Don't give up!
Age and kidneys
Cats without a home
There are veterinarians who give up too early. If they can't make a diagnosis (which can be difficult) they sometimes have a tendency to say that if the animal doesn't eat there is nothing you can do. We say this out of our own experience with Snurre: This can be so completely wrong, especially when the symptoms don't lead to a diagnosis.
Snurre had a mysterious disease in 2005 and didn't want to eat. The veterinarian gave up and said that he was so old anyway. Imagine someone saying that about a human! (Whoever wants to can amuse oneself with the tiresome cliché about humans being something completely different from animals, but that is not the point here). We fed him for several weeks eight times a day with wet food. Then - after all these weeks - a veterinarian came up with the idea that one could try cortison. And it turned everything around! Snurre became more alert from the cortison and started to eat by his own and the nighmare was over. Of course, cortison can affect the immun system negatively, but not to eat is far worse.
So, if a cat doesn't want to eat (regardless of diagnosis but especially if it is unclear), ask for cortison! A cat who doesn't eat won't get better, and a cat who eats of course gains strength, perhaps even enough to get well!