A verruca is a caused by a virus and a corn is a lump of hard skin caused by stress on the tissues. They sound pretty different, so they should look different, right?
Usually, it is easy. Verrucae often form a perfect ring shape, or mosaic of rings, on the sole of the foot and they sometimes have the little black dots that everyone knows about. If the patient is a child, it is more likely to be a verruca, if they are older, it in more likely to be a corn. If it doesn’t hurt it is more likely to be a verucca, if it does, it is more likely to be a corn.
Like many medical things, even such an easy- sounding thing is not sounding such an exact science!
When I look at the lump, I am looking for a change in the finger print pattern and loops of capillaries. I also look if it bleeds easily and how the callus forms. There is also a way of pressing it that helps me to tell me if I am seeing a verruca or a corn.
Sometimes, despite looking at the two for too many years, I still get it wrong. I am more likely to mistake a verucca for a corn than the other way round. I am more likely to make a mistake with a painful young verucca that has not yet formed the ring and capillary structure, or if the area is covered by a big plaque of callus and the skin structure is altered by that.
Usually in these cases, a good clue is if a patient ends up back at the clinic because the pain is back too quickly. Veruccae replace their callus more quickly than corns. On this visit, the finger-print and capillary patterns are often easier to see.
(Oh, and just in case you are worried, neither veruccae nor corns are fatal !!!!)