Extreme Weght Extreme Appetite

Hi. He's thirteen years old, domestic short hair, neutered, inside/outside cat. He was once a large cat weighing in at 18 pounds. Now he's under 8 pounds. Voracious appetite and makes sure we know it. Been to three vets; all followed convention, despite my pleas to think outside the box. Parasites, hypothyroid, bloodwork, chemistry tests: all items tested for were negative, and/or within reference range. Stool seems OK. I was told that there are no symptoms of cancer.
He eats probably three times what he should. We switched to hi quality/hi protein EVO catfood, and tried goats milk. Probiotics/enzyme powder doesn't seem to be helping. Skin and bones is descriptive as he has lost a lot of muscle mass. He is wasting away. Every problem has an answer, I just need to find the person who has that answer.
 

Meant to say   "Extreme Weight Loss /  Extreme Appetite

Was diabetes ruled out? There is a specific blood work test for that called the fructosamine. Ask the vet if that was done. Does the litter box use seem normal or excessive? Any large sticky clumps of sugary smelling urine? Does the cat's breath smell normal or does ti smell like nail polish remover?

How much EVO are you feeding? Is it dry or canned?

See if your vet can contact other vets to get their opinion. VIN.com is a popular vet-only web site with a forum for vets to discuss cases and get opnions. The vet school your vet attended is another good resource. Your vet can get a consult from any number of vet specialists at this vet hospital.

Hmmm, you are the 2nd person with this issue within just a few days!  Only different is the other cat is young,  Just about one year old and female. 

The ONLY thing I can think of might be Malabsorption Syndrome, but usually with that there is some issue with their stools, so not feeling confident that's what it might be.

Curiouis...what are the "symptoms of cancer"?  Sometimes elevated WBC, but not always, I don't think.  Think it depends on the type.

Wish I had some answers, or even some ideas for you.  Please keep us posted as you learn  more.  Maybe your Vet could even contact a Veterinary University like UC Davis.  They're usually on the cutting edge.

I'd second the inquiry about Diabetes. I'd make sure they completely rule that out with a glucose curve. Any excessive peeing? Has the weightless stabilized? I have had more than one cat lose a lot of weight as part of the aging process 13 is about that age, but not 10 lbs more like 5 or 6lbs.