Thom is about 7 yrs old. I found him by the roadside hunting bugs when he was small enough to fit in the palm of my hand. He had a pretty rough beginning including a 'D' ride via the fan belt of my car about a week after I rescued him from traffic. Shortly after recovering from that he bailed off the 'cat walk' in my house and re-injured himself. He walks with bowed legs that remind one of a cowhand off a long cattle drive. Anyway, this past New Years Eve he visited the Cat Dr not feeling well. Hair loss, blisters, flakes, sores, weight loss, vomiting... All of these things have come and gone... He weighed 10.44# on 12-31-08 He's been to see the Dr a total of 7 times between then and 7-21-09 at which time he weighed 8.06#. We've had him on Royal Canin Hypo-Allergenic Diet and Royal Canin IVD Green Pea and Lamb. (We are feeding the same diet to our other cat Chuck so he doesn't cross contaminate Thom when he grooms him). We tried a couple bouts of Derm Caps. At this point I think we've about decided he may be allergic to fish oils. He's had antibiotic shots, he just completed a week of Orbax 22.7 mg tabs. This just seems to keep going on and on and on.... Poor fella. We joke that he has Sympathetic Lupus in honor of my mom. She wondered if he might have diabetes. That has been ruled out. Dad has Parkinson's. I will run away if he developes that! I'm sole caregiver to both my parents... I know that's not funny but I have to have a sense humor or else... Oh yeah, I forgot to mention that New Years Day 08 he went to ER because he was passing bloody urine. So as you see he has a fairly extensive medical history and to get to the point do you have any idea as to what his problem might be? And what we could feed him that might be more affordable. Royal Canin just went up again and is almost $40 per 6# bag. I have no income and Mom and Dad are on a fixed income that is stretched pretty darn thin... Any suggestions you have would be greatly appreciated.Unfortunately, Kathy, this isn't a lot to go on. But based on what you're telling me, I can make a few assumptions and guesses. I will also assume that he has had a full chemistry panel and blood cell count since you said that diabetes was ruled out. If not, then this is the very next thing that needs to be done. If they haven't checked his thyroid level, then this should be done right away, as cats can be prone to hyperthyroidism which can lead to symptoms similar to what you describe.
If he was placed on one of these diets, I would assume that your vet is considering a food allergy. Allergies such as this are due to a reaction to one or more ingredients, usually something that he has been exposed to before and has developed a hypersensitivity to. There is no specific test for these allergies (well, tests exist but are notoriously inaccurate) so the affected pets are placed on a hypoallergenic diet to limit their ingredients. You also have to limit ANY other foods, snacks, treats, etc. during this trial period. If it is related to dietary ingredients, it can take 8-10 weeks to see any results. There are NO, I repeat NO foods other than veterinary diets that are truly hypoallergenic. Yes, these foods are expensive, but you can't look at them as strictly providing sustenance. The foods are a form of medical therapy as much as any injection or pills. For food allergic pets the diets are usually the ONLY form of therapy that really works. In situations like this, there really is no good alternate options, and you need to rearrange your budget to account for the cost.
Allergies can lead to skin irritation, which can allow secondary bacterial infections to affect the pet. Antibiotics are prescribed to help resolve the infection, but this does not treat the underlying condition that led to it in the first place. As far as the other conditions you mentioned...Diabetes is easily ruled out with blood and urine testing, but wouldn't cause skin problems like this. Lupus doesn't really affect cats and dogs like it does in humans, and has different symptoms that what it sounds like Thom has. Parkinson's isn't a concern you need to worry about. Fish oils are an uncommon food allergy, but not impossible. In fact, the omega fatty acids in fish oils are usually beneficial to skin problems by reducing inflammation. The bloody urine doesn't sound related to any of the rest, and urinary tract infections are a risk in male cats.
So to summarize the steps....(1) Perform a complete blood chemistry, blood cell count, urinalysis (not just for an infection), thyroid test, and test for feline leukemia and FIV. These tests will reveal a lot of information and can at least rule out possibilities even if it doesn't give you a specific answer. (2) Do a food trial on hypoallergenic diet for a minimum of 8-10 weeks. If this helps, then there really is no other option. (3) The next step is likely seeing a specialist. If the weight loss and vomiting is the main concern, then an internal medicine specialist may be needed. If the skin is the main problem then a dermatology specialist is your choice.
I realize that money may be tight, but in cases like this you aren't likely to get easy answers. The only way to get to the bottom of the problem is to follow the diagnostic pathways.
Kathy had an unrelated "P.S." on her email, which I'll address tomorrow.