Arab Board Dermatology Final cheat sheet

Epidermal turnover: keratinocytes transit from basal layer to stratum corneum in ~28 days; psoriatic epidermis turns over in 3–5 days.

Langerhans cells are CD1a+/CD207(langerin)+ antigen-presenting cells of the epidermis; they migrate to draining lymph nodes via CCR7.

Th17 axis (IL-17A/F, IL-23) drives psoriatic inflammation; IL-17 also recruits neutrophils via CXCL8.

Th2 cytokines (IL-4, IL-13) dominate atopic dermatitis; dupilumab blocks IL-4Rα, inhibiting both IL-4 and IL-13 signaling.

Type I hypersensitivity is IgE/mast-cell mediated (wheal-and-flare within minutes); type IV is T-cell mediated (48–72 h, e.g., allergic contact dermatitis).

Basement membrane zone antigens: BP180 (BPAG2/collagen XVII) and BP230 in bullous pemphigoid; type VII collagen in epidermolysis bullosa acquisita.

Skin barrier: filaggrin deficiency (FLG null mutations) impairs stratum corneum hydration and predisposes to atopic dermatitis and ichthyosis vulgaris.

Dermal papillae contain capillary loops; the subpapillary plexus supplies the papillary dermis, and the deep plexus supplies the reticular dermis and subcutis.

Psoriasis: well-demarcated erythematous plaques with silvery scale on extensor surfaces; Auspitz sign (pinpoint bleeding on scale removal) and Koebner phenomenon.

PASI (Psoriasis Area and Severity Index) combines erythema, induration, and desquamation weighted by body surface area; score 0–72.

Atopic dermatitis: pruritus is essential; flexural distribution in adults, face/extensor in infants; Hanifin–Rajka criteria are the diagnostic standard.

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

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

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

Chronic plaque psoriasis first-line: topical corticosteroids plus vitamin D analogue; phototherapy (NB-UVB) for extensive disease; biologics (TNF, IL-17, IL-23 inhibitors) for moderate-to-severe.

Stasis dermatitis: erythema, scaling, and hemosiderin staining of the lower legs; treat with compression and emollients, not just topical steroids.

Impetigo: honey-colored crusts; Staphylococcus aureus and Streptococcus pyogenes; non-bullous form most common; treat with topical mupirocin or oral antistaphylococcal antibiotics.

Tinea capitis: scaly alopecia with broken hairs; Wood's lamp shows blue-green fluorescence for Microsporum; treat with oral griseofulvin or terbinafine (topicals ineffective).

Scabies: nocturnal pruritus, burrows in web spaces/wrists; treat with permethrin 5% cream (whole body, repeat in 7 days) or oral ivermectin; treat contacts simultaneously.

Herpes zoster: dermatomal vesicular rash; risk of postherpetic neuralgia increases with age; antivirals (acyclovir, valacyclovir) within 72 h of rash onset.

Onychomycosis: distal and lateral subungual type most common; confirm with KOH or culture before oral terbinafine; terbinafine requires baseline LFTs.

Cutaneous leishmaniasis: painless ulcer with raised violaceous border (volcano sign) after sandfly bite; diagnose with Giemsa-stained smear showing amastigotes.

Erysipelas vs cellulitis: erysipelas involves upper dermis with sharply demarcated raised border (Streptococcus); cellulitis involves deeper dermis/subcutis with ill-defined borders.

Molluscum contagiosum: umbilicated pearly papules caused by a poxvirus; resolves spontaneously; treat with curettage or cantharidin if desired.

SLE mucocutaneous criteria include malar rash, discoid rash, photosensitivity, oral ulcers, and nonscarring alopecia; ANA is the screening test, anti-dsDNA and anti-Sm are specific.

Dermatomyositis: heliotrope rash, Gottron papules, shawl sign, and proximal muscle weakness; anti-Mi-2, anti-TIF1γ (cancer-associated), and anti-MDA5 (rapidly progressive ILD) are key antibodies.

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

Pemphigus vulgaris: flaccid blisters and erosions; IgG against desmoglein 3 (and 1); direct immunofluorescence shows intercellular IgG deposits (chicken-wire pattern).

Bullous pemphigoid: tense subepidermal blisters; IgG against BP180/BP230; DIF shows linear IgG and C3 along the basement membrane zone.

Vasculitis: palpable purpura is the hallmark of leukocytoclastic vasculitis; direct immunofluorescence showing IgA deposits suggests Henoch–Schönlein purpura (IgA vasculitis).

Behçet disease: recurrent oral and genital ulcers, uveitis, and pathergy; diagnose clinically; treat with colchicine, corticosteroids, or TNF inhibitors.

Basal cell carcinoma: pearly papule with telangiectasia; histology shows basaloid islands with peripheral palisading and clefting; rarely metastasizes.

Squamous cell carcinoma: hyperkeratotic nodule or ulcer; histology shows atypical keratinocytes invading the dermis; risk factors include UV, chronic wounds, and immunosuppression.

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

Sentinel lymph node biopsy is recommended for melanoma with Breslow thickness ≥1.0 mm (or ≥0.8 mm with ulceration).

Dermatofibroma: firm dermal nodule with dimple sign; histology shows spindle cells with collagen trapping at the periphery.

Seborrheic keratosis: stuck-on waxy plaque; histology shows horn cysts and basaloid proliferation; Leser–Trélat sign (sudden eruptive) warrants malignancy workup.

Mycosis fungoides: epidermotropic CD4+ T-cell lymphoma; patches, plaques, and tumors; Pautrier microabscesses are characteristic.

Atopic dermatitis in infants: face and extensor surfaces; in children: flexural creases; treat with emollients and low-potency topical corticosteroids.

Hemangioma of infancy: appears in first weeks, proliferates for 3–6 months, then involutes; treat problematic lesions with oral propranolol.

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

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

Tuberous sclerosis: ash-leaf spots, facial angiofibromas, Shagreen patch, seizures, and hamartomas; mutations in TSC1 or TSC2.

Ichthyosis vulgaris: filaggrin deficiency causing fine white scale and hyperlinear palms; associated with atopic dermatitis and keratosis pilaris.

Incontinentia pigmenti: X-linked dominant (IKBKG mutation); vesicular, verrucous, hyperpigmented, and hypopigmented stages along Blaschko lines; lethal in males.

Mohs micrographic surgery: stage-by-stage excision with complete margin examination; indicated for high-risk basal cell carcinoma, squamous cell carcinoma, and melanoma in situ on the face.

Excision margins: basal cell carcinoma low-risk 4 mm; squamous cell carcinoma low-risk 4–6 mm; melanoma in situ 5 mm; melanoma ≤1 mm Breslow 1 cm.

Pulsed dye laser (595 nm) targets oxyhemoglobin; used for port-wine stains and telangiectasias; risk of purpura and pigmentary alteration.

Q-switched lasers (532, 694, 1064 nm) target melanin and tattoo pigments; nanosecond pulses; risk of hypopigmentation and scarring.

Fractional ablative lasers (CO2, Er:YAG) create microthermal zones; used for rhytides and scarring; require wound care and infection precautions.

Botulinum toxin type A chemodenervation: onset 3–7 days, duration 3–4 months; avoid in pregnancy and neuromuscular disorders.

Sclerotherapy for varicose veins: sodium tetradecyl sulfate or polidocanol; complications include hyperpigmentation, ulceration, and DVT (rare).

Alopecia areata: nonscarring patchy hair loss with exclamation-mark hairs; associated with autoimmune disease; treat with topical or intralesional corticosteroids.

Androgenetic alopecia: patterned hair loss driven by dihydrotestosterone; treat with topical minoxidil and oral finasteride (men).

Telogen effluvium: diffuse shedding 2–3 months after a trigger (illness, childbirth, stress); self-limited; no specific treatment.

Lichen planopilaris: scarring alopecia with perifollicular erythema and scale; histology shows lichenoid interface dermatitis at the follicular infundibulum.

Onychomycosis: subungual hyperkeratosis and onycholysis; confirm with KOH or culture; treat with oral terbinafine or itraconazole.

Longitudinal melanonychia: brown-black nail streak; Hutchinson sign (pigment on cuticle) suggests subungual melanoma; biopsy the nail matrix.

Oral lichen planus: white reticular striae (Wickham striae) on buccal mucosa; risk of squamous cell carcinoma; monitor and biopsy suspicious lesions.

UVB (290–320 nm) causes sunburn and direct DNA damage (cyclobutane pyrimidine dimers); UVA (320–400 nm) causes photoaging and drug photosensitivity.

Sunscreen SPF measures UVB protection; PA grading (or broad-spectrum label) indicates UVA protection; reapply every 2 hours and after swimming.

Vitiligo: depigmented macules with sharp borders; associated with thyroid disease and other autoimmune conditions; treat with topical corticosteroids, calcineurin inhibitors, NB-UVB, or surgical grafting.

Melasma: symmetric hyperpigmentation on sun-exposed areas; treat with hydroquinone, tretinoin, and sun protection; risk of rebound with monotherapy.

Postinflammatory hyperpigmentation: occurs after inflammation, more common in darker skin; treat with sun protection and topical lightening agents.

Phototoxic drug reactions: exaggerated sunburn within hours (e.g., tetracyclines, amiodarone); photoallergic reactions are eczematous and delayed.

Porphyria cutanea tarda: blistering on sun-exposed skin, fragility, and hypertrichosis; associated with hepatitis C, alcohol, and hemochromatosis; treat with phlebotomy or low-dose hydroxychloroquine.

Topical corticosteroid potency: class I (superpotent, e.g., clobetasol) to class VII (mild, e.g., hydrocortisone 1%); risk of atrophy, striae, and tachyphylaxis with prolonged use.

Methotrexate for psoriasis: weekly dosing (not daily); monitor CBC, LFTs, and renal function; supplement folic acid; avoid in pregnancy.

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

Biologics for psoriasis: TNF inhibitors (adalimumab, etanercept), IL-17 inhibitors (secukinumab, ixekizumab), IL-23 inhibitors (guselkumab, risankizumab); screen for tuberculosis before TNF inhibitors.

Isotretinoin: teratogenic; requires pregnancy testing and two contraceptive methods; monitor lipids and liver enzymes; risk of depression and pseudotumor cerebri.

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

Systemic corticosteroids: taper to avoid adrenal insufficiency; long-term use causes osteoporosis, diabetes, and infection risk.

Stevens–Johnson syndrome/toxic epidermal necrolysis: mucosal erosions, blistering, and epidermal detachment; mortality increased with greater body surface area involved; treat with supportive care and consider IVIG or cyclosporine.

Erythema multiforme: target lesions, often after herpes simplex infection; usually self-limited; treat with antivirals for recurrent cases.

Toxic shock syndrome: fever, rash, hypotension, and multiorgan involvement; associated with Staphylococcus aureus toxin; treat with antibiotics and supportive care.

Necrotizing fasciitis: rapidly spreading erythema, pain out of proportion, and systemic toxicity; surgical debridement is urgent; antibiotics cover polymicrobial or group A Streptococcus.

DRESS syndrome: drug reaction with eosinophilia and systemic symptoms; fever, rash, lymphadenopathy, and organ involvement; treat with systemic corticosteroids.

Paraneoplastic dermatoses: acanthosis nigricans (gastric cancer), dermatomyositis (ovarian cancer), and migratory thrombophlebitis (pancreatic cancer).

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