Devon Rex 8yo chronic diarrhea

I'm about to go back to the vet for the umpteenth time, and I'm trying to get some outside advice because I'm really getting worried that my cat is declining in health while the vet dilly dallies. 

Cat is a male 8yo devon rex, and in the past 6-7 months, has begun eliminating outside of the box. It 2 months after we got a Litter Robot, and at first, we thought he was just scared of the LR. After 3 weeks, we finally gave up on the LR and put back normal litterboxes, and it did not solve the problem. 

At the same time, we were noticing that the stool was getting softer and softer. It went from being soft to now, just being pure liquid. 

The cat is on a plan with Banfield so we take him in, no problem, but he does see different vets almost every time. First vet said no parasites in the stool but put us on something to kill any worms and stuff. 

In the past 2 months, he started growling like something hurt him after he ate, and then he would go eliminate, sometimes in the box and sometimes out. We finally begged them to XRay the cat and turned up a rubber band (hairtie) in his stomach, which $1700 later, was removed. 

They put him on 2 weeks of pill metronizadale and he had his first solid bowel movement in months. Everything was great for 3-4 days! Of course, he was lethargic and all from the pain killers but he was going in the box, not growling, and the movements were somewhat firm. 

After stopping the metro, he got worse pretty quickly. Took him back in, they took another xray and confirmed there is no blockage but he still has lots of gas. I got them to put him on hydrolized amino acid food as well.  as 2 weeks of metronizadole. 

4 weeks later, he was going on the floor but only 1 per day, unlike before when he might go 7-8 times overnight.  we noticed he was really light and took him back in. He normally weighs 8 lbs, has gotten as high as 8.9lb, and now, he's 7lb. Vet put him back in liquid metro and he HATES it. 

Now, he's going outside the box even after a week of metro. It's pure liquid brown stuff, and several times we've watched him walking like it hurts to walk, leaking a light brown liquid in spurts. He is lethargic and is hiding himself under the covers which he never does, but when he does come out, for some petting, he seems happy enough. 

Thyroid is the opposite direction of what would be happening if he had a thyroid problem. Still no parasites in the stool. Kidneys test normal too. He's eating, not like he's starving, but he does eat regularly, and he seems to be drinking ok. The Vet's quote to me was "other than this stool issue, he's a perfectly healthy cat." 

He has a follow up in 4 days but I'm thinking to take him back early. The metronizadole is not having the same good effect as last time, and I want to discuss putting him on prednisalone. I don't want to pay for another surgery for diagnosis, my research seems to show that metronizadole should help fix, and if not, then the prednisalone, if it works, can basically confirm IBD, and we can then discuss keeping the cat on the medicine for long term. But, the vet seems happy to just keep putting him on more and more metronizadole, and while they drag out these trials and various options, my cat is wasting away and ruining all of the carpet. We are now 6-7 weeks on the hydrolized amino acid diet, which I know might not be enough to rule out food allergy. 

The 11 yo female Devon/Siamese mix is doing fine, just happy as pie. If anything she's happier because the boy isn't chasing her around as much. 

Gosh, sounds like your little guy has been though the ringer these past several months . 

From what I understand, 1)  metro can actually CAUSE diarrhea (one of the side effects), which may be why you are now continuing to see it, and 2), the only way to be 100% certain of IBD is with a biopsy.   Also, on the food, since you've got at least one other cat, is your female eating the same "new" food, or is she eating her usual food?  Is there a chance your boy is eating ANYTHING other than the hydrolyzed amino acid food...any treats, HER food, anything food with his meds, etc?  Anything like that can mess things up. What food are you using BTW?

Have you read this article on IBD?  I find it very insightful: http://www.vet.cornell.edu/fhc/Health_Information/brochure_ibd.cfm

With diarrhea, often we recommend using probiotics and/or  slippery elm bark, but I just don't know since you ARE in a food trial how they might effect that.  That's something you could ask whatever Vet you see.  I'm guessing probably not.  Here's another article I found on food trials:  http://www.peteducation.com/article.cfm?c=1+2141&aid=142

What prescription food are you on? I've had problems with both Hills z/d and Purina HA causing diarrhea in cats when the diet is fed for more than 3-4 weeks. I didn't feed the Royal Canin long enough to know if that causes issues as well.

Also, does your cat have access to outside? Are the fecal tests being done in clinic or are they being sent to an outside lab?

What food was he eating before the prescription?

Both cats are on the same food, and nothing else is given to them. Royal Canin hydrolized food. 

They don't go outside or have access. 

Before this, they were on a mix of dry Purina Focus, and a few wet foods, mostly Friskies. Two years ago we had a vet who thought some minor skin irritation was due to beef and fish oils in the foods, so we only used foods without those. We'd feed some wet, then some dry, but they've mostly preferred the dry the whole time. 

I decided to stop the metronizadole for a day to see, and so far the cat is a little perkier tonight. Still diarhea, but I think the metro was making the cat very lethargic and that scared me. I'll see when I can get the cat in for another vet appointment and ask if we can try something else other than metronizadole. 

Never heard of slippery elm bark but what probiotics do you recommend? We've used some random ones in the past, the current one I have is the GNC powdered one, but I haven't been giving it. 

These are the probiotics my cats get:  http://www.thecatsite.com/products/category/vitamins-supplements/natural-factors-mfgr  1/2 capsule mixed into there food in the morning and 1/2 at night.   Some people give this one: 
Slippery Elm Bark is used by many, many people for themselves and their animals for digestive issues.  It's a natural product. 

But as I said, since you are on a food trial, I would definitely discuss with my Vet whether adding any of these would be ok before doing it.