Necrobiosis lipoidica — SCE Dermatology MCQ

Instant feedback + full explanation. One question, done properly.

ModerateGeneral dermatology & dermatology in primary health careNecrobiosis lipoidicaSCE Dermatology

A 44-year-old woman has yellow-brown atrophic plaques with telangiectasia on the shins. The borders are violaceous and slightly raised, and sensation is normal. She has no previous diagnosis of diabetes. What is the most appropriate investigation?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: D — HbA1c or fasting glucose assessment

The correct answer is D, HbA1c or fasting glucose assessment. The clinical picture of yellow-brown atrophic plaques with telangiectasia and violaceous, slightly raised borders on the shin is classic for necrobiosis lipoidica, a condition strongly associated with diabetes mellitus. Around two thirds of cases occur in people with diabetes, and necrobiosis lipoidica can be the presenting feature of previously undiagnosed diabetes, so any new case in a non-diabetic patient warrants glycaemic screening. Normal sensation excludes a neuropathic ulcer as the concern and confirms this is a diagnosis-driven screening decision rather than a wound care issue. Diagnosis is usually clinical, but screening bloods (HbA1c or fasting glucose) are the appropriate next step to identify undiagnosed diabetes or prediabetes. Why the other options are wrong: B. Skin-prick testing to insulin: this tests for immediate hypersensitivity to insulin, relevant only in patients already using insulin who develop urticarial or anaphylactic reactions, not for diagnosing the skin lesion or its systemic association. A. Patch testing to topical steroids: this investigates allergic contact dermatitis to steroid preparations, which is irrelevant here as there is no history of topical steroid use or eczematous reaction pattern. C. Dermoscopy for melanoma features: the described lesion (atrophic, telangiectatic, violaceous border) is not consistent with melanocytic pathology, and dermoscopy for melanoma is not the discriminating investigation for a granulomatous shin plaque. E. Bacterial swab from intact plaque: there is no indication of infection (no discharge, ulceration or signs of cellulitis), so swabbing intact skin would not be clinically useful. Key point: new necrobiosis lipoidica-type shin plaques in a patient without known diabetes should prompt HbA1c or fasting glucose testing, as this is a recognised marker of undiagnosed diabetes.

Reference: DermNet NZ, Necrobiosis Lipoidica, 2021, https://dermnetnz.org/topics/necrobiosis-lipoidica