According to Dr. Karen Tobias, a veterinary surgeon at Washington State University, in 1974 an increase of PSS was discovered at California Davis Veterinarian School. At that time it was questioned whether the frequency had increased or if knowledge for identifying the disorder had improved. There is a difference in the type of shunt that develops for large and small dogs. Shunts develop as small side branches connecting the hepatic portal vein and major gesture-intestinal veins. Blood is divertedaround the liver without undergoing hepatic detoxification.
Shunts involve a single large vessel or multiple small veins.
The ductus venous should undergo functional closure within the first three days after birth. Many are shunted, thin, depressed and have trouble gaining weight. Nearly all have some type of central nervous system signs that may be the best clue to identify the problem. Particularly bizarre behavioral signs or loss of intellectual function, unpredictable bouts of aggression, staggering, pacing, circling, head pressing, blindness, deafness, tremors, seizures and coma may be seen. The cause of hepatic encephalopathy is now known, but probably is a result of toxins effecting the brain.