The detection of icterus in the dog and cat poses a diagnostic challenge to the veterinary practitioner. Because icterus has several very different etiologies, it is best to pursue the cause initially by attempting to answer the question: Is the icterus due to a prehepatic, hepatic or posthepatic disorder?

Prehepatic

This particular cause of icterus accompanies a hemolytic condition that allows for the accumulation of unconjugated bilirubin. Some of the causes of hemolysis in the cat are hemobartonellosis (Mycoplasma haemofelis), adverse drug reactions (acetaminophen, methylene blue), autoimmune hemolytic anemia (often FeLV positive), transfusion reactions, and hemolytic disease of the newborn. The history and the physical examination findings will often help to differentiate the causes of prehepatic icterus.

The laboratory findings will support the prehepatic origin of icterus based on the presence of a regenerative anemia and other features depending on the particular etiology as shown with RBC Heinz body formation with certain drug toxicities such as acetaminophen and methylene blue. Hemobartonella (Mycoplasma) should be searched for. In the cat, it should be noted that many of the positive cases of Mycoplasma haemofelis or the Coombs positive hemolytic anemia are also FeLV positive. Hemoglobinuria and hemoglobinemia usually accompany an intravascular hemolysis.

Treatment depends on the particular etiology. Acceptable cross-matched blood should be given if the patient is weak and depressed or if it has a packed cell volume of <15%. Discontinuing any causative offending drug should be immediate if the hemolysis is drug related. In the case of IMHA, immunosuppressive doses of glucocorticoid (prednisone 1-2 mg/kg once or twice daily) are begun immediately. Other immunosuppressive or immune modifying drugs can be given depending on the patient's status and its initial response to treatment. Persistently FeLV positive cats usually have a very guarded to grave prognosis.

Hepatic

This includes both primary and secondary causes of hepatic disease (Table 1). Only the primary and more common types will be discussed here.

Table 1. Some of the causes of liver diseases in the cat.

Primary

1.  Lipidosis

2.  Lymphocytic cholangiohepatitis

3.  Suppurative cholangiohepatitis

4.  Parasitic cholangiohepatitis

5.  Primary neoplasia

6.  Congenital portosystemic anomalies

7.  Infections (FIP, toxoplasmosis, hepatitis)

Secondary

1.  Toxins

2.  Drugs

3.  Metastatic neoplasia

4.  Metabolic

5.  Sepsis

Feline Primary Idiopathic Hepatic Lipidosis

This is a common syndrome in the indoor cat. The history often provides a stressful event that triggered the inappetence. Anorexia and its effects on protein and lipid metabolism may play an important pathogenetic role. Abnormal triglyceride metabolism is thought to reflect other derangements in hepatocyte functions that contribute to hepatic failure.

There is no age, breed or sex predisposition, but obesity is considered a contributing factor. The common clinical features include anorexia of several days to weeks duration, lethargy, and depression. Intermittent vomiting and diarrhea can also occur. The physical examination often detects a palpably enlarged smooth surfaced liver, icterus, varying degrees of dehydration, and evidence of weight loss.

The clinical pathologic abnormalities include a nonregenerative anemia and elevated serum transaminase, alkaline phosphatase, and bilirubin levels. Bilirubinuria is common and indicative of liver disease in the cat in the absence of hemolysis. Coagulation abnormalities occur with the advanced form of disease. The presence of hepatic fat deposits found on cytology specimens obtained by fine needle aspiration or histopathologically on a liver biopsy specimen are confirmative.

Treatment

Treatment for idiopathic hepatic lipidosis entails restoring hydration along with the provision of nutritionally balanced feedings. The latter can be accomplished with "finger feeding" baby food (without onion powder) or more efficiently through nasogastric, pharyngostomy, or gastrostomy tubes. Tube feeding will allow for the delivery of a more nutritionally balanced diet.

Ursodeoxycholic acid (Ursodiol) is a choleretic agent that increases bile flow and decreases bile toxicity. It is dosed at 10-15 mg/kg once daily orally.

S-Adenosylmethionine (SAM e) is a product that increases hepatic glutathione levels thereby providing a protective antioxidant effort for the liver. The dose is 18 mg/kg once daily orally.

Milk thistle also has protective effects on the liver. The compound containing silymarin extract is dosed at 0.25 ml for small breed dogs, 0.5 ml for medium-sized dogs, and 1.0 ml for large breed dogs, and be given q8-12h. Cats should receive 0.25 ml q8-12h.

B vitamins are generally administered. This author prefers not to use benzodiazepine tranquilizers to stimulate the appetite because of sedative side effects and their potential for hepatotoxicity in the cat.

The prognosis is fair to guarded depending on whether or not the anorexia disappears and the appetite returns. Predisposing psychological stressors might be difficult to reverse.

Canine Hepatic Lipidosis

Hepatic lipidosis in the dog is generally a secondary disease associated with diabetic ketoacidosis. It will resolve once the primary disorder is cured.

Cholangiohepatitis

This is an inflammatory disorder of the hepatobiliary tree. In the cat it has 2 main types: 1) suppurative cholangitis/cholangiohepatitis, and 2) nonsuppurative cholangiohepatitis. Advanced inflammatory disease can progress to cirrhosis. These syndromes can be associated with other conditions such as duodenitis, pancreatitis, and cholecystitis. In the tropics, cholangiohepatitis can be caused by the liver fluke, Platynosomum concinnum. Cholangiohepatitis in the cat can occur with cholecystitis with the latter often becoming a surgical disorder when it becomes emphysematous or if it is associated with biliary outflow obstruction.

The clinical signs include varying degrees of anorexia, weight loss, dehydration, vomiting, diarrhea, hepatomegaly, and jaundice. Fever is sometimes present especially in the cat with suppurative cholangiohepatitis. Anterior right-sided abdominal discomfort might be evident on palpation. The clinical pathologic features include elevated serum transaminases, alkaline phosphatase, and bilirubin levels and bilirubinuria. A neutrophilia is common with the suppurative type. Eosinophilia is occasionally present with fluke infections in the cat. A liver biopsy is necessary for a definitive diagnosis. Some advocate ultrasound guided percutaneous gall bladder aspiration for culture and cytology, but this procedure might cause leakage and bile peritonitis.

Treatment

Fluid therapy and B vitamins are important for both types of cholangiohepatitis. Vitamin K₁ should be given when there is obstruction to bile flow. Antibiotics are strongly recommended for the suppurative form; those commonly used include those effective against gram-negative bacteria. SAM e and milk thistle are also used as liver support drugs.

For nonsuppurative cholangiohepatitis in the cat, prednisone is recommended at a daily dose 2.2 mg/kg for 1-2 weeks and then slowly tapered to an alternate day regimen over a 4-6 week period.

Feline liver flukes are treated with praziquantel at 20 mg/kg once daily for 3 consecutive days. Fenbendazole at 50 mg/kg PO can also be given for 5 consecutive days. The prognosis is fair to good if the condition is treated before biliary fibrosis becomes established.

Cholestasis

Cholestatic hepatopathy is characterized by bile stasis within the canaliculi. It can occur with cholangitis, cholangiohepatitis, or it can be due to adverse drug reactions on the liver. Other causes include various enterotoxins, sepsis, and certain inflammatory disorders such as acute pancreatitis. These conditions are managed medically along with the discontinuation of any predisposing medications, herbs, or other hepatotoxins and the treatment of the primary underlying disorder. Liver supportive measures can include the administration of ursodiol, SAM e, milk thistle, and adequate nutrition and vitamins.

Posthepatic

The posthepatic causes of jaundice in the cat include those disorders that cause common bile duct obstruction. These conditions are listed in Table 2.

Table 2. Causes of posthepatic jaundice in the cat.

The clinical pathological features of this group of disorders include remarkably elevated serum alkaline phosphatase, cholesterol, and bilirubin levels. Serum transaminase levels will vary from mild to moderately elevated. The hemogram is seldom contributory, except for prolonged coagulation times due to the inactive vitamin K dependent factors II, VII, IX, and X. Parenteral vitamin K₁ treatment is recommended.

Radiographs and abdominal ultrasound examinations might suggest masses or markedly dilated bile ducts. Surgical exploratory is essential for an absolute diagnosis and the determination of the treatment plan and prognosis.