Cat skin irritation

Question
Ever since I moved into my new place last october my cat has been suffering from skin irritations on his chest and inner forearms. If left long enough the irritations are licked raw. The patches feel like scar tissue and appear in the exact same place everytime. Every month or two I visit the vet. He gives my cat a shot of cortizon and we've tried antibiotics as well as hormone supplements. Recently  we've been using the cortizon and a topical spray. This seemed to keep the irritation away the longest, but now it is returning. Currently my cat just has the rough patches on his chest but they are not as irritated and red as usual. My vest has suggested a biopsy to get to the root of the problem and find out if he is allergic to something in the house. But I find that expensive and I worry about putting my cat into surgery. Have you ever heard of something like this before? Is there an easier and cheaper way to cure him?

Answer
You are describing one way that cats show skin allergies.  If the cortisone shot helps, it may last 6-8 weeks if your vet is using a drug called DepoMedrol.  We use that a lot in cats.  There is an antihistamine that helps some cats.  It is called chlorpheniramine and I usually give 2mg twice a day.  In addition, some cats do this because they are in a new environment and they have a psychological reaction that causes them to pull out the hair.  For that I use a drug called amitryptyline at 5-10 mg per day.  Check with your vet about these treatments.