Thank you again,
Now the dilemma here is that her recently diagnosed health issue very much could have been the initial trigger for this inappropriate elimination. The problem is that if she has been doing this for a month, there is serious concern that her reasons now are just based in habit. Therefore, we are likely facing an uphill battle for her. Of course, we do also have to consider that cats can become aversive to their litter boxes if they do not like their location (either from a negative experience or if they find going into the basement daunting).
With these issues in mind, the first step here would be ensure that you are cleaning any where she has gone thoroughly. To do so, I would advise using an enzymatic odor neutralizing cleaner (ie Nature's Miracle, Fizzion) wherever she has gone because while normal cleaners will eliminate the smell to us, she may still be able to smell her own scent and thus choose to go there again. And this is something we really need to remove here since that would just re-establish her going out of the box out of habit. And just to note, if you want to find all the places she has gone, I would note that cat urine does glow under black light and this can help you find all the sites that need to be addressed.
Otherwise, at her age, arthritis would be another concern that could still play a role even with her current diagnosis and treatment. And I would note that age associated arthritis often does manifest in this manner. Cats, unlike dogs, go to great lengths to modify their lives around avoiding things that cause them discomfort. Where a dog will run on a sore leg until she can’t use it, a cat will just decrease doing the things that are causing the pain. It is wise for the cat, harder for us to pick up when there is a problem.
Unfortunately, in cats with pain derived litter box issues, trips to the litter box aren’t something that can be skipped. So no matter how much discomfort it can cause, life demands that a cat not stop using the toilet. And in these cases, this behavior is often related to
discomfort in the back, hips, and back legs. And again it is possible that if this is mild at this point, than these litter box signs might be our only hints and the only time we can appreciate that she isn’t 100%. And it is understandable, because if you imagine, toileting requires significant forces on the body, which they do while balancing on pebble like litter, while standing on two feet. Often in cats with back pain or arthritis, this can be a bit much. And this is when they just decide that it is easier to go outside the box (often choosing a substrate that they can get better grip on like carpets or hard floors are free of the pebble like texture that litter has). For some cats this will then become an all the time occurrence, while others will just do it intermittently (when they can't be asked to deal with the box). The problem is the more they do it, the more likely they are to continue to do so as it goes from being a lapse to a habit.
So, I would also advise making sure that we are addressing any lurking joint discomfort she may have. To start, I would note that there are some joint supplements that can be of benefit. First, you may consider trying glucosamine/chondroitin supplementation with her. This is a nutrient supplement that is available at your vets, pet shops, and health food stores (as capsules, liquids, and even treats). It works by aiding joint suppleness by helping cartilage replenish itself and blocking enzyme destruction of cartilage in the joint. Often we can find this helpful in animals with mild signs, but it might be enough to take some of the discomfort away and help her to comfortably use the litter box. Normally we give kitties 50mg glucosamine + 15mg chondroitin a day per 10 pounds of body weight. So, do consider trying this with her.
As well, we do find fish oil ( omega 3+ 6) beneficial for cats with arthritis. This is a natural anti-inflammatory and can reduce inflammation in sore joints. Typically, we will give 90 mg EPA and 60 mg DHA per 5lbs of body weight. So, this too would be something to consider for her. And if you did think she was very sore, you could also speak to her vet about kitty safe pain relief (ie Metacam
Further to joint supportive care, do consider trying a litter box on the first floor in one of the common sites she has targeted. And do make sure that it is a box with a lower lip, so that she has no excuse/difficulty getting into the box. As well, you may also consider changing her litter to a paper or sand based litter to see if this just takes some of the strain of litter box time. And of course, if you are concerned that she is 'forgetting' where her box is, do try a litter attractant as a reminder.
Overall, we do have a few concerns for her signs but the extra complication that this could be becoming a habit. Therefore, I would advise addressing and ruling out arthritis since its so common a cause at her age. But also we need to ensure we are thoroughly cleaning the areas to a level that they remove the smell for her as well. And if we do that, we can hopefully get her back into the box and break this habit.
Please take care,