If you haven't recently changed his diet or exposed him to any possible allergens, then, at 9, his skin problem and weight loss could be due to an internal problem.
The most common senior cat disease that can cause this type of hairloss, weightloss, increased urination, and increased drinking is hyperthyroidism. This is an overactive thyroid gland which causes an increase in the cat's metabolism. It is very common and easily treated with either medication or radioactive iodine treatment. It is easily diagnosed with a simple blood test. Owners of hyperthyroid cats often feel that their cats are not sick, because the increased metabolism causes a cat to have lots of energy and a great appetite. It is important to diagnose and treat hyperthyroidism, however, because excess thyroid hormone is toxic to heart muscle and can eventually lead to high blood pressure and heart disease.
Here are a few links for you about hyperthyroidism:
http://maxshouse.com/Hyperthyroidism_in_Cats.htm
http://www.avmi.net/NewFiles/Hyperthyroidism/Hyperthyroidism.html
http://www.fabcats.org/hyperthyroidism.html
Other possible internal causes of weightloss, skin problems, and increased urination and drinking include diabetes or certain cancers. It is also possible that your kitty has been exposed to something like ringworm, a type of fungal infection. If this is the case, then the problem will worsen and the patch will get bigger.
Please do have your cat looked at by a veterinarian - I know it is difficult to come up with the funds, especially at this time of year - but if it is hyperthyroidism, it is very treatable and fairly inexpensive to treat.
Best of luck to you and your cat and Happy New Year!
Dr. Olivia
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