Jules, so sorry for your friend and the 13 yr old cat and hope it had nothing to do w/ the food because all of us are trying to be careful, do the right thing. Yet somehow we feel completely guilty when something like this occurs.
Now for some good news! Jake's vet quickly locacted what she thought to be the problem. He has inflammation between last lumbar disk and the sacrum. Her exam told her this was most likely cause and so he was sedated for digital radiographs. Right where she told us she thought he had a problem we could see it plain as day. SM is not the cause, which would be much worse to deal with. So he's already had his first laser treatment and home to be kept quiet for a week. Rimadyl 2X daily and back in a week for another laser treatment. We'll see how he's doing at that point as far as activity that will be allowed. Right now it is no walks and to be carried down the 3 steps into the yard just for necessities, carried back in. We're due snow Sat and Sun. Rain, too, and down in the teens. That means ice, naturally. Speaking of ice, a Cavalier friend has suggested we ice the area to reduce inflammation and also for some additional pain relief. Am also wondering about accupuncture.