1st April 2022

A 55-year-old man presents with a rash

A 55-year-old man presents with a rash. He has multiple small patches of dry red skin, mainly on his legs, which he says are very itchy. He had eczema as a child, but has not had any issues with his skin for many years. He is otherwise fit and well and takes no regular medications. There are no features of the history suggestive of a new skin contacts. An example of the lesions are shown below:

Image: By James Heilman, MD – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=40647837

What is the most appropriate investigation? Select the SINGLE most appropriate investigation from