28th May 2025

A 68-year-old man with a history of COPD presents to his GP with a several month history of 2-stones weight loss and skin changes in his armpits.

A 68-year-old man with a history of COPD presents to his GP with a several month history of 2-stones weight loss and skin changes in his armpits. On examination, he has dark, velvety, plaque-like skin lesions in both axillae. A diagnosis of acanthosis nigricans is made. His BMI is 21, and a random blood glucose is normal. He had a non-contrast trauma series CT chest/abdomen/pelvis 2 weeks ago when he was in a road traffic accident, which demonstrated no abnormality.

Which investigation is likely to reveal the underlying diagnosis?

Select the SINGLE most appropriate option from the list below. Select ONE option only.