I'm no expert, but when Jasper went through a phase of chewing paws, I was advised that it can be a form of transfering pain relief to an area they can get to IYSWIM, Jasper was having some anal gland issues at the time, when that was sorted, the paw chewing stopped. He couldn't chew his glands, so chewed his feet instead.
I'd get a general check up at the vets and not concentrate soley on the paws.