Scabs on elderly indoor cat

Thanks so much in advance for your advice! My cat is ~15 and has an increasing number of scabs on her back. Our vet doesn't know what might be causing them besides overgrooming, but we don't really see her do anything that would cause them. She is on Revolution Plus and has tested negative for ringworm multiple times. Any thoughts on what might be causing this or how to prevent it would be very helpful!

Hello  Overgrooming is common in older cats, particularly those that may suffer from joint or spinal pain due to arthritis.  Cats did not evolve for social living in the same way that dogs have and as a result, do not communicate pain to one another particularly well.  They keep any signs of discomfort extremely subtle.  Indeed, when we mention pain, most owners say 'I don't think my cat is in pain,' but many of these cats do have arthritis or pancreatitis. They don't always lick where the pain is, but somewhere easy to reach in the general direction.

I wonder which test is being used for Ringworm? - as some Ringworm does not show up using common methods.  Alopecia linked to demodex mites is more rare in cats than in dogs, but may happen if for some reason immunity is low.  Thyroid, cancers and some other rare systemic diseases may also present with coat changes, as can incidental scabs that have fallen off.  I hope that something there is useful;  good questions for your vet are always:  What have you ruled out, what could still be present and what makes most sense to do next.  Wishing you both all the best.