OCPs, TB — find trigger, NSAIDs, treat cause
•Pyoderma gangrenosum: rapidly enlarging painful ulcer with violaceous edge; IBD, RA — steroids; do NOT debride (pathergy)
•Lipoma: soft mobile painless subcutaneous mass; observe unless symptomatic
•Sister Mary Joseph nodule: periumbilical metastatic node — GI/GU malignancy

•Superficial (1st): erythema only, painful — supportive (aloe, NSAIDs)
•Partial-thickness (2nd): blisters, painful — wound care, topical antibiotics (silver sulfadiazine — NOT in sulfa allergy/face)
•Full-thickness (3rd): leathery, painless, white/charred — surgical excision + skin grafting
•Parkland formula: 4 mL × kg × % BSA burned (lactated Ringers) over 24 hours, half in first 8 hours
•Burns >20% BSA or to face/hands/perineum → transfer to burn center
•Inhalation injury (carbonaceous sputum, hoarseness, facial burns) → early intubation

◆Pearly papule + telangiectasia + sun-exposed face = BCC — Mohs surgery
◆Punched-out vesicles on eczema = eczema herpeticum → IV acyclovir, NOT steroids
◆Severe nocturnal pruritus + household members itching = scabies → permethrin for everyone, wash bedding
◆Tinea CAPITIS needs ORAL antifungal (topical can't penetrate hair shaft)
◆Sudden eruption of many seborrheic keratoses (Leser-Trélat sign) → think GI malignancy

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