FFinalistSouthampton · 2027
Dermatology
AKT · Dermatology/Reactive & systemic signs

Acanthosis nigricans

Insulin-resistance (or paraneoplastic) epidermal change

Overview

Symmetrical, velvety, hyperpigmented thickening of flexural skin (neck, axillae, groin). Almost always a sign of INSULIN RESISTANCE (obesity, type 2 diabetes, PCOS); a sudden, extensive or atypical-site onset in a thin adult is the paraneoplastic red flag for an internal (classically gastric) adenocarcinoma.

Recognise

  • Velvety, hyperpigmented, thickened plaques in the flexures — posterior neck, axillae and groin
  • Symmetrical and gradually progressive; skin tags often coexist
  • Most cases reflect insulin resistance — obesity, type 2 diabetes, PCOS

Red flags

  • Sudden, rapidly extensive, or unusual-site (palms/mucosae — "tripe palms") acanthosis nigricans in a non-obese adult → paraneoplastic marker of internal malignancy (gastric adenocarcinoma)

Differentials & how to tell them apart

Confluent and reticulated papillomatosisreticulated brown patches on the trunk (a separate entity)
Tinea/erythrasma (flexural)scaly or coral-red fluorescent, not velvety thickening
Post-inflammatory pigmentationfollows a prior dermatosis, not velvety

Clinical image

We can't host this one — the image is DermNet's and their licence doesn't cover us republishing it. Their page for it is free to view.

Acanthosis nigricans — clinical imagesDermNet

Investigations

Clinical. Investigate the cause: fasting glucose/HbA1c, lipids, and a PCOS work-up where relevant; if the onset is sudden/extensive/atypical → investigate for underlying malignancy.

Management

Treat the underlying cause — weight loss and improved insulin sensitivity (or the malignancy)

  1. 1Identify and treat the cause: weight loss and glycaemic control for the common insulin-resistance form; topical keratolytics/retinoids as cosmetic adjuncts.Gate: A SUDDEN, extensive acanthosis nigricans (± tripe palms, mucosal involvement) in a non-obese adult is PARANEOPLASTIC → investigate for an internal malignancy (classically gastric adenocarcinoma) rather than just managing the skin
  2. 2Optimise diabetes/PCOS; paraneoplastic disease → treat the underlying cancer (the skin improves if the tumour is controlled).
Treat the underlying insulin resistance — weight loss + glycaemic control improve the skin
Topical retinoids/keratolytics — cosmetic adjuncts
Investigate + treat malignancy — if paraneoplastic

Key points

It is a window onto metabolic health — the commonest message is insulin resistance. The exam trap is the abrupt paraneoplastic onset signalling gastric cancer.

Monitor & prognosis

Metabolic parameters; malignancy work-up if paraneoplastic.

Improves with treatment of the underlying cause.

Source: DermNet; StatPearls