Arab Board Dermatology Part 1 cheat sheet

Epidermis turns over in ~28 days; keratinocytes migrate from basal layer through spinous, granular, and cornified layers.

Skin pH averages 4.5-5.5 (acid mantle); sweat and sebum contribute to antimicrobial barrier.

Langerhans cells are CD1a+, Birbeck granule-bearing antigen-presenting cells of the epidermis.

Type IV collagen anchors basal keratinocytes via hemidesmosomes to the lamina densa of the basement membrane.

Dermal papillae contain capillary loops; the superficial vascular plexus lies at the papillary-reticular junction.

Melanocytes derive from neural crest; each melanocyte supplies melanin to ~36 keratinocytes via the epidermal melanin unit.

Eccrine glands are cholinergic (sympathetic) and distributed over most of the body; apocrine glands are adrenergic and confined to axillae, anogenital, and areolar skin.

Normal skin flora includes Staphylococcus epidermidis, Corynebacterium, and Malassezia; disruption of flora predisposes to overgrowth.

Direct immunofluorescence in pemphigus vulgaris shows intercellular IgG in a net-like epidermal pattern; bullous pemphigoid shows linear IgG/C3 at the basement membrane.

Lupus band test: granular IgG/C3 at basement membrane zone; positive in lesional skin of SLE and in sun-exposed nonlesional skin.

Dermoscopy: pigment network, blue-white veil, irregular dots/globules, and regression are melanoma criteria; comma vessels favor dermal nevi.

Patch testing reads at 48-72 hours and again at day 7; positive reactions graded + (erythema, infiltration) to +++ (vesicles/bullae).

KOH microscopy: fungal hyphae appear as septate branching structures; scabies shows mites, eggs, or scybala.

Tzanck smear demonstrates multinucleated giant cells in herpesvirus infections and acantholytic cells in pemphigus.

Periodic acid-Schiff (PAS) stain highlights fungi and basement membrane; Fontana-Masson stains melanin; Congo red stains amyloid.

Serum tryptase, anti-BP180/BP230, and desmoglein ELISA are used to confirm mastocytosis and autoimmune blistering diseases.

Psoriasis: well-demarcated erythematous plaques with silvery scale; Auspitz sign (pinpoint bleeding) and Koebner phenomenon; histology shows parakeratosis, Munro microabscesses, and regular acanthosis.

Psoriasis severity: BSA <3% mild, 3-10% moderate, >10% severe; PASI and DLQI guide systemic therapy.

Atopic dermatitis: flexural distribution in adults; filaggrin mutations impair barrier; treat with emollients, topical corticosteroids, and calcineurin inhibitors.

Lichen planus: pruritic, purple, polygonal, planar papules with Wickham striae; histology shows band-like lymphocytic infiltrate at the dermoepidermal junction.

Acne vulgaris: comedones (open/closed), papules, pustules, nodules; Cutibacterium acnes colonization and follicular hyperkeratosis are key.

Rosacea: centrofacial erythema, telangiectasias, papules/pustules; triggers include heat, sun, alcohol, and spicy food; treat with metronidazole, ivermectin, or doxycycline.

Seborrheic dermatitis: greasy scale on scalp, eyebrows, nasolabial folds; associated with Malassezia; responds to ketoconazole or mild topical corticosteroids.

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

Impetigo: honey-colored crusts from Staphylococcus aureus or Streptococcus pyogenes; nonbullous form most common in children.

Erysipelas involves upper dermis (sharply demarcated, raised); cellulitis involves deep dermis/subcutis (ill-defined borders).

Herpes simplex: grouped vesicles on erythematous base; Tzanck smear shows multinucleated giant cells; treat with acyclovir, valacyclovir, or famciclovir.

Herpes zoster: dermatomal vesicular eruption; risk of postherpetic neuralgia increases with age; vaccinate adults ≥50 years.

Dermatophytosis: annular scaly plaques with central clearing; KOH positive; treat tinea capitis with oral griseofulvin or terbinafine (topical insufficient).

Scabies: pruritic burrows in web spaces, wrists, and genitalia; treat patient and close contacts with permethrin 5% or oral ivermectin.

Syphilis: primary chancre (painless, indurated); secondary rash involves palms and soles; treat with benzathine penicillin G.

Leprosy (Hansen disease): hypopigmented anesthetic patches; Mycobacterium leprae stains with Fite-Faraco; multidrug therapy with rifampicin, dapsone, and clofazimine.

Pemphigus vulgaris: IgG against desmoglein 3 (and 1); flaccid bullae, mucosal involvement, positive Nikolsky sign.

Bullous pemphigoid: IgG against BP180/BP230; tense subepidermal bullae in elderly; linear IgG/C3 on DIF.

Dermatitis herpetiformis: granular IgA in dermal papillae; associated with celiac disease; treat with dapsone and gluten-free diet.

SLE: malar rash, photosensitivity, discoid lesions; ANA positive in >95%; anti-dsDNA and anti-Sm are specific.

Dermatomyositis: heliotrope rash, Gottron papules, periungual telangiectasias; anti-Mi-2, anti-MDA5, anti-TIF1-γ antibodies; screen for malignancy.

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

Leukocytoclastic vasculitis: palpable purpura; histology shows fibrinoid necrosis of vessel walls with neutrophil infiltrate; direct immunofluorescence shows IgA in Henoch-Schönlein purpura.

Morphea: localized scleroderma with indurated plaques; no Raynaud or systemic involvement.

Vitiligo: depigmented macules with absent melanocytes; associated with thyroid disease, pernicious anemia, and Addison disease.

Melasma: symmetric hyperpigmentation on sun-exposed face; treat with photoprotection, hydroquinone, tretinoin, and azelaic acid.

Alopecia areata: well-circumscribed non-scarring patches; exclamation-mark hairs; associated with autoimmune disease.

Androgenetic alopecia: patterned hair loss from dihydrotestosterone effect; treat with minoxidil and finasteride.

Telogen effluvium: diffuse shedding 2-3 months after trigger; self-limited; pull test positive.

Onychomycosis: distal subungual hyperkeratosis and onycholysis; confirm with KOH or culture before systemic therapy.

Psoriatic nails: pitting, oil-drop spots, onycholysis; associated with psoriatic arthritis.

Hidradenitis suppurativa: recurrent nodules, abscesses, and sinus tracts in intertriginous areas; treat with antibiotics, biologics (adalimumab), or surgery.

Atopic dermatitis is the most common pediatric dermatosis; starts in infancy with facial and extensor involvement, later flexural.

Epidermolysis bullosa: mutations in keratin, laminin-332, or collagen VII; subtypes differ in level of cleavage (intraepidermal, junctional, subepidermal).

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

Tuberous sclerosis: hypopigmented ash-leaf macules, facial angiofibromas, shagreen patch; TSC1/TSC2 mutations.

Incontinentia pigmenti: X-linked dominant, lethal in males; vesicular, verrucous, hyperpigmented, then hypopigmented stages.

Sturge-Weber syndrome: port-wine stain in trigeminal distribution with leptomeningeal angioma and seizures.

Kawasaki disease: fever >5 days, conjunctivitis, mucositis, rash, extremity changes, cervical lymphadenopathy; risk of coronary aneurysms.

Diaper dermatitis: irritant most common; Candida causes satellite pustules; treat with barrier cream or topical antifungal.

Basal cell carcinoma: pearly papule with telangiectasias, rolled border; most common skin cancer; rarely metastasizes.

Squamous cell carcinoma: hyperkeratotic nodule or ulcer; risk factors include UV, immunosuppression, and chronic wounds.

Melanoma ABCDE: Asymmetry, Border irregularity, Color variation, Diameter >6 mm, Evolving lesion.

Breslow thickness is the strongest prognostic factor for melanoma; sentinel lymph node biopsy considered for thickness >1 mm or ulceration.

Actinic keratosis: precancerous erythematous scaly macule on sun-exposed skin; treat with cryotherapy, 5-fluorouracil, or imiquimod.

Mycosis fungoides: cutaneous T-cell lymphoma with patches, plaques, and tumors; histology shows Pautrier microabscesses and CD4+ T cells.

Dermatofibrosarcoma protuberans: locally aggressive spindle-cell tumor; COL1A1-PDGFB fusion; treat with wide excision or imatinib.

Seborrheic keratosis: stuck-on waxy plaque; sign of Leser-Trélat when eruptive and associated with malignancy.

Mohs micrographic surgery offers highest cure rates for basal and squamous cell carcinoma, especially in high-risk or cosmetically sensitive sites.

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

Pulsed dye laser (585-595 nm) targets oxyhemoglobin for vascular lesions such as port-wine stains.

Q-switched lasers (532, 694, 755, 1064 nm) target pigment for tattoos and melasma.

Fractional CO2 and erbium:YAG lasers resurface skin; complications include scarring, dyspigmentation, and infection.

Botulinum toxin type A blocks acetylcholine release at neuromuscular junctions; effect lasts 3-4 months.

Hyaluronic acid fillers are reversible with hyaluronidase; nodules and vascular occlusion are key complications.

Sclerotherapy for varicose and telangiectatic veins uses polidocanol or sodium tetradecyl sulfate.

Allergic contact dermatitis is type IV hypersensitivity; irritant contact dermatitis is direct cytotoxic injury without prior sensitization.

Common allergens: nickel, cobalt, fragrance mix, balsam of Peru, rubber accelerators, paraphenylenediamine, and preservatives.

Nickel allergy: positive patch test to nickel sulfate; associated with ear piercing and metal jewelry.

Occupational dermatitis: evaluate work exposure, patch testing, and workplace modification; common in hairdressers, healthcare workers, and construction workers.

Photodermatoses: polymorphous light eruption, actinic prurigo, solar urticaria, and chronic actinic dermatitis.

Porphyria cutanea tarda: blisters on sun-exposed skin, urine fluoresces coral-red; associated with hepatitis C, alcohol, and hemochromatosis.

Photoprotection: broad-spectrum SPF ≥30, reapply every 2 hours; physical blockers include zinc oxide and titanium dioxide.

Drug-induced photosensitivity: thiazides, tetracyclines, fluoroquinolones, and amiodarone are common culprits.

Topical corticosteroid potency classes: class I (superpotent, e.g., clobetasol) to class VII (least potent, e.g., hydrocortisone 1%).

Stevens-Johnson syndrome/toxic epidermal necrolysis: mucosal erosions, epidermal detachment; SCORTEN predicts mortality; withdraw culprit drug.

DRESS syndrome: fever, eosinophilia, rash, and internal organ involvement 2-8 weeks after drug initiation.

Methotrexate: folate antagonist; monitor CBC, liver enzymes, and renal function; supplement folic acid; teratogenic.

Isotretinoin: teratogenic; requires pregnancy testing and contraception; monitor lipids and liver enzymes.

Cyclosporine: calcineurin inhibitor; monitor blood pressure, renal function, and drug levels; risk of nephrotoxicity.

Biologics: anti-TNF agents (adalimumab, infliximab) increase risk of infection and reactivation of tuberculosis; screen before starting.

Antihistamines: first-generation (diphenhydramine) cause sedation; second-generation (loratadine, cetirizine) are preferred for chronic urticaria.