Cat Allergic and on Royal Canin HP but still has problems

Hi all , 
I have a 4 year old black cat Jake and in the past year he's developed a habit of licking himself raw in patches of his underbelly. This developed when I had gone on vacation for 3 weeks and he had been with a cat sitter and two other cats we own. The vet diagnosed it as allergies and gave him an allergy shot and steroid shot which calmed him down and his hair regrew but the problem is that in the meantime he had been eating the Natural Balance Limited PD food and was fine with it til 2 months after he got the shot when he restarted. 

At this point we took him to the vet again and put him on Royal Canin's Hypo PD food which seemed to help til he suddenly stopped eating it and started licking himself again. I took him again to the vet where they gave him the same two shots as before and switched him to Royal Canin's Hypo Hydrolized Protein food which he has been eating. 

However now he's been meowing consistently for food every hour! It's driving me crazy because I keep filling his bowl and he eats it all but is never full and acts as if he's starving. Our house does not have fleas and he has never had fleas so we can confirm its not a tape worm but then could it be the food? I know HP has no real meat in it but if so I am nearing the end of options I have right now of what I can do for him, help please!

Is he eating HP dry or wet? What was the allergy shot? Have you considered other possible allergens, such as cat litter?

He's eating the dry food and I'd been supplementing it with the royal canin wet hypo PD food since he's started asking frequently for food. I need to find receipts to verify but I remember the shots being hydrocortisone shots and since his allergies started we've switched his litter from clay to sand to no change.

If a steroid was given, it might explain the increase in his appetite. We recently did a food trial with a different Royal Canin food...PR... and at least with that particular variety, the calorie content was significantly less that what we had been previously feeding him... the dry was 100 calories less per cup, and the wet almost 60 calories less, per can.  So that is something to consider, as well.

Are your other cats being fed something different? Is it possible he snuck a bite of their food? One little crumb of a food allergen can set things off.

It's also possible for him to be allergic to something in his environment. A food change did not help our cat, and allergy testing revealed that dust and mold spores, as well as a few pollens, are the likely culprits in his case.

About 50% of cats with allergy related skin conditions will respond favorably to daily antihistamines. If you're certain he hasn't eaten anything except his prescribed food, this is the next route I would discuss with your vet. We are trying it with our George.

Other than the increased appetite, which could be from the steroid shot as @Burkey mentioned, are you seeing improvement with the licking on the HP? Is Jake also scratching, or it mostly just licking? In my experience, a food allergy that is affecting the skin will cause a lot of scratching, especially around the neck, face, and ears.

Are you sure Jake's licking isn't behavior/psychological? There's a condition called Psychogenic Alopecia, which is basically overgrooming caused by stress. This seems something to consider, especially if the food is not helping and you said this started when you went away for three weeks. That could have been a "trigger" for Jake.

Here's a good article about it: http://www.catbehaviorassociates.com/psychogenic-alopecia-in-cats/

Cats are very sensitive to changes in their routine and can get stressed easily, even when it doesn't seem to us that they are stressed. Psychogenic Alopecia is not uncommon, so it might be worth looking into. For mild cases, simply putting a few Feliway diffusers around the home and/or offering a calming treat once or twice a day might help. Jackson Galaxy makes a Spirit Essence called "Obsession Remedy" that you could try. For more severe cases, people have had to put their cat on an anti-anxiety medication.

Burkey said:

About 50% of cats with allergy related skin conditions will respond favorably to daily antihistamines. If you're certain he hasn't eaten anything except his prescribed food, this is the next route I would discuss with your vet. We are trying it with our George.

Click to expand...

Just a quick thought on this...

Some antihistamines can cause drowsiness and sedation, which may create a sense of calm in the cat. Some vets use antihistamines to address temporary anxiety (my sister's vet did this for her cat who was defecating outside the box). This might make it difficult to discern whether it is helping with a true allergy or stress.

Since George is getting visible lumps on his skin, it does sound he has a true allergy. But with Jake's relentless licking, it does make me question an allergy.