Hepatic Amyloidosis

Hepatic amyloidosis is a systemic or localized disease characterized by the extracellular deposition of amyloid, an insoluble fibrillar protein, in the liver parenchyma. In veterinary medicine, it is most commonly associated with reactive systemic amyloidosis, where chronic inflammation or infection leads to overproduction of serum amyloid A (SAA), an acute-phase protein. The liver is a major site of deposition due to its high blood flow and reticuloendothelial activity. Hepatic amyloidosis can lead to progressive hepatomegaly, hepatic dysfunction, and ultimately liver failure. The disease may be primary (immunocyte dyscrasia) or secondary (reactive), with the latter being more common in animals. In cats, hepatic amyloidosis is often seen in association with chronic inflammatory diseases such as feline infectious peritonitis (FIP) or chronic abscesses. In dogs, it is less common but may occur with chronic infections or neoplasia. The clinical presentation varies from asymptomatic to acute hepatic rupture with hemoabdomen, particularly in Shar-Pei dogs, which have a familial form of reactive amyloidosis.

The etiology of hepatic amyloidosis is multifactorial. The most common form is reactive (secondary) amyloidosis, which occurs secondary to chronic inflammatory, infectious, or neoplastic conditions. In dogs, chronic infections such as ehrlichiosis, leishmaniasis, and bacterial abscesses can trigger amyloid deposition. In cats, feline infectious peritonitis (FIP) is a well-recognized cause, as is chronic suppurative inflammation. Familial amyloidosis has been documented in Chinese Shar-Pei dogs, where a genetic predisposition leads to recurrent fever and inflammatory episodes, resulting in amyloid deposition. Primary amyloidosis, associated with plasma cell dyscrasias or multiple myeloma, is rare in veterinary patients. The amyloid fibrils in reactive amyloidosis are derived from serum amyloid A (SAA), an acute-phase protein produced by the liver in response to inflammatory cytokines such as IL-1, IL-6, and TNF-alpha. Chronic overproduction of SAA overwhelms the normal degradation pathways, leading to fibril formation and tissue deposition. In some cases, the cause may be idiopathic, with no identifiable underlying inflammatory condition.

Hepatic amyloidosis is uncommon in dogs and cats but is more frequently reported in certain breeds. In dogs, the Chinese Shar-Pei is overrepresented, with a familial form of reactive amyloidosis that often affects young to middle-aged dogs (1-6 years). Abyssinian cats are also predisposed to hepatic amyloidosis, often in association with FIP or chronic inflammatory disease. Siamese and Oriental Shorthair cats may also be at increased risk. There is no clear sex predilection, although some studies suggest a slight male predominance in Shar-Pei dogs. The disease is more common in middle-aged to older animals, except in Shar-Pei where it can occur in younger dogs. Geographic distribution may reflect the prevalence of underlying infectious diseases, such as leishmaniasis in Mediterranean regions or ehrlichiosis in tropical and subtropical areas. The overall incidence is low, but it is an important differential for hepatomegaly and liver dysfunction in predisposed breeds.

The pathophysiology of hepatic amyloidosis involves the overproduction and deposition of amyloid fibrils in the liver. In reactive amyloidosis, chronic inflammation stimulates the release of pro-inflammatory cytokines (IL-1, IL-6, TNF-alpha) from activated macrophages. These cytokines induce hepatocytes to synthesize and secrete serum amyloid A (SAA), an acute-phase protein. Normally, SAA is degraded by proteases, but in chronic inflammation, the production exceeds degradation, leading to the accumulation of SAA fragments. These fragments polymerize into beta-pleated sheet fibrils, which are resistant to proteolysis and deposit in the extracellular space. In the liver, amyloid deposits initially accumulate in the space of Disse (perisinusoidal), compressing hepatocytes and leading to hepatocyte atrophy. As the disease progresses, amyloid deposition extends to the portal areas and can cause sinusoidal obstruction, leading to portal hypertension and impaired hepatic perfusion. The liver becomes enlarged, pale, and friable. In severe cases, the liver may rupture spontaneously, causing hemoabdomen. The deposition also disrupts normal hepatic architecture, leading to progressive liver dysfunction, coagulopathy, and eventually liver failure. In familial Shar-Pei amyloidosis, there is a genetic mutation that predisposes to recurrent inflammatory episodes, but the exact molecular mechanism is not fully understood.

Predisposing factors for hepatic amyloidosis include chronic inflammatory diseases, infectious agents, and genetic predisposition. In dogs, chronic infections such as ehrlichiosis, leishmaniasis, and bacterial abscesses are significant risk factors. In cats, FIP is a major trigger. Any condition that causes persistent inflammation, such as autoimmune diseases, chronic dermatitis, or arthritis, can predispose to reactive amyloidosis. Genetic factors play a crucial role in certain breeds: Chinese Shar-Pei dogs have a hereditary form of amyloidosis associated with recurrent fever and inflammation, and Abyssinian cats have a familial predisposition. Age is a factor, as chronic inflammation accumulates over time, but Shar-Pei dogs can develop amyloidosis at a young age. Sex may influence risk, with some studies suggesting males are more affected. Environmental factors, such as exposure to infectious agents in endemic areas, increase the risk. Additionally, immunosuppressive therapy may predispose to chronic infections, indirectly increasing the risk of amyloidosis.

Clinical signs of hepatic amyloidosis are often nonspecific and may be absent in early stages. As the disease progresses, common signs include lethargy, anorexia, weight loss, vomiting, and diarrhea. Hepatomegaly is frequently detected on physical examination. In advanced cases, signs of liver failure may develop, including icterus, ascites, hepatic encephalopathy, and bleeding tendencies due to coagulopathy. In Shar-Pei dogs, acute episodes of fever and joint pain may precede the onset of clinical signs. A catastrophic presentation is acute hepatic rupture, leading to hemoabdomen, which manifests as acute collapse, pale mucous membranes, tachycardia, and abdominal distension. In cats, hepatic amyloidosis may be associated with signs of the underlying disease, such as FIP, including fever, effusions, and ocular signs. Chronic cases may show progressive weight loss and muscle wasting. The clinical course can be insidious or acute, depending on the rate of amyloid deposition and the occurrence of complications.

Differential diagnoses for hepatic amyloidosis include other causes of hepatomegaly and liver dysfunction. Key differentials include: 1) Chronic hepatitis (lymphocytic or neutrophilic), which can be differentiated by histopathology showing inflammatory infiltrates rather than amyloid deposits. 2) Hepatic neoplasia (e.g., lymphoma, hepatocellular carcinoma), which may present with hepatomegaly and elevated liver enzymes; imaging and cytology/histopathology are needed. 3) Hepatic lipidosis, especially in cats, which is characterized by vacuolar hepatopathy on cytology. 4) Cirrhosis, which shows fibrosis and nodular regeneration on histopathology. 5) Hepatic abscess or granuloma, which may be detected on imaging and culture. 6) Cholangiohepatitis, particularly in cats, which is inflammatory and may be associated with biliary tract disease. 7) Congenital portosystemic shunts, which cause liver dysfunction but typically present in young animals with neurologic signs. 8) Toxic hepatopathy (e.g., from drugs or plants), which may have a history of exposure. Definitive diagnosis requires liver biopsy with special stains (Congo red) to identify amyloid deposits.

The diagnostic approach to hepatic amyloidosis begins with a thorough history and physical examination, focusing on breed, age, and any signs of chronic inflammation. Initial laboratory tests include a complete blood count (CBC), serum biochemistry profile, and urinalysis. Common findings include elevated liver enzymes (ALP, ALT, GGT), hyperbilirubinemia, hypoalbuminemia, and elevated globulins. In Shar-Pei dogs, a marked inflammatory leukogram may be present. Coagulation testing (PT, aPTT) is recommended due to the risk of bleeding. Abdominal imaging, particularly ultrasonography, is useful to assess liver size and echogenicity, but findings are nonspecific. The gold standard for diagnosis is liver biopsy, which can be obtained via ultrasound-guided needle biopsy, laparoscopic biopsy, or surgical biopsy. The biopsy should be stained with Congo red and examined under polarized light to demonstrate apple-green birefringence, confirming amyloid. In cases of suspected hepatic rupture, emergency stabilization and exploratory surgery may be necessary. Additional tests to identify underlying causes include serology for infectious diseases (e.g., Ehrlichia, Leishmania, FIP), and genetic testing for Shar-Pei amyloidosis if available.

Laboratory findings in hepatic amyloidosis are variable and often reflect the underlying inflammatory condition. On CBC, there may be leukocytosis with a left shift due to chronic inflammation, or leukopenia in cases of viral infection (e.g., FIP). Anemia may be present due to chronic disease or blood loss. Serum biochemistry typically reveals elevated liver enzymes: alkaline phosphatase (ALP) and alanine aminotransferase (ALT) are commonly increased, but the degree of elevation is variable. Gamma-glutamyl transferase (GGT) may also be elevated. Hyperbilirubinemia is seen in advanced cases. Hypoalbuminemia is common due to hepatic dysfunction and protein-losing nephropathy (if renal amyloidosis is concurrent). Globulins may be elevated due to chronic inflammation. Coagulation abnormalities, such as prolonged PT and aPTT, may be present due to decreased synthesis of clotting factors. Urinalysis may show proteinuria if renal amyloidosis is present, and the urine protein-to-creatinine ratio (UPC) may be elevated. Specific biomarkers such as serum amyloid A (SAA) may be elevated, but this is not routinely measured. In Shar-Pei dogs, a marked acute-phase response may be seen. Blood gas analysis may reveal metabolic acidosis in cases of liver failure.

Imaging findings in hepatic amyloidosis are nonspecific but can support the diagnosis. On abdominal radiography, hepatomegaly may be evident, with an enlarged liver silhouette. In cases of hepatic rupture, there may be loss of abdominal detail due to peritoneal effusion. Ultrasonography is more sensitive and may show an enlarged liver with increased echogenicity, sometimes with a heterogeneous pattern. The liver margins may be rounded. In some cases, hypoechoic or hyperechoic nodules may be seen, but these are not specific. Doppler ultrasound may show altered hepatic blood flow. Computed tomography (CT) can provide more detailed assessment of liver size and perfusion, but is rarely necessary. Magnetic resonance imaging (MRI) is not commonly used for hepatic amyloidosis. In cases of suspected portal hypertension, Doppler ultrasound can assess portal vein flow. If hepatic rupture is suspected, ultrasound can detect free abdominal fluid, and abdominocentesis may reveal hemorrhagic effusion. Imaging is also useful to guide liver biopsy.

Cytology from fine-needle aspirates of the liver is often inconclusive for amyloidosis, as amyloid appears as amorphous eosinophilic material that may be mistaken for other deposits. However, in some cases, cytology may show extracellular pink material. Histopathology is the gold standard. On hematoxylin and eosin (H&E) staining, amyloid appears as homogeneous, eosinophilic, extracellular material that may be deposited in the space of Disse, compressing hepatocytes. The liver architecture may be distorted, with hepatocyte atrophy and fibrosis in chronic cases. Special stains are essential for confirmation: Congo red staining shows apple-green birefringence under polarized light. Other stains such as thioflavin T can also be used. In cases of hepatic rupture, histopathology may show areas of hemorrhage and necrosis. Immunohistochemistry can be used to identify the type of amyloid (e.g., AA vs. AL), but this is not routinely performed. Biopsy samples should be taken from multiple liver lobes, as amyloid deposition may be patchy.

Treatment of hepatic amyloidosis focuses on managing the underlying inflammatory condition, supportive care, and addressing complications. If an underlying infection or inflammatory disease is identified, specific therapy should be instituted (e.g., doxycycline for ehrlichiosis, allopurinol for leishmaniasis, or appropriate antibiotics for abscesses). In cats with FIP, antiviral therapy (e.g., remdesivir or GS-441524) may be considered, though availability varies. For Shar-Pei dogs with familial amyloidosis, management of recurrent fevers with anti-inflammatory drugs may be attempted, but there is no cure. Supportive care includes fluid therapy with balanced crystalloids, nutritional support (e.g., high-quality protein diet, but restricted in cases of hepatic encephalopathy), and hepatoprotectants such as S-adenosylmethionine (SAMe) and ursodeoxycholic acid (UDCA). In cases of hepatic rupture, emergency surgery is required to control hemorrhage, which may involve partial hepatectomy or packing. Coagulopathy should be managed with fresh frozen plasma or vitamin K. In severe liver failure, management of hepatic encephalopathy with lactulose and dietary modification is necessary. Colchicine has been used in humans to reduce amyloid deposition, but its efficacy in veterinary patients is unproven and it is not routinely recommended. In some cases, immunosuppressive doses of corticosteroids may be used to reduce inflammation, but this is controversial and may worsen underlying infections.

The prognosis for hepatic amyloidosis is generally guarded to poor, depending on the underlying cause and the extent of liver damage. In dogs with Shar-Pei amyloidosis, the prognosis is poor, with many dogs dying from hepatic rupture or progressive liver failure within months to a few years of diagnosis. In cats with FIP-associated amyloidosis, the prognosis is also poor, as FIP is often fatal. If the underlying inflammatory condition can be successfully treated, the progression of amyloidosis may be halted, but existing amyloid deposits are not reversible. The prognosis is worse in cases with hepatic rupture, coagulopathy, or concurrent renal amyloidosis. Median survival times are not well-documented, but in one study of Shar-Pei dogs, the median survival was approximately 6 months after diagnosis. Negative prognostic indicators include the presence of hemoabdomen, severe hypoalbuminemia, hyperbilirubinemia, and elevated creatinine (indicating renal involvement). Early diagnosis and aggressive management of the underlying condition may improve outcomes, but overall, the prognosis is guarded.

Follow-up for patients with hepatic amyloidosis should be tailored to the underlying disease and the severity of liver dysfunction. Initially, re-evaluation should occur every 2-4 weeks to monitor clinical signs, body weight, and laboratory parameters (CBC, biochemistry, coagulation profile). Once stabilized, re-checks can be extended to every 1-3 months. Serial ultrasonography may be performed to assess liver size and detect any changes, such as the development of nodules or rupture. Blood pressure should be monitored, as hypertension can develop in cases of renal involvement. If the patient is on medications (e.g., antibiotics, anti-inflammatories), appropriate monitoring for adverse effects is necessary. In Shar-Pei dogs, monitoring for recurrent fever episodes is important. Owners should be educated on the signs of hepatic rupture, such as acute collapse, and advised to seek immediate veterinary care. Long-term management includes dietary modifications (e.g., liver support diets), supplementation with SAMe and UDCA, and avoidance of hepatotoxic drugs. Regular monitoring of renal function (SDMA, UPC) is recommended, as amyloidosis often affects the kidneys.

Pearls: 1) Always consider hepatic amyloidosis in Shar-Pei dogs and Abyssinian cats with hepatomegaly and chronic inflammatory disease. 2) Liver biopsy with Congo red staining is essential for definitive diagnosis; do not rely on cytology alone. 3) In cases of acute hemoabdomen in a Shar-Pei, hepatic rupture due to amyloidosis should be a top differential. 4) Coagulation testing is crucial before biopsy due to the risk of bleeding. 5) Treat the underlying inflammatory condition aggressively to halt further amyloid deposition. Pitfalls: 1) Failing to perform a liver biopsy may lead to misdiagnosis of chronic hepatitis. 2) Using corticosteroids indiscriminately may worsen underlying infections and increase amyloid deposition. 3) Overlooking concurrent renal amyloidosis can lead to progressive renal failure. 4) Not recognizing the risk of hepatic rupture can result in sudden death. 5) Assuming that elevated liver enzymes are always due to hepatitis without considering amyloidosis.

Drug protocols for hepatic amyloidosis are primarily supportive and directed at the underlying cause. For bacterial infections, appropriate antibiotics should be chosen based on culture and sensitivity. For example, doxycycline (5-10 mg/kg PO q12h) for ehrlichiosis, or allopurinol (10 mg/kg PO q12h) for leishmaniasis. In cats with FIP, antiviral drugs such as remdesivir (10 mg/kg IV q24h) or GS-441524 (4 mg/kg SC q24h) may be used, but availability and legal status vary. For inflammation, nonsteroidal anti-inflammatory drugs (NSAIDs) may be used cautiously, but they can be hepatotoxic and nephrotoxic; alternatives include corticosteroids (e.g., prednisolone 0.5-1 mg/kg PO q24h) but only if infection is ruled out. Hepatoprotectants: S-adenosylmethionine (SAMe) at 20 mg/kg PO q24h, and ursodeoxycholic acid (UDCA) at 10-15 mg/kg PO q24h. For hepatic encephalopathy, lactulose (0.5-1 mL/kg PO q8h) and a low-protein diet. For coagulopathy, vitamin K1 (0.5-1.5 mg/kg SC q12h) and fresh frozen plasma (10-20 mL/kg IV) as needed. For pain management, opioids such as buprenorphine (0.01-0.02 mg/kg IV/IM q8-12h) are preferred. In cases of hepatic rupture, emergency surgery and blood transfusion may be required. Colchicine (0.03 mg/kg PO q12h) has been used experimentally but is not standard. Always adjust dosages for hepatic impairment and monitor for adverse effects.

Evidence for the management of hepatic amyloidosis in veterinary medicine is limited to case reports and small case series. A study by Rivas et al. (2016) described the clinical features and outcomes of Shar-Pei dogs with amyloidosis, reporting a median survival of 6 months and a high incidence of hepatic rupture. Another study by Beatty et al. (2002) evaluated Abyssinian cats with amyloidosis, finding an association with FIP and a poor prognosis. There are no randomized controlled trials for treatment, but consensus guidelines from ACVIM and ECVIM recommend supportive care and treatment of the underlying inflammatory condition. The use of colchicine is extrapolated from human medicine, but evidence in animals is lacking. A retrospective study by van der Laan et al. (2018) suggested that early diagnosis and aggressive management of underlying infections may improve outcomes. Overall, the literature emphasizes the importance of histopathology for diagnosis and the need for a thorough search for underlying inflammatory diseases.