Dermatology
Dermatology tests morphological description, recognition of common inflammatory dermatoses, skin cancer screening and severe drug reactions.
Morphology
- Macule: flat, <1 cm. Papule: raised, <1 cm. Plaque: raised, >1 cm. Vesicle: fluid-filled, <1 cm. Bulla: fluid-filled, >1 cm. Pustule: pus-filled.
- Distribution and symmetry narrow the differential more than any single lesion.
Inflammatory dermatoses
- Psoriasis: well-demarcated erythematous plaques with silvery scale on extensor surfaces and scalp; Auspitz sign on removal of scale.
- Eczema: ill-defined, intensely pruritic, flexural in older children and adults.
- Scabies: burrows in web spaces, nocturnal itch; treat with permethrin 5% to the whole body and treat close contacts.
Skin cancer
- Melanoma: ABCDE criteria; Breslow thickness is the strongest prognostic factor.
- Basal cell carcinoma: pearly papule with telangiectasia and a rolled edge.
- Squamous cell carcinoma: keratotic, ulcerated lesion on sun-exposed skin.
Severe reactions
- SJS/TEN is a drug reaction with mucosal involvement; SJS <10% body surface area, overlap 10–30%, TEN >30%. Withdraw the culprit drug and manage in a burns-type unit.
Worked example
A child has a golden honey-crusted lesion around the nose. This is non-bullous impetigo, usually staphylococcal or streptococcal, treated with topical mupirocin if limited or oral antibiotics if extensive.
Traps
Missing mucosal involvement in a drug eruption, calling every scaly plaque eczema, and ignoring that melanoma can be amelanotic.