My mom's RB yorkie was like that. He lost a lot of hair, mostly on his back. The vet said it was just old age. He was 151/2 years old when they had to have him PTS. He was missing hair for a couple years before that though. He was deaf and was on medication of arthritis. He had a battle with kidney stones when he was 12 or 13 and was on a prescription diet. The stone came back and after doing some blood work the outlook didn't look too good. The vet didn't think he'd make it through the surgery to remove the stones. So my mom felt rather than making him go through that it be better to have him PTS.

Anyway the point of my story was that my mom's dog lived years after loosing some of his hair. He was later PTS, which had nothing to do with the hair loss. So hopefully Mooch will make it to 20.