JPC SYSTEMIC PATHOLOGY

DIGESTIVE SYSTEM

September 2024

D-M20 (NP)

 

Signalment (JPC #3102662): Three-year-old spayed Collie dog

 

HISTORY: Vomiting post feeding for a week. Exploratory surgery revealed small nodular liver.

 

HISTOPATHOLOGIC DESCRIPTION:  Affecting 80% of the section, there is loss of hepatocytes with replacement by numerous macrophages, often arranged in sheets, with abundant golden-brown, irregular, intracytoplasmic, granular pigment (hemosiderin, hemosiderosis). Admixed with the hemosiderin-laden macrophages are fewer lymphocytes, foreign body-type multinucleated giant cells rarely with greater than 80 nuclei, scant hemorrhage, fibrin, and edema, and hypertrophied fibroblasts with variably mature fibrous connective tissue that often centers on and bridges between portal areas (portal bridging fibrosis). Within areas of fibrosis, there are increased numbers of bile duct profiles; these are often lined by hyperplastic, hypertrophic epithelial cells that often pile up to 4 cell layers thick and are enlarged with swollen nuclei, respectively (biliary ductular reaction). Small islands of hepatocytes containing similar intracytoplasmic hemosiderin remain within the sheets of macrophages. There are variably sized, up to 4mm diameter, irregular nodules of hepatocytes that retain hepatic chord architecture (nodular regeneration). Hepatocytes at the margin of regenerative lobules and islands are often either enlarged with vacuolated cytoplasm (degeneration) or are shrunken and angular with hypereosinophilic cytoplasm and pyknotic nuclei (necrosis). Within remaining sinusoids there are numerous hemosiderin-laden Kupffer cells. Individual hepatocytes often have abundant brown intracytolasmic pigment (hemosiderin or lipfuscin). Collagen fibers are multifocally deeply basophilic (mineralization). There is increased subcapsular clear space and multifocally the lymphatics are markedly dilated (edema). 

 

MORPHOLOGIC DIAGNOSIS: Liver: Hepatocellular degeneration and necrosis, chronic, multifocal to coalescing, severe, with nodular regeneration, marked hemosiderosis, portal bridging fibrosis, biliary ductular reaction, and collagen mineralization, Collie dog, canine.

 

ETIOLOGIC DIAGNOSIS: Hepatic hemochromatosis

 

CAUSE: Iron overload

 

CONDITION: Hemochromatosis

 

SYNONYM: None

 

GENERAL DISCUSSION:

• Affects various mammals, including bats, primates, rhinoceros, marine mammals, and birds; affects sheep and cattle exposed to high levels of iron in pasture and water 
• Hepatic iron overload is divided into two sub-categories:
  • Hemosiderosis: Only excess accumulation of hepatocellular iron (no hepatic damage)
  • Hemochromatosis: Excess iron storage leads to fibrosis, inflammation and hepatic injury
• Iron is stored predominantly in lysosomes 

 

PATHOGENESIS:

• Pathogenesis of nutritional iron overload is unknown; suspect diet, environment, genetic, but not confirmed
  • Iatrogenic: Hepatic damage due to excessive iron storage from excessive iron supplementation in animals: Ferrous fumarate intoxication in newborn foals
  • Excess ingestion of a hematinic in calves
  • Iron injections administered inappropriately to animals suspected of being iron deficient: Fe cannot be excreted fast enough by urine and feces, hyperferremia will develop
    • Iron-dextran intoxication in piglets (for prevention of anemia) 
    • Racehorses
• Hereditary:
  1. In humans, the hereditary hemochromatosis is associated with point mutation in hfe gene and intestinal absorption is not appropriately regulated 
  2. Salers breed cattle, intestinal absorption of Fe is not appropriately regulated
• Increased glucocorticoid hormones: Hyperferremia can occur after administration of dexamethasone in horses and dogs but hypoferremia occurs in cattle; reason unknown
• Release of iron from tissues: 
  1. Hepatocytes contain iron-rich ferritin; hyperferremia can occur secondary to hepatocyte damage
  2. Intra and extravascular hemolysis: Iron released from degraded Hgb binds to transferrin so Fe^3+ can be transported in plasma for utilization or storage
• Has been described in horses, with animals displaying signs of liver failure and neurological impairment

 

TYPICAL CLINICAL FINDINGS:

• Clinical symptoms of liver failure
• Weight loss, lethargy, and anorexia

 

TYPICAL GROSS FINDINGS:

• Enlarged brown liver with diffuse fine nodules
• Dark-brown discolored, firm liver and adjacent lymph nodes 
• Brown discoloration of bone marrow

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Massive hepatic necrosis, hyperplasia of bile ducts (possibly due to hepatic progenitor cell proliferation 
• Hemosiderin accumulation in hepatocytes
• Periportal and perivenular bridging fibrosis, with nodular regeneration
• Hemosiderosis in Kupffer cells, lymph nodes, kidney, pancreas, spleen, other organs

 

ADDITIONAL DIAGNOSTIC TESTS:

• Histochemical stains:
  • For iron: Prussian blue, Perl’s
  • For fibrosis: Masson’s trichrome
• Serum iron: May be helpful in confirming an Fe-deficient or an iron overload state, but serum [Fe] alone is an unreliable reflection of body Fe stores
• Gold standard: Hepatic iron measurement on 1 gm biopsy of liver, rarely performed on live animals
• Cytology:
  1. Liver: Hemosiderin (insoluble iron containing protein: refractile golden brown to blue-black granules on H&E, dark blue granules with Prussian blue
     • In diseased states can be seen within hepatocytes, Kupffer cells, and other macrophages with or without phagocytized erythrocytes
  2. Bone Marrow: Dogs, marrow storage iron seen as hemosiderin in macrophages is a good indicator of total body iron stores. A few clumps of iron are normal in adult healthy canines, but iron may be increased with hemochromatosis

 

DIFFERENTIAL DIAGNOSIS:

 

COMPARATIVE PATHOLOGY:

• Form of heritable hemochromatosis reported in Salers or Salers-cross cattle
  • Develop a wasting disease < 2 years of age 
  • 30-100 fold increase in liver iron content
  • Develop a dark brown, firm liver with accumulation of hemosiderin in hepatocytes and Kupffer cells, fibrosis, and nodular regeneration
  • Can have periosteal dysplasia and osteopenia
• Avian:
  • Common in mynah bird (starling family)- Heritable; highly efficient at absorbing dietary iron and do not downregulate iron absorption sufficiently when fed iron-rich diets.
  • Hemosiderosis (iron seen in hepatocytes and Kupffer cells with no observable biochemical, cellular, or tissue damage) is common in toucans, mynahs, hornbills, aracaris, kingfishers, jays, hummingbirds, and birds-of-paradise
  • Hemochromatosis can be seen in birds being fed iron rich diet or supplementsà similar histological findings to other species
• Black and Sumatran rhinoceros and tapirs: Iron overload disorder can lead to organ dysfunction 

• Excessive iron deposition observed only in captive animals due to diet with high iron bioavailability (in wild populations, their diet is rich in iron chelating compounds (tannins, phytates, etc) that bind to iron and then pass through the GI tract without being absorbed)
• Typically lesions are seen in the spleen, liver, small intestines, and lungs

• Egyptian fruit bats (Rousettus aegyptiacus): Frequently develop iron storage disease, with consistently large amounts in liver and spleen; less amounts in other organs (pancreas, kidney, skeletal muscle, and lung)
• Bottle-nose dolphins (cetaceans): High circulating levels of serum iron and elevated transferrin saturation, histologically accumulation of iron in hypertrophied Kupffer cells and hepatocytes with or without hepatic necrosis, hepatitis, and fibrosis; associated with diabetes and metabolic syndrome, as well as chronic inflammation, iron sequestration secondary to acute sepsis, excessive dietary iron consumption or supplementation, emaciation, inborn errors of metabolism, and a maladaptive type syndrome
• Osteichthyes (e.g., seahorses, sea dragons, goldfish, clownfish, tangs, salmon, cod, catfish, and tilapia): Hepatocellular iron accumulation in fish exposed to high environmental iron levels has been documented experimentally and has also been associated with exposure to heavy metal- and PCB-contaminated sites in wild fish
• New World and Old world monkeys: May be associated with increased susceptibility to infections; common marmosets there is a correlation between dietary iron, severity of hemosiderosis and death (Dubin-Johnson-like disease in tamarins is a differential diagnosis)
• Prosimians (lemurs): Captive lemurs with excessive iron accumulation can have hemochromatosis (fibrosis, hepatocyte necrosis, hepatocyte fatty degeneration, bile duct hyperplasia, and/or nodular regeneration), less common than hemosiderosis; can be associated with benign and malignant neoplasms; recent studies have not found a relationship with clinical disease and excessive hepatic hemosiderosis 
• Captive Afghan pikas (lagomorphs) due to iron overload
• Hyrax: Presumed to be diet related in combination with genetic influences
• Captive Kori bustards: Hemosiderosis and hemochromatosis with evidence of iron accumulation in the kidney, GI tract, adrenal gland, and spleen (Cudd, Vet Pathol. 2021)

 

REFERENCES:

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3. Arenales A, Silva FL, Miranda F, et al. Pathologic findings in 36 sloths from Brazil. J Zoo Wildl Med. 2020; 51(3): 672-677.
4. Cudd SK, Garner MM, Cartoceti AN, LaDouceur EEB. Hepatic lesions associated with iron accumulation in captive kori bustards (Ardeotis kori) [published online ahead of print]. Vet Pathol. 2021 
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