Hepatic lipidosis

Hepatic lipidosis is the accumulation of fat, usually in the form of triglycerides, in the cytoplasm of the hepatocyte due to deficient lipid metabolism in the liver. It affects both dogs and cats, but is more common in the latter.

Although a distinction is often made between secondary hepatic lipidosis and primary or idiopathic hepatic lipidosis (unique to cats), it now widely accepted that the vast majority of cats with hepatic lipidosis have an underlying disorder that triggers the syndrome (Table 1). Hepatic lipidosis can affect cats of any age, but is most common in those aged between 6 and 7 years.

The pathophysiology of the disease is characterized by increased transport of fatty acids in the liver and a decrease in their mitochondrial oxidation combined with an alteration in the storage and/or secretion of lipoproteins.

Symptoms

In cats, hepatic lipidosis is usually triggered when the body enters a state of catabolism due to anorexia, poor assimilation or poor digestion of food. The cat will typically have a history of overweight, anorexia for 5-7 days, weight loss of up to 25% of body weight (mostly peripheral fat deposits), and a variety of gastrointestinal disorders. These will be accompanied by other symptoms depending on the underlying or primary disease (Table 1).

Most cats are icteric and present uniform, nontender hepatomegaly with rounded edges. They may present vomiting, dehydration, and in some cases deep ventroflexion of the head and neck associated with severe electrolyte disturbances, as well as hypersalivation due to nausea and hepatic encephalopathy.

Interpretation of laboratory tests

General Tests

• Complete blood count.
  Poikilocytosis and Heinz bodies are often reported. Anaemia is found in some cases. The leukogram varies, and usually reflects the underlying disease.
• Blood biochemistry/electrolytes:
  • Total bilirubin and alkaline phosphatase: extremely elevated due to severe cholestasis caused by build-up of triglycerides in the liver. A determination of the conjugated and unconjugated forms of bilirubin are not useful for diagnostic purposes.
  • ALT / AST: generally elevated, but normal in some cases.
  • GGT: normal if there is no lipidosis-related disorder that causes necroinflammation in the liver; otherwise, moderate to severe elevation (e.g. cholangitis-cholangiohepatitis-related lipidosis, pancreatitis)
  • Urea: low (>50% of cases) even in dehydrated animals, due to partial inhibition of the urea cycle.
  • Cholesterol, glucose: levels vary, depending on the underlying disease.
  • Potassium / phosphorus / magnesium: A marked electrolyte imbalance that reduces the levels of these electrolytes is usually observed either initially or over the course of treatment.
• Clotting tests.
  (Prothrombin time/Partial thromboplastin time): prolonged in approximately 50% of cases.

Specific tests

• Liver cytology / liver biopsy
  The lesion typically found is hepatocellular vacuolization with signs of cholestasis.
  This test is only used when the animal does not respond to balanced medical treatment, as there is a high risk of lethal iatrogenic complications (poor tolerance to sedatives and anaesthetics, tendency to bleed)

Complementary tests

• Radiography / ultrasound
  Both show hepatomegaly, and ultrasound shows a diffusely hyperechoic liver.

Bibliography

• BENITAH, N. ; MARKS, S.L. (2004): Waltham Focus 14(2): pg.28-35
• CENTER, S.A. (2004): Waltham Focus 14(2): pg.12-21
• CENTER, S.A. (2005): Veterinary Clinics of North America: Small Animal Practice vol. 35, nº 1, pg. 225-269
• DEN BOER, M.; VOSHOL, P.J.; KUIPERS, F.; HAVEKES, L.M.; ROMIJN, J.A.: (2004) Arteriosclerosis, Thrombosis, and Vascular Biology vol. 24, pg.644-649
• WEBSTER, C.R.L. (2004) : en Morgan-Bright-Swartout (Ed.): Clínica Veterinaria de Pequeños Animales ( 4ª ed.) Saunders-Elsevier, pg. 399-400