Master Dermatology
for MRCP Part 1

What the MRCP Part 1 Tests in Dermatology

MRCP Part 1 Dermatology tests recognition of common and serious skin conditions from high-quality clinical images and brief histories. Candidates must differentiate between eczemas, psoriasis variants, infections (fungal, viral, bacterial), drug eruptions, vasculitic rashes, and cutaneous signs of systemic disease (e.g., lupus, dermatomyositis, sarcoidosis). Knowledge of first-line topical and systemic therapies, including potency classes of corticosteroids, is essential. The exam emphasizes pattern recognition of morphology (e.g., target lesions, Nikolsky sign, Koebner phenomenon) and association with internal malignancy (e.g., acanthosis nigricans, erythroderma). Candidates must also know diagnostic criteria (e.g., for atopic dermatitis, psoriasis arthritis) and when to suspect emergencies like toxic epidermal necrolysis or meningococcal sepsis.

High-Yield Concepts

• Psoriasis subtypes and treatment: Chronic plaque psoriasis: first-line topical potent corticosteroid + vitamin D analogue (calcipotriol). Guttate psoriasis often follows streptococcal pharyngitis; may clear spontaneously. Pustular psoriasis (von Zumbusch) and erythrodermic psoriasis are emergencies requiring systemic therapy (acitretin, methotrexate, or ciclosporin). Nail psoriasis: pitting, onycholysis, oil-drop sign.
• Eczema and contact dermatitis: Atopic dermatitis: diagnostic criteria include pruritus, flexural involvement, early age onset, and personal/family history of atopy. First-line: emollients and moderate-potency topical corticosteroids (e.g., betamethasone valerate 0.1%). Acute allergic contact dermatitis: patch testing, common allergens nickel, fragrance, neomycin. Venous eczema: associated with lipodermatosclerosis and ulceration.
• Drug eruptions and severe cutaneous adverse reactions: Morbilliform rash: most common, often with amoxicillin, allopurinol. Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN): epidermal detachment >10% BSA (SJS) or >30% (TEN); Nikolsky sign positive. Common triggers: lamotrigine, carbamazepine, allopurinol, sulfonamides. Immediate withdrawal of culprit drug and supportive care in ICU/burns unit. DRESS syndrome: eosinophilia, fever, lymphadenopathy, internal organ involvement; associated with anticonvulsants, allopurinol.
• Skin infections: bacterial and viral: Cellulitis: unilateral, warm, tender erythema; treat with flucloxacillin. Erysipelas: well-demarcated, raised edge, often facial; penicillin. Herpes zoster: dermatomal vesicular rash, treat within 72 hours with aciclovir or valaciclovir; risk of postherpetic neuralgia increases with age. Molluscum contagiosum: self-limiting in children; in adults consider HIV testing.
• Cutaneous vasculitis and purpura: Palpable purpura: leukocytoclastic vasculitis; Henoch-Schönlein purpura (IgA vasculitis) – palpable purpura on lower limbs, arthritis, abdominal pain, renal involvement. Urticarial vasculitis: wheals lasting >24 hours, painful rather than pruritic, may indicate lupus or hypocomplementemia. Meningococcal sepsis: non-blanching purpura, petechiae, fever, hypotension – urgent IV ceftriaxone.
• Autoimmune blistering disorders: Bullous pemphigoid: tense blisters on flexural areas and trunk, elderly, treat with potent topical corticosteroids (clobetasol propionate) or oral prednisolone. Pemphigus vulgaris: flaccid blisters, mucosal involvement (oral), positive Nikolsky sign, treat with high-dose prednisolone and azathioprine or mycophenolate mofetil. Dermatitis herpetiformis: intensely pruritic vesicles on elbows, knees, buttocks; associated with coeliac disease; treat with dapsone and gluten-free diet.
• Cutaneous manifestations of systemic disease: Dermatomyositis: Gottron's papules (knuckles), heliotrope rash (periorbital), shawl sign; screen for malignancy (ovary, lung, GI). Systemic lupus erythematosus: malar rash, discoid lesions, photosensitivity; anti-Ro antibodies associated with subacute cutaneous lupus. Sarcoidosis: lupus pernio (violaceous nasal/ear plaques), erythema nodosum (pretibial tender nodules), scar infiltration. Acanthosis nigricans: velvety hyperpigmentation in flexures; associated with insulin resistance and internal malignancy (gastric, lung).
• Fungal infections and treatment: Tinea pedis (athlete's foot): interdigital scaling, treat with topical terbinafine or clotrimazole. Tinea capitis: scaly patches with hair loss, oral griseofulvin or terbinafine (depending on species). Onychomycosis: distal subungual thickening, oral terbinafine 250mg daily for 6-12 weeks (fingernails) or 12-24 weeks (toenails). Pityriasis versicolor: hypopigmented or hyperpigmented scaly macules on trunk, caused by Malassezia; treat with topical ketoconazole or oral itraconazole.

Common Traps in Dermatology Questions

• Confusing psoriasis with seborrhoeic dermatitis: psoriasis plaques are well-demarcated with silvery scale, while seborrhoeic dermatitis has greasy, yellowish scale on scalp, nasolabial folds, and chest.
• Assuming all blistering rashes are pemphigus: tense blisters with no mucosal involvement suggest bullous pemphigoid, not pemphigus vulgaris.
• Missing drug-induced lupus: minocycline, hydralazine, and procainamide can cause lupus-like syndrome with positive ANA and anti-histone antibodies.
• Forgetting that erythema multiforme is usually triggered by infection (HSV, Mycoplasma) not drugs, unlike SJS/TEN which are drug-induced.
• Treating tinea capitis with topical antifungals alone: systemic therapy is always required because the fungus invades hair follicles.
• Misdiagnosing cellulitis as venous eczema: bilateral leg redness with varicose veins, itch, and scaling suggests venous eczema; unilateral pain, fever, and swelling suggests cellulitis.

How to Revise Dermatology for the MRCP Part 1

For MRCP Part 1 Dermatology, focus on high-yield pattern recognition: know the morphology and distribution of common rashes (psoriasis, eczema, tinea, drug eruptions) and their distinguishing features. Practice with clinical images to identify conditions like erythema nodosum, lupus pernio, and dermatomyositis. Memorize first-line treatments for common infections (cellulitis: flucloxacillin; shingles: aciclovir) and severe reactions (SJS/TEN: withdrawal and supportive care). Be comfortable with diagnostic criteria (e.g., atopic dermatitis, psoriasis arthritis) and associations with malignancy (e.g., acanthosis nigricans, dermatomyositis). Questions often present a brief history with a photo; focus on the key morphological term (e.g., 'target lesion' for erythema multiforme, 'palpable purpura' for vasculitis). Rehearse the common traps listed above.

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