cat pooping outside litter box

Question
Hi my female cat (six years old) has stopped using the litter box and is pooping on the floor of my furnace room instead. She seems otherwise healthy, good appetite, playful, affectionate and purrs a lot. This behaviour started after one of my other cats had to be euthanized due to chronic renal failure. The other cat used to use the boxes so they may have her scent on them, although I clean them with an enzymatic cleaner. She'll go outside in the garden but doesn't want to have anything to do with the boxes. She does have occasional bouts of diarrhea for a day or so then it clears up, but the vet doesn't know what's causing it. She also steals inappropriate food which doesn't help (ie bread etc) and chews on everything, a habit she's had since she was a kitten. Any ideas?

Answer
This is always a tough one Lynn. You pretty much have it figured out however- it started after your other cat died. So there is some anxiety going on as well as maybe some confusion between going outside and using the boxes.

I would get rid of these boxes or bleach them out completely, and get fresh litter for them. That might clear all scent of the other cat out of there.
Sometimes laying aluminum foil under and around the box also helps the cat to not go outside of it, as they don't like touching the foil.

Since it's almost always a behavioral issue, things must be undone or changed to change the direction of that behavior. You can't undo the loss of your cat, but the foil, or a new box, or even rugs (scrap pieces) under the boxes might help change her patterns.

This page might help some with this issue. It's full of tips and tricks:
http://www.peteducation.com/article_print.cfm?c=1+2174&aid=158

Hopefully you will hit on something that works. Sometimes it's easy, sometimes it takes some doing.

Please let me know how it goes.