A 45-year-old man presents with sudden-onset of velvety, hyperpigmented, thickened skin in the axillae and nape of neck. He is non-obese with no family history of similar changes. The lesions have appeared over 3 months and are rapidly progressive. The most important next step is:

• A Skin biopsy to confirm acanthosis nigricans
• B CT abdomen/thorax to exclude underlying visceral malignancy ✓
• C Fasting blood glucose and insulin resistance assessment
• D Thyroid function test for hypothyroidism

Explanation

Malignant acanthosis nigricans is distinguished from benign AN by: non-obese patient, rapid onset, extensive distribution (beyond axillae — oral mucosa, palms, soles — tripe palms), and absence of metabolic syndrome. It is a paraneoplastic phenomenon most commonly associated with gastric adenocarcinoma (intra-abdominal malignancy), and less commonly lung, uterine, or breast carcinoma. The rapid progression in a non-obese adult mandates urgent malignancy workup including imaging. Benign AN is associated with obesity and insulin resistance.

Reference: Neena Khanna Illustrated Synopsis of Dermatology & STD, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.