Feline Hepatic Lipidosis Study Guide

Overview and Clinical Importance

Feline hepatic lipidosis (FHL), also known as fatty liver syndrome, is the most common acquired hepatobiliary disease in cats, accounting for approximately 50% of all feline liver disease diagnoses. This potentially fatal intrahepatic cholestatic syndrome is characterized by excessive accumulation of triglycerides within hepatocytes (greater than 80% of hepatocytes affected), leading to hepatocyte dysfunction, intrahepatic cholestasis, and liver failure.

The condition develops when cats experience a period of anorexia (as short as 2-7 days), triggering peripheral fat mobilization that overwhelms the liver's capacity to process and export lipids. Understanding FHL is essential for the NAVLE as it represents a true veterinary emergency requiring aggressive nutritional intervention.

Etiology and Classification

Primary (Idiopathic) Hepatic Lipidosis

Primary or idiopathic FHL occurs in approximately 5-10% of cases when no underlying disease can be identified after thorough investigation. These cases typically occur in obese cats following stressful events such as diet changes, new household members, moving to a new home, boarding, or accidental confinement. Environmental stressors lead to anorexia, which triggers the metabolic cascade resulting in hepatic lipid accumulation.

Secondary Hepatic Lipidosis

Secondary FHL is far more common, occurring in 90-95% of cases. The lipidosis develops secondary to another disease process causing anorexia.

Common Underlying Diseases Associated with Secondary FHL

Pathophysiology

The pathophysiology of FHL is complex and involves an imbalance between the influx of fatty acids into the liver, de novo lipid synthesis, hepatic oxidation of fatty acids, and export of lipids via very low-density lipoproteins (VLDL).

Key Pathophysiologic Mechanisms

• Peripheral Fat Mobilization: During anorexia, hormone-sensitive lipase (HSL) is activated by catecholamines, glucagon, and glucocorticoids, releasing massive amounts of free fatty acids from adipose tissue into the circulation.
• Hepatic Fatty Acid Overload: The liver becomes overwhelmed with fatty acids, which are converted to triglycerides and stored in hepatocytes as cytoplasmic vacuoles.
• Impaired VLDL Export: Cats require specific apolipoproteins to package and export triglycerides as VLDL. Protein deficiency from anorexia reduces apolipoprotein synthesis, trapping triglycerides in hepatocytes.
• Reduced Beta-Oxidation: Deficiency of essential cofactors (carnitine, methionine, taurine, arginine) impairs mitochondrial fatty acid oxidation.
• Intrahepatic Cholestasis: Swollen, triglyceride-laden hepatocytes compress bile canaliculi, causing cholestasis and hyperbilirubinemia.

Signalment and Clinical Presentation

Typical Signalment

• Age: Middle-aged cats (median age 7 years; range 0.5-20 years)
• Body Condition: Overweight or obese cats are at highest risk; normal weight cats can also be affected
• Sex: No sex predisposition (some studies suggest slight female predisposition)
• Breed: No breed predisposition; domestic shorthairs most commonly represented
• History: Partial to complete anorexia for days to weeks; often greater than 25% weight loss

Clinical Signs

Exam Focus: Cats with hepatic lipidosis are often paradoxically bright and alert despite profound jaundice and weight loss, unless they have concurrent hepatic encephalopathy, severe hypokalemia, or underlying disease complications.

Diagnosis

Laboratory Findings

Serum Biochemistry - Classic Pattern

Hematology

• Poikilocytosis: Variable red blood cell morphology due to altered membrane lipid content
• Heinz body anemia: May develop secondary to hypophosphatemia during refeeding
• Nonregenerative anemia: Common finding

Coagulation Profile

Approximately 50% of cats with FHL have coagulation abnormalities. Cats can become vitamin K deficient in less than 7 days due to cholestasis impairing fat-soluble vitamin absorption. Always evaluate PT and PTT before invasive procedures.

Diagnostic Imaging

Abdominal Radiography

Hepatomegaly with rounded liver margins may be visible. Often shows retained falciform fat despite weight loss.

Abdominal Ultrasonography - Key Findings

Cytologic and Histopathologic Diagnosis

Fine Needle Aspirate Cytology

Ultrasound-guided fine needle aspiration is the preferred diagnostic method as it is less invasive than biopsy and can often be performed without sedation. Use a 22-23G needle.

Classic cytologic findings: Hepatocytes are distended with multiple clear, sharply demarcated cytoplasmic vacuoles (lipid). Vacuoles may be macrovesicular (large vacuoles displacing nucleus to periphery creating "signet ring" appearance) or microvesicular (multiple small vacuoles). Greater than 80% of hepatocytes must be affected for diagnosis.

Treatment

Nutritional support is the CORNERSTONE of treatment. Without adequate caloric intake, hepatic lipidosis will not resolve. Survival rates of 80-90% can be achieved with aggressive, early nutritional intervention.

Initial Stabilization

• Fluid Therapy: Correct dehydration with balanced crystalloid solutions (0.9% NaCl or Normosol-R). AVOID lactated Ringer's (impaired lactate metabolism) and dextrose supplementation (promotes lipogenesis unless hypoglycemic).
• Electrolyte Correction: Supplement potassium (20-40 mEq/L added to fluids). Monitor and correct hypophosphatemia and hypomagnesemia.
• Vitamin K1 Supplementation: 0.5-1.5 mg/kg SC or IM every 12 hours for 3 doses. Complete before invasive procedures.
• Antiemetic Therapy: Maropitant (Cerenia) 1 mg/kg SC or IV q24h is preferred. Ondansetron 0.1-0.5 mg/kg IV q8-12h as alternative.

Nutritional Support - Feeding Tubes

Feeding Protocol and Refeeding Syndrome Prevention

Refeeding syndrome is a potentially fatal complication caused by rapid intracellular shifts of potassium, phosphorus, and magnesium when nutrition is reintroduced. Prevention requires gradual caloric introduction.

RER Calculation: RER (kcal/day) = 70 x (body weight in kg)^0.75 OR for cats greater than 2 kg: (30 x body weight in kg) + 70

Diet Recommendations

• Protein: High protein (33-45% DM basis) - essential for cats; DO NOT restrict protein unless hepatic encephalopathy present
• Fat: Moderate fat content (25-40% DM)
• Carbohydrates: Low carbohydrate - excessive carbs inhibit fatty acid oxidation
• Potassium: Potassium-replete (0.8-1.0% DM) or supplement with potassium gluconate (2-6 mEq/day)

Supportive Medications and Supplements

Prognosis and Monitoring

Prognostic Factors

Survival Rates: With aggressive nutritional support: 75-90% survival. Without treatment: 5-20% survival. Average tube feeding duration: 4-6 weeks (range 3-8 weeks). Recurrence after recovery is rare.