Thank you for the additional information! I wanted to rule out any type of parasites. There are a couple of things in older cats that can cause hair loss/thinning hair. It's usually best to have them checked by your vet to rule out any serious issues, but in most cases hairloss can be caused by a condition call hyperthyroidism. This also sometimes exhibits itself by having your cat be much hungrier, but not gaining any excessive weight - in fact, many times they appear to loose muscle mass or weight. Another thing that can cause hair loss in this area is simply hair follicles that have been damaged by a vaccine or vaccines over the years. Sometimes, the hair follicles will start dropping hair - similiar to a man that is balding, due to trauma from a vaccine or just due to aging.

If you can't see any other symptoms other than the thinning hair in that area, you might try using a product called Megatek Coat Rebuilder. You can see it here:

http://www.revivalanimal.com/store/p/693-Mega-Tek-Coat-Rebuilder-for-Pets.aspx

It is very effective - I have used it on girls that were shaved for spaying trying to get their coats re-established for showing, and it does work. I would definitely keep an eye on her demeanor and if nothing else seems out of the ordinary with her, then you might try the Megatek.....if you see any physical changes other than the coat loss, I would contact your vet and have him do some routine checks and possibly some bloodwork to ensure nothing serious is going on.

Please let me know if I can help further in any way!