JPC SYSTEMIC PATHOLOGY
SIGNALMENT (JPC# 1965664): A sheep.
HISTORY: This tissue is from a sheep that died during a hemolytic crisis. Levels of copper in the liver were 1,183 ppm wet weight (normal=70-188 ppm wet weight).
MICROSCOPIC DESCRIPTION: Kidney: Multifocally, numerous cortical and medullary tubular lumina and less commonly Bowman’s space are ectatic and contain a bright red, hyaline to granular material (hemoglobin casts) or less often a pale eosinophilic homogenous to proteinaceous fluid that is often admixed with erythrocytes. Multifocally, tubular epithelial cells demonstrate one or more of the following changes: are attenuated, contain pale vacuolated cytoplasm and swollen nuclei (degeneration), contain hypereosinophilic cytoplasm and pyknotic nuclei (necrosis), or contain numerous eosinophilic intracytoplasmic granules (hyaline droplets). Multifocally medullary tubular lumina contain variably sized aggregates of deeply basophilic granular material (mineral). Rarely there are interstitial aggregates of few lymphocytes and plasma cells. Multifocally the capsular surface is mildly undulant.
MORPHOLOGIC DIAGNOSIS: Kidney: Tubular degeneration and necrosis, acute, diffuse, severe, with protein and hemoglobin casts, hyaline droplet formation, and mineralization, breed not specified, ovine.
ETIOLOGY: Chronic copper toxicity
ETIOLOGIC DIAGNOSIS: Hemoglobinuria-associated acute tubular injury (previously hemoglobinuric nephrosis) secondary to chronic copper toxicity
50b: SINGALMENT (JPC # 2292838): A dog.
HISTORY: Tissue from a dog that had several coins composed of zinc (pennies) in its stomach at necropsy.
MORPHOLOGIC DESCRIPTION: Kidney: Multifocally, numerous cortical and medullary tubules are ectatic, lined by attenuated epithelium and contain a bright red, hyaline to granular material (hemoglobin casts) or less often a pale eosinophilic homogenous material (protein). Multifocally, tubular epithelial cells are necrotic with hypereosinophilic cytoplasm and pyknotic nuclei or degenerative with pale vacuolated cytoplasm and swollen nuclei or contain variably sized light brown intracytoplasmic globules (hemosiderin). Within more severely affected tubules, there is variable disruption of basement membranes (tubulorrhexis). The interstitium is expanded and partially effaced by fibrin, hemorrhage, and edema and admixed with scattered aggregates of few lymphocytes and plasma cells. Multifocally within Bowman’s space there is attachment of visceral to parietal epithelium (synechiae).
MORPHOLOGIC DIAGNOSIS: Kidney: Tubular degeneration and necrosis, acute, diffuse, severe, with hemoglobin casts, tubulorrhexis, and glomerular synechia, breed not specified, canine.
ETIOLOGY: Zinc toxicity
ETIOLOGIC DIAGNOSIS: Hemoglobinuria-associated acute tubular injury (previously hemoglobinuric nephrosis) secondary to zinc toxicity
- Metabolism: Copper is absorbed from the small intestine by divalent metal transporter (DMT1) and copper transporter (Ctr1) then bound to ceruloplasmin, transcuprein, and albumin and transported to liver where it is sequestered in metallothionein or glutathione; excretion in bile or blood is through proteins such as ATP7A with excess stored in lysozomes
- Copper toxicity is seen in two forms: acute and chronic; the acute form causes gastroenteritis characterized by abdominal pain, diarrhea, anorexia, dehydration, and shock; chronic form is the result of an acute precipitous hemolytic crisis; the chronic form is more commonly seen
- Sheep are the most susceptible species to copper toxicity because of reduced biliary excretion and the liver’s avidity for copper; North Ronaldsay sheep are unusually susceptible to copper toxicity as their normal diet is rich in zinc which inhibits copper uptake; they experience copper poisoning when they are switched to a normal pasture. They are also known to have overexpression of CTR1 in the blood-brain barrier and blood-cerebrospinal barrier which causes an enhanced uptake of copper into the brain.
- Risk factors that predispose/cause chronic copper toxicity
- Primary metabolic defect in hepatic copper metabolism
- Altered hepatic biliary excretion
- Dietary excess
- Sources include hardware, coins containing zinc such as pennies minted after 1982, galvanized metals, zinc sulfate (emetic) and zinc oxide ointment
- Young animals are generally more susceptible
- Toxic at high levels because of it has two redox states that mediate free-radical production àdirect oxidation of cellular components
- Acute copper poisoning occurs following ingestion of excess amounts and is usually in animal deficient in vitamin E or molybdenum
- Chronic toxicosis is a result of three factors in sheep: excessive copper intake; increased availability of dietary copper when dietary levels of molybdenum are low (Mo forms complexes with Cu in gut and liver, making it inert); and hepatotoxins, most importantly pyrrolizidine alkaloids
- High levels of copper in diet à accumulation in liver à exhausts lysosomal storage capacity à hepatocellular necrosis à acute release of copper into the serum à exhaustion of serum binding (ceruloplasmin and albumin) and the antioxidant glutathione à free radical damage and blood cell fragility à intravascular hemolysis à anemia and hemoglobinuria à cast formation, obstruction, and anoxia à acute ischemic/toxic tubular necrosis (hemoglobinuric nephrosis)
- Hemolysis and anemia accelerates rate of hepatocellular necrosis à more copper release à lethal clinical syndrome of intravascular hemolysis and liver failure
- Cytotoxicity of hemoglobin and myoglobin as well as reduction in renal blood flow and anemia likely all contribute the renal lesions
- Copper levels usually exceed 1000 ppm before they are clinically significant
- Liver copper levels above 300 ppm causes hepatocellular apoptosis resulting in compensatory mitosis/regeneration
- Specific mechanism of zinc-induced hemolysis is unknown
- Zinc interferes with absorption of copper and iron leading to anemia
- Proposed mechanisms include erythrocyte enzyme inhibition as in copper toxicity, direct cell membrane damage, and hapten-induced immune-mediated destruction
- Acute tubular injury secondary to copper or zinc (hemoglobinuria-associated ATI):
- Previously called hemogloburinic nephrosis. Hemoglobin passes into glomerular filtrate after haptoglobin saturation resulting in formation of granular casts; Cytotoxicity of hemoglobin and myoglobin as well as reduction in renal blood flow and anemia likely all contribute the renal lesions; additionally, hypotension, as well as tubular obstruction, and interstitial edema likely also contribute to the tubular necrosis
TYPICAL CLINICAL FINDINGS:
- Intravascular hemolysis
- Hemoglobinemia is the principal feature of intravascular hemolysis and can be followed by hemoglobinuria
- Heinz body anemia: Heinz body formation results from oxidative damage results in aggregation and precipitation of hemoglobin in the cell
- Elevated liver enzymes/bilirubin
- Dogs: most common clinicopathologic findings is anemia and hyperbilirubinemia
TYPICAL GROSS FINDINGS:
- Liver: Soft, swollen & deep orange; fibrotic & nodular in later stages
- Kidney: Very dark almost black “gunmetal blue” discoloration due to entrapped hemoglobin with deep red urine
- Icteric carcass with superimposed red or brown coloration due to free hemoglobin/methemoglobin
- Kidney: Reddish-brown kidneys in dogs
- Pancreas: Enlarged and pale with lobulation
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Intravascular hemolysis from either copper or zinc results in ischemic acute tubular injury characterized by:
- Severe acute focal necrosis of tubules, particularly of the proximal tubules plus disruption of the basement membrane (tubulorrhexis)
- Occlusion of tubular lumina by eosinophilic hyaline and hemoglobin casts (orange-red granular material)
- Fine red granules (hemoglobin) may also present in tubular epithelial cells
- Normal glomeruli
- Tubular regeneration
- Liver: Multifocal centrilobular necrosis with foci of macrophages, plasma cells, neutrophils & intracytoplasmic copper predominately within centrilobular region
- Pancreas: Degeneration and necrosis of exocrine pancreas and with chronicity the exocrine acinar cells become atrophic and form dilated ductule-like structures without discernible zymogen granules (tubular complexes) which are often mistaken for hyperplastic ductules
- Liver: Postnecrotic scarring
- Kidneys: Acute tubular injury similar to copper but is known to target the loops of Henle
ADDITIONAL DIAGNOSTIC TESTS:
- Copper: Positive rhodanine or rubeanic acid stains; blood and kidney copper levels
- Zinc: Abdominal radiographs for ingested zinc products
- Heavy metal concentrations in tissue
- JMS silver stain to look for tubulorrhexis in kidneys
Histologically, red pigment in kidneys (copper & zinc):
- Hemoglobinuric nephrosis (intravascular hemolysis)
- Leptospirosis or babesiosis in cattle
- Red maple toxicity in horses
- Autoimmune hemolytic anemia in dogs
- Myoglobinuric nephrosis (indistinguishable from hemoglobin casts)
- Rhabdomyolysis in horses
- Capture myopathy of wild animals
- Severe trauma in any species
- Heinz body hemolytic anemia
- Onion ingestion (dog, cattle, horse)
- Acetaminophen (cat)
- Rape or kale (cattle, sheep)
- Phenothiazine (horse)
- Methylene blue, a urine acidifier (cat)
- Red maple Acer rubum (horse)
- Inherited glucose-6-phosphate deficiency (rarely in sheep and dog)
- Normal finding (cat 5%)
- Postparturient hemoglobinuria (cattle)
- Selenium deficiency
- Dogs: Hepatic copper accumulation is most important mechanism(three causes)
- Primary accumulation disease due to a metabolic defect that impairs biliary copper excretion; accumulation is centrilobular and concentrations greater than 2,000 ppm
- Bedlington Terriers – mutation of the COMMD1 gene
- Breed associated copper accumulation hepatitis (mutations unknown) – Skye terrier, dalmation, West Highland white terrier, Doberman pinscher, cocker spaniel, and Labrador retriever
- Secondary to hepatic inflammation that alters the biliary excretion; accumulation is primarily periportal and less than 2,000 ppm
- Dietary excess
- Other ruminants: acute poisoning most often seen after accidental administration of large doses of copper; chronic poisoning is most often due to feed exposed to high levels of fertilizer
- Goats, especially adults, are considered resistant to chronic copper toxicosis and do not develop a hemolytic crisis, except Boer goats; meat breeds generally more resistant
- Rabbits are considered sensitive to copper: Hemolytic anemia with intravascular hemolysis, erythrophagocytosis in spleen, hematuria with tubular casts, hepatic centrilobular necrosis with Kupffer cells containin blue-green granules that stain positive for rhodamine
- Marine Invertebrates: Primary lesion in California sea hare is branchial and nephridial necrosis; echinoderms often have epidermal necrosis, ulceration and increased numbers of coelomocytes in water-vascular system; sunburst anemone had necrosis of epidermis and gastrodermis with expulsion of zooxanthellae
- Bone & joint lesions resembling osteochondrosis in pigs
- Necrotizing abomasitis & duodenitis in ruminants
- Ferrets: Clinical-Pale mucous membranes from anemia, posterior weakness and lethargy; Gross-Kidneys are large, pale, and soft with capsular depressions; liver is orange and gastric erosions are present; Histo-Kidneys have collapsed glomeruli and dilated tubules; liver has periacinar fatty infiltration; gastric erosions and hemorrhage; bone marrow has depressed erythroid precursors
- Birds: Pancreas is the target organ of zinc toxicity but may also cause ventricular ulceration; renal and hepatic lesions are similar to mammals
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