Dermatology Study Guide

📖 Core Concepts Dermatology – Medical specialty focused on skin, hair, nails, and related structures; includes both medical and surgical care. Dermatologic emergency – Life‑threatening conditions (e.g., severe burns, angioedema, necrotizing fasciitis, Stevens‑Johnson syndrome) that need rapid recognition and treatment. Subspecialties – Cosmetic (injectables, lasers), Dermatopathology (microscopic diagnosis), Trichology (hair disorders), Immunodermatology (immune‑mediated diseases), Mohs surgery (margin‑controlled cancer removal), Pediatric dermatology, Teledermatology (remote care). Therapeutic modalities – Systemic/topical meds, surgery (cryosurgery, Mohs), physical agents (laser, phototherapy, photodynamic therapy), chemical peels, allergy testing (patch), intralesional injections. --- 📌 Must Remember Training path (US): 1‑yr internship → 3‑yr dermatology residency (total 4 yrs post‑MD/DO). Top emergencies: Burns, angioedema, necrotizing fasciitis, Stevens‑Johnson syndrome. Phototherapy types: narrowband UVB, broadband UVB, psoralen‑UVA (PUVA), UVB for psoriasis. Mohs surgery = stepwise excision + intra‑operative microscopic margin check. Patch testing = apply standardized allergens → read reaction → diagnose contact dermatitis. Common cosmetic procedures: botulinum toxin, dermal fillers, laser resurfacing. --- 🔄 Key Processes Patch testing workflow Apply set of allergens on back. Occlude for 48 h. Remove patches, read at 48 h and 96 h for erythema/vesiculation. Mohs micrographic surgery Remove visible tumor layer. Map and examine tissue margins microscopically. Repeat excision only where cancer persists until margins are clear. Phototherapy administration Determine indication (e.g., psoriasis). Choose UVB type (narrowband preferred). Start with low dose, increase gradually; monitor for erythema. Laser therapy sequence Identify target (birthmark, tattoo, vitiligo). Choose appropriate laser wavelength. Deliver controlled pulses; repeat sessions as needed. Cryosurgery Apply liquid nitrogen to lesion (freeze‑thaw‑freeze). Observe for adequate tissue destruction; wound heals by secondary intention. --- 🔍 Key Comparisons Cryosurgery vs. Laser therapy Cryosurgery: uses extreme cold; simple, cheap; limited depth control. Laser: uses specific light wavelength; precise depth; higher equipment cost. Phototherapy vs. Photodynamic therapy (PDT) Phototherapy: UV light alone; treats psoriasis, vitiligo. PDT: photosensitizer + light; targets precancerous lesions & certain skin cancers. Cosmetic dermatology vs. Immunodermatology Cosmetic: aesthetic improvements (botox, fillers, lasers). Immunodermatology: treats immune‑mediated diseases (lupus, pemphigus). Dermatopathology vs. Clinical dermatology Dermatopathology: microscopic diagnosis, often by pathologist/dermatologist. Clinical dermatology: bedside diagnosis & management. --- ⚠️ Common Misunderstandings “All skin cancers need Mohs surgery.” – Only high‑risk, cosmetically sensitive, or recurrent tumors typically merit Mohs; many can be excised with standard surgery. “Laser therapy is always safe.” – Different lasers have specific risks (pigment changes, scarring); contraindications include active infection or certain skin types. “Phototherapy cures psoriasis permanently.” – It controls flares; disease may recur after cessation. “Patch testing diagnoses all rashes.” – It only identifies allergic contact dermatitis; other rash etiologies require different work‑ups. --- 🧠 Mental Models / Intuition “Layered approach” – Think of skin treatment as moving from surface (topical, cryo, lasers) to deeper layers (systemic meds, surgery). Choose the least invasive method that reaches the pathology depth. “Emergency triage ladder” – If a dermatologic presentation includes systemic toxicity, rapid airway compromise, or widespread necrosis → treat as emergency first, then address the underlying skin issue. “Spectrum of light” – UVB = anti‑proliferative (psoriasis); UVA + psoralen = deeper penetration (PUVA); laser = targeted wavelength → match the wavelength to the chromophore (pigment, water, hemoglobin). --- 🚩 Exceptions & Edge Cases PUVA contraindicated in pregnancy – teratogenic risk; use narrowband UVB instead. Botulinum toxin in patients with neuromuscular disorders – higher risk of systemic spread; may be avoided. Cryosurgery on acral (hands/feet) skin – higher chance of scarring; consider alternative modalities. Teledermatology limitation – poor image quality can miss subtle pigment changes; in‑person exam may be required. --- 📍 When to Use Which Burn vs. Angioedema vs. SJS – Immediate airway/vascular support for angioedema; burn center referral for >10% TBSA; ICU admission for SJS. Laser vs. Cryosurgery – Use laser for precise pigment or vascular lesions; cryosurgery for warts and superficial cancers where cost is a concern. Phototherapy vs. Systemic immunomodulators – Start phototherapy for mild‑moderate psoriasis; jump to systemic agents if disease is extensive or phototherapy fails. Patch testing vs. Skin biopsy – Patch test when allergic contact dermatitis suspected; biopsy when rash is atypical, neoplastic, or unresponsive. --- 👀 Patterns to Recognize “Targetoid” lesions → think erythema multiforme or early Stevens‑Johnson syndrome. “Dusky, violaceous plaques with tense blisters” → suggests bullous pemphigoid (immunodermatology). “Well‑demarcated, scaly plaques on extensor surfaces” → classic plaque psoriasis (phototherapy candidate). “Rapidly enlarging, painful erythema with systemic signs” → necrotizing fasciitis (emergency). --- 🗂️ Exam Traps Choosing “Mohs surgery” for all basal cell carcinomas – many low‑risk BCCs are adequately treated with simple excision; Mohs is reserved for high‑risk locations (nose, eyelids) or recurrent tumors. Assuming all laser procedures are “cosmetic only.” – Certain lasers treat medical conditions (e.g., vascular lasers for hemangiomas). Confusing PUVA with narrowband UVB – PUVA requires psoralen ingestion and UVA exposure; UVB does not. Patch test positive = definitive allergy – False‑positives occur; clinical correlation is essential. ---