Hi Pumpkin's Mom,
First up, have some of these:


As BJ and Sharon have advised above, sometimes if there is an underlying problem it can lead a cat to eliminate inappropriately. If he's that obvious behaviourally it may be his way of trying to let you know that something is wrong. I suggest you ask your vet to check:
- whether Pumpkin may be suffering from (possibly occult) diabetic neuropathy (not jumping up onto things as often and also flat-footed walking are clinical signs to look for). Check B12/folate levels. B12 methylcobalamin and better BG regulation can resolve neuropathy problems.
- Check potassium levels (if they're off they can lead to hindquarter weakness - supplementation should only be done under close veterinary supervision of blood potassium levels as too high and too low a potassium level are dangerous).
- Check for urinary tract issues (infection, inflammation, environmental or physical stressors). Diabetics are more prone to infections and glucose in the urine of poorly-regulated kitties can increase risk of infection.
- Check kidney function including specific gravity of urine (cats who produce very dilute urine are also more at risk for infection).
Is Pumpkin fed wet or dry food? If he has been fed dry food most of the time this can leave a cat with chronic dehydration problems; descended from desert dwellers, cats have a low thirst drive and don't tend to drink enough water when they're fed dry food. Switching to a wet diet (and perhaps adding a teaspoon or two of water to each meal) can help improve hydration levels. (For info, both myself and another FDMB member have cats whose inappropriate elimination issues resolved upon switching to a wet diet.)
More info on urinary tract issues at this well-respected, vet-authored site:
http://catinfo.org/?link=urinarytracthealth
I hope for both of you that you're able to find something to help the situation very soon.
Mogs
.