Cats,  Vet 101

Vet 101 – Q & A: Feline Sores (Eosinophilic Skin Disorder)

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Our vet, feline specialist Dr. Rich Goldstein from Mobile Vet Squad answers one reader question about mysterious sores.

Q: I have a dear kitty, a rescue spayed female Zoe maybe 6 years old. She has something called ‘rodent plaque’ from obsessive grooming. She gets blister-like sores on her lips that hurt her. The only cure has been to give her cortisone shots at the vet’s every 6-8 weeks. They say it is not good to do it more often. However, she gets itchy again in about a week, and I can’t seem to find what her allergy is. I would be so grateful if you have any suggestions.

Vet 101-rodent plaque-cats

Zoe (posted with permission)

A: Indolent, or rodent ulcers, and plaques, are part of a syndrome in cats called “eosinophilic skin diseases” (ESD). Typically, ulcers are found on the lips of affected cats, and appear as indented inflamed sores. Plaques are raised, hairless red areas that can be found on other parts of the body, especially the hind limbs. All of these lesions are named for the type of inflammatory cell usually seen, called the eosinophil.

There are many potential causes for eosinophilic skin diseases, although the exact cause is not always able to be determined. Since the sores are caused by inflammation, we need to look for possible underlying explanations for the inflammation. The list includes: allergies (to food, fleas, pollens, insects, environmental allergens), infections (viruses, fungi, bacteria), parasites (mange), cancers, immune reactions, stress, and the catch-all “idiopathic” (which is doctor-speak for a shrug of the shoulders).

The diagnosis of ESD is often based on the appearance and location of the sores, as well as response to treatment. Very often, the first step is to use the most potent anti-inflammatory of them all: corticosteroids (cortisone). Cortisone injections work quickly to remove the inflammation and make the cat feel better. But they don’t usually cure the problem. If the underlying cause is still there, the lesions will reappear at some point, which will require another cortisone injection. Over the long term, steroid injections can cause many problems, including diabetes, liver disease, kidney disease, and increased risk of urinary tract infections and pneumonia.

You can see the importance of trying to determine an underlying cause, and looking for alternative treatments if possible. So, let’s attack the list of possible explanations and see if we can narrow down the cause so that we can limit the use of steroids.

  • Food allergies are one of the more common causes of ESD. Usually it’s due to a specific ingredient in a food. But finding that ingredient can be very tricky. Using a specific hypoallergenic diet, made of either “novel protein sources” (i.e. a protein source that is not found in commercial cat foods) or “pulverized proteins” (i.e. proteins that are crushed to be too small to evoke an inflammatory response by the body), is often indicated. The key is: this is the ONLY food your kitty can eat for an 8-12 week trial period. If the problem comes under control or improves, continue the hypoallergenic diet for life.
  • Flea allergies. Now I know what you’re thinking: “My cat never goes outside, so it is impossible for her to have fleas.” Ah, if I had a nickel for every time I heard that… Believe it or not, flea allergies are a huge cause of eosinophilic skin diseases in cats. Sensitive cats are allergic to the saliva of the flea. So one – yes, ONE – flea that bites your cat can start the inflammatory reaction. Kind of like that person with a peanut allergy – “well, I only ate ONE…” Yup. It only takes one. So, unless your kitty lives in a hermetically sealed glass box (or in Alaska), preventatively treating cats with ESD for fleas is essential. Because 1 flea is too many.
  • Insect allergies, especially to mosquitos and (eek) cockroaches can also cause flare-ups, so light up the citronella and call the exterminator if needed!
  • Infections, like viruses (calicivirus or feline herpesvirus), bacteria, fungi, and parasites can sometimes be detected by microscopic examination of a skin scraping, impression smear, or fungal culture.
  • Cancers are not very common causes of rodent ulcers or plaques, but may need to be considered in cases that are not responding to treatment. In these cases, a small biopsy of the lesion may reveal the underlying answer.
  • Stress is now being recognized as a common underlying cause of many health issues in cats. Follow me on this one: If a behavioral issue rather than an allergic issue is causing your kitty to groom excessively, steroids may not help. In a case like this, dealing with whatever is triggering the excessive grooming behavior may alleviate the skin issues, and thereby resolve the lip ulcers. Pain (from arthritis, pinched nerves, or other causes) can also cause some cats to groom excessively, and may need to be investigated.

As you can see, there are lots of potential triggers for the ESD. Since steroids almost always help – even if only temporarily – they are often given initially to provide immediate relief (either as a long or short-acting injection, or orally) and to help narrow down the diagnosis. Based on the list of potential underlying causes, here are some other treatment options to consider speaking with your vet about:

  • Treat for fleas, even if you don’t see them. Remember: 1 flea is too many.
  • Transition to a hypoallergenic diet for at least 8 to 12 weeks before determining if it’s helping.
  • Make sure your home is free of insects like mosquitos and cockroaches.
  • Use a Hepa filter to help filter out environmental allergens.
  • Sometimes an antibiotic trial, with doxycycline, may show improvement. Doxycycline has the added benefit of having anti-inflammatory properties.
  • If your kitty uses plastic or ceramic bowls, try switching to stainless steel. Plastic and ceramic can elicit allergic reactions in some cats.
  • If your kitty is not responding to all of these “general” therapies, talk to your vet about possibly pursuing diagnostic testing (like a skin scrape, cytology, fungal culture, biopsy, and/or xrays of the areas the cat excessively grooms).
  • If there is a possibility that stress is a factor, a trial with a Feliway diffuser or Rescue Remedy may be worthwhile.
  • If your kitty does have ESD, and does not respond to steroids, or the injections are becoming too frequent, or he has other medical reasons not to use steroids, talk to your vet about possible alternative therapies, including cyclosporine, chlorambucil, interferon, and even acupuncture.
  • Keep in mind that sometimes steroids are the only thing that can give your cat relief. With proper monitoring by your vet, in these cases, steroids can be your cat’s friend.

Good luck and here’s to relief from the itch and mouth sores!

Have a question for Dr. G.? Email it to [email protected] Include a photo if you like.


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