Conference 1 - 2016 Case: 2 20160824

Signalment:

16 year old, female, domestic shorthair, Felis catus.The cat had decreased appetite and weight loss. It was icteric with a temperature of 38°C. The heart rate was 220 beats/min and the respiration rate was 92 breaths/min. Lymph nodes were unremarkable by palpation. Ultrasound of the abdomen showed moderate amounts of fluid, and a liver with rounded edges and a marbled parenchyma with reduced number of visible hepatic- and portal veins. Lymph nodes in the cranial abdomen, near the spleen and pancreas were enlarged and hypoechoic.

Gross Description:

The cat was thin and icteric. The abdominal cavity contained 50 ml clear yellow fluid with a few floccules. The liver was slightly enlarged with rounded edges and lighter in color than normal with a lobular pattern and a decreased texture. Multifocally scattered, light gray, soft nodules, 0.5-5.0 mm in diameter were present in the hepatic parenchyma. The mesenteric lymph node was enlarged, light yellow-gray, moderately firm, and measured 4.0x1.5x1.5 cm. The pancreas was macroscopically normal.

Histopathologic Description:

In the liver, there are multifocal to confluent, randomly spaced areas with numerous infiltrating small lymphoid cells. The cells are located both in the sinusoids and appear to be located within the cytoplasm of hepatocytes. Some of the cells are also located close to or in invaginations of the hepatocellular mem-brane. The cells are small, with a narrow rim of eosinophilic cytoplasm. They have a small, densely stained round to irregular nucleus with indistinct nucleolus. There is little degree of anisocytosis and an-isokaryosis. There is <1 mitotic figure per 10 HPF. The lymphoid cells present within the hepatocellular cytoplasm are surrounded by a clear halo. There is severe dissociation of hepatocytes, seen as single rounded large hepatocytes with up to 8 lymphoid cells within the cytoplasm. In areas with few lymphoid cells, there are moderate vac-uolation of hepatocytes with variably sized clear vacuoles.

Morphologic Diagnosis:

Liver: malignant lymphoma with emp-eripolesis of lymphocytes and severe dissociation of hepatocytes.

Lab Results:

Clinical pathology: AST: 193 U/L (ref: 0-60), ALT: 258 U/L (ref: 0-75), AP: 339 U/L (ref: 0-40), amylase: 880 U/L (ref: 0-800), total protein: 56 g/L (ref: 60-82), albumin: 21 g/L (ref: 25-39), bile acids: 392 ?mol/L (ref: 0-5), total bilirubin: 215 Μmol/L (ref: 0-4), WBC: 4.2 x 10e9/L (ref: 5.5-17), lymphocytes: 0.6 x 10e9/L (ref: 1.5-7.0), platelets: 30 x 10e9/L (ref: 180-400).

Immunohistochemical staining of mesenteric lymph node and liver showed immunoreactivity with rabbit anti-human CD3 (DakoCytomation, A 0452) and confirmed that the infiltrating cells were T lymphocytes.

Condition:

Malignant lymphoma

Contributor Comment:

Feline lymphoma commonly occurs as thymic, alimentary multicentric and cutaneous syndromes.⁸ This cat had involvement of the mesenteric lymph node and liver. It is indicated that Feline leukemia virus (FeLV) positive cats are associated with the mediastinal and multicentric form of lymphoma and that the thymic and alimentary forms predominate in FeLV negative cats.^2,8 The FeLV status of this cat was not known.

Hepatic lesions morphologically identical to those in this cat, has been reported earlier in two cats diagnosed with lymphoblastic lymphosarcoma.³Although emperipolesis is the phenomenon of viable cells entering the cytoplasm of other cells without damage to either host cell or the engulfed cells,³ the clinical pathology of this cat, similar to the cats presented by Ossent et al,⁵ indicates severe hepatic failure. In addition, histology of the liver shows extensive hepatocellular dissociation.

JPC Diagnosis:

1. Liver: T-cell lymphoma, hepatocytotropic.

2. Liver: Regeneration, micronodular, multifocal, mild.

Conference Comment:

This case generated discussion amongst the conference par-ticipants regarding the use of the term emperipolesis. As mentioned by the con-tributor, emperipolesis is an uncommon biological process, in which a cell penetrates the cytoplasm of another living cell. ^1,4,6,7Unlike phagocytosis where the engulfed cell is killed by lysosomal enzymes of the macrophage, the engulfed cell exists as a viable cell within another.⁷ The pathogenesis and significance of this phenomenon is currently unknown.¹ Emperipolesis has been rarely reported in the human literature associated with autoimmune hemolytic anemia, multiple myeloma, leukemia, and malignant lymphoma.¹ In this case, there is clear evidence of hepatocellular injury and cholestasis supported by the animals cl-inical icterus along with severe serum bio-chemistry abnormalities. Clinicopathologic serum elevations in AST and ALT, as well as hypoalbuminemia and hypoproteinemia support hepatocellular injury in addition to hepatocellular swelling, lipofuscin dep-osition, and hepatic lipidosis. Cholestasis is confirmed by severe elevations in bile acids, total bilirubin, and elevated ALP.

Given the degree of hepatocellular injury and cholestasis, conference participants unanimously preferred the term hep-atocytotropism over emperipolesis as a more representative term for the infiltrating T-cell lymphocytes in this case. This terminology was recently proposed as an alternative to emperipolesis in similar cases malignant lymphoma in the dog with distinct tropism for hepatocytes.⁴ Transmission electron microscopy in the dog as well as the previously reported cases in cats, showed lymphocytes within invaginations of the hepatocyte cell membrane rather than within the cytoplasm, as required for em-peripolesis.^4,6,7 In addition, hepatocyto-tropism is more analogous to the epi-theliotropism present in cutaneous and intestinal T-cell lymphoma in the dog and cat.⁴

Several conference participants also commented on the degree of hepatic cord discohesion with dislocation of hepatic plates and diffuse loss of normal architecture in this case. Some speculated this to be partially due to moderate autolysis of the tissue. There was further discussion and some speculation that hepatic discohesion could be due to a defect in β-catenin through the Wnt signaling pathway, common in hepatic neoplasms.⁹ This pathway has a major role in cell adhesion to the basement membrane and cell polarity in the liver and gastrointestinal tract. In addition, β-catenin binding to E-cadherin is responsible for maintaining intercellular adhesion.⁵ Nor-mally, after acute hepatocellular insult, the liver is stimulated to regenerate via the Wnt pathway. The Wnt receptor signals through cell surface receptor, frizzled (FRZ), to deactivate the destruction complex, APC. The tumor suppressor APC normally binds to and destroys β-catenin.⁵With the APC deactivated, β-catenin signaling drives the expression of target genes that are critical for cell cycle progression and contribute to initiation of the regeneration process.^5,9 Even in the multifocal microregenerative nodules without hepatocytotropic lym-phocytes, there is hepatic cord discohesion. Regardless of the pathogenesis, the dis-association of the hepatic cords likely disrupts bile canalicular transport and sec-retion of bilirubin leading to severe hepatic cholestasis and icterus in this case.⁶

References:

1. Amita K, Shankar S, et al. Emeripolesis in a case of adult T cell lymphoblastic lymphoma (mediastinal type)-detected at FNAC and imprint cytology. Online J Health Allied Scs. 2011;10:11.

2. Fry, M, McGavin M. Bone marrow, blood cells, and the lymphatic system. In: Zachary JF, McGavin MD, eds. Pathologic Basis of Veterinary Disease. 5th ed. St. Louis, MO: Elsevier; 2012:698-705.

3. Humble JG, Jayne WHW, Pulvertaft RJV: Biological interaction between lymphocytes and other cells. Br J Heamatol 1956;2:283-294.

4. Keller S, Vernau W, et al. Hepatosplenic and hepatocytotropic T-cell lymphoma: two distinct types of lymphoma in dogs. Vet Pathol. 2012;50:281-290. 5. Kumar V, Abbas A, Aster J. Neoplasia. In: Kumar V, Abbas A, Aster J, eds. Robbins and Cotran Pathologic Basis of Disease. 9^th ed. Philadelphia, PA; Saunders Elsevier; 2015: 296-297.

6. Ossent P, Stöckli RM, Pospischil A: Emperipolesis of lymphoid cells in feline hepatocytes. Vet Pathol. 1989;26:279-280.

7. Suzuki M, Kanae Y, et al. Emperipolesis-like invasion of neoplastic lymphocytes into hepatocytes in feline T-cell lymphoma. J Comp Path. 2011;144:312-316.

8. Valli V, Kiupel M, Bienzle D. Hematopoietic system. In: Jubb, Kennedy, and Palmers Pathology of Domestic Animals, ed. Maxie MG, 4th ed., Vol. 3. Saunders Elsevier, Philadelphia, PA, 2016:103-104.

9. Wang E, Yeh S. et al. Depletion of β-catenin from mature hepatocytes of mice promotes expansion of hepatic progenitor cells and tumor development. PNAS. 2011;108:18384-18389.