OSCE — yellow pretibial plaques: diagnose necrobiosis lipoidica and prevent ulceration

Brief (to candidate)

A 42-year-old woman with longstanding type 1 diabetes has shiny yellow-brown pretibial plaques with telangiectasia and a violaceous rim; one plaque recently ulcerated after minor trauma. You have 8 minutes to diagnose necrobiosis lipoidica, organise metabolic assessment, and manage ulcer risk.

Candidate instructions

1. Give the classic morphology and site of NL.
2. State the diabetes association and other differentials of pretibial plaques/ulcers.
3. Indicate when to biopsy and expected histology concept (necrobiosis/granulomatous degeneration).
4. Outline treatment ladder for non-ulcerated and ulcerated NL.
5. Counsel on trauma avoidance and red flags (including rare SCC in chronic ulcer).

Examiner checklist (mark each domain / 10)

Model key actions

• Recognise classic pretibial NL morphology and link to diabetes screening/optimisation.^[1][8]
• Prevent and manage ulceration with trauma avoidance and structured wound care.^[6]
• Escalate atypical or refractory disease along guideline-informed pathways.^[3]

Common errors

• Calling every pretibial rash NL without considering stasis dermatitis, GA, sarcoid, pretibial myxoedema.
• Aggressive debridement of inflammatory NL ulcers as if purely venous without diagnosis.
• Ignoring glycaemic assessment.
• Missing malignant change in chronic ulcerated plaques.
• Promising that tight HbA1c alone will reliably reverse established NL.