We went through this with our beloved Bischon last year. We experienced a long and sad 18 month road with continual vet visits and expensive medication in an attempt to give him some quality to the life he had left. The end was the same as you described. As a nurse who is familiar with the road Bischee travelled, it was a very horrific experience to see him go downhill. And as his loving owners, are mental state was terribly affected as well. Take care and know that you are not alone.