OMSB Dermatology (OED) cheat sheet

Pemphigus vulgaris: intraepidermal suprabasal acantholysis, IgG against desmoglein 3; direct immunofluorescence shows intercellular ('chicken-wire') epidermal IgG and C3.

Bullous pemphigoid: subepidermal blister, linear IgG/C3 along the basement membrane zone; targets BP180 (BPAG2) and BP230; tense blisters in elderly patients.

Dermatitis herpetiformis: granular IgA at dermal papillae tips; associated with celiac disease; treat with dapsone plus gluten-free diet.

Guttate psoriasis follows streptococcal pharyngitis; Auspitz sign (pinpoint bleeding on scale removal) and Koebner phenomenon support psoriasis.

Erythema multiforme is targetoid and often HSV-triggered; Stevens-Johnson syndrome/TEN shows mucosal involvement and sheet-like epidermal detachment (>30% BSA in TEN).

Lichen planus: pruritic, purple, polygonal, planar papules with Wickham striae; histology shows band-like lymphocytic infiltrate and saw-tooth rete ridges.

Systemic lupus erythematosus: interface dermatitis with mucin; direct immunofluorescence of lesional skin shows the lupus band (granular IgG/C3 at the dermoepidermal junction).

Sarcoidosis: naked non-caseating granulomas; cutaneous lesions include erythema nodosum and lupus pernio; check serum ACE and chest imaging.

Mohs micrographic surgery examines 100% of the surgical margin; indications include basal cell carcinoma in high-risk anatomic sites (nose, ear, periorbital) and recurrent tumors.

Excision margins for primary basal cell carcinoma: 3-4 mm for well-defined low-risk lesions; melanoma margins follow Breslow thickness (e.g., 1 cm for lesions <=1 mm).

Sclerotherapy for telangiectasias uses sodium tetradecyl sulfate or polidocanol; risk of hyperpigmentation and ulceration if extravasated.

Cryotherapy with liquid nitrogen: freeze time and thaw cycles determine tissue destruction; risks include hypopigmentation and scarring, so avoid in dark skin on visible sites.

Intralesional corticosteroids (triamcinolone 2.5-10 mg/mL) are used for keloids, hypertrophic scars, and alopecia areata; higher concentrations risk atrophy.

Punch biopsy (3-4 mm) is preferred for inflammatory dermatoses to preserve architecture; shave biopsy is adequate for exophytic lesions but inadequate for depth assessment.

Laser selection: pulsed dye laser targets oxyhemoglobin (vascular lesions); Q-switched lasers target pigment; ablative fractional lasers resurface skin.

Surgical site infection prophylaxis: single preoperative dose of antibiotic for clean-contaminated or high-risk procedures; avoid unnecessary antibiotics for clean dermatologic surgery.

Spongiosis: intercellular edema in the epidermis; hallmark of eczematous dermatitis (e.g., atopic dermatitis, contact dermatitis).

Acantholysis: loss of intercellular cohesion; seen in pemphigus, Hailey-Hailey disease, and Darier disease.

Interface dermatitis: lymphocytic infiltrate obscuring the dermoepidermal junction; causes include lichen planus, lupus erythematosus, and erythema multiforme.

Parakeratosis with neutrophils in the stratum corneum suggests psoriasis; regular acanthosis with thinned suprapapillary plates supports the diagnosis.

Pautrier microabscesses (intraepidermal collections of atypical lymphocytes) are characteristic of mycosis fungoides.

Dermatofibroma: dermal spindle cell proliferation with collagen trapping at the periphery; positive for factor XIIIa, negative for CD34.

Seborrheic keratosis: horn pseudocysts and basaloid cells; 'stuck-on' appearance clinically; no atypia.

Amyloidosis (macular or lichen): deposition of amorphous eosinophilic material in the dermis; stain with Congo red and examine under polarized light for apple-green birefringence.

Atopic dermatitis in infants: face and extensor surfaces; in older children: flexural distribution; first-line therapy is emollients plus topical corticosteroids.

Topical corticosteroid potency: low-potency (hydrocortisone 1%) for face and intertriginous areas in children; medium-potency for trunk and limbs.

Kawasaki disease: fever >=5 days, conjunctivitis, oral mucositis, polymorphous rash, extremity changes, cervical lymphadenopathy; risk of coronary aneurysms; treat with IVIG and aspirin.

Molluscum contagiosum: umbilicated papules caused by a poxvirus; often self-resolving; cantharidin or cryotherapy for persistent lesions.

Hemangioma of infancy: proliferation in first months, involution over years; oral propranolol is first-line for problematic or complicated hemangiomas.

Neonatal acne (acne neonatorum) appears in first weeks and resolves spontaneously; do not confuse with neonatal cephalic pustulosis.

Measles: Koplik spots (white lesions on buccal mucosa) precede the maculopapular rash; rash spreads cephalocaudally.

Topical calcineurin inhibitors (tacrolimus, pimecrolimus) are steroid-sparing for atopic dermatitis; avoid in children under 2 years per labeling.

Psoriasis: well-demarcated erythematous plaques with silvery scale; histology shows parakeratosis, Munro microabscesses, and regular acanthosis.

Pityriasis rosea: herald patch followed by a 'Christmas tree' distribution of oval scaly macules; self-limiting, often linked to HHV-6/7.

Tinea corporis: annular scaly plaque with central clearing; KOH microscopy shows septate hyphae; treat with topical antifungals.

Urticaria: wheals lasting <24 hours; if individual lesions persist >24 hours, consider urticarial vasculitis and biopsy.

Erythema nodosum: tender nodules on shins; associated with streptococcal infection, sarcoidosis, IBD, and drugs (e.g., oral contraceptives).

Acne vulgaris: comedones, papules, pustules; Cutibacterium acnes colonization; isotretinoin for severe nodulocystic disease with monitoring of lipids and liver enzymes.

Vitiligo: depigmented macules with loss of melanocytes; associated with autoimmune thyroid disease; NBUVB and topical corticosteroids are treatment options.

Drug reaction with eosinophilia and systemic symptoms (DRESS): fever, rash, eosinophilia, and internal organ involvement; commonly triggered by anticonvulsants and allopurinol.

Curettage and electrodesiccation: suitable for low-risk superficial basal cell carcinoma and squamous cell carcinoma in situ; not for sclerosing or deep lesions.

Wide local excision for melanoma: in situ margin 0.5-1 cm; invasive <=1 mm margin 1 cm; 1-2 mm margin 1-2 cm; >2 mm margin 2 cm.

Sentinel lymph node biopsy: consider for melanoma >1 mm Breslow thickness or thinner lesions with ulceration or high mitotic rate.

Nail surgery: nail matrix biopsy for longitudinal melanonychia suspicious for melanoma; partial nail avulsion with matricectomy for ingrown nails.

Local anesthesia: lidocaine with epinephrine (1:100,000) prolongs anesthesia and reduces bleeding; avoid in digits only with caution due to historical concerns (now considered safe).

Flap and graft principles: random pattern flaps require length-to-width ratio limits; full-thickness grafts for cosmetic sites, split-thickness for large defects.

Electrosurgery: use for hemostasis and destruction; avoid in patients with pacemakers or implanted defibrillators unless precautions taken.

Wound care: keep clean and moist; sutures on face removed at 5-7 days, trunk 7-10 days, extremities 10-14 days.

Epidermal necrosis with 'smudged' keratinocytes and eosinophilic bodies (Civatte bodies) suggests lichenoid tissue reaction.

Lymphocytic vasculitis: fibrinoid necrosis of vessel walls with nuclear dust; consider connective tissue disease or drug reaction.

Granuloma annulare: palisading granulomas around mucin in the dermis; clinically annular plaques.

Necrobiosis lipoidica: layered granulomatous inflammation with collagen degeneration; associated with diabetes mellitus.

Xanthogranuloma: foamy histiocytes (Touton giant cells); juvenile xanthogranuloma in children.

Pigmented lesions: Breslow thickness measured from granular layer to deepest melanoma cell; Clark level describes anatomic depth.

Basal cell carcinoma: nests of basaloid cells with peripheral palisading and clefting; mucin in stroma.

Squamous cell carcinoma: atypical keratinocytes with keratin pearls and intercellular bridges; depth of invasion and perineural invasion affect prognosis.

Neonatal lupus: annular erythematous plaques on face/scalp; associated with maternal anti-Ro/SSA antibodies; usually resolves with maternal antibody clearance.

Diaper dermatitis: irritant contact most common; Candida superinfection shows satellite pustules; treat with barrier cream and topical antifungal if candidal.

Scabies in infants: burrows on palms and soles; treat with permethrin 5% cream (safe in infants >=2 months) and treat close contacts.

Impetigo: honey-crusted lesions caused by Staphylococcus aureus or Streptococcus pyogenes; topical mupirocin for limited disease, oral antibiotics for extensive.

Pediatric psoriasis: often presents after streptococcal infection (guttate); topical corticosteroids and calcipotriene are first-line.

Topical therapy in children: use lowest effective potency, limit duration, and monitor for hypothalamic-pituitary-adrenal axis suppression with potent steroids.

Hand-foot-and-mouth disease: coxsackievirus; oral vesicles and acral papulovesicles; supportive care.

Epidermolysis bullosa: genetic blistering disorders; avoid trauma, use protective dressings; multidisciplinary care for severe forms.

Contact dermatitis: allergic type is type IV delayed hypersensitivity; patch testing identifies allergens; irritant type is direct toxicity.

Seborrheic dermatitis: Malassezia yeast implicated; treat with ketoconazole shampoo and topical corticosteroids.

Rosacea: flushing, telangiectasias, papules; triggers include heat and spicy food; treat with metronidazole or ivermectin topically.

Hidradenitis suppurativa: follicular occlusion in intertriginous areas; treat with antibiotics, biologics (adalimumab), and surgical deroofing.

Pemphigus foliaceus: superficial acantholysis, IgG against desmoglein 1; direct immunofluorescence shows intercellular IgG in upper epidermis.

Lichen sclerosus: white atrophic plaques on genital skin; risk of squamous cell carcinoma; treat with potent topical corticosteroids.

Erythema multiforme major: target lesions plus mucosal involvement; often HSV-triggered; supportive care and antivirals for recurrent cases.

Sweet syndrome: tender erythematous plaques with fever and neutrophilia; histology shows dense neutrophilic dermal infiltrate without vasculitis.

Chemical peels: superficial (glycolic acid 20-70%, salicylic acid) for epidermal lesions; medium (trichloroacetic acid 35%) for pigmentary and premalignant lesions; deep peels carry scarring risk.

Botulinum toxin: used for dynamic wrinkles and hyperhidrosis; effect lasts 3-6 months; avoid in neuromuscular disorders.

Dermabrasion and microneedling: stimulate collagen for scars and rejuvenation; caution in patients with active infection or keloid tendency.

Liposuction: tumescent technique with lidocaine and epinephrine; risks include seroma, infection, and fat embolism.

Hair transplantation: follicular unit extraction or strip harvest; androgenic alopecia is the most common indication.

Sclerotherapy complications: telangiectatic matting, hyperpigmentation, and deep vein thrombosis (rare).

Cryosurgery for warts: repeat freeze-thaw cycles; avoid on genital warts and in young children without anesthesia.

Suture selection: absorbable (polyglactin) for deep layers; nonabsorbable (nylon, polypropylene) for skin surface; monofilament reduces infection risk.

Panniculitis: septal (erythema nodosum) vs lobular (pancreatic panniculitis, lupus panniculitis); biopsy deep enough to include subcutis.

Mastocytosis: increased dermal mast cells; stain with tryptase and Giemsa; Darier sign (urtication on rubbing) is clinical clue.

Mycosis fungoides: epidermotropism of atypical lymphocytes with Pautrier microabscesses; early patch stage may mimic eczema.

Langerhans cell histiocytosis: Birbeck granules on electron microscopy; CD1a and Langerin positive; may present as seborrheic-like rash in infants.

Kaposi sarcoma: spindle cells with slit-like vascular spaces; HHV-8 positive; associated with immunosuppression.

Dermatofibrosarcoma protuberans: CD34 positive spindle cell tumor; locally aggressive; treated with Mohs or wide excision.

Melanoma: asymmetry, border irregularity, color variation, diameter >6 mm, evolution; histology shows atypical melanocytes at dermoepidermal junction and pagetoid spread.

Pemphigus vulgaris immunofluorescence: intercellular IgG and C3 in epidermis; ELISA for desmoglein 3 antibodies.

Tinea capitis: Trichophyton tonsurans most common in the US; treat with oral griseofulvin or terbinafine; topical therapy alone is inadequate.

Alopecia areata in children: well-demarcated nonscarring hair loss; associated with autoimmune disease; topical corticosteroids or contact immunotherapy.

Keratosis pilaris: rough follicular papules on extensor surfaces; treat with emollients and keratolytics (urea, lactic acid).

Miliaria: sweat duct obstruction; crystallina (superficial) vs rubra (deeper); keep cool and avoid occlusive clothing.

Seborrheic dermatitis of infancy (cradle cap): greasy scales on scalp; treat with baby shampoo and emollients; resolves spontaneously.

Henoch-Schönlein purpura (IgA vasculitis): palpable purpura on lower extremities, abdominal pain, arthritis, renal involvement; monitor urinalysis.

Stevens-Johnson syndrome in children: often drug-induced (anticonvulsants, sulfonamides); supportive care and wound management.

Phototherapy in children: NBUVB for psoriasis and vitiligo; caution regarding long-term skin cancer risk; use minimal effective dose.

Herpes zoster: dermatomal vesicular rash; treat with antivirals within 72 hours; risk of postherpetic neuralgia increases with age.

Erysipelas: superficial dermal infection, often group A Streptococcus; sharply demarcated erythema; treat with penicillin.

Cellulitis: deeper dermal/subcutaneous infection; common organisms Staphylococcus aureus and Streptococcus pyogenes; elevate limb and use antibiotics.

Lyme disease: erythema migrans (bull's-eye); treat with doxycycline; early disseminated disease may cause multiple lesions.

Tinea versicolor: Malassezia furfur; hypopigmented or hyperpigmented macules on trunk; KOH shows spaghetti and meatballs; treat with selenium sulfide or ketoconazole.

Scabies: pruritic burrows in web spaces; treat with permethrin 5% or oral ivermectin; treat contacts simultaneously.

Cutaneous larva migrans: serpiginous track from hookworm larvae; treat with albendazole or ivermectin.

Erythema ab igne: reticulated hyperpigmentation from chronic heat exposure; remove heat source.

Excision of epidermoid cyst: complete removal of cyst wall to prevent recurrence; avoid rupture and inflammation.

Pilonidal cyst: excision with secondary intention healing or flap closure; common in sacrococcygeal area.

Nail avulsion: use digital block; for ingrown toenail, partial matricectomy reduces recurrence.

Biopsy techniques: punch for deep dermal/subcutaneous lesions; excisional for suspected melanoma to allow accurate Breslow measurement.

Hemostasis: electrocautery, topical thrombin, or pressure; avoid epinephrine in patients with peripheral vascular disease.

Suture removal timing: face 5-7 days, scalp 7-10 days, trunk 10-14 days, extremities 14 days; longer for high-tension areas.

Scar management: silicone gel sheets, intralesional steroids, and pressure therapy for hypertrophic scars and keloids.

Mohs for dermatofibrosarcoma protuberans: margin-controlled excision reduces recurrence; CD34 positivity confirms diagnosis.

Epidermal hyperplasia with thinning of suprapapillary plates and dilated capillaries in dermal papillae suggests psoriasis.

Lichenoid infiltrate with basal vacuolar change and Civatte bodies suggests lichen planus or lupus.

Neutrophilic dermatoses: Sweet syndrome shows dense neutrophilic infiltrate without vasculitis; pyoderma gangrenosum shows neutrophilic infiltrate with ulceration.

Vasculitis: leukocytoclastic vasculitis shows fibrinoid necrosis of small vessel walls with nuclear dust and extravasated erythrocytes.

Alopecia biopsy: horizontal sections assess follicular density and miniaturization; vertical sections assess depth and inflammation.

Pigmented purpuric dermatoses: perivascular lymphocytic infiltrate with hemosiderin deposition; clinical petechiae.

Epidermal cyst: cystic space lined by stratified squamous epithelium with granular layer and keratin debris.

Neurofibroma: spindle cells with wavy nuclei and mast cells; S100 positive; associated with neurofibromatosis type 1.

Neonatal herpes simplex: vesicular lesions, lethargy, poor feeding; treat with IV acyclovir; risk of disseminated disease.

Miliaria rubra: erythematous papules in intertriginous areas; avoid occlusive clothing and keep skin cool.

Erythema toxicum neonatorum: benign pustules with eosinophils; appears in first days and resolves spontaneously.

Transient neonatal pustular melanosis: pustules with pigmented macules; no treatment needed.

Kawasaki disease: treat with IVIG 2 g/kg and aspirin; echocardiography to monitor coronary arteries.

Pediatric atopic dermatitis: use emollients liberally; topical corticosteroids for flares; avoid triggers such as harsh soaps.

Verruca vulgaris: common warts in children; treat with salicylic acid or cryotherapy; often resolve spontaneously.

Psoriasis in children: guttate type common after streptococcal infection; topical corticosteroids and phototherapy for severe cases.

Basal cell carcinoma: pearly papule with telangiectasia; most common skin cancer; treat with excision or Mohs for high-risk sites.

Squamous cell carcinoma: scaly, ulcerated lesion; risk factors include UV exposure and immunosuppression; metastasis risk higher than BCC.

Melanoma: ABCDE criteria; Breslow thickness determines prognosis and margins.

Actinic keratosis: premalignant scaly lesion; treat with cryotherapy, 5-fluorouracil, or imiquimod.

Cutaneous T-cell lymphoma: patches, plaques, tumors; mycosis fungoides is most common; treat with phototherapy or systemic therapy.

Kaposi sarcoma: violaceous plaques/nodules; HHV-8 associated; treat underlying immunosuppression.

Merkel cell carcinoma: aggressive neuroendocrine tumor; CK20 positive; wide excision and sentinel lymph node biopsy.

Dermatofibrosarcoma protuberans: locally aggressive; CD34 positive; Mohs or wide excision.

Mohs micrographic surgery: indicated for high-risk basal cell carcinoma, squamous cell carcinoma, and dermatofibrosarcoma protuberans; preserves tissue.

Excision margins for squamous cell carcinoma: 4-6 mm for low-risk; wider for high-risk or recurrent lesions.

Sentinel lymph node biopsy for melanoma: consider for Breslow >1 mm or ulceration; provides prognostic information.

Curettage and electrodesiccation: for low-risk superficial basal cell carcinoma; not for morpheaform or recurrent lesions.

Cryotherapy: for actinic keratosis, warts, and seborrheic keratosis; avoid on pigmented lesions suspicious for melanoma.

Intralesional steroids: for keloids, hypertrophic scars, and alopecia areata; triamcinolone 2.5-10 mg/mL.

Laser therapy: pulsed dye laser for vascular lesions; Q-switched laser for pigmented lesions; fractional laser for rejuvenation.

Surgical complications: infection, bleeding, scarring, and nerve injury; proper technique and hemostasis reduce risk.

Psoriasis histology: parakeratosis, Munro microabscesses, regular acanthosis, thinned suprapapillary plates, dilated capillaries.

Lichen planus: hyperkeratosis, wedge-shaped hypergranulosis, saw-tooth rete ridges, band-like lymphocytic infiltrate.

Lupus erythematosus: interface dermatitis, mucin deposition, perivascular lymphocytic infiltrate; lupus band on DIF.

Pemphigus vulgaris: suprabasal acantholysis, 'tombstone' row of basal cells; intercellular IgG on DIF.

Bullous pemphigoid: subepidermal blister, eosinophils; linear IgG/C3 along basement membrane zone.

Dermatitis herpetiformis: granular IgA at dermal papillae tips; associated with celiac disease.

Mycosis fungoides: epidermotropism, Pautrier microabscesses, atypical lymphocytes with cerebriform nuclei.

Seborrheic keratosis: horn pseudocysts, basaloid cells, no atypia; 'stuck-on' appearance.

Atopic dermatitis: emollients and topical corticosteroids; avoid triggers; antihistamines for pruritus.

Kawasaki disease: IVIG and aspirin; monitor coronary arteries with echocardiography.

Hemangioma of infancy: propranolol first-line for problematic lesions; monitor for hypoglycemia and bradycardia.

Molluscum contagiosum: self-limiting; cantharidin or cryotherapy for persistent lesions.

Tinea capitis: oral griseofulvin or terbinafine; topical therapy alone inadequate.

Scabies: permethrin 5% for infants >=2 months; treat contacts.

Impetigo: mupirocin for limited disease; oral antibiotics for extensive.

Neonatal lupus: maternal anti-Ro/SSA antibodies; resolves with maternal antibody clearance.

Urticaria: wheals lasting <24 hours; if >24 hours consider urticarial vasculitis and biopsy.

Erythema nodosum: tender nodules on shins; associated with streptococcal infection, sarcoidosis, IBD, and drugs.

Sweet syndrome: tender plaques with fever and neutrophilia; neutrophilic dermal infiltrate without vasculitis.

DRESS: fever, rash, eosinophilia, internal organ involvement; triggered by anticonvulsants and allopurinol.

Pityriasis rosea: herald patch, 'Christmas tree' distribution; self-limiting; HHV-6/7 associated.

Tinea corporis: annular scaly plaque with central clearing; KOH shows septate hyphae.

Vitiligo: depigmented macules; associated with autoimmune thyroid disease; NBUVB and topical steroids.

Acne vulgaris: comedones, papules, pustules; isotretinoin for severe nodulocystic disease with monitoring.

Wide local excision for melanoma: in situ 0.5-1 cm; <=1 mm 1 cm; 1-2 mm 1-2 cm; >2 mm 2 cm.

Sentinel lymph node biopsy: consider for melanoma >1 mm or ulceration; prognostic value.

Nail matrix biopsy: for longitudinal melanonychia suspicious for melanoma.

Local anesthesia: lidocaine with epinephrine prolongs anesthesia and reduces bleeding; safe in digits with caution.

Flap and graft principles: random pattern flaps have length-to-width limits; full-thickness grafts for cosmetic sites.

Electrosurgery: avoid in pacemaker patients unless precautions taken.

Wound care: keep clean and moist; suture removal timing varies by site.

Chemical peels: superficial for epidermal lesions; medium for pigmentary and premalignant; deep peels carry scarring risk.

Spongiosis: intercellular edema; hallmark of eczematous dermatitis.

Acantholysis: loss of intercellular cohesion; seen in pemphigus and Hailey-Hailey disease.

Interface dermatitis: lymphocytic infiltrate obscuring dermoepidermal junction; lichen planus, lupus, erythema multiforme.

Parakeratosis with neutrophils suggests psoriasis; regular acanthosis with thinned suprapapillary plates.

Pautrier microabscesses: intraepidermal atypical lymphocytes; mycosis fungoides.

Dermatofibroma: dermal spindle cells with collagen trapping; factor XIIIa positive, CD34 negative.

Seborrheic keratosis: horn pseudocysts, basaloid cells; no atypia.

Amyloidosis: eosinophilic dermal deposits; Congo red shows apple-green birefringence under polarized light.

Neonatal acne: resolves spontaneously; do not confuse with neonatal cephalic pustulosis.

Measles: Koplik spots precede maculopapular rash; rash spreads cephalocaudally.

Topical calcineurin inhibitors: steroid-sparing for atopic dermatitis; avoid in children under 2 years per labeling.

Diaper dermatitis: irritant contact most common; Candida superinfection shows satellite pustules.

Scabies in infants: burrows on palms and soles; permethrin 5% safe in infants >=2 months.

Impetigo: honey-crusted lesions; mupirocin for limited disease.

Pediatric psoriasis: guttate after streptococcal infection; topical corticosteroids and calcipotriene first-line.

Hand-foot-and-mouth disease: coxsackievirus; oral vesicles and acral papulovesicles; supportive care.

Pemphigus vulgaris: suprabasal acantholysis, IgG against desmoglein 3; intercellular IgG/C3 on DIF.

Bullous pemphigoid: subepidermal blister, linear IgG/C3 at basement membrane zone; targets BP180/BP230.

Dermatitis herpetiformis: granular IgA at dermal papillae tips; celiac disease association; dapsone plus gluten-free diet.

Guttate psoriasis: follows streptococcal pharyngitis; Auspitz sign and Koebner phenomenon.

Erythema multiforme: targetoid lesions, often HSV-triggered; SJS/TEN shows mucosal involvement and epidermal detachment.

Lichen planus: purple polygonal papules with Wickham striae; band-like lymphocytic infiltrate and saw-tooth rete ridges.

Systemic lupus erythematosus: interface dermatitis with mucin; lupus band on DIF.

Sarcoidosis: non-caseating granulomas; erythema nodosum and lupus pernio; check ACE and chest imaging.

Mohs micrographic surgery: examines 100% of margins; for high-risk BCC, SCC, and DFSP.

Excision margins for primary BCC: 3-4 mm for well-defined low-risk lesions.

Sclerotherapy: sodium tetradecyl sulfate or polidocanol; risks include hyperpigmentation and ulceration.

Cryotherapy: freeze time and thaw cycles determine destruction; avoid in dark skin on visible sites.

Intralesional corticosteroids: triamcinolone 2.5-10 mg/mL for keloids, hypertrophic scars, alopecia areata.

Punch biopsy (3-4 mm) preserves architecture for inflammatory dermatoses; shave biopsy inadequate for depth.

Laser selection: pulsed dye for vascular; Q-switched for pigment; ablative fractional for resurfacing.

Surgical site infection prophylaxis: single preoperative dose for clean-contaminated or high-risk procedures.

Epidermal necrosis with Civatte bodies suggests lichenoid tissue reaction.

Lymphocytic vasculitis: fibrinoid necrosis with nuclear dust; consider connective tissue disease or drug reaction.

Granuloma annulare: palisading granulomas around mucin; annular plaques.

Necrobiosis lipoidica: layered granulomatous inflammation with collagen degeneration; diabetes association.

Xanthogranuloma: foamy histiocytes with Touton giant cells; juvenile xanthogranuloma in children.

Pigmented lesions: Breslow thickness from granular layer to deepest melanoma cell; Clark level describes anatomic depth.

Basal cell carcinoma: basaloid nests with peripheral palisading and clefting; stromal mucin.

Squamous cell carcinoma: atypical keratinocytes with keratin pearls and intercellular bridges; depth and perineural invasion affect prognosis.

Neonatal lupus: annular plaques on face/scalp; maternal anti-Ro/SSA antibodies; resolves with antibody clearance.

Diaper dermatitis: barrier cream; topical antifungal if candidal superinfection (satellite pustules).

Scabies in infants: permethrin 5% safe in infants >=2 months; treat contacts.

Impetigo: mupirocin for limited disease; oral antibiotics for extensive.

Pediatric psoriasis: topical corticosteroids and calcipotriene first-line; guttate after streptococcal infection.

Topical therapy in children: lowest effective potency, limit duration, monitor for HPA axis suppression.

Hand-foot-and-mouth disease: coxsackievirus; supportive care.

Epidermolysis bullosa: genetic blistering; avoid trauma, protective dressings, multidisciplinary care.

Contact dermatitis: allergic type is type IV delayed hypersensitivity; patch testing identifies allergens.

Seborrheic dermatitis: Malassezia implicated; ketoconazole shampoo and topical corticosteroids.

Rosacea: flushing, telangiectasias, papules; triggers include heat and spicy food; topical metronidazole or ivermectin.

Hidradenitis suppurativa: follicular occlusion in intertriginous areas; antibiotics, adalimumab, surgical deroofing.

Pemphigus foliaceus: superficial acantholysis, IgG against desmoglein 1; intercellular IgG in upper epidermis on DIF.

Lichen sclerosus: white atrophic plaques on genital skin; risk of SCC; potent topical corticosteroids.

Erythema multiforme major: target lesions plus mucosal involvement; HSV-triggered; supportive care and antivirals for recurrent cases.

Sweet syndrome: tender erythematous plaques with fever and neutrophilia; neutrophilic dermal infiltrate without vasculitis.

Chemical peels: superficial (glycolic acid, salicylic acid) for epidermal lesions; medium (TCA 35%) for pigmentary and premalignant lesions; deep peels carry scarring risk.

Botulinum toxin: dynamic wrinkles and hyperhidrosis; effect lasts 3-6 months; avoid in neuromuscular disorders.

Dermabrasion and microneedling: stimulate collagen for scars and rejuvenation; caution with active infection or keloid tendency.

Liposuction: tumescent technique with lidocaine and epinephrine; risks include seroma, infection, fat embolism.

Hair transplantation: follicular unit extraction or strip harvest; androgenic alopecia most common indication.

Sclerotherapy complications: telangiectatic matting, hyperpigmentation, deep vein thrombosis (rare).

Cryosurgery for warts: repeat freeze-thaw cycles; avoid on genital warts and in young children without anesthesia.

Suture selection: absorbable (polyglactin) for deep layers; nonabsorbable (nylon, polypropylene) for skin surface; monofilament reduces infection risk.

Panniculitis: septal (erythema nodosum) vs lobular (pancreatic panniculitis, lupus panniculitis); biopsy deep enough to include subcutis.

Mastocytosis: increased dermal mast cells; tryptase and Giemsa stain; Darier sign (urtication on rubbing).

Mycosis fungoides: epidermotropism of atypical lymphocytes with Pautrier microabscesses; early patch stage may mimic eczema.

Langerhans cell histiocytosis: Birbeck granules on electron microscopy; CD1a and Langerin positive; seborrheic-like rash in infants.

Kaposi sarcoma: spindle cells with slit-like vascular spaces; HHV-8 positive; immunosuppression associated.

Dermatofibrosarcoma protuberans: CD34 positive spindle cell tumor; locally aggressive; Mohs or wide excision.

Melanoma: atypical melanocytes at dermoepidermal junction and pagetoid spread; ABCDE criteria.

Pemphigus vulgaris immunofluorescence: intercellular IgG and C3 in epidermis; ELISA for desmoglein 3 antibodies.

Tinea capitis: Trichophyton tonsurans most common in the US; oral griseofulvin or terbinafine; topical therapy alone inadequate.

Alopecia areata in children: nonscarring hair loss; topical corticosteroids or contact immunotherapy.

Keratosis pilaris: rough follicular papules on extensor surfaces; emollients and keratolytics (urea, lactic acid).

Miliaria: sweat duct obstruction; crystallina vs rubra; keep cool and avoid occlusive clothing.

Seborrheic dermatitis of infancy (cradle cap): greasy scales on scalp; baby shampoo and emollients; resolves spontaneously.

Henoch-Schönlein purpura (IgA vasculitis): palpable purpura on lower extremities, abdominal pain, arthritis, renal involvement; monitor urinalysis.

Stevens-Johnson syndrome in children: often drug-induced (anticonvulsants, sulfonamides); supportive care and wound management.

Phototherapy in children: NBUVB for psoriasis and vitiligo; caution regarding long-term skin cancer risk; minimal effective dose.

Herpes zoster: dermatomal vesicular rash; antivirals within 72 hours; risk of postherpetic neuralgia increases with age.

Erysipelas: superficial dermal infection, often group A Streptococcus; sharply demarcated erythema; penicillin.

Cellulitis: deeper dermal/subcutaneous infection; Staphylococcus aureus and Streptococcus pyogenes; elevate limb and antibiotics.

Lyme disease: erythema migrans (bull's-eye); doxycycline; early disseminated disease may cause multiple lesions.

Tinea versicolor: Malassezia furfur; hypopigmented or hyperpigmented macules on trunk; KOH shows spaghetti and meatballs; selenium sulfide or ketoconazole.

Scabies: pruritic burrows in web spaces; permethrin 5% or oral ivermectin; treat contacts simultaneously.

Cutaneous larva migrans: serpiginous track from hookworm larvae; albendazole or ivermectin.

Erythema ab igne: reticulated hyperpigmentation from chronic heat exposure; remove heat source.

Excision of epidermoid cyst: complete removal of cyst wall to prevent recurrence; avoid rupture and inflammation.

Pilonidal cyst: excision with secondary intention healing or flap closure; sacrococcygeal area.

Nail avulsion: digital block; partial matricectomy reduces recurrence for ingrown toenail.

Biopsy techniques: punch for deep dermal/subcutaneous lesions; excisional for suspected melanoma to allow accurate Breslow measurement.

Hemostasis: electrocautery, topical thrombin, or pressure; avoid epinephrine in peripheral vascular disease.

Suture removal timing: face 5-7 days, scalp 7-10 days, trunk 10-14 days, extremities 14 days; longer for high-tension areas.

Scar management: silicone gel sheets, intralesional steroids, pressure therapy for hypertrophic scars and keloids.

Mohs for dermatofibrosarcoma protuberans: margin-controlled excision reduces recurrence; CD34 positivity confirms diagnosis.

Epidermal hyperplasia with thinning of suprapapillary plates and dilated capillaries in dermal papillae suggests psoriasis.

Lichenoid infiltrate with basal vacuolar change and Civatte bodies suggests lichen planus or lupus.

Neutrophilic dermatoses: Sweet syndrome shows dense neutrophilic infiltrate without vasculitis; pyoderma gangrenosum shows neutrophilic infiltrate with ulceration.

Vasculitis: leukocytoclastic vasculitis shows fibrinoid necrosis of small vessel walls with nuclear dust and extravasated erythrocytes.

Alopecia biopsy: horizontal sections assess follicular density and miniaturization; vertical sections assess depth and inflammation.

Pigmented purpuric dermatoses: perivascular lymphocytic infiltrate with hemosiderin deposition; clinical petechiae.

Epidermal cyst: cystic space lined by stratified squamous epithelium with granular layer and keratin debris.

Neurofibroma: spindle cells with wavy nuclei and mast cells; S100 positive; associated with neurofibromatosis type 1.

Neonatal herpes simplex: vesicular lesions, lethargy, poor feeding; IV acyclovir; risk of disseminated disease.

Miliaria rubra: erythematous papules in intertriginous areas; avoid occlusive clothing and keep skin cool.

Erythema toxicum neonatorum: benign pustules with eosinophils; appears in first days and resolves spontaneously.

Transient neonatal pustular melanosis: pustules with pigmented macules; no treatment needed.

Kawasaki disease: IVIG 2 g/kg and aspirin; echocardiography to monitor coronary arteries.

Pediatric atopic dermatitis: emollients liberally; topical corticosteroids for flares; avoid triggers such as harsh soaps.

Verruca vulgaris: common warts in children; salicylic acid or cryotherapy; often resolve spontaneously.

Psoriasis in children: guttate type common after streptococcal infection; topical corticosteroids and phototherapy for severe cases.