Eruptive xanthomas — SCE Dermatology MCQ

Correct answer: A — Severe hypertriglyceridaemia with lipid-laden macrophages

The correct answer is A, severe hypertriglyceridaemia with lipid-laden macrophages. This man has eruptive xanthomas, crops of yellow red papules with erythematous halos over extensor surfaces and buttocks, occurring in the context of poorly controlled diabetes and a markedly raised fasting triglyceride of 32 mmol/L. At such extreme triglyceride levels, chylomicronaemia leads to lipid extravasation into the dermis, where macrophages phagocytose the lipid to form foam cells, producing the characteristic papular eruption. This is a recognised cutaneous marker of severe hypertriglyceridaemia and predicts significant risk of acute pancreatitis, which is why UK lipid guidance mandates urgent specialist referral once triglycerides exceed 20 mmol/L. Why the other options are wrong: C. Autoantibodies against desmoglein proteins: this describes pemphigus vulgaris/foliaceus, causing flaccid bullae and mucosal erosions via acantholysis, not firm papules linked to lipid levels. E. IgA deposition in dermal papillae: this is the mechanism of dermatitis herpetiformis, producing intensely pruritic vesicles on extensor surfaces in coeliac disease, not tender xanthomatous papules. B. Mutation in keratin 5 or 14: this causes epidermolysis bullosa simplex, with skin fragility and blistering after minor trauma, unrelated to lipid metabolism. D. Complement-mediated dermal vessel inflammation: this describes cutaneous small vessel vasculitis, presenting as palpable purpura, not lipid-filled papules, and does not correlate with triglyceride levels. Key point: crops of tender yellow papules with erythematous halos plus grossly elevated triglycerides equals eruptive xanthoma, a marker of pancreatitis risk requiring urgent lipid-lowering treatment and specialist referral.

Reference: NICE Clinical Knowledge Summaries: Lipid modification - CVD prevention; specialist referral advised for triglycerides >20 mmol/L due to pancreatitis risk (https://cks.nice.org.uk/topics/lipid-modification-cvd-prevention/)