Iraqi Board Dermatology cheat sheet

Epidermis turnover ~28 days; keratinocyte maturation follows basal→spinous→granular→cornified layers, with filaggrin aggregating keratin filaments in the granular layer.

Basement membrane zones: hemidesmosome (BPAG1/BPAG2, integrin α6β4) at basal cell, lamina lucida, lamina densa (type IV collagen), anchoring fibrils (type VII collagen).

Dermal collagen: type I ~80-85%, type III ~10-15%; type III dominates early wound repair and is the collagen of reticulin-positive fibers.

Langerhans cells (CD1a+, Birbeck granules) are epidermal antigen-presenting cells; dermal dendrocytes and macrophages handle deeper antigen processing.

Skin immune sentinels: Toll-like receptors on keratinocytes; Th17 axis (IL-17/IL-23) drives neutrophilic and psoriasiform inflammation.

Normal skin flora: Staphylococcus epidermidis, Corynebacterium, Propionibacterium (Cutibacterium); transient pathogens include S. aureus and β-hemolytic streptococci.

Pigment genetics: MC1R variants shift pheomelanin/eumelanin balance; TYR, OCA2, TYRP1 mutations cause oculocutaneous albinism.

Cutaneous pathology patterns: spongiotic, psoriasiform, lichenoid/interface, vesiculobullous, granulomatous, vasculopathic - pattern drives differential diagnosis.

Primary lesions: macule (<1 cm flat), patch (≥1 cm flat), papule (<1 cm raised), plaque (≥1 cm raised), nodule (deep, ≥1 cm), vesicle (<1 cm fluid), bulla (≥1 cm fluid), pustule (pus), wheal (edema).

Secondary lesions: scale, crust, erosion (epidermal loss), ulcer (dermal loss), fissure, excoriation, lichenification, atrophy, scar, maceration.

Dermatoscopic melanoma rules: asymmetry, atypical network, blue-white veil, irregular dots/globules, regression structures, irregular vessels; ABCD of dermatoscopy.

Pigmented lesion patterns: reticular vs globular vs homogeneous vs starburst; acral lesions show parallel ridge pattern in melanoma vs lattice/fibrillar in benign nevi.

Nailfold capillaroscopy: dilated, tortuous loops and dropout suggest systemic sclerosis; giant capillaries with hemorrhage suggest dermatomyositis.

Dermatopathology stains: PAS for fungi and basement membrane, Fite/Fite-Faraco for M. leprae, Ziehl-Neelsen for mycobacteria, Congo red for amyloid, Perls for iron.

Direct immunofluorescence patterns: linear IgG/C3 at BMZ (bullous pemphigoid), intercellular IgG (pemphigus), granular IgA at dermal papillae (dermatitis herpetiformis), lupus band.

Biopsy selection: punch for deep dermal/subcutaneous lesions, shave for exophytic epidermal lesions, excisional for suspected melanoma or panniculitis.

Psoriasis: well-demarcated erythematous plaques with silvery scale on extensor surfaces; Auspitz sign, Koebner phenomenon, nail pitting and oil spots; histology shows parakeratosis, Munro microabscesses, acanthosis.

Atopic dermatitis: pruritus is essential; flexural distribution in adults, face/extensor in infants; filaggrin loss-of-function mutations impair barrier; associated with asthma/allergic rhinitis.

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

Seborrheic dermatitis: greasy yellow scale on scalp, eyebrows, nasolabial folds; Malassezia-driven; responds to topical azoles.

Pityriasis rosea: herald patch followed by Christmas-tree distribution of oval scaly macules; HHV-6/7 association; self-limited over 6-8 weeks.

Lichenoid drug eruption: resembles lichen planus but often photo-distributed, with parakeratosis and eosinophils on histology; common culprits include gold, antimalarials, thiazides.

Eczema herpeticum: widespread monomorphic vesicles/pustules in atopic patient; HSV superinfection; treat with systemic acyclovir.

Erythroderma causes: psoriasis, atopic dermatitis, drug eruption, cutaneous T-cell lymphoma, pityriasis rubra pilaris; evaluate for systemic complications (fluid loss, hypothermia, high-output failure).

Impetigo: honey-colored crusts; nonbullous caused by S. aureus or group A streptococci; bullous form is S. aureus toxin-mediated; treat with topical mupirocin or oral antibiotics.

Erysipelas vs cellulitis: erysipelas involves upper dermis with sharp raised border (streptococcal); cellulitis involves deeper dermis/subcutis with ill-defined border.

Herpes simplex: grouped vesicles on erythematous base; Tzanck smear shows multinucleated giant cells; HSV-1 orolabial, HSV-2 genital; recurrences triggered by stress/UV.

Herpes zoster: dermatomal vesicular eruption; Ramsay Hunt syndrome = zoster of geniculate ganglion with facial palsy and ear vesicles; treat within 72 hours.

Dermatophytosis: KOH microscopy shows branching septate hyphae; Trichophyton rubrum most common; tinea capitis in children requires oral griseofulvin or terbinafine.

Candida: pseudohyphae and budding yeasts on KOH; intertriginous and mucosal disease; treat with topical or oral azoles.

Leprosy: M. leprae; Ridley-Jopling spectrum from tuberculoid (paucibacillary, strong Th1) to lepromatous (multibacillary, Th2); Fite stain; treat with rifampicin, dapsone, clofazimine.

Scabies: Sarcoptes scabiei; burrows, nocturnal pruritus, web spaces; treat with permethrin 5% or oral ivermectin; treat contacts simultaneously.

Syphilis: primary chancre, secondary maculopapular rash with palmar/plantar involvement and condylomata lata; treat with benzathine penicillin; Jarisch-Herxheimer reaction possible.

Basal cell carcinoma: pearly papule with telangiectasia, rolled border, central ulceration; subtypes nodular, superficial, morpheaform; Mohs surgery for high-risk sites.

Squamous cell carcinoma: keratotic nodule or ulcer in sun-exposed skin; risk factors include UV, immunosuppression, chronic wounds; metastasis risk higher than BCC.

Actinic keratosis: rough erythematous macule on sun-damaged skin; premalignant; treat with cryotherapy, 5-fluorouracil, imiquimod, or photodynamic therapy.

Melanoma ABCDE: Asymmetry, Border irregularity, Color variation, Diameter >6 mm, Evolution; Breslow thickness is the strongest prognostic factor.

Melanoma subtypes: superficial spreading (most common), nodular (fastest growth), lentigo maligna (sun-damaged elderly face), acral lentiginous (palms/soles, nail apparatus).

Dermatofibroma: firm brown papule with dimple sign; histology shows spindle cell proliferation with collagen trapping; benign, no treatment needed.

Mycosis fungoides: cutaneous T-cell lymphoma; patches, plaques, tumors; histology shows epidermotropic atypical lymphocytes with Pautrier microabscesses; Sézary syndrome has blood involvement.

Kaposi sarcoma: HHV-8 associated; violaceous plaques/nodules in HIV, elderly Mediterranean, or transplant patients; histology shows spindle cells with slit-like vascular spaces.

Pemphigus vulgaris: flaccid bullae, oral erosions, positive Nikolsky sign; IgG against desmoglein 3 (and 1); DIF shows intercellular IgG in chicken-wire pattern.

Bullous pemphigoid: tense bullae on normal/urticarial skin in elderly; IgG against BPAG1/BPAG2; DIF shows linear IgG and C3 at BMZ; treat with topical or systemic steroids.

Dermatitis herpetiformis: intensely pruritic grouped vesicles on elbows, knees, buttocks; granular IgA in dermal papillae; associated with celiac disease; treat with dapsone and gluten-free diet.

Lupus erythematosus: malar rash, photosensitivity, discoid lesions; ANA, anti-dsDNA, anti-Sm; histology shows interface dermatitis with mucin; DIF shows lupus band.

Systemic sclerosis: Raynaud phenomenon, sclerodactyly, digital ulcers, telangiectasias; anti-centromere (limited), anti-Scl-70/topoisomerase (diffuse), anti-RNA polymerase III.

Dermatomyositis: heliotrope rash, Gottron papules, periungual telangiectasias, proximal muscle weakness; anti-Mi-2, anti-Jo-1, anti-MDA5 (rapidly progressive ILD); screen for malignancy.

Sjögren syndrome: dry eyes/mouth, annular erythema, anti-Ro/SSA and anti-La/SSB; increased lymphoma risk.

Linear IgA bullous dermatosis: linear IgA at BMZ on DIF; drug-induced by vancomycin; treat with dapsone.

Vitiligo: depigmented macules with Wood lamp accentuation; autoimmune melanocyte destruction; associations with thyroid disease, pernicious anemia, Addison disease; treat with topical steroids, tacrolimus, NB-UVB.

Melasma: symmetrical hyperpigmentation on malar cheeks, forehead, upper lip; triggered by UV and pregnancy; treat with hydroquinone, tretinoin, azelaic acid, sun protection.

Post-inflammatory hyperpigmentation: follows inflammation, more common in darker skin types (Fitzpatrick IV-VI); treat with topical retinoids, hydroquinone, chemical peels.

Alopecia areata: well-demarcated non-scarring patches with exclamation-mark hairs; nail pitting; associated with autoimmune thyroid disease; treat with intralesional steroids, topical immunotherapy.

Androgenetic alopecia: frontal/temporal recession and vertex thinning in men; diffuse thinning in women; minoxidil and finasteride are mainstays.

Telogen effluvium: diffuse hair shedding 2-3 months after trigger (illness, childbirth, drugs); self-limited; treat underlying cause.

Nail psoriasis: pitting, oil spots, onycholysis, subungual hyperkeratosis; distinguish from onychomycosis with KOH/PAS.

Oral lichen planus: white reticular striae (Wickham), erosions; risk of squamous cell carcinoma in erosive forms; biopsy persistent lesions.

Mohs micrographic surgery: staged excision with frozen-section margin control; indicated for high-risk BCC/SCC, recurrent tumors, and tissue-sparing sites (face, digits, genitalia).

Excision margins: BCC low-risk 4 mm; SCC low-risk 4-6 mm; melanoma in situ 5 mm, invasive ≤1 mm 1 cm, 1-2 mm 1-2 cm, >2 mm 2 cm.

Laser selection: pulsed dye laser (585/595 nm) for vascular lesions; Q-switched lasers for pigment; ablative fractional CO2/Er:YAG for resurfacing; Nd:YAG for hair removal.

Cryotherapy: liquid nitrogen at -196°C; treat actinic keratosis, warts, seborrheic keratosis; freeze-thaw cycles 2-3; risk of hypopigmentation and scarring.

Sclerotherapy: sodium tetradecyl sulfate or polidocanol for telangiectasias and small varicose veins; compression after treatment.

Flap and graft principles: random pattern flaps need length-to-width ratio ≤3:1; full-thickness grafts for face, split-thickness for large defects.

Anesthesia: lidocaine with epinephrine (1:100,000) prolongs effect and reduces bleeding; maximum lidocaine dose 7 mg/kg with epinephrine, 4.5 mg/kg without.

Suture removal: face 5-7 days, scalp 7-10 days, trunk/extremities 10-14 days, joints 14 days.

Atopic dermatitis in infants: face, scalp, extensor surfaces; in children: flexural; management includes emollients, topical corticosteroids, calcineurin inhibitors.

Hemangioma of infancy: appears in first weeks, proliferates then involutes; treat with oral propranolol; indications include vision obstruction, airway compromise, ulceration.

Port-wine stain: present at birth, grows proportionally; Sturge-Weber syndrome if V1 distribution with CNS/eye involvement; treat with pulsed dye laser.

Epidermolysis bullosa: inherited blistering; EB simplex (keratin 5/14), junctional (laminin-332, BPAG2), dystrophic (type VII collagen); handle with minimal trauma.

Ichthyosis vulgaris: filaggrin mutation; fine white scale, sparing of flexures; associated with atopic dermatitis and keratosis pilaris.

Neurofibromatosis type 1: café-au-lait macules (≥6), axillary/inguinal freckling, neurofibromas, Lisch nodules, optic glioma; NF1 gene on chromosome 17.

Tuberous sclerosis: ash-leaf spots, facial angiofibromas, shagreen patch, periungual fibromas; TSC1/TSC2 mutations; screen for renal angiomyolipoma and cardiac rhabdomyoma.

Incontinentia pigmenti: X-linked dominant, lethal in males; stages vesicular, verrucous, hyperpigmented, hypopigmented; associated with dental and ocular anomalies.

Acanthosis nigricans: velvety hyperpigmentation of neck/axillae; associated with insulin resistance, obesity, and malignancy (gastric adenocarcinoma in sudden-onset adult).

Erythema nodosum: tender red nodules on shins; associated with streptococcal infection, sarcoidosis, IBD, TB, drugs (OCP, sulfa); biopsy shows septal panniculitis.

Pyoderma gangrenosum: painful ulcer with violaceous undermined border; associated with IBD, rheumatoid arthritis, hematologic malignancy; treat with systemic steroids, cyclosporine, biologics.

Sweet syndrome: tender erythematous plaques with fever and neutrophilia; associated with malignancy (AML), drugs; histology shows dense neutrophilic dermal infiltrate.

Necrobiosis lipoidica: yellow-brown atrophic plaques on shins; associated with diabetes mellitus; histology shows layered granulomatous inflammation with collagen degeneration.

Drug eruption patterns: morbilliform (most common), urticarial, fixed drug, DRESS (eosinophilia, organ involvement), Stevens-Johnson syndrome/TEN (mucosal involvement, epidermal detachment).

Paraneoplastic dermatoses: acanthosis nigricans (GI cancer), dermatomyositis (ovarian, lung), acquired ichthyosis (Hodgkin lymphoma), Bazex syndrome (upper airway/GI).

Calciphylaxis: painful necrotic ulcers in ESRD patients; medial calcification of small vessels; high mortality; treat with sodium thiosulfate, wound care.

Topical corticosteroid potency: class I superpotent (clobetasol propionate 0.05%) to class VII least potent (hydrocortisone 1%); apply sparingly, avoid face/flexures with superpotent agents.

Topical calcineurin inhibitors: tacrolimus and pimecrolimus; no skin atrophy; FDA boxed warning for malignancy (lymphoma) - use second-line for atopic dermatitis.

Methotrexate: folate antagonist; monitor CBC, LFTs, renal function; supplement folic acid; contraindicated in pregnancy and hepatic disease.

Cyclosporine: calcineurin inhibitor; monitor blood pressure, renal function, potassium; drug interactions via CYP3A4; useful for severe psoriasis and atopic dermatitis.

Biologics for psoriasis: TNF inhibitors (adalimumab, etanercept, infliximab), IL-17 inhibitors (secukinumab, ixekizumab), IL-23 inhibitors (ustekinumab, guselkumab, risankizumab); screen for TB and hepatitis before starting.

Isotretinoin: for severe nodulocystic acne; teratogenic - requires iPledge program, two forms of contraception; monitor LFTs, lipids, CBC; adverse effects include cheilitis, dry skin, photosensitivity.

Phototherapy: NB-UVB (311-313 nm) for psoriasis, vitiligo, atopic dermatitis; PUVA (psoralen + UVA) for psoriasis, CTCL; risks include erythema, photoaging, skin cancer.

Antihistamines: first-generation (diphenhydramine, hydroxyzine) cause sedation; second-generation (loratadine, cetirizine, fexofenadine) preferred for daytime; topical doxepin for pruritus.

Study designs: randomized controlled trial (strongest for therapy), cohort (incidence, prognosis), case-control (rare diseases), cross-sectional (prevalence), case series (hypothesis-generating).

Levels of evidence: systematic reviews/meta-analyses of RCTs at top; then RCTs, cohort studies, case-control, case series, expert opinion.

Sensitivity = true positives / (true positives + false negatives); specificity = true negatives / (true negatives + false positives); PPV depends on prevalence.

Number needed to treat (NNT) = 1 / absolute risk reduction; number needed to harm (NNH) = 1 / absolute risk increase.

Intention-to-treat analysis preserves randomization; per-protocol analysis can introduce bias; blinding reduces detection and performance bias.

Consent and confidentiality: informed consent requires capacity, disclosure, voluntariness; minors and cognitively impaired patients need surrogate consent; report adverse events.

Patient safety in dermatology: verify biopsy site and laterality, use checklist for Mohs and excisions, confirm drug allergies, monitor for drug interactions (e.g., methotrexate + trimethoprim).

Publication bias: positive studies more likely published; funnel plot asymmetry suggests bias; trial registration reduces selective reporting.

Epidermis turnover ~28 days; keratinocyte maturation follows basal→spinous→granular→cornified layers, with filaggrin aggregating keratin filaments in the granular layer.

Basement membrane zones: hemidesmosome (BPAG1/BPAG2, integrin α6β4) at basal cell, lamina lucida, lamina densa (type IV collagen), anchoring fibrils (type VII collagen).

Dermal collagen: type I ~80-85%, type III ~10-15%; type III dominates early wound repair and is the collagen of reticulin-positive fibers.

Langerhans cells (CD1a+, Birbeck granules) are epidermal antigen-presenting cells; dermal dendrocytes and macrophages handle deeper antigen processing.

Skin immune sentinels: Toll-like receptors on keratinocytes; Th17 axis (IL-17/IL-23) drives neutrophilic and psoriasiform inflammation.

Normal skin flora: Staphylococcus epidermidis, Corynebacterium, Propionibacterium (Cutibacterium); transient pathogens include S. aureus and β-hemolytic streptococci.

Pigment genetics: MC1R variants shift pheomelanin/eumelanin balance; TYR, OCA2, TYRP1 mutations cause oculocutaneous albinism.

Cutaneous pathology patterns: spongiotic, psoriasiform, lichenoid/interface, vesiculobullous, granulomatous, vasculopathic - pattern drives differential diagnosis.

Primary lesions: macule (<1 cm flat), patch (≥1 cm flat), papule (<1 cm raised), plaque (≥1 cm raised), nodule (deep, ≥1 cm), vesicle (<1 cm fluid), bulla (≥1 cm fluid), pustule (pus), wheal (edema).

Secondary lesions: scale, crust, erosion (epidermal loss), ulcer (dermal loss), fissure, excoriation, lichenification, atrophy, scar, maceration.

Dermatoscopic melanoma rules: asymmetry, atypical network, blue-white veil, irregular dots/globules, regression structures, irregular vessels; ABCD of dermatoscopy.

Pigmented lesion patterns: reticular vs globular vs homogeneous vs starburst; acral lesions show parallel ridge pattern in melanoma vs lattice/fibrillar in benign nevi.

Nailfold capillaroscopy: dilated, tortuous loops and dropout suggest systemic sclerosis; giant capillaries with hemorrhage suggest dermatomyositis.

Dermatopathology stains: PAS for fungi and basement membrane, Fite/Fite-Faraco for M. leprae, Ziehl-Neelsen for mycobacteria, Congo red for amyloid, Perls for iron.

Direct immunofluorescence patterns: linear IgG/C3 at BMZ (bullous pemphigoid), intercellular IgG (pemphigus), granular IgA at dermal papillae (dermatitis herpetiformis), lupus band.

Biopsy selection: punch for deep dermal/subcutaneous lesions, shave for exophytic epidermal lesions, excisional for suspected melanoma or panniculitis.

Psoriasis: well-demarcated erythematous plaques with silvery scale on extensor surfaces; Auspitz sign, Koebner phenomenon, nail pitting and oil spots; histology shows parakeratosis, Munro microabscesses, acanthosis.

Atopic dermatitis: pruritus is essential; flexural distribution in adults, face/extensor in infants; filaggrin loss-of-function mutations impair barrier; associated with asthma/allergic rhinitis.

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

Seborrheic dermatitis: greasy yellow scale on scalp, eyebrows, nasolabial folds; Malassezia-driven; responds to topical azoles.

Pityriasis rosea: herald patch followed by Christmas-tree distribution of oval scaly macules; HHV-6/7 association; self-limited over 6-8 weeks.

Lichenoid drug eruption: resembles lichen planus but often photo-distributed, with parakeratosis and eosinophils on histology; common culprits include gold, antimalarials, thiazides.

Eczema herpeticum: widespread monomorphic vesicles/pustules in atopic patient; HSV superinfection; treat with systemic acyclovir.

Erythroderma causes: psoriasis, atopic dermatitis, drug eruption, cutaneous T-cell lymphoma, pityriasis rubra pilaris; evaluate for systemic complications (fluid loss, hypothermia, high-output failure).

Impetigo: honey-colored crusts; nonbullous caused by S. aureus or group A streptococci; bullous form is S. aureus toxin-mediated; treat with topical mupirocin or oral antibiotics.

Erysipelas vs cellulitis: erysipelas involves upper dermis with sharp raised border (streptococcal); cellulitis involves deeper dermis/subcutis with ill-defined border.

Herpes simplex: grouped vesicles on erythematous base; Tzanck smear shows multinucleated giant cells; HSV-1 orolabial, HSV-2 genital; recurrences triggered by stress/UV.

Herpes zoster: dermatomal vesicular eruption; Ramsay Hunt syndrome = zoster of geniculate ganglion with facial palsy and ear vesicles; treat within 72 hours.

Dermatophytosis: KOH microscopy shows branching septate hyphae; Trichophyton rubrum most common; tinea capitis in children requires oral griseofulvin or terbinafine.

Candida: pseudohyphae and budding yeasts on KOH; intertriginous and mucosal disease; treat with topical or oral azoles.

Leprosy: M. leprae; Ridley-Jopling spectrum from tuberculoid (paucibacillary, strong Th1) to lepromatous (multibacillary, Th2); Fite stain; treat with rifampicin, dapsone, clofazimine.

Scabies: Sarcoptes scabiei; burrows, nocturnal pruritus, web spaces; treat with permethrin 5% or oral ivermectin; treat contacts simultaneously.

Syphilis: primary chancre, secondary maculopapular rash with palmar/plantar involvement and condylomata lata; treat with benzathine penicillin; Jarisch-Herxheimer reaction possible.

Basal cell carcinoma: pearly papule with telangiectasia, rolled border, central ulceration; subtypes nodular, superficial, morpheaform; Mohs surgery for high-risk sites.

Squamous cell carcinoma: keratotic nodule or ulcer in sun-exposed skin; risk factors include UV, immunosuppression, chronic wounds; metastasis risk higher than BCC.

Actinic keratosis: rough erythematous macule on sun-damaged skin; premalignant; treat with cryotherapy, 5-fluorouracil, imiquimod, or photodynamic therapy.

Melanoma ABCDE: Asymmetry, Border irregularity, Color variation, Diameter >6 mm, Evolution; Breslow thickness is the strongest prognostic factor.

Melanoma subtypes: superficial spreading (most common), nodular (fastest growth), lentigo maligna (sun-damaged elderly face), acral lentiginous (palms/soles, nail apparatus).

Dermatofibroma: firm brown papule with dimple sign; histology shows spindle cell proliferation with collagen trapping; benign, no treatment needed.

Mycosis fungoides: cutaneous T-cell lymphoma; patches, plaques, tumors; histology shows epidermotropic atypical lymphocytes with Pautrier microabscesses; Sézary syndrome has blood involvement.

Kaposi sarcoma: HHV-8 associated; violaceous plaques/nodules in HIV, elderly Mediterranean, or transplant patients; histology shows spindle cells with slit-like vascular spaces.

Pemphigus vulgaris: flaccid bullae, oral erosions, positive Nikolsky sign; IgG against desmoglein 3 (and 1); DIF shows intercellular IgG in chicken-wire pattern.

Bullous pemphigoid: tense bullae on normal/urticarial skin in elderly; IgG against BPAG1/BPAG2; DIF shows linear IgG and C3 at BMZ; treat with topical or systemic steroids.

Dermatitis herpetiformis: intensely pruritic grouped vesicles on elbows, knees, buttocks; granular IgA in dermal papillae; associated with celiac disease; treat with dapsone and gluten-free diet.

Lupus erythematosus: malar rash, photosensitivity, discoid lesions; ANA, anti-dsDNA, anti-Sm; histology shows interface dermatitis with mucin; DIF shows lupus band.

Systemic sclerosis: Raynaud phenomenon, sclerodactyly, digital ulcers, telangiectasias; anti-centromere (limited), anti-Scl-70/topoisomerase (diffuse), anti-RNA polymerase III.

Dermatomyositis: heliotrope rash, Gottron papules, periungual telangiectasias, proximal muscle weakness; anti-Mi-2, anti-Jo-1, anti-MDA5 (rapidly progressive ILD); screen for malignancy.

Sjögren syndrome: dry eyes/mouth, annular erythema, anti-Ro/SSA and anti-La/SSB; increased lymphoma risk.

Linear IgA bullous dermatosis: linear IgA at BMZ on DIF; drug-induced by vancomycin; treat with dapsone.

Vitiligo: depigmented macules with Wood lamp accentuation; autoimmune melanocyte destruction; associations with thyroid disease, pernicious anemia, Addison disease; treat with topical steroids, tacrolimus, NB-UVB.

Melasma: symmetrical hyperpigmentation on malar cheeks, forehead, upper lip; triggered by UV and pregnancy; treat with hydroquinone, tretinoin, azelaic acid, sun protection.

Post-inflammatory hyperpigmentation: follows inflammation, more common in darker skin types (Fitzpatrick IV-VI); treat with topical retinoids, hydroquinone, chemical peels.

Alopecia areata: well-demarcated non-scarring patches with exclamation-mark hairs; nail pitting; associated with autoimmune thyroid disease; treat with intralesional steroids, topical immunotherapy.

Androgenetic alopecia: frontal/temporal recession and vertex thinning in men; diffuse thinning in women; minoxidil and finasteride are mainstays.

Telogen effluvium: diffuse hair shedding 2-3 months after trigger (illness, childbirth, drugs); self-limited; treat underlying cause.

Nail psoriasis: pitting, oil spots, onycholysis, subungual hyperkeratosis; distinguish from onychomycosis with KOH/PAS.

Oral lichen planus: white reticular striae (Wickham), erosions; risk of squamous cell carcinoma in erosive forms; biopsy persistent lesions.

Mohs micrographic surgery: staged excision with frozen-section margin control; indicated for high-risk BCC/SCC, recurrent tumors, and tissue-sparing sites (face, digits, genitalia).

Excision margins: BCC low-risk 4 mm; SCC low-risk 4-6 mm; melanoma in situ 5 mm, invasive ≤1 mm 1 cm, 1-2 mm 1-2 cm, >2 mm 2 cm.

Laser selection: pulsed dye laser (585/595 nm) for vascular lesions; Q-switched lasers for pigment; ablative fractional CO2/Er:YAG for resurfacing; Nd:YAG for hair removal.

Cryotherapy: liquid nitrogen at -196°C; treat actinic keratosis, warts, seborrheic keratosis; freeze-thaw cycles 2-3; risk of hypopigmentation and scarring.

Sclerotherapy: sodium tetradecyl sulfate or polidocanol for telangiectasias and small varicose veins; compression after treatment.

Flap and graft principles: random pattern flaps need length-to-width ratio ≤3:1; full-thickness grafts for face, split-thickness for large defects.

Anesthesia: lidocaine with epinephrine (1:100,000) prolongs effect and reduces bleeding; maximum lidocaine dose 7 mg/kg with epinephrine, 4.5 mg/kg without.

Suture removal: face 5-7 days, scalp 7-10 days, trunk/extremities 10-14 days, joints 14 days.

Atopic dermatitis in infants: face, scalp, extensor surfaces; in children: flexural; management includes emollients, topical corticosteroids, calcineurin inhibitors.

Hemangioma of infancy: appears in first weeks, proliferates then involutes; treat with oral propranolol; indications include vision obstruction, airway compromise, ulceration.

Port-wine stain: present at birth, grows proportionally; Sturge-Weber syndrome if V1 distribution with CNS/eye involvement; treat with pulsed dye laser.

Epidermolysis bullosa: inherited blistering; EB simplex (keratin 5/14), junctional (laminin-332, BPAG2), dystrophic (type VII collagen); handle with minimal trauma.

Ichthyosis vulgaris: filaggrin mutation; fine white scale, sparing of flexures; associated with atopic dermatitis and keratosis pilaris.

Neurofibromatosis type 1: café-au-lait macules (≥6), axillary/inguinal freckling, neurofibromas, Lisch nodules, optic glioma; NF1 gene on chromosome 17.

Tuberous sclerosis: ash-leaf spots, facial angiofibromas, shagreen patch, periungual fibromas; TSC1/TSC2 mutations; screen for renal angiomyolipoma and cardiac rhabdomyoma.

Incontinentia pigmenti: X-linked dominant, lethal in males; stages vesicular, verrucous, hyperpigmented, hypopigmented; associated with dental and ocular anomalies.

Acanthosis nigricans: velvety hyperpigmentation of neck/axillae; associated with insulin resistance, obesity, and malignancy (gastric adenocarcinoma in sudden-onset adult).

Erythema nodosum: tender red nodules on shins; associated with streptococcal infection, sarcoidosis, IBD, TB, drugs (OCP, sulfa); biopsy shows septal panniculitis.

Pyoderma gangrenosum: painful ulcer with violaceous undermined border; associated with IBD, rheumatoid arthritis, hematologic malignancy; treat with systemic steroids, cyclosporine, biologics.

Sweet syndrome: tender erythematous plaques with fever and neutrophilia; associated with malignancy (AML), drugs; histology shows dense neutrophilic dermal infiltrate.

Necrobiosis lipoidica: yellow-brown atrophic plaques on shins; associated with diabetes mellitus; histology shows layered granulomatous inflammation with collagen degeneration.

Drug eruption patterns: morbilliform (most common), urticarial, fixed drug, DRESS (eosinophilia, organ involvement), Stevens-Johnson syndrome/TEN (mucosal involvement, epidermal detachment).

Paraneoplastic dermatoses: acanthosis nigricans (GI cancer), dermatomyositis (ovarian, lung), acquired ichthyosis (Hodgkin lymphoma), Bazex syndrome (upper airway/GI).

Calciphylaxis: painful necrotic ulcers in ESRD patients; medial calcification of small vessels; high mortality; treat with sodium thiosulfate, wound care.

Topical corticosteroid potency: class I superpotent (clobetasol propionate 0.05%) to class VII least potent (hydrocortisone 1%); apply sparingly, avoid face/flexures with superpotent agents.

Topical calcineurin inhibitors: tacrolimus and pimecrolimus; no skin atrophy; FDA boxed warning for malignancy (lymphoma) - use second-line for atopic dermatitis.

Methotrexate: folate antagonist; monitor CBC, LFTs, renal function; supplement folic acid; contraindicated in pregnancy and hepatic disease.

Cyclosporine: calcineurin inhibitor; monitor blood pressure, renal function, potassium; drug interactions via CYP3A4; useful for severe psoriasis and atopic dermatitis.

Biologics for psoriasis: TNF inhibitors (adalimumab, etanercept, infliximab), IL-17 inhibitors (secukinumab, ixekizumab), IL-23 inhibitors (ustekinumab, guselkumab, risankizumab); screen for TB and hepatitis before starting.

Isotretinoin: for severe nodulocystic acne; teratogenic - requires iPledge program, two forms of contraception; monitor LFTs, lipids, CBC; adverse effects include cheilitis, dry skin, photosensitivity.

Phototherapy: NB-UVB (311-313 nm) for psoriasis, vitiligo, atopic dermatitis; PUVA (psoralen + UVA) for psoriasis, CTCL; risks include erythema, photoaging, skin cancer.

Antihistamines: first-generation (diphenhydramine, hydroxyzine) cause sedation; second-generation (loratadine, cetirizine, fexofenadine) preferred for daytime; topical doxepin for pruritus.

Study designs: randomized controlled trial (strongest for therapy), cohort (incidence, prognosis), case-control (rare diseases), cross-sectional (prevalence), case series (hypothesis-generating).

Levels of evidence: systematic reviews/meta-analyses of RCTs at top; then RCTs, cohort studies, case-control, case series, expert opinion.

Sensitivity = true positives / (true positives + false negatives); specificity = true negatives / (true negatives + false positives); PPV depends on prevalence.

Number needed to treat (NNT) = 1 / absolute risk reduction; number needed to harm (NNH) = 1 / absolute risk increase.

Intention-to-treat analysis preserves randomization; per-protocol analysis can introduce bias; blinding reduces detection and performance bias.

Consent and confidentiality: informed consent requires capacity, disclosure, voluntariness; minors and cognitively impaired patients need surrogate consent; report adverse events.

Patient safety in dermatology: verify biopsy site and laterality, use checklist for Mohs and excisions, confirm drug allergies, monitor for drug interactions (e.g., methotrexate + trimethoprim).

Publication bias: positive studies more likely published; funnel plot asymmetry suggests bias; trial registration reduces selective reporting.