my elderly cat

Question
Since July 2007 my cat has been losing weight. He started off at 17lbs and is now down to below 10. He had a kidney scare that turned out to not be a kidney problem at all. He has chronic constipation. He is on tapazol for his hyper thyroid and is on lactulose for his constipation. He has had both conditions for several years. He has had numerous complete blood tests, including checking his thyroid, and X-rays and an ultrasound. They all come back normal. The vets here don't know what is wrong with him. He eats pretty normal and he drinks normal. I have spent over 2000 dollars on my big precious since July, only to find the vets here say it is probably just old age. He is turning into a bag of bones and I don't know what else to do. I have taken him to all the available vets here to get other opinions. Again, everything is normal. He does have black scabby areas around his shoulders. I am not sure what they are caused from. He is a house cat and doesn't go outside. Do you have any idea what can be causing his weight loss. Please help.

Answer
It sounds like your kitty has had a pretty thorough work up. I have some thoughts but they may have already been addressed. Has he had an Leukemia/FIV test run recently? This is unlikely being indoors but is still part of a complete work up. Has he had a urine culture to check for infection in his kidneys or bladder? If not,  chronic kidney or bladder infection could be causing weight loss. Did the ultrasound show any enlarged lymph nodes? I always worry about Lymphoma in older cats that are losing weight with no obvious outward signs.  Feel free to send a follow-up reply.
Dr. G