Cat - Eosinophilic Granulomatous Disease

Question
Female 7-8 years old. Indoor after first two years.

EGD for about 1.5 - 2 years manifested by classic "Rodent" ulcers of her upper lips and upper palate. Mild generalized thinning of facial hair around chin and lips and ear rims. No bald spots just thinning.

Eosinophil count in the 4000's on differential blood test.

Initial treatment commenced Feb 2009:

Flea treatment (Advantage) given as she did have some fleas.

Food changed to Prescriptive Z/D hypoallergenic.

Water dish - glass,  food plate ceramic.

Environment changed. Took her to a different house and room never having pets. (Carpeted floor (Nylon)).

****From age 3 to present she has been in the company of her niece. They sleep and huddle together.  This has not changed - they are a twosome.

One year ago given 3 biweekly injections of 20mg Depomedrol. All lesions completely healed in less than 1 month.

At ~ 2 1/2 to just short of 3 months following the final Depo shot mild inflammation started to appear on her upper left palate.

Started oral Prednisolone at 5mg/day for 2 1/2 weeks but no effect. Increased to 10mg/day 2 weeks with no reversing effect. Lesions were worsening on both upper palate and lip.  Went to 15mg/day for 10 days and started to see mild reversal of lesions. Started a taper off over then next 5 weeks by the end of which her lesions were worsening and after 2 weeks off all steroids her lesions were almost (but not quite) as bad as initial diagnosis. The interesting thing was the lesions were only left sided this time. (Lip and upper palate).

Jan 2nd 2010 gave 20 mg Depo shot. 3 weeks later palate lesion healed. Lip lesion 85% healed.
Jan 23rd gave second 20mg Depo shot. Lip lesion continuing to improve.
=====================================================
It has been suggested to me to consider Atopica at 25mg/day for a month then see if no lesions return. If so, reduce to every other day for a month then every 3rd day.

OR consider Dermatological testing (SKIN) to try and find what she is allergic to and treat via allergy shots.

My question to you is - in your experience what is the success rate if any, in treating cats with EGD via allergy testing and shots if a specific allergen can be identified?

She has been flea free for a year. Eats only Z/D. Glass and ceramic food and water bowls.

Could she be allergic to her niece? They are always together.

Answer
Allergy testing in cats has not been perfected as in dogs. So you may never know what this cat is allergic to.  Eosinophilic Granuloma Complex is an allergic disease and that's why the depomedrol has helped. Some cats will also respond to an antihistamine, like chlorpheniramine.  Many cats develop diabetes from depo, so that's why we like Atopica if it works.  Another thing to do is to keep the cat on oral Clavamox for 30 days. This has been shown to decrease the reactivity of the mouth tissues and it can actually decrease the size of rodent ulcers.

I have used the CO2 Laser to debulk these rodent ulcers with some success in preventing them from coming back larger each time.