Portosytemic shunts, or liver shunts, can occur in both cats and dogs. These shunts are blood vessels that allow blood to bypass the liver as it circulates through our pet’s body. Because the liver is responsible for removing toxins from the blood, liver shunts result in the buildup of toxins in the bloodstream, causing clinical signs and illness.
Liver shunts can be congenital, meaning that they are present at birth, or they can be acquired at an older age. Most shunts are congenital in nature, but about twenty percent of shunts are acquired. Acquired shunts are most commonly secondary to liver problems, such as exposure to toxins or chronic hepatitis. In these cases, the body routes blood through whatever blood vessels are available, even if it means bypassing the liver.
When portosystemic shunts occur, hormones are not available to encourage liver growth, so the liver can begin to atrophy. Poor protein production and abnormal fat metabolism can also occur, as well as blood clotting disorders. And the toxins that are normally eliminated by the liver begin to accumulate in the body, causing what is known as hepatic encephalopathy.
Clinical signs of hepatic encephalopathy include seizures, spaciness and disorientation, circling, and “head pressing,” when pets press their heads against hard objects, such as a wall or the side of their crate. Pets with liver shunts may also have gastrointestinal signs, drink excessive amounts of water, and urinate excessively.
Congenital liver shunts can often be managed surgically, as there tends to be only one anomalous vessel shunting blood, and it can be ligated easily. However, in most cases of acquired shunts, multiple small vessels are present, and surgical correction is not a viable option. Instead, medical management must be pursued.
Medical management of portosystemic shunts is not corrective in nature. It is intended to lessen the clinical signs by targeting the factors that contribute to hepatic encephalopathy. Here are the basics of a treatment program to manage the condition:
Diet change. A low protein, low magnesium diet should be started. Several prescription diets will fit the bill, with the added benefit of increased zinc and vitamin E levels. Prescription diets specific for liver disease lessen the burden on the liver.
Decrease ammonia production in the colon. Warm water enemas can be used during periods of severe hepatic encephalopathy to decrease the amount of ammonia producing bacteria present.
Decrease ammonia production in the gut. Antibiotics are used daily to reduce the amount of bacteria present in the gastrointestinal tract.
Lower the pH of the colon. An oral medication called lactulose is given to lower the colonic pH, resulting in lowered ammonia levels.
If surgery is not an option when considering treatment for portosystemic shunts, medical therapy should be instituted. Prognosis is good for pets with mild signs of hepatic encephalopathy, especially in the case of pets who are diagnosed with a liver shunt in their golden years.