Hepatic Encephalopathy in Cats
Dr. Arnold Plotnick
Diagnosis In-depth Complete blood count (CBC). A CBC is performed to help support a diagnosis of liver disease. A high white blood cell count might be present if an infectious cause of liver disease is present. Changes in the size – usually smaller than normal red blood cells – and shape of red blood cells are often seen in cases of liver disease.
Hepatic encephalopathy is a syndrome that is diagnosed by a combination of history, physical exam findings and laboratory data that shows significant liver disease is present in an animal for which no other cause of the neurological signs can be attributed.
Serum chemistry panel. Depending on the nature of the liver disorder present, various liver parameters will be abnormal on the chemistry panel. Changes in the enzymes ALT, AST, and ALP, may be seen, as well as decreased levels of albumin, and increased levels of bilirubin. Other changes, such as a low urea level and low blood sugar, are sometimes seen.
Urinalysis. Blood and protein may be present in urine secondary to urinary tract inflammation. This inflammation is caused by ammonium urate crystals or stones that tend to form when there is liver disease, especially portosystemic shunts. The crystals or stones form because of high concentrations of ammonia in the urine.
Blood clotting tests. Patients with HE can exhibit clotting problems caused by the diseased liver's inability to make adequate amounts of clotting factors.
Blood ammonia level or ammonia tolerance test. High ammonia levels in the bloodstream is one factor that contributes to HE. Detection of high levels of ammonia in the bloodstream supports a diagnosis of HE. Alternatively, an ammonia tolerance test can be performed, whereby the animal is given a standard amount of ammonium chloride by stomach tube, and measuring the amount of ammonia in the bloodstream before the test, and then 30 minutes after giving the ammonium chloride. These tests are rarely performed anymore due to the limited clinical availability of the test, the unreliability of the values if the test is not run within 30 minutes of collection, and the fact that some animals with HE have normal blood ammonia concentrations.
Bile acid test. This is a simple blood test that is very sensitive in detecting serious liver dysfunction or portosystemic shunts. Bile acids are very stable in serum, so no extraordinary sample processing is required, as with blood ammonia measurements.
Abdominal radiographs or special dye studies. Abdominal radiographs are important diagnostic tools in evaluating patients with possible HE. Most animals with portosystemic shunts have markedly small livers. An enlarged liver silhouette can be seen in patients with HE secondary to acute hepatitis, liver tumors, or other infiltrative liver diseases. A special radiographic dye study in which dye is injected into an intestinal blood vessel to determine whether the dye flows to the liver in the proper fashion can be performed, however, this is a specialized test that is almost always performed at referral centers or universities.
Abdominal ultrasound. This test is an excellent, non-invasive way to evaluate the liver. Liver tumors and infiltrative liver diseases can often be diagnosed via ultrasound and portosystemic shunts can sometimes be diagnosed by an experienced ultrasonographer. A liver biopsy can also be obtained using ultrasonographic methods.
Liver biopsy. Exploratory surgery and liver biopsy will nearly always diagnose the cause of the liver disorder that has led to the development of HE. Animals with severe liver disease and resultant HE are often not the ideal candidates for anesthesia and surgery, and non-invasive diagnostic methods are preferred.
Transcolonic scintigraphy. This is a specialized, non-invasive test performed only at referral centers or universities. The test is designed to diagnose a portosystemic shunt, the most common condition that leads to HE. Radioactive material is infused into the animal's colon. In normal animals, the radioactive material enters the intestinal blood supply and arrives at the liver first, and then flows to the heart. If the patient has a portosystemic shunt, the intestinal blood is diverted around the liver, so that the radioactive material arrives at the heart before, or at the same time as, the liver.