The doctor may ask questions about your symptoms to rule out other conditions. She/he will try to work out what has caused the flare-up, e. g another illness, stress, some medications, smoking. She/he will examine the patches. This may be enough to make a diagnosis. However, in some cases, she/he may need to get a small sample of the patches so that they can be looked at under a microscope.
Attribution: Avallain