The vet centre tested the dog's blood to establish the condition of her kidneys, which Dr Wolland said were "under a great deal of stress" with a high salt content.
The dog was "very timid" especially around other dogs.
SPCA animal welfare inspector Lesley Gibson said on a scale of one to nine, with nine being healthy, the dog was a one.
"It's the skinniest little dog I've ever seen."
The dog had been found on Hinau Gully Road on Saturday and it had taken the woman who found it a day to catch the dog.
Mrs Gibson said the dog had no collar and no microchip, and because of the expensiveness of the breed she was surprised it had been in such a condition.
Mrs Gibson said papillons can be worth $800 to $1000.
"You don't lose papillons," she said.
Midweek shared the story of the missing papillon with the Wairarapa Times-Age, who published the dog's picture in its Wednesday edition, as well as on its website and on Facebook.
Carterton woman Grace Gatfield recognised the dog and said she had been feeding it scraps for about two months. She had wondered whether its skinny condition might be part of the breed.
The story also brought out the dog's owner's partner, Mike Neal, and the owners are now in contact with the SPCA while the dog is in foster care.
Mr Neal told the Wairarapa Times-Age that the dog, whose name is Poppy, had a medical condition and they could not work out why it had been losing weight.
"You should come and see my other dog; he's in healthy nick," Mr Neal said.
Mr Neal said the dog was not "starved to death".
"It was lost. We don't like seeing her [the dog] like that either."
Mr Neal said they had taken the dog to a vet, who could not find what was wrong.
Mrs Gibson yesterday confirmed Wairarapa SPCA was due to talk to the papillon's owners, as there were some "unanswered questions".
Because the dog was not registered, the SPCA could not legally release it to the owners at this stage, and there were also its medical costs to consider.