I am so sorry that you are havving to go through this. I had a similar experience as yours with my first hav. He was asymptomatic but had elevated BAT and ALT for his entire life. Btw, he lived 11 wonderful years and passed from heart failure. When the vet raised the possiblity of a liver shunt because of his small size and the labs were abnormal, I was a so worried for quite some time. I consulted a vet at a teaching hospital in TN who specialized in micro and macro shunts ( Dr. Tobias). After many discussions with my vet, breeder andspecialists, I decided only to have the ultrasound done (essentially normal, which did not exclude MVD). Weighing all optionsa nd knowing how traumatic the liver biopsy could be, I decided to take a watchful waiting approach. His ALT remained chronically elevated, slightly waxing and waning over the years. Keeping his teeth extra clean with regular cleanings also seemed to help. An elevated BUN can simply mean the pup is dehydrated when the blood is drawn. My havs have never been great at drinking enough water and always seem to have marginally elevated BUN on their labs. I stopped worrying about that years ago. Since you have been through this with your yorkie, I hope it give you strength to know even if the labs are abnormal, they can still live long happy lives. After all of that, I decided to become less fixated on the labs and just tried to watch my pup to see how he seemed to be doing (which was just fine). I hope that helps a little.
Dr. Tobias sent me this in back in 2009:
Accuracy of unltrasonography depends on the radiolgist or internist. Some specialists are 95-100% accurate and others are less. We use transplenic scintigraphy here to rule out shunting when we suspect MVD from congenital portal hypoplasia (CPH).
MVD/CPH is the most common cause of increased bile acids in clinically normal dogs with normal chem panels. A diagnosis would require ruling out a shunt (since PSS results in the same histologic liver changes) and then obtaining a piece of liver large enough to include at least 5 portal triads. This may require a minimally invasive approach (mini-lap or lalparoscopy), since we often do not get enough tissue on needle/trucut biopsies to be certain of a microvascular anomaly, and because that approach is less dangerous than ultrasound guided biopsy in a small breed dog with a small liver.
No one knows about diet change. No one has compared long term outcome of dogs with CPH/MVD that are on regular and protein restricted diets. At the very least, I wouldn't give any extra protein, puppy chow, or performance diets. No need to stress the liver.
With CPH/MVD, bile acids will always be high and they do not correlate with severity of disease. Better indicators are albumin, BUN, total protein, urine specific gravity, and urine sediment (for urate crystals and infection). Yearly lab work unless clinical signs occur.
We use scintigraphy here because it's easy and inexpensive, and we have seen dogs with shunts that have normal chemistry panels and mildly increased bile acids. So, for my own dog, I would do a transplenic scintigraphy. If it was normal, I'd probably leave it at that. Denamarin now comes in chewable tablets that have better absorption. Again, research has not been done in dogs with CPH/MVD to determine if it makes a difference, but its contents (milk thistle and SAM-e) have been shown to improve liver function. Owner preference.
No idea about long term prognosis. We tested 139 healthy Yorkies and found that 2/3's had increased bile acids. Most likely this condition is present in the majority of Yorkies, Maltese, and Havanese, so most will live normal lifespans.