18-day-old thoroughbred colt (Equus caballus)A healthy newborn foal nursed and the next day, became lethargic and had hemoglobinuria. With progressive stupor, icterus, hyperbilirubinemia and anemia, the foal was presented to the clinic at 2 days of age.
Yellow mucous membranes and tissues (icterus); ~200ml abdominal transudate with fibrin strands; myocardial mottling grey and red (hemorrhage and necrosis) a small Thebsian vein in the noncoronary aortic sinus; urachus patent.
The section of liver has widespread atrophy of hepatocytes with hypertrophied and occasionally binucleate nuclei. Some hepatocyte syncytia contain 6-8 nuclei. Often, the hepatocytes exhibit feathery degeneration, but centrilobular hepatocytes are degenerating or have individual cell necrosis. The spaces of Disse are expanded (edema), and sinus leukocytosis is common with leucocytes often concentrated in areas of hepatocyte loss. Scattered lipofuscin-laden macrophages are often near the pale staining triads, and bile casts and mild bile duct proliferation are noted. Throughout the section are syncytia similar to Langhans type multinucleate giant cells with nuclei surrounding a tan, granular cytoplasm (lipofuscin). Erythrophagocytosis by Kupffer cells is noted, and iron-staining Kupffer cells are in sinusoids. Hepatic cords are disassociated (shock).
Liver: Subacute hepatopathy with centrilo-bular hepatocellular degeneration, necrosis and collapse; edema, lipofuscinosis, bile casts and mild bile duct proliferation; hepatocyte syncytia; erythrophagocytosis and hemosiderosis; multifocal neutrophilic hepatitis.
PCV=12 (32-53) no Nrbcs
Platelets 470,000/ul (100-350,000)
TP 4.7g/dl (5.3-7.3)
Total bilirubin 14.5 mg/dl (0-1.9)
GGT 124U/L (0-53)
Alkaline phosphatase 553U/L (128-512)
ALT 850U/L (134-643)
Saline agglutination test positive
Mare serum Anti-Qab positive
Equine neonatal isoerythrolysis
This is a classic case of equine neonatal isoerythrolysis /isoimmune hemolytic anemia (NI). The animal was treated with dexamethasone, banamine, and antibiotics; clinical and post-mortem blood cultures were sterile. No organisms were noted with Gram or GMS stains. While there is inflammation is in the lesion, it was felt to reflect secondary, cholestasis-induced hepatitis.
When reviewing the case with the resident, the pathologist commented that the giant cells were classically seen with NI; however, the resident noted that this lesion is not mentioned in textbooks as a lesion associated with NI. Young horse hepatocytes often form syncytia, and giant cell hepatopathies/ hepatidides are described; especially associated with leptospirosis,(13,20) but idiopathic hepatocyte syncytia have been described in 5-7 month-old, equine abortuses(3) and have been seen by this contributor in leptospira PCR-negative cases. In human infants with jaundice, it was described as giant cell hepatitis(17) or syncytial giant cell hepatitis.*(15) Initially, some considered it an expression of viral hepatitis, particularly serum hepatitis, in infancy. Some feel the lesion reflects a specific insult such as blood group incompatibility between mother and infant. It has been considered a nonspecific response of liver regeneration to any injury.(10,19) Still others consider it a congenital defect in the formation of bile canaliculi or another genetically transmitted abnormality.(5,14) Popper and Schaffner(14) concluded hepatocyte giant cell formation was a feature of cholestasis in infancy, and that it may be associated with some inflammatory changes. Syncytial cell hepatitis has been reported in humans and is associated with bacterial sepsis (especially toxoplasmosis, syphilis listeriosis, tuberculosis), viral diseases (cytomegalovirus, herpes simplex, varicella, echovirus, parvovirus B19, enterovirus, rubella, human herpesvirus-6, human immunodeficiency virus, hepatitis types A, B and C, Marburg virus and paramyxovirus), liver transplantation and death from severe liver failure.(8,16) However, in the neonatal period it is considered a non-specific reaction of immature hepatocytes to various forms of aggression,10 and the syncytia stain with nuclear proliferation and growth factors.(7) Just as in autoimmune hemolytic anemia in early childhood, syncytial cell hepatopathy has been reported in cases of equine NI.(2) It was noted in a case of NI presented in the WSC of 5-14-86. How does one explain the lack of the lesion description? Foal livers in fatal cases of NI are busy, and the syncytial cells, while typical, may be down-played in face of the catastrophic clinical and autopsy findings. Because our cases are often referral cases and are subacute to chronic, it may also be that syncytia are just more frequent in long-standing, fatal cases. Syncytia are characteristic. Foals seem prone to respond this way. Although neonatal infections may complicate clinical NI, infectious agents are not always documentable. We should remember that only recently a viral agent of equine Theilers disease has been identified,(4) which may play a role (though I doubt it).
Kernicterus is always a concern in cases of prolonged unconjugated hyperbilirubinemia in neonates. This foal had no macroscopic lesions of kernicterus, the cortex did not fluoresce and no neuronal lesions were noted in the cerebral cortex, Purkinje cells or hippocampus, where it has been described in foals with NI.(12) Its of interest that syncytia were not reported in any of their autopsy cases, even their chronic cases. There is a case report of NI in a three-day-old foal with kernicterus and neuronal necrosis represented macroscopically by yellow-discolored nuclei.(6)
For completeness, it is interesting that this colt had a persistent neutrophilia and developed a thrombocytosis. Alloimmune, neonatal neutropenia has been described in a foal with Ka antibodies in a recent report of NI.(21) The most complete study of antierythrocyte antibodies in mare serum and colostrum was done in thoroughbred and standardbred mares and Qa and Aa seemed to be the most common alloantibodies found at large;(1) however, these alloantibodies may not be the most common seen in clinical cases of NI.(2, 9) Alloantibodies to Qa antigens were found in the mare of our case. The colt of our study did not show a regenerative erythroid response. Over the 2-week hospitalization, no nucleated erythrocytes were noted and the bone marrow had erythrocytic hypoplasia. We wondered if this may have reflected a specific destruction of precursors of the erythroid series.
Liver: Hepatocellular degeneration and atrophy, diffuse, severe with Kupffer siderosis, cholestasis, and hepatocellular syncytial cell formation.
Neonatal isoerythrolysis is a type II hypersensitivity reaction that results from antibodies directed against neonatal red blood cells, most frequently IgG or IgM. This leads to activation of complement component C1q and eventual formation of the membrane attack complex which lyses the red blood cell. Red blood cell lysis can also result from opsonization of red blood cells by complement component C3b, or by antibody, followed by phagocytosis.(18)
Lipofuscin is an intracellular pigment thought to accumulate as a result of aging and cellular wear and tear, including processing of senescent cellular organelles and other material. It accumulates within lysosomes most significantly in post mitotic or slowly dividing cells as an end product of autophagy and is often seen as a perinuclear golden brown pigment. It looks very similar histologically to ceroid, which is more commonly associated with pathologic conditions such as severe malnutrition and vitamin E deficiency or can be seen in certain inherited conditions such as neuronal ceroid lipofuscinosis (see WSC 2015-16, conference 10, case 1). Ceroid is known to accumulate in both Kupffer cells and hepatocytes as well as other tissues and can be intracellular or extracellular. Lipofuscin is thought to accumulate slowly over the life of the animal, whereas ceroid usually accumulates rapidly depending on the associated condition. Histochemical tech-niques which can aid in identifying both ceroid and lipofuscin include Sudan black, oil-red-O, PAS and Ziehl-Neelsen stains. Although differences in content of the two pigments have been demonstrated by special histochemical techniques, it is not possible to differentiate the two pigments in standard H&E stained sections.(11)
The primary histologic features in this case include hepatocyte degeneration and atrophy, with formation of syncytial cells. Extensive pigmentation of hepatocytes and Kupffer cells was present throughout the section prompting extensive discussion. The brown granular to globular intracellular pigment within hepatocytes was interpreted as lipofuscin and within Kupffer cells as hemosiderin. An iron stain confirmed the presence of moderate amounts of hemo-siderin within Kupffer cells and occasionally within hepatocytes. Viewing under fluor-escence confirmed the presence of small amounts of autoflourescent pigment within hepatocytes consistent with lipofuscin. Abundant birefringent, yellow-brown spiculated material was ultimately identified as acid hematin. Numerous dilated bile canal-iculi were also noted, indicating cholestatic disease. A Halls stain for bile confirmed this finding.
We thank the contributor for providing clinical pathology data with the submission, which greatly adds to the teaching value of the case. One of the best indicators of regenerative anemia is reticulocyte count, but horses do not release reticulocytes. The absence of nucleated red blood cells may suggest a nonregenerative anemia; however, the best way to determine regenerative status would be a bone marrow sample. In this case, a bone marrow aspirate revealed erythrocytic hypoplasia, as indicated above in the contributors comment. Conference participants briefly discussed bilirubin metabolism and the elevated total bilirubin in this case was interpreted as both pre-hepatic and hepatic, which fits with both the pathogenesis and histologic findings.
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