Arab Board Dermatology Clinical cheat sheet

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-filled), wheal (transient edema).

Secondary lesions: scale, crust, erosion (epidermal loss, heals without scar), ulcer (dermal loss, scars), fissure, lichenification, atrophy, excoriation.

ABCDE melanoma criteria: Asymmetry, Border irregularity, Color variegation, Diameter >6 mm, Evolution/change.

Distribution patterns localize disease: acral (syphilis, palmoplantar psoriasis), flexural (atopic dermatitis, tinea), extensor (psoriasis), photoexposed (lupus, porphyria, polymorphous light eruption).

Koebner phenomenon (isomorphic response) occurs in psoriasis, lichen planus, vitiligo, and molluscum; Nikolsky sign positivity suggests intraepidermal acantholysis (pemphigus) or toxic epidermal necrolysis.

Darier sign (urticarial wheal on rubbing) indicates mastocytosis; Auspitz sign (pinpoint bleeding on scale removal) indicates psoriasis.

Wood lamp: 365 nm UV; coral-red fluorescence in erythrasma (Corynebacterium), green in Microsporum, bright blue-white in vitiligo depigmentation.

Diagnostic tests by indication: KOH for hyphae/scabies, Tzanck smear for herpesvirus, patch testing for allergic contact dermatitis, direct immunofluorescence for autoimmune blistering disease.

Psoriasis: well-demarcated erythematous plaques with silvery scale on extensor surfaces; Auspitz sign, Koebner phenomenon; associated with psoriatic arthritis, metabolic syndrome, and cardiometabolic risk.

Psoriasis severity: BSA <3% = mild, 3-10% = moderate, >10% = severe; PASI quantifies erythema, induration, and scale by area.

Atopic dermatitis: Hanifin-Rajka criteria; flexural distribution in adults, face/extensor in infants; filaggrin (FLG) loss-of-function mutations impair barrier function.

Atopic dermatitis treatment ladder: emollients, topical corticosteroids or calcineurin inhibitors, phototherapy (NB-UVB), then systemic agents (dupilumab, JAK inhibitors, cyclosporine, methotrexate).

Lichen planus: pruritic, purple, polygonal, planar papules (6 Ps); Wickham striae on mucosa; histology shows band-like lymphocytic infiltrate at dermoepidermal junction with saw-tooth rete ridges.

Pityriasis rosea: herald patch followed by collarette-scaled oval macules along Langer lines (Christmas tree pattern); associated with HHV-6/HHV-7 reactivation.

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

Eczema herpeticum: painful monomorphic vesicles/punched-out erosions in atopic skin; dermatologic emergency requiring systemic acyclovir.

Acne pathogenesis: follicular hyperkeratinization, increased sebum (androgenic), Cutibacterium acnes colonization, and inflammation; four-factor model.

Acne lesion types: comedones (open/closed), inflammatory papules/pustules, nodules/cysts; scarring includes icepick, boxcar, and rolling types.

Acne treatment: topical retinoid is first-line for comedonal and mild inflammatory acne; benzoyl peroxide plus topical antibiotic reduces resistance; oral isotretinoin for severe nodulocystic or refractory disease.

Isotretinoin monitoring: baseline and periodic lipids, liver enzymes, and pregnancy testing (iPLEDGE-type programs); teratogenicity requires two contraception methods.

Rosacea subtypes: erythematotelangiectatic, papulopustular, phymatous (rhinophyma), and ocular; triggers include heat, sun, alcohol, and spicy food.

Rosacea treatment: topical metronidazole, azelaic acid, or ivermectin for papulopustular; brimonidine or oxymetazoline for flushing; oral doxycycline (subantimicrobial) for moderate-severe.

Hidradenitis suppurativa: painful nodules, sinus tracts, and scarring in intertriginous areas (axillae, groin); Hurley staging I-III guides therapy; TNF inhibitors (adalimumab) for moderate-severe.

Folliculitis decalvans: neutrophilic scarring alopecia of the scalp with tufted hairs; treat with rifampin plus clindamycin or oral doxycycline.

Tinea corporis: annular, scaly plaque with central clearing and active raised border; KOH shows septate branching hyphae; treat with topical azoles or oral terbinafine for extensive disease.

Tinea capitis: scaly alopecia with broken hairs and possible kerion; requires oral griseofulvin or terbinafine because topical agents do not penetrate the hair follicle.

Onychomycosis: distal and lateral subungual type most common; KOH or PAS staining confirms; oral terbinafine for dermatophyte infection after confirming liver function.

Cellulitis: acute spreading erythema, warmth, and tenderness; Streptococcus pyogenes and Staphylococcus aureus are common; erysipelas has a sharply demarcated raised border.

Scabies: pruritic burrows in web spaces, wrists, and genitalia; KOH mineral oil prep or dermoscopy showing the mite and delta-wing sign; treat with permethrin 5% or oral ivermectin.

Cutaneous larva migrans: serpiginous erythematous tract from animal hookworm; treat with albendazole or ivermectin.

Herpes zoster: dermatomal vesicular eruption; antiviral therapy within 72 hours of onset reduces duration; ophthalmic involvement requires urgent ophthalmology referral.

Molluscum contagiosum: umbilicated pearly papules caused by a poxvirus; resolves spontaneously in immunocompetent hosts; cryotherapy or cantharidin for persistent lesions.

Lupus erythematosus: malar rash spares nasolabial folds; discoid lesions show follicular plugging and scarring; subacute cutaneous lupus is photosensitive and annular/papulosquamous.

Lupus serology: ANA sensitive but nonspecific; anti-dsDNA and anti-Sm specific for SLE; anti-Ro/SSA associated with subacute cutaneous lupus and neonatal lupus.

Systemic sclerosis: CREST syndrome (calcinosis, Raynaud, esophageal dysmotility, sclerodactyly, telangiectasia); anti-centromere in limited, anti-Scl-70 (topoisomerase I) in diffuse disease.

Dermatomyositis: heliotrope rash, Gottron papules, shawl sign, and nail-fold capillary changes; anti-Mi-2, anti-MDA5 (with rapidly progressive interstitial lung disease), and anti-TIF1-gamma (malignancy-associated).

Morphea: localized scleroderma with indurated plaques and lilac border; no Raynaud or systemic organ involvement.

Sjogren syndrome: dry eyes and mouth with anti-Ro/SSA and anti-La/SSB; cutaneous findings include annular erythema and vasculitis.

Mixed connective tissue disease: high-titer anti-U1-RNP; features overlap SLE, systemic sclerosis, and polymyositis.

Raynaud phenomenon: triphasic color change (white-blue-red); primary is symmetric and benign; secondary warrants evaluation for connective tissue disease.

Pemphigus vulgaris: flaccid bullae and oral erosions; suprabasal acantholysis with tombstoning on histology; direct immunofluorescence shows intercellular IgG and C3 ('chicken wire').

Bullous pemphigoid: tense pruritic bullae in elderly; subepidermal split with eosinophils; DIF shows linear IgG and C3 along basement membrane zone; anti-BP180/BP230 antibodies.

Dermatitis herpetiformis: intensely pruritic grouped vesicles on extensor surfaces; granular IgA at dermal papillae; associated with celiac disease and responds to dapsone.

Epidermolysis bullosa acquisita: trauma-induced blisters in mechanized skin; linear IgG on salt-split skin localizes to the dermal floor; associated with inflammatory bowel disease.

Stevens-Johnson syndrome and toxic epidermal necrolysis: mucosal erosions with epidermal detachment; SJS <10% BSA, TEN >30%, overlap 10-30%; SCORTEN predicts mortality.

Drug reaction with eosinophilia and systemic symptoms (DRESS): latency 2-8 weeks, facial edema, eosinophilia, hepatitis, and reactivation of HHV-6; common culprits are anticonvulsants, allopurinol, and sulfonamides.

TEN management: immediate withdrawal of the culprit drug, supportive care in a burn unit, ophthalmologic and mucosal care; systemic corticosteroids and IVIG are used but evidence is limited.

Linear IgA bullous dermatosis: subepidermal blisters with linear IgA at the basement membrane; drug-induced cases are linked to vancomycin.

Vitiligo: acquired depigmented macules with sharp borders; Wood lamp enhances; associated with autoimmune thyroid disease and other autoimmune conditions; segmental type is dermatomal and stable.

Melasma: symmetric hyperpigmentation on sun-exposed face; triggered by UV, hormones, and pregnancy; first-line treatment is photoprotection plus topical hydroquinone, tretinoin, and corticosteroid.

Post-inflammatory hyperpigmentation: darkening after inflammation, more common in darker phototypes; treatment includes photoprotection and topical retinoids or hydroquinone.

Polymorphous light eruption: pruritic papules and plaques on sun-exposed skin hours to days after UV exposure; provocation testing with UVA or UVB reproduces lesions.

Porphyria cutanea tarda: fragile skin, blisters, and hypertrichosis on sun-exposed areas; associated with hepatitis C, alcohol, and hemochromatosis; uroporphyrin elevated in urine.

Photoprotection: broad-spectrum SPF 30 or higher; organic filters absorb UV, inorganic (zinc oxide, titanium dioxide) scatter; tinted formulations reduce visible light-induced pigmentation in melasma.

Keloids: scar tissue extending beyond the original wound; more common in darker skin; treated with intralesional corticosteroids, silicone gel, or excision plus adjuvant therapy.

Erythema dyschromicum perstans (ashy dermatosis): gray-blue hyperpigmented macules in skin of color; biopsy shows vacuolar interface change; treat with photoprotection and topical agents.

Basal cell carcinoma: pearly papule with telangiectasia, rolled border, and central ulceration; dermoscopy shows arborizing vessels, blue-gray ovoid nests, and maple-leaf areas.

Squamous cell carcinoma: hyperkeratotic nodule or ulcer on sun-exposed skin; dermoscopy shows glomerular vessels, keratin, and white structureless areas; risk factors include UV and immunosuppression.

Melanoma dermoscopy: atypical network, irregular dots/globules, blue-white veil, regression structures, and irregular streaks; use the 7-point or 3-point checklist.

Benign nevus dermoscopy: symmetric network with regular dots and globules; dermatofibroma shows a central white patch and pigment network (dimple sign on lateral pressure).

Seborrheic keratosis: 'stuck-on' verrucous plaque; dermoscopy shows milia-like cysts, comedo-like openings, and fissures/ridges (cerebriform pattern).

Actinic keratosis: rough, scaly macule on sun-damaged skin; dermoscopy shows a strawberry pattern with red pseudonetwork; risk of progression to SCC.

Mycosis fungoides: patches, plaques, and tumors with epidermotropism and Pautrier microabscesses; CD4+ T-cell clone; treat with topical corticosteroids, phototherapy, or systemic agents.

Dermatofibrosarcoma protuberans: indurated plaque with tentacle-like infiltration; histology shows a storiform pattern with CD34 positivity; treated by wide local excision or Mohs micrographic surgery.

Alopecia areata: well-demarcated smooth patches without scarring; exclamation-mark hairs and yellow dots on dermoscopy; associated with autoimmune thyroid disease and vitiligo.

Androgenetic alopecia: patterned hair thinning; frontal hairline recession and vertex loss in men; diffuse central part widening in women; treat with topical minoxidil and oral finasteride (men).

Telogen effluvium: diffuse shedding 2-3 months after a trigger (illness, childbirth, medication); trichogram shows increased telogen hairs; usually self-limited.

Scarring alopecias: lichen planopilaris (perifollicular erythema, loss of follicular ostia) and frontal fibrosing alopecia (receding frontal hairline, eyebrow loss); biopsy confirms lymphocytic folliculitis.

Traction alopecia: caused by tight hairstyles; early changes are reversible, but prolonged traction causes permanent scarring; common in skin of color.

Onychomycosis: yellow-brown discoloration, subungual hyperkeratosis, and onycholysis; confirm with KOH or culture before systemic therapy.

Psoriatic nail disease: pitting, oil-drop spots, onycholysis, and subungual hyperkeratosis; associated with psoriatic arthritis.

Longitudinal melanonychia: brown-black nail streak; Hutchinson sign (pigment on the proximal nail fold) suggests subungual melanoma and requires biopsy.

Atopic dermatitis in infants: face, scalp, and extensor surfaces; in older children, flexural involvement predominates; management emphasizes emollients and low-potency topical corticosteroids.

Hemangioma of infancy: appears in the first weeks of life, proliferates for months, then involutes; complications include ulceration and visual obstruction; treat with oral propranolol.

Port-wine stain: capillary malformation present at birth; associated with Sturge-Weber syndrome when in the V1 trigeminal distribution; treat with pulsed dye laser.

Neurofibromatosis type 1: cafe-au-lait macules (>=6), axillary/inguinal freckling, neurofibromas, Lisch nodules, and optic glioma; caused by NF1 mutation.

Tuberous sclerosis: ash-leaf spots, facial angiofibromas, Shagreen patch, and subungual fibromas; associated with seizures and renal angiomyolipomas.

Epidermolysis bullosa: inherited blistering from trauma; subtypes simplex (intraepidermal), junctional (lamina lucida), and dystrophic (sublamina densa, COL7A1 mutation).

Ichthyosis vulgaris: fine white scale with flexural sparing; caused by filaggrin mutations; associated with atopic dermatitis and keratosis pilaris.

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

Mohs micrographic surgery: staged excision with intraoperative margin assessment; indicated for basal cell carcinoma and squamous cell carcinoma in high-risk locations, recurrent tumors, and large tumors.

Excision margins: basal cell carcinoma 3-4 mm for low-risk lesions; squamous cell carcinoma 4-6 mm; melanoma margins depend on Breslow thickness (0.5-2 cm).

Pulsed dye laser (585-595 nm): targets oxyhemoglobin; used for port-wine stains, hemangiomas, and telangiectasias; complications include purpura and pigmentary alteration.

Q-switched lasers (532, 694, 1064 nm): target melanin for pigmented lesions and tattoos; nanosecond pulses; risk of hypopigmentation and scarring.

Ablative fractional lasers (CO2, erbium:YAG): resurface skin for scars and photoaging; require wound care and carry risk of infection and dyspigmentation, especially in darker skin.

Botulinum toxin: chemodenervation for dynamic rhytides and hyperhidrosis; effect lasts 3-4 months; contraindicated in neuromuscular disorders.

Dermal fillers: hyaluronic acid fillers are reversible with hyaluronidase; complications include nodules, vascular occlusion, and granulomas.

Sclerotherapy: injection of sclerosant (polidocanol, sodium tetradecyl sulfate) for varicose and spider veins; compression stockings after treatment reduce recurrence.

Erythroderma: generalized erythema and scaling involving >90% BSA; causes include psoriasis, atopic dermatitis, drug reaction, and cutaneous T-cell lymphoma; risk of hypothermia, dehydration, and high-output heart failure.

Stevens-Johnson syndrome and toxic epidermal necrolysis: mucosal involvement and epidermal detachment; SCORTEN uses age, malignancy, tachycardia, BSA, urea, bicarbonate, and glucose to predict mortality.

Necrotizing fasciitis: rapidly spreading erythema, bullae, and crepitus with severe pain out of proportion; surgical debridement is urgent; group A Streptococcus and polymicrobial flora are common.

Toxic shock syndrome: fever, hypotension, diffuse macular erythroderma, and multi-organ involvement; associated with Staphylococcus aureus toxin and tampon use.

Meningococcemia: petechial and purpuric rash with fever and hemodynamic instability; requires immediate antibiotics and supportive care.

Calciphylaxis: painful purpuric plaques and ulcers in end-stage renal disease with hyperparathyroidism; biopsy shows medial calcification of small vessels; treat with sodium thiosulfate and wound care.

Paraneoplastic dermatoses: acanthosis nigricans (gastric cancer), dermatomyositis (ovarian and lung cancer), and acquired ichthyosis (lymphoma) indicate underlying malignancy.

Sweet syndrome: tender erythematous plaques with fever and neutrophilia; associated with malignancy, infection, and drugs; responds to systemic corticosteroids.

Lesion morphology and distribution guide the differential diagnosis; a full skin examination includes scalp, nails, mucosa, palms, and soles.

History elements: onset, evolution, pruritus or pain, triggers, medications, occupational exposures, family history, and sexual history.

Dermoscopy improves diagnostic accuracy for pigmented lesions; use pattern analysis and the 7-point checklist for melanoma.

Patch testing is indicated for suspected allergic contact dermatitis; reading at 48 and 72-96 hours improves detection.

Punch biopsy (3-4 mm) is preferred for inflammatory dermatoses; excisional biopsy is preferred for suspected melanoma.

Direct immunofluorescence is essential for autoimmune blistering disease; perilesional skin is the preferred biopsy site.

Wood lamp examination helps detect pigmentary disorders, fungal infections, and porphyria.

Clinical photographs and serial measurements document disease progression and treatment response.

Psoriasis: well-demarcated erythematous plaques with silvery scale on extensor surfaces; Auspitz sign and Koebner phenomenon are characteristic.

Psoriasis severity: BSA <3% mild, 3-10% moderate, >10% severe; PASI quantifies erythema, induration, and scale.

Atopic dermatitis: Hanifin-Rajka criteria; flexural distribution in adults, face and extensor surfaces in infants; filaggrin mutations impair barrier function.

Atopic dermatitis treatment ladder: emollients, topical corticosteroids or calcineurin inhibitors, phototherapy, then systemic agents (dupilumab, JAK inhibitors).

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

Pityriasis rosea: herald patch followed by collarette-scaled oval macules along Langer lines; associated with HHV-6/HHV-7 reactivation.

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

Eczema herpeticum: painful monomorphic vesicles and punched-out erosions in atopic skin; requires systemic acyclovir.

Acne pathogenesis: follicular hyperkeratinization, increased sebum, Cutibacterium acnes colonization, and inflammation.

Acne lesion types: comedones (open/closed), inflammatory papules and pustules, nodules and cysts; scarring includes icepick, boxcar, and rolling types.

Acne treatment: topical retinoid is first-line for comedonal and mild inflammatory acne; benzoyl peroxide plus topical antibiotic reduces resistance; oral isotretinoin for severe nodulocystic disease.

Isotretinoin monitoring: baseline and periodic lipids, liver enzymes, and pregnancy testing; teratogenicity requires two contraception methods.

Rosacea subtypes: erythematotelangiectatic, papulopustular, phymatous, and ocular; triggers include heat, sun, alcohol, and spicy food.

Rosacea treatment: topical metronidazole, azelaic acid, or ivermectin for papulopustular; brimonidine or oxymetazoline for flushing; oral doxycycline for moderate-severe disease.

Hidradenitis suppurativa: painful nodules, sinus tracts, and scarring in intertriginous areas; Hurley staging guides therapy; adalimumab for moderate-severe disease.

Folliculitis decalvans: neutrophilic scarring alopecia with tufted hairs; treat with rifampin plus clindamycin or oral doxycycline.

Tinea corporis: annular scaly plaque with central clearing; KOH shows septate branching hyphae; topical azoles or oral terbinafine for extensive disease.

Tinea capitis: scaly alopecia with broken hairs and possible kerion; requires oral griseofulvin or terbinafine.

Onychomycosis: distal and lateral subungual type most common; KOH or PAS confirms; oral terbinafine for dermatophyte infection after liver function testing.

Cellulitis: acute spreading erythema, warmth, and tenderness; Streptococcus pyogenes and Staphylococcus aureus are common; erysipelas has a sharply demarcated raised border.

Scabies: pruritic burrows in web spaces, wrists, and genitalia; KOH mineral oil prep or dermoscopy shows the mite; treat with permethrin 5% or oral ivermectin.

Cutaneous larva migrans: serpiginous erythematous tract from animal hookworm; treat with albendazole or ivermectin.

Herpes zoster: dermatomal vesicular eruption; antiviral therapy within 72 hours reduces duration; ophthalmic involvement requires urgent referral.

Molluscum contagiosum: umbilicated pearly papules caused by a poxvirus; resolves spontaneously; cryotherapy or cantharidin for persistent lesions.

Lupus erythematosus: malar rash spares nasolabial folds; discoid lesions show follicular plugging and scarring; subacute cutaneous lupus is photosensitive.

Lupus serology: ANA is sensitive but nonspecific; anti-dsDNA and anti-Sm are specific for SLE; anti-Ro/SSA is associated with subacute cutaneous lupus.

Systemic sclerosis: CREST syndrome; anti-centromere in limited disease, anti-Scl-70 in diffuse disease.

Dermatomyositis: heliotrope rash, Gottron papules, shawl sign, and nail-fold capillary changes; anti-MDA5 is associated with interstitial lung disease.

Morphea: localized scleroderma with indurated plaques and a lilac border; no Raynaud or systemic organ involvement.

Sjogren syndrome: dry eyes and mouth with anti-Ro/SSA and anti-La/SSB; cutaneous findings include annular erythema and vasculitis.

Mixed connective tissue disease: high-titer anti-U1-RNP; features overlap SLE, systemic sclerosis, and polymyositis.

Raynaud phenomenon: triphasic color change; primary is symmetric and benign; secondary warrants evaluation for connective tissue disease.

Pemphigus vulgaris: flaccid bullae and oral erosions; suprabasal acantholysis with tombstoning; DIF shows intercellular IgG and C3.

Bullous pemphigoid: tense pruritic bullae in elderly; subepidermal split with eosinophils; DIF shows linear IgG and C3 along the basement membrane zone.

Dermatitis herpetiformis: intensely pruritic grouped vesicles on extensor surfaces; granular IgA at dermal papillae; associated with celiac disease.

Epidermolysis bullosa acquisita: trauma-induced blisters; linear IgG on salt-split skin localizes to the dermal floor; associated with inflammatory bowel disease.

SJS/TEN: mucosal erosions with epidermal detachment; SJS <10% BSA, TEN >30%; SCORTEN predicts mortality.

DRESS: latency 2-8 weeks, facial edema, eosinophilia, hepatitis, and HHV-6 reactivation; common culprits are anticonvulsants, allopurinol, and sulfonamides.

TEN management: immediate withdrawal of the culprit drug, supportive care in a burn unit, ophthalmologic and mucosal care.

Linear IgA bullous dermatosis: subepidermal blisters with linear IgA at the basement membrane; drug-induced cases are linked to vancomycin.

Vitiligo: acquired depigmented macules with sharp borders; Wood lamp enhances; associated with autoimmune thyroid disease; segmental type is dermatomal and stable.

Melasma: symmetric hyperpigmentation on sun-exposed face; triggered by UV, hormones, and pregnancy; first-line treatment is photoprotection plus topical hydroquinone, tretinoin, and corticosteroid.

Post-inflammatory hyperpigmentation: darkening after inflammation, more common in darker phototypes; treatment includes photoprotection and topical retinoids or hydroquinone.

Polymorphous light eruption: pruritic papules and plaques on sun-exposed skin hours to days after UV exposure; provocation testing with UVA or UVB reproduces lesions.

Porphyria cutanea tarda: fragile skin, blisters, and hypertrichosis on sun-exposed areas; associated with hepatitis C, alcohol, and hemochromatosis.

Photoprotection: broad-spectrum SPF 30 or higher; organic filters absorb UV, inorganic filters scatter; tinted formulations reduce visible light-induced pigmentation.

Keloids: scar tissue extending beyond the original wound; more common in darker skin; treated with intralesional corticosteroids, silicone gel, or excision plus adjuvant therapy.

Erythema dyschromicum perstans: gray-blue hyperpigmented macules in skin of color; biopsy shows vacuolar interface change.

Basal cell carcinoma: pearly papule with telangiectasia, rolled border, and central ulceration; dermoscopy shows arborizing vessels and blue-gray ovoid nests.

Squamous cell carcinoma: hyperkeratotic nodule or ulcer on sun-exposed skin; dermoscopy shows glomerular vessels and keratin; risk factors include UV and immunosuppression.

Melanoma dermoscopy: atypical network, irregular dots/globules, blue-white veil, regression structures, and irregular streaks.

Benign nevus dermoscopy: symmetric network with regular dots and globules; dermatofibroma shows a central white patch and pigment network.

Seborrheic keratosis: stuck-on verrucous plaque; dermoscopy shows milia-like cysts, comedo-like openings, and fissures.

Actinic keratosis: rough scaly macule on sun-damaged skin; dermoscopy shows a strawberry pattern with red pseudonetwork.

Mycosis fungoides: patches, plaques, and tumors with epidermotropism and Pautrier microabscesses; CD4+ T-cell clone.

Dermatofibrosarcoma protuberans: indurated plaque with tentacle-like infiltration; storiform pattern with CD34 positivity; treated by wide local excision or Mohs surgery.

Alopecia areata: well-demarcated smooth patches without scarring; exclamation-mark hairs and yellow dots on dermoscopy; associated with autoimmune thyroid disease.

Androgenetic alopecia: patterned hair thinning; frontal hairline recession in men, diffuse central part widening in women; treat with topical minoxidil and oral finasteride.

Telogen effluvium: diffuse shedding 2-3 months after a trigger; trichogram shows increased telogen hairs; usually self-limited.

Scarring alopecias: lichen planopilaris and frontal fibrosing alopecia; biopsy confirms lymphocytic folliculitis.

Traction alopecia: caused by tight hairstyles; early changes are reversible, but prolonged traction causes permanent scarring.

Onychomycosis: yellow-brown discoloration, subungual hyperkeratosis, and onycholysis; confirm with KOH or culture before systemic therapy.

Psoriatic nail disease: pitting, oil-drop spots, onycholysis, and subungual hyperkeratosis; associated with psoriatic arthritis.

Longitudinal melanonychia: brown-black nail streak; Hutchinson sign suggests subungual melanoma and requires biopsy.

Atopic dermatitis in infants: face, scalp, and extensor surfaces; in older children, flexural involvement predominates.

Hemangioma of infancy: appears in the first weeks of life, proliferates for months, then involutes; treat with oral propranolol for complications.

Port-wine stain: capillary malformation present at birth; associated with Sturge-Weber syndrome in the V1 distribution; treat with pulsed dye laser.

Neurofibromatosis type 1: cafe-au-lait macules, axillary freckling, neurofibromas, Lisch nodules, and optic glioma; caused by NF1 mutation.

Tuberous sclerosis: ash-leaf spots, facial angiofibromas, Shagreen patch, and subungual fibromas; associated with seizures and renal angiomyolipomas.

Epidermolysis bullosa: inherited blistering from trauma; subtypes simplex, junctional, and dystrophic (COL7A1 mutation).

Ichthyosis vulgaris: fine white scale with flexural sparing; caused by filaggrin mutations; associated with atopic dermatitis.

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

Mohs micrographic surgery: staged excision with intraoperative margin assessment; indicated for high-risk basal cell carcinoma and squamous cell carcinoma.

Excision margins: basal cell carcinoma 3-4 mm for low-risk lesions; squamous cell carcinoma 4-6 mm; melanoma margins depend on Breslow thickness.

Pulsed dye laser (585-595 nm): targets oxyhemoglobin; used for port-wine stains, hemangiomas, and telangiectasias.

Q-switched lasers (532, 694, 1064 nm): target melanin for pigmented lesions and tattoos; risk of hypopigmentation and scarring.

Ablative fractional lasers (CO2, erbium:YAG): resurface skin for scars and photoaging; require wound care and carry risk of dyspigmentation.

Botulinum toxin: chemodenervation for dynamic rhytides and hyperhidrosis; effect lasts 3-4 months.

Dermal fillers: hyaluronic acid fillers are reversible with hyaluronidase; complications include nodules and vascular occlusion.

Sclerotherapy: injection of sclerosant for varicose and spider veins; compression stockings after treatment reduce recurrence.

Erythroderma: generalized erythema and scaling involving >90% BSA; causes include psoriasis, atopic dermatitis, drug reaction, and cutaneous T-cell lymphoma.

SJS/TEN: mucosal involvement and epidermal detachment; SCORTEN uses age, malignancy, tachycardia, BSA, urea, bicarbonate, and glucose to predict mortality.

Necrotizing fasciitis: rapidly spreading erythema, bullae, and crepitus with severe pain out of proportion; surgical debridement is urgent.

Toxic shock syndrome: fever, hypotension, diffuse macular erythroderma, and multi-organ involvement; associated with Staphylococcus aureus toxin.

Meningococcemia: petechial and purpuric rash with fever and hemodynamic instability; requires immediate antibiotics.

Calciphylaxis: painful purpuric plaques and ulcers in end-stage renal disease with hyperparathyroidism; biopsy shows medial calcification of small vessels.

Paraneoplastic dermatoses: acanthosis nigricans (gastric cancer), dermatomyositis (ovarian and lung cancer), and acquired ichthyosis (lymphoma).

Sweet syndrome: tender erythematous plaques with fever and neutrophilia; associated with malignancy, infection, and drugs; responds to systemic corticosteroids.