Dermatology — High-yield Conditions

Skin cancers, infections, autoimmune skin diseases, life-threatening eruptions.

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◆Skin cancer

•Basal cell: pearly papule + telangiectasias; sun-exposed; rarely metastasizes; Mohs surgery for face
•Squamous cell: scaly/ulcerative on sun-exposed; arises from actinic keratosis or Bowen disease (in situ); metastasis more than BCC; excision
•Melanoma: ABCDE; Breslow depth predicts prognosis; sentinel lymph node biopsy if >1 mm; targeted (BRAF V600E → vemurafenib) + immunotherapy (nivolumab/ipilimumab) for advanced
•Mycosis fungoides: CTCL; patches → plaques → tumors; Sezary syndrome = leukemic phase
•Kaposi sarcoma: HHV-8; AIDS or transplant; purple plaques

•Stevens-Johnson syndrome / TEN: mucocutaneous + epidermal detachment; SJS <10% BSA, TEN >30%, overlap 10–30%; Nikolsky sign +; causes: sulfa, allopurinol, NSAIDs, lamotrigine, anticonvulsants; STOP drug + burn unit care
•DRESS syndrome: drug rash + eosinophilia + systemic (fever, LAD, hepatitis); 2–8 weeks after drug; stop drug + steroids
•Erythema multiforme: target lesions; HSV most common trigger
•Staphylococcal scalded skin syndrome (SSSS): infants; exfoliative toxin from S. aureus; Nikolsky +; spares mucous membranes; nafcillin
•Necrotizing fasciitis: rapid + pain out of proportion + crepitus + 'dishwater pus'; Group A Strep or polymicrobial; emergent surgical debridement + IV broad-spectrum abx

•Pemphigus vulgaris: intra-epidermal (suprabasal); Nikolsky +; flaccid bullae + mucosal involvement; anti-desmoglein 1 + 3; net-like IgG on IF; steroids + rituximab
•Bullous pemphigoid: subepidermal; Nikolsky NEGATIVE; tense bullae; elderly; anti-BPAg1/2; linear IgG/C3 along BM; topical/systemic steroids
•Dermatitis herpetiformis: celiac association; intensely pruritic vesicles on extensor surfaces; granular IgA in dermal papillae; gluten-free diet + dapsone

•Cellulitis: warm, red, tender; β-hemolytic Strep or Staph; cephalexin/dicloxacillin (or clinda); MRSA → TMP-SMX or doxycycline
•Erysipelas: well-demarcated, raised; usually Group A Strep
•Impetigo: honey-crusted; topical mupirocin
•Tinea (corporis, pedis, capitis, cruris): topical antifungal; oral terbinafine/griseofulvin for capitis
•Pityriasis rosea: 'herald patch' → Christmas tree on trunk; self-limiting
•Psoriasis: salmon plaques with silvery scale; nail pitting + onycholysis; Auspitz sign (bleeding when scale removed); topical steroids/vit D analog; biologics for severe
•Atopic dermatitis (eczema): flexural in kids; emollients + topical steroids
•Seborrheic dermatitis: greasy scale on scalp/face; Malassezia; topical antifungal + steroid
•Acne: comedones + papules + pustules; topical retinoids + benzoyl peroxide + abx; isotretinoin for severe (teratogenic — iPLEDGE)
•Rosacea: facial flushing + papules + telangiectasias; topical metronidazole/ivermectin

•Erythema nodosum: tender red nodules on shins; sarcoid, IBD, strep, OCPs, coccidioides, TB
•Pyoderma gangrenosum: rapidly enlarging painful ulcer with violaceous border; IBD, RA association
•Acanthosis nigricans: dark velvety skin on neck/axilla; insulin resistance OR underlying malignancy (gastric)
•Lichen planus: 6 P's — Purple, Polygonal, Pruritic, Planar, Papules, Plaques; Wickham striae; HCV association

◆Nikolsky + : SJS/TEN, pemphigus, SSSS. Nikolsky - : bullous pemphigoid
◆DRESS: think Drug Rash + Eosinophilia + Systemic + Sustained (weeks after start)
◆Isotretinoin: 2 forms of contraception + monthly pregnancy tests (iPLEDGE)
◆Acanthosis nigricans new onset in older patient → look for visceral malignancy (gastric)
◆Erythema nodosum + bilateral hilar LAD = Löfgren syndrome (sarcoidosis)

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