NAVLE Multisystemic

Feline Hepatic Encephalopathy Study Guide

📅 March 28, 2026 ⏱ 25 min read

Hepatic encephalopathy (HE) is a metabolic neurologic syndrome characterized by neuropsychiatric abnormalities resulting from liver dysfunction or portosystemic shunting.

Overview and Clinical Importance

Hepatic encephalopathy (HE) is a metabolic neurologic syndrome characterized by neuropsychiatric abnormalities resulting from liver dysfunction or portosystemic shunting. In cats, HE most commonly occurs secondary to congenital portosystemic shunts (CPSS), although it may also develop with severe hepatic insufficiency from conditions such as hepatic lipidosis, cholangiohepatitis, or acute liver failure.

The pathophysiology centers on the liver's inability to detoxify ammonia and other neurotoxins, leading to their accumulation in systemic circulation and subsequent neurologic dysfunction. Early recognition and appropriate management are essential for optimal patient outcomes and represent a commonly tested topic on the NAVLE.

Shunt Type	Location	Key Features
Extrahepatic CPSS	Outside liver parenchyma; branches from portal vein before entering liver	Most common in cats; usually portocaval or portoazygous
Intrahepatic CPSS	Within hepatic parenchyma; arises from intrahepatic portal vein branch	Less common in cats; may represent patent ductus venosus
Acquired PSS	Multiple vessels secondary to portal hypertension	Develops with chronic liver disease; surgical ligation contraindicated

Etiology and Underlying Causes

Congenital Portosystemic Shunts (Most Common)

Congenital portosystemic shunts represent the most common cause of HE in cats, with a reported incidence of approximately 2.5 per 10,000 cats in referral practice. These abnormal vascular connections allow portal blood to bypass the liver and enter systemic circulation directly, preventing normal hepatic detoxification.

High-YieldIn cats, approximately 80% of portosystemic shunts are congenital and single, with extrahepatic shunts being more common than intrahepatic shunts. Persian and Himalayan cats have breed predisposition.

Classification of Portosystemic Shunts

Other Causes of Hepatic Encephalopathy in Cats

Hepatic lipidosis: Most common acquired liver disease in cats; HE develops when greater than 70% of hepatic function is lost
Cholangiohepatitis syndrome: Neutrophilic or lymphocytic forms; often associated with triaditis
Acute liver failure: Toxins, drugs, or infectious agents causing rapid hepatocyte destruction
Urea cycle enzyme deficiencies: Rare inherited metabolic disorders

Neurotoxin	Source	Mechanism of Toxicity
Ammonia	GI bacterial urease activity; enterocyte glutaminase	Astrocyte glutamine accumulation causing cytotoxic edema; altered neurotransmission
Mercaptans	Bacterial metabolism of methionine in gut	Synergistic toxicity with ammonia and short-chain fatty acids
Endogenous benzodiazepines	Unknown origin; accumulate with liver dysfunction	Potentiate GABA receptor activity causing increased inhibitory tone
Manganese	Normally excreted via hepatobiliary route	Astrocyte dysfunction; neuronal loss; visible as T1 hyperintensity on MRI
Aromatic amino acids	Decreased hepatic metabolism; decreased BCAAs	False neurotransmitter production; altered dopaminergic transmission

Pathophysiology

Normal Ammonia Metabolism

Under normal physiological conditions, ammonia is produced primarily in the gastrointestinal tract through bacterial degradation of dietary proteins and urea, as well as enterocyte glutaminase activity. This ammonia is absorbed into the portal circulation and transported to the liver, where it undergoes detoxification via two primary pathways:

Urea cycle (Krebs-Henseleit cycle): Located in zone 1 hepatocytes; converts ammonia to water-soluble urea for renal excretion
Glutamine synthetase pathway: Located in zone 3 perivenous hepatocytes; converts ammonia plus glutamate to glutamine

Mechanisms of Neurotoxicity in HE

When hepatic function is compromised or portal blood bypasses the liver through portosystemic shunts, multiple neurotoxins accumulate in systemic circulation:

NAVLE TipAmmonia is the primary neurotoxin implicated in HE. The brain lacks urea cycle enzymes and relies on glutamine synthetase in astrocytes for ammonia detoxification. Excess ammonia leads to glutamine accumulation, causing osmotic astrocyte swelling and cerebral edema.

Grade	Clinical Signs	Management Level
Grade 1	Mild lethargy, decreased alertness, subtle personality changes, polyuria/polydipsia	Outpatient management; dietary modification
Grade 2	Disorientation, ataxia, circling, head pressing, inappropriate behavior, ptyalism	Hospitalization recommended; medical management
Grade 3	Stupor, marked confusion, amaurotic blindness, severe ataxia, aggression, somnolence	Hospitalization required; intensive medical management
Grade 4	Coma, seizures, unresponsive recumbency, risk of cerebral edema and death	ICU; aggressive intervention; guarded to poor prognosis

Clinical Presentation

Neurologic Signs

Clinical signs of HE are characteristically episodic and wax-and-wane, often worsening after meals due to increased ammonia production following protein digestion. Signs may range from subtle behavioral changes to coma.

Modified West Haven Criteria for Veterinary Patients

Feline-Specific Clinical Features

Ptyalism (hypersalivation) is a hallmark clinical sign in cats with HE and is much more prominent than in dogs. Additionally, cats with chronic portosystemic shunts often develop distinctive copper-colored or golden irises secondary to decreased hepatic copper metabolism.

High-YieldWhen you see a young cat (less than 1 year) presenting with episodic neurologic signs that worsen after eating, ptyalism, and copper-colored irises, immediately think congenital portosystemic shunt with hepatic encephalopathy!

Non-Neurologic Signs

Failure to thrive and stunted growth (in young animals)
Weight loss and poor body condition
Vomiting and diarrhea
Polyuria and polydipsia
Lower urinary tract signs (ammonium biurate urolithiasis)
Ascites (with advanced liver disease)

Test Category	Expected Findings	Clinical Significance
CBC	Microcytosis (common), mild nonregenerative anemia, target cells	Microcytosis due to altered iron transport; suggests chronic hepatic dysfunction
BUN	Decreased (often less than 10 mg/dL)	Reduced urea cycle function; highly suggestive of PSS
Albumin	Decreased (hypoalbuminemia)	Decreased hepatic synthetic function
Glucose	Hypoglycemia (especially young animals)	Decreased glycogen storage and gluconeogenesis
Cholesterol	Hypocholesterolemia	Decreased hepatic synthesis
Liver enzymes	Normal to mildly elevated ALT/AST; ALP may be mildly increased	CPSS: enzymes often normal due to hepatic atrophy rather than active damage

Diagnostic Approach

Diagnosis of HE requires demonstrating consistent clinical signs in a patient with confirmed liver disease or portosystemic shunting, after exclusion of other causes of encephalopathy.

Laboratory Findings

Liver Function Tests

Serum Bile Acids

Pre- and post-prandial serum bile acid measurement is the gold standard screening test for portosystemic shunting. Bile acids are synthesized by the liver from cholesterol, secreted into bile, undergo enterohepatic circulation, and are efficiently extracted by the liver during first-pass metabolism.

Fasting sample: Collected after 12-hour fast
Post-prandial sample: Collected 2 hours after feeding
Interpretation: Elevated values (greater than 25 micromol/L fasting or greater than 50 micromol/L post-prandial) indicate hepatic dysfunction or portosystemic shunting

Blood Ammonia

Fasting blood ammonia levels are elevated in most cats with HE due to PSS. However, ammonia is unstable and requires immediate analysis on ice within 30 minutes of collection.

NAVLE TipAmmonia levels do not always correlate with HE severity. A cat can have normal ammonia and still have HE due to other neurotoxins. Bile acids are more stable and reliable for diagnosing hepatic dysfunction.

Urinalysis Findings

Ammonium biurate crystals are highly suggestive of hepatic dysfunction or PSS. These crystals appear as brown or yellow-brown spherical bodies with irregular projections, classically described as having a "thorn apple" or "datura" appearance. Their presence indicates high urinary ammonia and uric acid concentrations.

Diagnostic Imaging

Abdominal Radiography

Microhepatica (small liver) is commonly observed in cats with CPSS due to hepatic atrophy from lack of hepatotrophic factors. Renomegaly may also be present.

Abdominal Ultrasonography

Ultrasonography can identify small liver size, reduced portal vein diameter, and may visualize the anomalous shunting vessel. However, operator experience significantly affects sensitivity (approximately 75-90% in experienced hands).

CT Angiography

Computed tomographic angiography is the gold standard for definitive diagnosis and surgical planning of CPSS. It provides excellent anatomical detail of shunt location, morphology, and vascular anatomy.

Classification	Definition	Prognosis/Notes
Type A	Associated with Acute liver failure (fulminant hepatic failure)	High risk of cerebral edema and herniation; severe and unremitting
Type B	Associated with portosystemic Bypass (shunting) without intrinsic liver disease	Liver function may be preserved; better prognosis with surgical correction
Type C	Associated with Cirrhosis with portal hypertension and acquired shunting	Combined shunting and decreased hepatic mass; variable prognosis

Classification of Hepatic Encephalopathy

Exam Focus: Remember: Type A = Acute liver failure, Type B = Bypass (shunting), Type C = Cirrhosis. Type B (CPSS) is most common in cats and has the best prognosis if surgically correctable.

Treatment	Dosage (Cats)	Mechanism/Notes
Lactulose	0.5-1 mL/kg PO q8-12h; titrate to 2-3 soft stools daily	First-line treatment; acidifies colon (traps NH4+), decreases bacterial ammonia production, osmotic catharsis
Metronidazole	7.5 mg/kg PO q12h	Reduces urease-producing bacteria; use cautiously - can cause neurotoxicity with prolonged use
Amoxicillin	10-20 mg/kg PO q12h	Alternative antibiotic; reduces ammonia-producing gut bacteria
Neomycin	10-20 mg/kg PO q8-12h	Poorly absorbed aminoglycoside; risk of ototoxicity and nephrotoxicity with chronic use
Hepatoprotectants	SAMe: 90 mg/cat daily; Silymarin: 5 mg/kg daily	Antioxidant support; may help protect remaining hepatocytes

Treatment and Management

Emergency Management of Acute HE Crisis

Cats presenting with severe HE (Grade 3-4) require immediate stabilization:

IV Fluid therapy: Use dextrose-supplemented crystalloids (2.5-5% dextrose); avoid lactated Ringer's in severe hepatic dysfunction
Correct hypoglycemia: Dextrose bolus (0.5 mL/kg 50% dextrose diluted 1:4) followed by CRI
Cerebral edema management: Mannitol (0.5-1.0 g/kg IV over 20 minutes); elevate head 25-35 degrees
Seizure control: Levetiracetam (20-60 mg/kg IV) preferred; AVOID benzodiazepines if possible
Cleansing enema: Warm water or lactulose enema to reduce colonic ammonia production

High-YieldAVOID benzodiazepines (diazepam, midazolam) in HE patients! Endogenous benzodiazepine-like substances accumulate in liver failure and potentiate GABA receptor activity. Benzodiazepines can worsen or prolong encephalopathy. Use levetiracetam for seizure control.

Medical Management

Lactulose Mechanism of Action

Lactulose is a synthetic non-absorbable disaccharide that is the cornerstone of HE management. Its therapeutic effects include:

Colonic acidification: Bacterial fermentation produces lactic and acetic acids, lowering colonic pH
Ion trapping: Acidic environment converts ammonia (NH3) to ammonium (NH4+), which cannot cross the intestinal mucosa
Cathartic effect: Osmotic action accelerates fecal elimination of ammonia
Microbiome modification: Promotes growth of non-urease-producing bacteria

Dietary Management

Dietary therapy is essential for long-term HE management. Current recommendations emphasize moderate protein restriction with high-quality protein sources rather than severe protein restriction, which can worsen muscle catabolism and promote further ammonia release.

Target: 4.0 g protein/kg body weight/day minimum for cats
Protein sources: Dairy and soy proteins produce less ammonia than meat-based proteins
Commercial hepatic diets are formulated with appropriate protein restriction and quality
Small, frequent meals help prevent post-prandial ammonia spikes

Surgical Treatment

For cats with congenital portosystemic shunts, surgical attenuation offers the best chance for long-term resolution. Options include:

Ameroid constrictor: Gradual shunt occlusion over 2-4 weeks via hygroscopic swelling
Cellophane banding: Induces fibrosis and gradual occlusion
Suture ligation: Partial or complete; requires intraoperative portal pressure monitoring

NAVLE TipComplete acute ligation of a CPSS can cause fatal portal hypertension. Gradual occlusion devices (ameroid constrictors, cellophane bands) allow hepatic vasculature to develop and accommodate increased portal flow. Prognosis is good to excellent in approximately 50% of cats following successful surgical correction.

Prognosis

CPSS with surgical correction: Good to excellent in 50% of cats; approximately 25% have fair prognosis
CPSS with medical management alone: Variable; clinical signs often recur
Acquired PSS (cirrhosis): Poor; reflects advanced liver disease
Acute liver failure (Type A): Guarded to poor; depends on underlying cause and reversibility

Memory Aids

Feline HE Clinical Signs: "SHUNT CAT"

S - Salivation (ptyalism - hallmark in cats!)
H - Head pressing
U - Urinary crystals (ammonium biurate)
N - Neurologic signs (episodic)
T - Tiny liver (microhepatica)
C - Copper-colored irises
A - Ammonia/bile acids elevated
T - Tortuous shunt vessel on imaging

Treatment Priority: "LAD"

L - Lactulose (first-line, always)
A - Antibiotics (metronidazole, amoxicillin)
D - Diet (moderate protein restriction)

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