Master Dermatology
for MRCP Part 1

Core Concepts

The skin comprises three layers: epidermis (keratinocytes, melanocytes, Langerhans, Merkel cells), dermis (collagen, elastin, blood vessels, nerves, adnexal structures), and subcutaneous tissue. Understanding primary (macule, papule, plaque, nodule, vesicle, bulla, pustule, wheal, patch) and secondary lesions (erosion, ulcer, crust, scale, lichenification, atrophy, scar) is fundamental for description and diagnosis. Key symptoms include pruritus (itch), pain, and altered sensation. Systemic diseases often manifest cutaneously (e.g., lupus, diabetes, IBD, internal malignancy).

Clinical Presentation

• Eczema (Dermatitis):
  • Atopic: Pruritic, erythematous, scaly patches, often lichenified. Flexural distribution (children), extensor (infants). Associated with asthma, hayfever.
  • Contact: Allergic (delayed hypersensitivity, e.g., nickel) or irritant (e.g., detergents). Erythema, vesicles, pruritus, localized to exposure.
  • Seborrheic: Greasy yellow scales on erythematous patches, typically face (nasolabial folds, eyebrows), scalp ("cradle cap" in infants). Often exacerbated by stress, Parkinson's, HIV.
  • Discoid (Nummular): Coin-shaped erythematous, vesicular, and crusted plaques, intensely pruritic. Lower legs/arms.
• Psoriasis: Chronic inflammatory. Well-demarcated erythematous plaques with silvery scales. Extensor surfaces, scalp, nails (pitting, onycholysis, subungual hyperkeratosis). Auspitz sign (pinpoint bleeding after scale removal).
  • Variants: Plaque (most common), Guttate (post-strep infection), Pustular (generalized/localized, acute fever), Erythrodermic (total body erythema, emergency).
  • Associated with Psoriatic Arthritis, metabolic syndrome, CVD.
• Urticaria (Hives): Transient, intensely pruritic wheals (erythematous, edematous papules/plaques) with surrounding flare. Acute (<6 weeks), Chronic (>6 weeks). Can be associated with angioedema. Causes: allergic (food, drugs), physical, autoimmune, idiopathic.
• Infections:
  • Bacterial: Impetigo (honey-crusted lesions, Staph/Strep), Cellulitis (erythema, warmth, swelling, pain, poorly demarcated, deeper dermis), Erysipelas (Strep, sharply demarcated, raised border, superficial dermis).
  • Fungal (Tinea): Ringworm (annular, scaly plaques with central clearing). Tinea pedis (athlete's foot), corporis (body), cruris (groin), capitis (scalp, can cause alopecia), unguium (onychomycosis, nail dystrophy).
  • Viral: Herpes Simplex (vesicles on erythematous base, grouped), Herpes Zoster (dermatomal vesicles, painful, unilateral), Warts (HPV), Molluscum Contagiosum (umbilicated papules).
• Blistering Disorders:
  • Bullous Pemphigoid: Subepidermal blisters (tense), older adults, often itchy, negative Nikolsky's sign.
  • Pemphigus Vulgaris: Intraepidermal blisters (flaccid), younger adults, often mucosal involvement, positive Nikolsky's sign.
• Drug Reactions: Morbilliform (maculopapular, most common), Urticarial, Fixed drug eruption, Erythema Multiforme (target lesions), SJS/TEN (severe, mucosal involvement, epidermal detachment).
• Skin Cancers:
  • Basal Cell Carcinoma (BCC): Pearly papule with telangiectasias, rolled border, often central ulceration. Most common skin cancer, rarely metastasizes.
  • Squamous Cell Carcinoma (SCC): Keratotic, crusted, nodular lesion, often ulcerated. Sun-exposed areas. Can metastasize. Precursor: Actinic Keratosis.
  • Melanoma: ABCDE criteria (Asymmetry, Border irregularity, Colour variability, Diameter >6mm, Evolving/Elevated). Highly metastatic.

Diagnosis (Gold Standard)

Clinical examination is paramount. For uncertain lesions, a skin biopsy (punch, shave, excisional) for histopathology provides definitive diagnosis (e.g., tumors, inflammatory dermatoses, blistering disorders). Direct immunofluorescence (DIF) on perilesional skin for blistering diseases. Dermatoscopy for pigmented lesions. KOH mount of skin scrapings for fungal infections. Patch testing for allergic contact dermatitis. Bacterial/viral swabs for culture/PCR.

Management (First Line)

Management often involves:

• Topical Steroids: Key for inflammatory conditions (eczema, psoriasis). Potency adjusted based on site, severity, and age.
• Emollients: Essential for dry skin conditions (eczema, psoriasis) to restore barrier function.
• Antihistamines: Oral H1-blockers for pruritus (urticaria, eczema).
• Antifungals: Topical (clotrimazole, terbinafine) or oral (terbinafine, fluconazole) depending on extent and site.
• Antibiotics: Topical (fusidic acid, mupirocin) or oral (flucloxacillin, erythromycin) for bacterial infections.
• Antivirals: Oral acyclovir/valacyclovir for herpes simplex/zoster.
• Immunosuppressants/Biologics: For severe chronic conditions (e.g., methotrexate, ciclosporin, biologics for psoriasis/atopic dermatitis).
• Phototherapy: UVB or PUVA for extensive psoriasis/eczema.
• Surgery: Excision for skin cancers (BCC, SCC, melanoma). Cryotherapy for actinic keratosis, warts.
• Drug Discontinuation: Immediate cessation of causative drug for drug eruptions (especially SJS/TEN).

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