I am so sorry to hear your baby isn't well. PLE is very serious, but your baby can live a full, long life with the proper care. If your vet doesn't specialize in small breeds and PLE, please look for someone else as the type of care & meds your baby receives can make all the difference in the world.
I have first-hand knowledge of this as my Sissy was dianosed with this two years ago. Today, she is pretty darn health and a happy yorkie!!!! I would strongly suggest a more holistic approach with treatment as this is what seems to make a huge difference very quickly and lasts. I consuted with Susan Davis and Dr. Gordon via a phone consultation through the Arroyo Animal Hospital in Southern California. Since my involvement with them, they have helped another very seriously ill yorkie recover from PLE as well.
Here is their information......
Pet Health Pet Nutritionist Holistic Pet
Please feel free to PM me with any questions. My Sissy's diet consists of The Honest Kitchen Keen for breakfast with The Honest Kitchen Preference with steamed Talapia for dinner. She gets several supplements daily; a probiotic, Lypozyme, BioLiv, Vitamineral Green, and Nupro Silver and she gets a once monthly B12 injection (in the beginning the B12 was weekly).