Acanthosis Nigricans — SCE Dermatology MCQ

Correct answer: A — Insulin resistance/type 2 diabetes mellitus

The correct answer is A, insulin resistance/type 2 diabetes mellitus. The combination of multiple acrochordons in flexural sites (axillae, neck) with acanthosis nigricans and obesity (BMI 38) is the classic cutaneous signature of hyperinsulinaemia. Acanthosis nigricans arises when high circulating insulin cross-reacts with insulin-like growth factor receptors on keratinocytes and dermal fibroblasts, driving epidermal thickening and the velvety hyperpigmentation seen in flexures, while insulin also has trophic effects on fibroblasts that promote skin tag formation. A UK case-control study in an overweight population confirmed that those with acanthosis nigricans have significantly higher fasting insulin and HOMA-IR scores than BMI-matched controls without it, supporting its use as a marker prompting screening for insulin resistance and type 2 diabetes with fasting glucose or HbA1c. Given the obesity and skin findings here, formal metabolic screening is indicated rather than treating the skin changes in isolation. Why the other options are wrong: C. Vitamin D deficiency: causes rickets, osteomalacia or nonspecific myalgia, not flexural pigmented plaques or skin tags, and has no mechanistic link to acrochordons. D. Iron deficiency: produces koilonychia, glossitis and pallor, not acanthosis nigricans or acrochordons; there is no pathophysiological connection to hyperinsulinaemia. B. Hypothyroidism: can cause dry, coarse skin and myxoedema but does not produce the velvety hyperpigmented flexural change or multiple skin tags characteristic of insulin resistance. E. Coeliac disease: associated with dermatitis herpetiformis (vesicular, extensor surfaces) and malabsorption features, not acanthosis nigricans or skin tags. Key point: Acrochordons plus acanthosis nigricans in an obese patient should trigger screening for insulin resistance and type 2 diabetes, as both are cutaneous markers of hyperinsulinaemia.

Reference: Single-centre case-control study investigating the association between acanthosis nigricans, insulin resistance and type 2 diabetes in a young, overweight, UK population, PMC 2022 (https://pmc.ncbi.nlm.nih.gov/articles/PMC9454057/); see also NICE NG28 Type 2 diabetes in adults: management, for HbA1c-based screening in at-risk individuals.