Master Dermatology
for DHA

What the DHA Tests in Dermatology

The DHA Dermatology section tests the ability to diagnose and manage common skin conditions in primary care and emergency settings. Emphasis is on recognizing morphology (e.g., macules, papules, vesicles, bullae, scales) and distinguishing between benign, premalignant, and malignant lesions. Candidates must demonstrate knowledge of evidence-based treatments, including topical and systemic therapies, with specific drug names and dosing. Key areas include eczema/dermatitis, psoriasis, acne, rosacea, skin infections (bacterial, viral, fungal), infestations (scabies, lice), and skin cancers (basal cell carcinoma, squamous cell carcinoma, melanoma). The exam also assesses understanding of systemic diseases with cutaneous manifestations (e.g., lupus erythematosus, dermatomyositis, sarcoidosis) and drug eruptions. Practical skills such as Wood's lamp use, dermoscopy features, and biopsy techniques are tested. Management of anaphylaxis and angioedema is also included.

High-Yield Concepts

• Psoriasis Plaque Morphology and Treatment: Plaque psoriasis = well-demarcated, erythematous plaques with silvery scale; Auspitz sign (bleeding upon scale removal). First-line topical: potent corticosteroid (e.g., betamethasone dipropionate 0.05%) plus vitamin D analogue (calcipotriol 0.005%) combination. Systemic for moderate-severe: methotrexate (7.5–25 mg weekly with folic acid 5 mg weekly), or biologic (adalimumab 40 mg SC every 2 weeks).
• Atopic Dermatitis Diagnostic Criteria and Step-Up Therapy: UK Working Party criteria: pruritus plus ≥3 of (1) flexural involvement, (2) personal/family atopy, (3) dry skin, (4) onset <2 years. Emollients (e.g., 50:50 liquid paraffin/white soft paraffin) are mainstay. Topical corticosteroids: hydrocortisone 1% (mild), betamethasone valerate 0.1% (moderate), clobetasol propionate 0.05% (severe) for short bursts. Calcineurin inhibitors (tacrolimus 0.1% ointment) for face/flexures.
• Acne Vulgaris Grading and First-Line Antibiotics: Graded as mild (comedones ± few papules), moderate (papules/pustules), severe (nodules/cysts). First-line for mild-moderate: topical benzoyl peroxide 5% or adapalene 0.1% gel. For moderate-severe: oral lymecycline 408 mg daily or doxycycline 100 mg daily for 8–12 weeks. Avoid topical antibiotics alone to prevent resistance. Isotretinoin for severe nodulocystic: 0.5–1 mg/kg/day.
• Rosacea Subtypes and Management: Erythematotelangiectatic (flushing, telangiectasias) – avoid triggers (sun, alcohol, spicy food). Papulopustular – topical metronidazole 0.75% gel or ivermectin 1% cream. Ocular rosacea – oral doxycycline 100 mg daily plus artificial tears. Phymatous – laser or surgical reduction. Avoid topical steroids (can worsen).
• Melanoma ABCDE Criteria and Breslow Thickness: ABCDE: Asymmetry, Border irregular, Color variegation (brown/black/red/white), Diameter >6 mm, Evolution. Breslow thickness (mm) is key prognostic factor: <0.8 mm (T1a) – wide local excision (1 cm margin); >0.8–1.0 mm (T1b) – excision + sentinel lymph node biopsy. Refer urgently if any suspicious lesion.
• Basal Cell Carcinoma (BCC) Subtypes and Excision Margins: Nodular BCC: pearly papule with telangiectasias; superficial BCC: scaly erythematous patch. Treatment: surgical excision with 4 mm margin for low-risk (nodular, <2 cm on trunk/limbs); 5 mm margin for high-risk (morpheaform, >2 cm, face, ears). Mohs micrographic surgery for high-risk facial lesions. Imiquimod 5% cream for superficial BCC <2 cm.
• Scabies Diagnosis and Permethrin Regimen: Intense pruritus, worse at night; burrows in finger webs, wrists, axillae, genitals. Diagnosis: dermoscopy (delta sign) or scraping for mites/eggs. First-line: permethrin 5% cream applied from neck down, washed off after 8–12 hours; repeat in 7 days. Treat all household contacts. Oral ivermectin 200 mcg/kg (two doses 7 days apart) for crusted scabies.
• Herpes Zoster (Shingles) Antiviral Timing and Postherpetic Neuralgia Prevention: Unilateral vesicular eruption in dermatomal distribution, often preceded by pain. Start antivirals (acyclovir 800 mg 5×/day or valacyclovir 1 g TID) within 72 hours of rash onset to reduce acute pain and risk of postherpetic neuralgia. For PHN: amitriptyline 10–25 mg nocte, gabapentin 300 mg TID, or lidocaine 5% patch. Vaccination (Zostavax/Shingrix) for ≥60 years.

Common Traps in Dermatology Questions

• Confusing seborrheic dermatitis (scalp, face, flexures, greasy scale) with psoriasis (extensor, silvery scale, nail pitting).
• Using topical corticosteroids on fungal infections (e.g., tinea) – worsens infection; always confirm with KOH or culture.
• Forgetting that oral doxycycline causes photosensitivity and should not be given to children <12 years or pregnant women.
• Assuming all red scaly rashes are psoriasis – consider mycosis fungoides (cutaneous T-cell lymphoma) if persistent, pruritic, and atypical distribution.
• Missing melanoma in subungual location (Hutchinson sign – pigmentation of nail fold) – often mistaken for trauma or fungal infection.
• Prescribing topical steroids for perioral dermatitis – use topical metronidazole or azelaic acid instead.

How to Revise Dermatology for the DHA

Focus on pattern recognition: DHA questions often present a clinical image of a rash or lesion and ask for the diagnosis and first-line management. Prioritise learning the morphology of common rashes (psoriasis, eczema, tinea, scabies) and the ABCD criteria for melanoma. Memorise first-line topical and systemic treatments with specific drug names and doses (e.g., betamethasone vs. clobetasol, lymecycline vs. doxycycline). Be able to differentiate between benign (seborrheic keratosis, cherry angioma) and malignant lesions (BCC, SCC, melanoma). Practise interpreting Wood's lamp findings (tinea capitis – green fluorescence) and dermoscopy patterns (pigment network in melanocytic nevi, blue-white veil in melanoma). Review management of drug eruptions (DRESS, SJS/TEN) and when to stop the offending drug. Use past DHA-style multiple-choice questions to build speed and accuracy.

Practise it: MedLumen has 90 Dermatology questions for the DHA, each with a full explanation and references.