The length of time that a cat lives after showing signs of dementia (cognitive dysfunction) varies from cat to cat. It depends on how well the cat is taken care of, how much interaction the cat has with people and if the dementia is caused by a brain tumour. According to Cat Owner's Home Veterinary Handbook, brain tumours are rare in cats, but still happen.
Any cat showing signs of dementia need to be taken to the vet to be sure it has dementia. Brain tumours, brain injury, lead poisoning, feline leukaemia, kidney and liver disease also cause symptoms similar to dementia.
According to Melissa Bain, DVM, over 40% of cats over 17 years old have dementia. The average life expectancy of a cat is 16, so the older the cat, the less likely it will live longer than a few years after diagnosis.
The only medication known to help feline cognitive dysfunction is Anypryil (deprenyl). Improvement should be seen within one month of taking it, according to Dr. Nicholas Dodman, writing for Pet Place.com.
A cat with dementia is more prone to injury, which can shorten its life. Do not rearrange the furniture, keep the cat indoors and make litter boxes easy to get to.
A theory is that senior cats with dementia can live for a couple more years comfortably with being encouraged to play, having a window to look out of and being talked to often by the human members of the family.