Special thanks to guest expert Christine (formerly of The Rabbit Lived) for being guest veterinarian for this post. Unlike me, Christine actually is an expert.
"Do you have any ideas how to deal with a cat who's lost its mind? Our cat adjusted very well to the baby when she arrived, but began acting up when she started walking 3 months ago. He now routinely craps outside of the litter box, and today did it ON MY BED...WHILE I WAS PETTING HIM!We've taken him to the vet, and there doesn't appear to be a medical reason for this behaviour, so I'm hoping feverishly that you and/or your readers can offer some advice that works."
First, sympathies on the situation. Any behavior problem is a pain, but housebreaking issues are horrible, because you really need it to stop! now!
Always, always, get the pet checked out (as you have) first and as soon as possible. Something that starts out as a medical problem can end up becoming a bad habit if you wait too long. Since you have ruled out a medical cause, I have a few more thoughts.
How old is the cat, and is he having difficulty either getting to or into his box? Does he have to jump a baby gate? When he goes, is he positioning properly? Sometimes cats will avoid the box because arthirits or a metabolic disease makes it uncomfortable for them to get into the box.
Also, think really long and hard about what may have changed in the cat's environment when this started. Did you change the box? Move the box? Start using a different litter? Did he get frightened while in his box (say, by a friendly toddler)? Get a dog? Get another cat? How often are you cleaning the box? Has that changed?
Where is the cat doing the deed? Is it always in the same place (I once had a patient that would poop only on the husband's clothes...the cat and the husband despised each other) or is it dependent upon where the cat is when the need arises?
Treating the problem is going to depend a lot of whether or not you can track down an inciting cause. If the cat has some arthritis, try a lower box or make the route to the box uninhibited (some people will use a tension gate that they can attach several inches above the floor - baby can't get through but cat can squeeze under). Let me be really clear that you should never, never medicate your cat without talking to your vet...even if you think the underlying problem is pain, cats don't tolerate a lot of OTC drugs well, and I've had several patients land in the hospital or worse because of ibuprofen or tylenol that the owner gave. If you had tried a new kind of litter, change back. If you can't get to cleaning the box as fastidiously as Cat would like, try a self-cleaning box. If the box is covered, try it uncovered for a while.
I always recommend Feliway, which is a diffuser of cat pheromones. It doesn't always work, but if the cat is feeling some stress it can help make him a little more zen. You can get it online or from your vet. You can also try dropping some Rescue Remedy in Cat's water bowl or mixing it with water and spritzing it about the house. Make sure to use a good odor neutralizer when cleaning the accidents, because you don't want him being drawn back to the location by the odor.
If you can't find a cause, or nothing you've tried seems to be working, I'm a big proponent of drugs. For the cat, I mean. I spent years fighting the use of behavior modifying drugs in animals, until I adopted a dog that developed severe separation anxiety. Sometimes the animals need a little help with their brain chemistry so that they can respond to behavior modification better. If your vet dislikes behavior problems (and most do) ask for a referral. You may have a behaviorist in the area or you can do a phone consult. A behaviorist is a fully qualified vet with extra training and board certification in behavior problems. This is not a trainer. This is someone who can get you the drugs. Or get the cat the drugs.
I know the inclination is to always blame the stress of the baby for this, but my first thought reading this (understanding that I don't have a lot of details) is that Cat is uncomfortable in the box or is having a hard time getting to it. Elimination problems in cats can be tremendously frustrating and are one of the most frequent reasons why a cat will be relinquished or euthanized. It's unlikely you're going to change one thing and the problem will be magically gone, but with patience and some creativity, I've had a lot of success working with owners on this. Keep the faith.
And send me an email if you have more questions.