Master Dermatology
for PLAB 1

What the PLAB 1 Tests in Dermatology

PLAB 1 Dermatology tests your ability to recognise common skin conditions from brief clinical vignettes, select appropriate first-line treatments (including topical steroids by potency), and identify emergencies (e.g., toxic epidermal necrolysis, meningococcal septicaemia). You must differentiate between eczema, psoriasis, fungal infections, and skin cancers. Questions often require interpretation of lesion morphology, distribution, and associated systemic features. You must know referral criteria for suspected melanoma (e.g., 7-point checklist), when to use oral antivirals for herpes zoster, and when to suspect scabies or cellulitis. Management decisions include choosing emollients, topical antifungals, or systemic immunosuppressants, and recognising when to admit or refer to dermatology.

High-Yield Concepts

• Eczema (atopic dermatitis) management: First-line: emollients (e.g., 50:50 white soft paraffin/liquid paraffin) and topical corticosteroids – use mild (1% hydrocortisone) for face/flexures, moderate (clobetasone butyrate 0.05%) for trunk/limbs, potent (betamethasone valerate 0.1%) for thick plaques. Step up potency if no response in 7 days. Avoid abrupt withdrawal. For severe acute flares, consider a short course of oral prednisolone 30 mg daily for 5-7 days.
• Psoriasis recognition and treatment: Well-demarcated, silvery scaly plaques on extensor surfaces (elbows, knees), scalp, and nails (pitting, onycholysis). First-line for mild-to-moderate: topical vitamin D analogue (calcipotriol) or potent corticosteroid (betamethasone). For moderate-to-severe: phototherapy (UVB) or systemic methotrexate (15-25 mg weekly with folic acid cover), ciclosporin, or biologic (adalimumab) if fails. Refer if acute guttate psoriasis with recent streptococcal infection.
• Malignant melanoma – 7-point checklist: Major features (each 2 points): change in size, shape (irregular border), colour (multiple shades). Minor features (each 1 point): diameter >6 mm, inflammation, crusting/bleeding, sensory change (itch/pain). Score ≥3 warrants urgent referral (2-week wait). Breslow thickness >0.8 mm or ulceration requires wide local excision and sentinel lymph node biopsy.
• Herpes zoster (shingles) treatment: Start oral aciclovir 800 mg five times daily or valaciclovir 1 g three times daily within 72 hours of rash onset (or if new vesicles still appearing). For ophthalmic zoster (V1 distribution), refer urgently to ophthalmology. Post-herpetic neuralgia: first-line amitriptyline 10-25 mg nocte or gabapentin 300 mg three times daily.
• Scabies diagnosis and treatment: Intense pruritus (worse at night), burrows in finger webs, wrists, axillae, genitals. Treat with permethrin 5% cream (apply whole body from chin down, wash off after 8-12 hours) – repeat after 7 days. Treat all household contacts simultaneously. If permethrin fails, oral ivermectin 200 mcg/kg single dose, repeat in 14 days.
• Cellulitis versus erysipelas: Cellulitis: diffuse, poorly demarcated erythema, swelling, warmth, pain – treat with oral flucloxacillin 500 mg four times daily for 7 days (or clindamycin 300 mg four times daily if penicillin-allergic). Erysipelas: well-demarcated, raised, shiny erythema (often on face or lower leg) – same antibiotics. If systemic signs (fever, tachycardia, hypotension) or lymphangitis, admit for IV antibiotics.
• Basal cell carcinoma (BCC) recognition: Slow-growing, pearly papule/nodule with telangiectasias, rolled border, central ulceration (rodent ulcer). Most common on sun-exposed areas (face, ears). Low-risk BCC (<2 cm, superficial, non-facial) can be treated with topical imiquimod 5% cream or cryotherapy. High-risk BCC (nodular, >2 cm, on H-zone of face) requires surgical excision with 4 mm margin or Mohs micrographic surgery.
• Toxic epidermal necrolysis (TEN) – emergency: Widespread erythema, blistering, and skin detachment >30% body surface area, often triggered by drugs (e.g., allopurinol, anticonvulsants, sulfonamides). Nikolsky sign positive (blister spreads with lateral pressure). Immediate management: stop culprit drug, admit to burns unit or intensive care, IV fluids, wound care, and consider IV immunoglobulin 1 g/kg daily for 3 days. Mortality up to 30%.

Common Traps in Dermatology Questions

• Confusing tinea corporis (ringworm) with nummular eczema – tinea has raised, scaly, annular border with central clearing; eczema is poorly defined and pruritic, treat with antifungal (terbinafine) not steroid.
• Assuming all itchy rashes are eczema – scabies has nocturnal itch and burrows, treat with permethrin, not steroids.
• Missing meningococcal septicaemia in a febrile child with a non-blanching purpuric rash – do not wait for lumbar puncture; give IV ceftriaxone 80 mg/kg immediately.
• Using potent topical steroids on the face for eczema – can cause perioral dermatitis or skin atrophy; use 1% hydrocortisone only.
• Forgetting to check for lymphadenopathy and hepatosplenomegaly in suspected cutaneous lymphoma (mycosis fungoides) – biopsy required for diagnosis.
• Treating impetigo with topical antibiotics alone when multiple lesions or systemic symptoms – oral flucloxacillin 500 mg four times daily for 7 days is first-line.

How to Revise Dermatology for the PLAB 1

Focus on pattern recognition: know the classic locations and morphologies of eczema (flexural), psoriasis (extensor), fungal infections (annular, scaly), and skin cancers (sun-exposed areas). Practice differentiating between benign (seborrhoeic keratosis) and malignant (melanoma) lesions using the 7-point checklist. Memorise first-line antibiotics for cellulitis, impetigo, and erysipelas, and when to escalate to IV. For paediatric questions, recognise atopic dermatitis, scabies, and meningococcal rash. Questions often present a photo or short description; practise describing lesions (macule, papule, plaque, nodule, vesicle, bulla, pustule, scale, crust). Also know red flags for referral: rapidly growing lesion, >6 mm diameter, irregular border, multiple colours, ulceration, bleeding, or systemic symptoms. Revise topical steroid potencies and when to use each.

Practise it: MedLumen has 50 Dermatology questions for the PLAB 1, each with a full explanation and references.