Master Dermatology
for PLAB 1

Core Concepts

Dermatology involves the study of skin, hair, and nails. Key terms describe primary and secondary lesions: Macule (<1cm, flat, discoloured), Patch (>1cm, flat, discoloured), Papule (<1cm, raised, solid), Plaque (>1cm, raised, solid), Nodule (>1cm, deep, solid), Vesicle (<1cm, fluid-filled), Bulla (>1cm, fluid-filled), Pustule (pus-filled), Urticaria (transient wheal), Erosion (epidermal loss), Ulcer (dermal loss), Scale (shedding keratin), Crust (dried exudate), Lichenification (thickening from rubbing), Atrophy (skin thinning). History taking is crucial: onset, duration, progression, itch/pain, associated symptoms, past medical history, drug history, travel, sun exposure, occupation. Examination includes site, size, shape, colour, texture, distribution, and palpation of lesions.

Clinical Presentation

• Eczema (Dermatitis):
  • Atopic: Pruritic, erythematous, papulovesicular, excoriated, lichenified lesions. Flexural distribution, dry skin. Often childhood onset, associated with asthma/hayfever (atopic triad).
  • Contact: Sharply demarcated, erythematous, oedematous, vesicular rash at site of irritant/allergen exposure.
  • Seborrheic: Greasy, yellow scales on erythematous base in sebaceous areas (scalp, face, chest, flexures). Dandruff in adults, cradle cap in infants.
  • Discoid: Coin-shaped, intensely pruritic, erythematous, vesicular, crusted plaques, typically on limbs.
• Psoriasis: Well-demarcated, erythematous plaques with silvery scales. Extensor surfaces (elbows, knees), scalp, sacrum. Auspitz sign (pinpoint bleeding after scale removal), Koebner phenomenon (lesions at trauma sites). Nail changes (pitting, onycholysis).
• Acne Vulgaris: Comedones (blackheads/whiteheads), papules, pustules, nodules, cysts on face, chest, back. Adolescents/young adults.
• Rosacea: Facial erythema, telangiectasias, papules, pustules (no comedones). Flushing exacerbated by triggers (heat, alcohol). Rhinophyma possible.
• Urticaria (Hives): Evanescent, itchy wheals (erythematous, raised, central pallor). May be acute or chronic, with or without angioedema.
• Tinea (Dermatophytosis): Annular (ring-shaped) lesions with active erythematous, scaly borders and central clearing. Pruritic. Specific types: pedis, cruris, corporis, capitis, unguium.
• Impetigo: Superficial bacterial infection. Honey-coloured crusts, typically perioral/perinasal. Non-bullous (Strep/Staph) or bullous (Staph).
• Cellulitis/Erysipelas: Spreading bacterial infection of dermis/subcutis (cellulitis) or superficial dermis (erysipelas). Erythema, warmth, swelling, pain. Erysipelas has well-demarcated raised border.
• Herpes Simplex (HSV): Grouped vesicles on erythematous base (cold sores, genital herpes). Recurrent.
• Varicella Zoster Virus (VZV):
  • Chickenpox: Generalized vesicular rash in different stages of healing.
  • Shingles (Herpes Zoster): Unilateral, painful vesicular rash in a dermatomal distribution.
• Scabies: Intensely pruritic rash, worse at night. Burrows (fine, wavy lines) in finger webs, wrists, elbows, axillae, umbilicus, genitals. Papules/nodules.
• Skin Cancers:
  • Actinic Keratosis: Pre-malignant, rough, scaly patch on sun-exposed skin.
  • Basal Cell Carcinoma (BCC): Most common. Pearly nodule, rolled edge, telangiectasia, central ulceration. Slow growing.
  • Squamous Cell Carcinoma (SCC): Keratotic nodule or plaque, often ulcerated, can grow rapidly. Higher metastatic risk than BCC.
  • Melanoma: ABCDE criteria (Asymmetry, Border irregularity, Colour variation, Diameter >6mm, Evolving). Pigmented lesion.

Diagnosis (Gold Standard)

Clinical assessment (history and examination) is paramount. Skin biopsy (histopathology) is the gold standard for definitive diagnosis of skin cancers and many inflammatory dermatoses. Other key diagnostics include dermoscopy (for pigmented lesions), KOH mount (fungal infections), skin scrapings (scabies mites), swabs for bacterial/viral culture, and patch testing (allergic contact dermatitis).

Management (First Line)

General: Emollients (e.g., aqueous cream, paraffin-based) for dry skin conditions. Sun protection. Patient education.

• Eczema: Emollients (daily), topical corticosteroids (potency based on site/severity), topical calcineurin inhibitors (e.g., tacrolimus), antihistamines for itch.
• Psoriasis: Topical corticosteroids, vitamin D analogues (e.g., calcipotriol), coal tar preparations. Phototherapy or systemic agents (e.g., methotrexate, biologics) for severe cases.
• Acne Vulgaris: Topical retinoids (e.g., tretinoin), benzoyl peroxide, topical antibiotics (e.g., clindamycin). Oral antibiotics (e.g., doxycycline, lymecycline), COCP, oral isotretinoin for severe cases.
• Rosacea: Topical metronidazole, azelaic acid. Oral tetracyclines (e.g., doxycycline).
• Tinea: Topical antifungals (e.g., clotrimazole, terbinafine). Oral antifungals (e.g., terbinafine, fluconazole) for extensive/scalp/nail infections.
• Impetigo: Topical antibiotics (e.g., fusidic acid, mupirocin) for localized. Oral antibiotics (e.g., flucloxacillin, erythromycin) for extensive.
• Cellulitis/Erysipelas: Oral antibiotics (e.g., flucloxacillin, clarithromycin). IV antibiotics for severe.
• Herpes Simplex/Zoster: Oral antivirals (e.g., aciclovir, valaciclovir) if presented early or in specific populations (e.g., immunocompromised, ophthalmic zoster).
• Scabies: Topical permethrin 5% cream (whole body, repeat in 7 days). Treat close contacts. Oral ivermectin as alternative.
• Urticaria: Oral H1 antihistamines (e.g., loratadine, cetirizine).
• Skin Cancers:
  • Actinic Keratosis: Cryotherapy, topical 5-fluorouracil, imiquimod.
  • BCC/SCC/Melanoma: Surgical excision is primary treatment. Mohs micrographic surgery for high-risk BCC/SCC.

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