My deepest heartfelt sympathy goes out to you groupfive.
I had to make the same agonizing decision two days ago. Our little girl is 18 months old and her count got down to 30 however her Spleen had swollen to double its size. Our vet was keen to do a blood transfusion and remove the spleen. At almost the same time her spleen seemed to grow, she was unable to hold herself up in her back legs. She was still able to move them and her tail so she was not paralysed but the vet thinks a clot must have lodged in her spinal cord or a nerve and that has made her unable to regain her strength. After a week on cortisone and full time vet care she wasn't improving and starting to go downhill. The hardest part is whilst on the cortisone she was still her normal happy self, I hope I don't ever have to make this decision again for such a young dog, but I hate to see them in pain.
My thoughts are with you, and I'm sorry to hijack your post.