Well, we finally got the results from Othello's necropsy yesterday, but they didn't shed any light on what was making him sick. The vet's office is mailing us a copy of the report so I'll be able to look it over more thoroughly, but what she told me on the phone is the following:
-his lung was collapsed and he had a large amount of fluid in the pleural cavity
-he had lesions on his kidney that were consistent with previous hypoxic damage, and his kidneys were inflamed
-his liver was fatty and enlarged
As far as the kidneys, the "previous hypoxic damage" means that he experienced lack of oxygen to his kidneys at some point, and from what she said it seemed to be in the past. She said it could have happened at birth or when he was under anesthesia when he got neutered. This seemed to be unrelated to whatever was causing him problems in his last two days from what I could tell. She didn't say what might have caused his kidneys to be inflamed and I seem to have forgotten to ask because I have no notes written next to that on my little sheet of paper.
His liver was probably fatty and enlarged because he wasn't eating for a period of time. She said he probably had been eating less over a period of a month. When cats don't eat, apparently fat stores from other parts of their bodies go to their livers. He weighed 12 pounds when we weighed him around Christmas, and he weighed 9 when they did the necropsy, so he lost 3 pounds from not eating.
There is apparently nothing to suggest a reason why he would have collected so much fluid in his pleural cavity, or why he had a collapsed lung. I read online that a collapsed lung can be caused when fluid is drawn out with a needle, which is exactly what they did when we first brought him to the vet ER, so I don't know if it was collapsed previously and is related to the fluid, or is merely the result of the medical procedure performed on him.
I'm upset and confused because they weren't able to identify the cause of his sudden illness. They didn't say it was kidney failure, but kidney failure might explain the problems he had with his kidney (oh, they also mentioned that the central area of his kidney had an elevated level of different types of white blood cells, but they didn't seem to know why), and it can cause pleural effusion. I don't know why they didn't think it was kidney failure. I still have a lot of questions, and I'll probably call them back once I get the full report. They did say that it definitely wasn't heart disease or cancer, but they can't rule out the possibility that it was something infectious like FIP. Fortunately, we already had Desdemona tested for the coronavirus associated with FIP and she came back negative.
She did say that this most likely wasn't preventable or curable, so I feel a little better - this means we did the right thing in putting him to sleep. However, I don't know how they can make any statements like that when they don't even know what happened. However, the fact that they don't know what happened makes me feel better about not taking him in earlier if it is true that there was nothing we could do to save him. If they couldn't even determine what was wrong with him through a necropsy, I'm sure they wouldn't have been able to figure out what was wrong while he was still alive. His last month alive would have just been full of repeated trips to the vet and lots of poking, prodding, and sticking. He would have been miserable until he died, and I'm honestly not sure he would have lasted as long as he did under the stress of all the trips in the car, etc.
It's still difficult for me to take, though. He was so full of life. How could he have been that sick? And sometimes you just want a reason, someone to blame. Even if it's yourself.