Dermatology
What this domain tests
Recognising common inflammatory rashes, spotting skin cancer early, and distinguishing conditions that need a same-day opinion from those that need a topical steroid.
Core rules
- Eczema. Emollients in generous quantity are the mainstay; topical corticosteroids by potency matched to site and severity - mild for the face, moderate to potent for the trunk and limbs. Step down when controlled. Warn about the difference between appropriate use and steroid phobia.
- Psoriasis. Well-demarcated plaques with scale on extensor surfaces; check for nail pitting and joint symptoms, since psoriatic arthritis changes management. Potent topical steroids under occlusion, vitamin D analogues, and referral for phototherapy or systemic therapy.
- Melanoma. Apply the ABCDE and seven-point checklist (change in size, shape, colour, diameter, inflammation, crusting or bleeding, sensory change) and refer urgently any lesion that is changing. Nodular melanoma may be uniform in colour, so "change" matters more than colour alone.
- Basal cell carcinoma is usually a pearly, telangiectatic nodule or a non-healing ulcer, most often on sun-exposed skin; refer for excision.
- Cellulitis versus eczema. Cellulitis is unilateral, warm, tender and spreading with systemic upset; bilateral lower-leg redness is rarely cellulitis.
- Infestation. Scabies is intensely itchy at night with burrows in web spaces; treat the whole household on the same day and wash bedding at 60°C.
Worked example
A 58-year-old presents with a 4 mm pigmented lesion on the calf that has darkened and enlarged over three months. You photograph it, measure it, and refer on the urgent suspected cancer pathway. The reasoning: evolution is the strongest historical clue, and a small diameter does not exclude melanoma.
Traps
- Reassuring because the lesion is small.
- Diagnosing bilateral cellulitis.
- Treating scabies in the patient alone.
- Under-treating eczema for fear of topical steroids.