Hello Davi, I'm Dr. Deb. I'll do my best to help you today.
I'm sorry for this concern for Griffen.
The ingestion of non-nutritional items is called Pica. The underlying cause of this condition is usually different for every cat (or dog, for that matter) but it's rarely secondary to a nutritional deficiency.
Cats who are anemic can develop pica but since his blood work was normal, then this isn't likely to be the cause.
Cats with underlying gastrointestinal disease, however, can develop this problem although we don't have a good understanding as to why.
Since his blood work was normal and thus many conditions such as diabetes, kidney issues and liver disease have been eliminated as possible causes, then there are likely to be two possible explanations for his new behavior:
1. Late onset Inflammatory Bowel Disease which is inflammation in the gastrointestinal tract.
Bloodwork would be normal, in most cases. Even an ultrasound wouldn't necessarily pick it up; it would take biopsies to diagnose. Obviously, most owners don't want to put their cats through this procedure, which is understandable.
Response to steroids can often be very useful in diagnosing IBD but there is usually a dietary component to this problem as well. Feeding grain free may help in some cases but often you have to feed more hypoallergenic diets such as Z/D (from your vet), or Natural BaXXXXX XXXXXmited Ingredient Diets, Nature's Variety Instincts line, Evo duck or venison, Nature's Variety Frozen Raw Medallions (I recommend that they be zapped in the microwave for 10-15 seconds on each side).
Sometimes this is a trial and error process---finding the food that your cat will eat as well as one that helps with the problem.
I often diagnose this condition based on a cat's response to steroids. If they are 100% better, then this is the presumptive diagnosis. It may seem like a crude way to diagnose this condition, but it's an effective one. And, since diabetes has been ruled out with blood work, then I don't worry about consequences of this drug since cats tolerate steroids better than any species I know.
Other treatment options include:
a. l-glutamine 500mg/day crush in food which is available at health food stores or online.
b. NuCat Senior which is a supplement which contains anti-oxidants.
c. Vitamin D3 1,000 IU day.. but not calcitriol. This amount of Vit D3 is not dangerous to cats
d) Probiotics such as Forti Flora which may be available from your vet, local pet or grain stores or online.
e) Over the counter Pepcid AC at a dose of 1/4th of a 10 mg tablet twice a day which may help with the nausea.
f) Cerenia which is a drug which would have to be prescribed by your vet but it's a very potent anti-vomiting drug which might help in this situation.
2. Unfortunately, cancer such as lymphoma can also present with the signs you're describing. Again, bloodwork would be normal in most cases. An ultrasound might detect abnormalities with a biopsy/aspirate needed to help confirm.
If you would consider pursuing additional testing, then steroids should not be given to Griffen since they might affect the results.
I hope this helps and gives you several options to consider for him. Deb