Any help appreciated.
We have a 12 year old calico cat which recently was diagnosed with a bit of arthritis in the rear legs but otherwise in good health.

About a week ago, 'it' stopped letting people touch her front paws - really hissing as if sensitive. We left her alone a few days but now she won't lie down...just sits up (the Egyptian cat look) but keeps shifting from paw to paw.
We took her to a Vet, but other then a bit more than normal 'red' look to the paws (normal temp) he was at a loss...suggesting that when he sees things like this, it is due to a burn or something new mopped on floors and rugs (neither of which we have seen or done).
He gave her a light pain medication (usually reserved for cleaning teeth and such).
Since then she does seem more comfortable, but now seems to have stopped going to the bathroom..BUT otherwise in good health (drinks and eats OK).

Still sensitive on the paws.
Does anyone have ANY idea what is going on here?

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Are you sure she's completely stopped going to the bathroom? Perhaps because of her sensitive paws, she is not using the litterbox, but going somewhere else in the house. Also, the cat hasn't been declawed, has it?
See my cats: Raw Diet Info: Declawing Info:
Still sensitive on the paws. Does anyone have ANY idea what is going on here?

If she was declawed, abnormal bone growth can occur late in life as arthritis develops. If it was done incorrectly, the claw can regrow inside the paw. Only x-rays will show this.
If she was not declawed, osteoarthritis can still cause misshapen bone growth in the "fingers" that may be painful to her. There are other (usually geriatric) bone diseases that can cause odd growths, too.

Also, I assume her claws, if she still has them, have been checked to be sure they aren't growing around and into the pads?

As to elimination, she's probably using a new spot. Check with a blacklight if you can't seem to find it, as the urine will glow. If she really isn't going, this would be a REALLY big emergency problem. So you should really look for her new spot to make sure she is eliminating properly.

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