My American Bulldog was diagnosed with interdigital cysts / pododermatitis a while ago. You treat with antibiotics. It can be a really tough thing to get rid of. Bulldogs are particularily prone to it. Sometimes, the cause of the cysts is unknown. However, it can be caused by contact dermatitis, trauma to the pad of the foot, food allergies, etc. If you believe that your vet has misdiagnosed your dog, seek a second opinion with a different doctor.

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Lesya & Sophie 

A Dog Owner's Prayer
Oh Lord, don't let me once forget how I love my trusty pet.
Help me learn to disregard canine craters in my yard.
Show me how to be a buddy even when my sofa's muddy.
Don't allow my pooch to munch postal carriers for lunch.
Shield my neighbor's cat from view--guide my steps around the doo.
Train me not to curse and scowl when it's puppy's night to howl.
Grant I shan't awake in fear with a cold nose in my ear.
Give me patience without end--help me be my dog's "best friend".
Author unknown
Thanks to Pattie Lawler
http://www.behaviour-problems.freeserve.co.uk/2/Poems/dogownerpray.htm