Leukemic small cell lymphoma or chronic lymphocytic leukemia in a horse

A 16‐year‐old, Irish Draft mare was admitted to the referring veterinarian for an annual health check. A mild generalized lymphadenomegaly was noted. Rectal palpation and transrectal ultrasonographic examination revealed prominent mesenteric lymph nodes. A transcutaneous abdominal ultrasonographic evaluation was unremarkable. A CBC revealed a marked leukocytosis (63.06 × 10³/μL) and lymphocytosis (58.2 × 10³/μL) due to increased numbers of small lymphocytes. No evidence of anemia or thrombocytopenia was found and neutrophil counts were low‐normal. Cytologic examination of fine‐needle aspirates of multiple lymph nodes and a bone‐marrow aspirate revealed the presence of a monomorphic population of small lymphocytes similar to those observed in the peripheral blood, suggesting a leukemic small cell lymphoma (SCL) or chronic lymphocytic leukemia (CLL). As the lymphadenomegaly and peripheral blood lymphocytosis were present simultaneously, the distinction between these 2 conditions was not possible. Immunophenotyping by immunocytochemistry and flow cytometry of the lymphoid cells in peripheral blood determined a T‐cell phenotype. As the horse was clinically stable, no treatment was initiated, but regular examinations were undertaken. A CBC repeated 120 days after the diagnosis showed a marked lymphocytosis (157.6 × 10³/μL) with no evidence of anemia or other cytopenias. The horse was euthanized 194 days after the initial diagnosis. Histopathology and immunohistochemistry of submandibular lymph nodes and bone marrow confirmed the diagnosis of leukemic SCL or CLL, and a T‐cell phenotype. SCL and CLL are rare in horses; previous immunohistochemical studies determined that the T‐cell phenotype is predominant. To the authors' knowledge, this is the first report of the combined use of immunocytochemistry and flow cytometry in a horse with leukemic SCL or CLL.     

Myoclonus and hypercalcemia in a dog with poorly differentiated lymphoproliferative neoplasia

A 1‐year, 8‐month‐old Rhodesian Ridgeback was presented with obtundation, ambulatory tetraparesis, and myoclonus. Initial clinical findings included ionized hypercalcemia with an apparent marked increase in parathyroid hormone, thrombocytopenia, and nonregenerative anemia. Low numbers of circulating atypical cells were noted on blood film evaluation. Brain magnetic resonance imaging identified an extra‐axial contrast enhancing subtentorial lesion, and cerebrospinal fluid (CSF) analysis documented a marked atypical lymphocytic pleocytosis. Flow cytometry performed on the CSF demonstrated expression of only CD45, CD90, and MHC class II, with Pax5 positivity on subsequent immunohistochemistry. The final diagnosis was of B‐cell lymphoblastic lymphoma or acute leukemia, given the distribution of disease and the presence of significant bone marrow infiltration alongside an aggressive clinical course. The unusual immunophenotype of the neoplastic cells and hypercalcemia presented antemortem diagnostic challenges, highlighting the need for a multidisciplinary approach and caution in the interpretation of clinical abnormalities in cases with multiple comorbidities.     

Nonregenerative immune‐mediated anemia associated with a diffuse large B‐cell lymphoma in a captive jaguar (Panthera onca)

An 18‐year‐old male castrated jaguar (Panthera onca) was presented with anorexia and continuous bleeding from the oral cavity after a history of fighting with the partner animal. Clinical evaluation revealed ulcerating lesions on the gingiva and hard palate and a hematoma on the tongue. Computed tomography of the head and endoscopic examination of the esophagus and stomach were unremarkable. Hematology and clinical chemistry revealed severe nonregenerative anemia, mild thrombocytopenia, and moderate azotemia. Several PCRs for feline hemotropic mycoplasmas (Mycoplasma haemofelis, M heamominutium, M turicensis), Babesia felis, and Bartonella spp., as well as an FeLV antigen test were negative. The cytologic examination of a bone marrow aspirate was consistent with ineffective erythropoiesis, most likely due to immune‐mediated destruction of the erythroid precursor cells. Prednisolone therapy was initiated (1.25 mg/kg/day), and the CBC returned to normal 16 days after the initiation of the therapy. Anemia relapsed after 4 months and severe splenomegaly was noted. A repeat bone marrow aspirate revealed active erythropoiesis in the presence of erythroid precursor phagocytosis suggesting an immune‐mediated process. Splenic fine‐needle aspiration and tissue biopsies were taken, and all findings including histology and immunohistochemistry were consistent with a diffuse large B‐cell lymphoma (DLBCL). Five days later, the clinical condition deteriorated and the jaguar died. Histopathology following necropsy showed infiltration with neoplastic lymphoblasts in the spleen, liver, and abdominal lymph nodes. This case report describes a nonregenerative immune‐mediated anemia associated with a DLBCL in a jaguar.     

Tumor staging in a Beagle dog with concomitant large B-cell lymphoma and T-cell acute lymphoblastic leukemia

An 8-y-old spayed female Beagle dog was presented with peripheral lymphadenomegaly. Lymph node cytology and flow cytometry led to the diagnosis of large B-cell lymphoma (LBCL). We detected minimal percentages of LBCL cells in peripheral blood and bone marrow samples. However, a monomorphic population of neoplastic cells different from those found in the lymph node was found in the bone marrow. T-cell acute lymphoblastic leukemia was suspected based on flow cytometric immunophenotyping. PCR for antigen receptor rearrangement (PARR) revealed clonal rearrangement of both B-cell and T-cell receptors, and the presence of both neoplastic clones in the lymph node, peripheral blood, and bone marrow. The dog was treated with multi-agent chemotherapy but died 46 d following diagnosis. Tumor staging and patient classification are needed to accurately establish a prognosis and select the most appropriate therapeutic protocol.     

Chinese Box turtle (Cuora flavomarginata) with lymphoid leukemia characterized by immunohistochemical and cytochemical phenotyping

Lymphoid leukemia of T‐cell origin was diagnosed in a male Chinese Box turtle, Cuora flavomarginata, of approximately 25 years of age. The turtle presented with a history of anorexia, open‐mouth breathing, and lethargy for one week. The CBC findings included a mildly increased PCV, and severe leukocytosis due to high numbers of atypical cells interpreted to be blasts. The blasts were medium‐sized cells with round to pleomorphic nuclei, slightly clumped chromatin, indistinct nucleoli, and scant moderate‐to‐dark blue cytoplasm with occasional red‐to‐purple cytoplasmic granulation. Cytochemical and immunohistochemical staining indicated that the neoplastic cells were positive for CD3 and α‐naphthyl butyrate esterase (ANBE), leading to the diagnosis of T‐cell lymphoid leukemia. Histology of tissues collected at necropsy showed multifocal infiltrations of neoplastic round cells in the liver, spleen, kidneys, testicles, pancreas, thyroid, duodenum, bone marrow, epicardium, and myocardium. Transmission electron microscopy failed to identify viral particles within the neoplastic cells. This article describes the hematologic, histologic, and ultrastructural abnormalities associated with lymphoid leukemia in this turtle, and advanced diagnostic methods used for phenotyping the T‐cell origin.     

Bone marrow necrosis and myelophthisis: manifestations of T‐cell lymphoma in a horse

Abstract: A 14‐year‐old spayed American Paint mare was evaluated for mild colic, anorexia, pyrexia, and pancytopenia. Physical examination revealed mild tachycardia, tachypnea, and pale mucous membranes. Serial laboratory analyses revealed progressive pancytopenia, hyperfibrinogenemia, and hyperglobulinemia. A few large atypical cells were observed in peripheral blood smears. Results of tests for equine infectious anemia and antipenicillin antibody were negative. Serum protein electrophoresis indicated a polyclonal gammopathy. Smears of bone marrow aspirates contained hypercellular particles, but cell lines could not be identified because the cells were karyolytic, with pale basophilic smudged nuclei and lack of cellular detail. A diagnosis of bone marrow necrosis was made. Treatment consisted of antimicrobials, nonsteroidal anti‐inflammatory drugs, and corticosteroids. The pyrexia resolved; however, the pancytopenia progressively worsened and petechiation and epistaxis developed. The horse was humanely euthanized. Postmortem examination revealed a diffuse round cell neoplasm infiltrating the kidneys, spleen, lymph nodes, lungs, and bone marrow. Immunophenotyping results (CD3+, CD79α−) indicated the neoplastic cells were of T‐cell lineage. Infiltration of lymphoma cells into the bone marrow appeared to have resulted in severe myelophthisis and bone marrow necrosis. Bone marrow necrosis has been associated previously with lymphoma in humans and dogs. To our knowledge, this is the first reported case of lymphoma resulting in bone marrow necrosis in a horse.     

A case of acute monocytic leukemia (AMoL or AML‐M5) in an adult FeLV/FIV‐positive cat

A 7‐year‐old castrated male domestic shorthair cat was presented for evaluation of decreased appetite and respiratory signs. A CBC run on presentation revealed severe nonregenerative anemia, thrombocytopenia, and leukocytosis characterized by a prominent population of blasts, having morphologic features suggestive of a monocytic lineage. The cat tested positive for FIV, FeLV, Mycoplasma haemominutum, and only mild abnormalities were identified on the chemistry panel. Bone marrow biopsies were obtained to investigate the bicytopenia and the possibility of a hematopoietic neoplasm. Although the bone marrow aspirate was nondiagnostic, the core biopsy was markedly hypercellular with a population of blasts, largely replacing the normal hematopoietic tissue. Immunohistochemical staining revealed that the blasts were CD3‐negative, Pax5‐negative, dimly CD18‐positive, and moderately positive for Iba1. These findings, in addition to the prominent monocytic differentiation seen in peripheral blood, supported a diagnosis of acute monocytic leukemia. Palliative antiviral and antibiotic treatment and blood transfusion were performed. The patient was discharged on his fourth day of hospitalization. However, 15 days following discharge, the cat was euthanized due to the worsening of his systemic signs. This report discusses the classifications of myeloid leukemias, implications of infectious diseases in the pathogenesis of neoplasia in cats, and the use of Iba1, a “pan‐monocytic/histiocytic” marker, in the diagnosis of acute leukemia.     

B‐cell lymphoma with plasmacytoid differentiation,atypical cytoplasmic inclusions,and secondary leukemia in a dog

A 7‐year‐old male castrated Jack Russell Terrier was presented to the oncology service at the University of California–Davis Veterinary Medical Teaching Hospital for evaluation of suspected lymphoma. The dog had several enlarged lymph nodes and moderate lymphocytosis. Aspirates of an enlarged inguinal lymph node contained a bimorphic population of large immature lymphocytes and smaller cells with plasmacytoid features. Both cell types often contained a single large cytoplasmic inclusion that varied from clear to pale pink to sky blue. Cytologic changes were interpreted as most consistent with lymphoid neoplasia. Based on the predominantly mature cell morphology and some morphologic heterogeneity, the peripheral lymphocytosis was interpreted as most likely reactive in nature. However, the immunophenotype of the cells (CD20+, CD21+, CD79a+, MUM‐1+, and MHCII+) and clonality assays showed that tissue and blood lymphocytes were neoplastic B cells with clonal identity despite their different morphologic appearances. The cytoplasmic inclusions were positive with periodic acid‐Schiff and were immunoreactive for IgM and IgG. By transmission electron microscopy, inclusions consisted of aberrant rough endoplasmic reticulum; a few small Russell bodies were also noted. A final diagnosis of high‐grade B‐cell lymphoma with plasmacytoid differentiation, atypical cytoplasmic inclusions, and secondary leukemia was made. Chemotherapy was initiated, but the dog was euthanized due to severe and uncontrolled seizures 9 months after the initial diagnosis. This case extends the morphologic repertoire of canine plasmacytoid neoplasms and emphasizes their continuum with multicentric lymphoma. This case also demonstrates the need for advanced diagnostic techniques in establishing blood involvement in lymphoma in some instances.     

Bone Marrow Cytological Findings in 4 Dogs and a Cat With Hemophagocytic Syndrome

Hemophagocytic syndrome or hemophagic histiocytosis was diagnosed in 4 dogs and 1 cat by evaluation of bone marrow aspirate smears. One of the dogs had a suspected infection with canine parvovirus and a confirmed infection with Salmonella spp, 2 dogs had presumptive diagnoses of myeloproliferative and lymphoproliferative disease, respectively, and 1 dog died without a diagnosis. The cat had hepatic lipidosis and lesions compatible with feline calicivirus infection. All animals had cytopenias involving 2 or more cell lines, and fragmented erythrocytes in the blood, along with mild to moderate increases in the number of macro-phages in the bone marrow. Numerous marrow macro-phages contained phagocytized hematopoietic cells. Other cytological features of the bone marrow were variable in each patient, but the degree of response in the blood was inadequate, even in those with bone marrow hyperplasia. The phagocytosis of hematopoietic elements did not appear to be caused by a primary immune disorder, but rather by the inappropriate activation of normal macrophages secondary to infectious, neoplastic, or metabolic diseases. These findings suggest that hemophagocytic syndrome may be an important factor in the development of cytopenias; the data also support the cytological evaluation of bone marrow aspirates as an aid in the diagnosis of hemophagocytic syndrome. J Vet Intern Med 1996;10:7–14. Copyright © 7996 by the American College of Veterinary Internal Medicine .     

Chronic lymphopenia and neutropenia in a dog with large granular lymphocytic leukemia

T‐cell large granular lymphocytic leukemia (T‐cell LGLL) is the most common presentation of chronic lymphocytic leukemia (CLL) in dogs. Aleukemic or subleukemic leukemia is a particularly rare variation in both humans and dogs, where bone marrow proliferation is either not or only sparsely translated in the peripheral blood. Neutropenia is a prominent feature in cases of human T‐cell LGLL but is normally absent in canine CLL. This report describes a case of a dog presented with an almost 3‐year history of asymptomatic neutropenia, lymphopenia, and thrombocytopenia (without anemia). A bone marrow examination, the exclusion of infectious diseases, and clonality testing led to the diagnosis of subleukemic LGLL that responded well to therapy (death occurred 2.5 years later due to an unrelated cause).     

Erythrophagocytic low‐grade extranodal T‐cell lymphoma in a cat

Abstract: A 13‐year‐old male castrated domestic shorthair cat was presented to the referring veterinarian with a 2‐month history of weight loss and lethargy. Splenomegaly, hepatomegaly, nonregenerative anemia, neutropenia, and hyperbilirubinemia were noted. Results of testing for feline immunodeficiency virus, feline leukemia virus, Toxoplasma gondii, and Mycoplasma sp. were negative. On cytologic examination of aspirates from the enlarged spleen and liver, a population of erythrophagocytic round cells was observed. Splenectomy and a liver biopsy were done which revealed a population of CD3+/CD79a– erythrophagocytic mononuclear round cells localized in the hepatic and splenic sinusoids. T‐cell PARR (PCR for antigen receptor gene rearrangements) analysis of bone marrow and spleen demonstrated a single band indicative of a clonal proliferation of T cells. Based on the marked splenomegaly, sinusoidal infiltration, lack of lymphadenopathy, and results of cytology, PARR, and immunophenotyping, a diagnosis of low‐grade extranodal T‐cell lymphoma was made. The cat was treated with chlorambucil and prednisolone; clinical and laboratory abnormalities resolved and the cat has remained clinically normal for 2.5 years. To our knowledge, this report documents the first case of an erythrophagocytic T‐cell lymphoma in a cat. The clinicopathologic findings were suggestive of hepatosplenic T‐cell lymphoma, a neoplasm described previously only in humans and dogs.     

Vertebral polyostotic lymphoma in a young dog.

An unusual clinical presentation of lymphoma with vertebral involvement in a dog is reported. A 20-month-old intact female Golden Retriever presented with progressive paraparesis and anorexia. Complete blood count and serum biochemistry profile demonstrated pancytopenia and hypercalcemia. Ventral fusion of the lumbar vertebrae by new bony tissue deposition was evident on X-ray and CT scan. Fine needle aspiration revealed neoplastic lymphoid cells in lymph nodes and bone marrow. Histologically, vertebral bone and osteophytes, liver, bone marrow, kidney, and lymph nodes were diffusely infiltrated by neoplastic, lymphoid cells, with scant cytoplasm and round hyperchromatic nuclei. Polyostotic and medullary T-cell lymphoma with spondylosis was diagnosed. Lymphoma mainly affecting bone is uncommon in the dog. The present case differs from previously described polyostotic lymphomas in clinical signs of the disease, mainly attributable to spondylarthrosis. In addition, lymphomatous proliferation was associated with osteoproductive lesions of the vertebrae.     

Gelatinous transformation of bone marrow in a rabbit

A 9-y-old, spayed female rabbit was presented for evaluation of hypoglycemia and lateral recumbency. The patient was hypothermic and had diffuse muscle wasting; weight loss since a previous visit was also noted. Hematologic abnormalities included progressive nonregenerative anemia and severe heteropenia. Evaluation of a bone marrow aspirate sample revealed active hematopoiesis with abundant pink matrix. The matrix material stained positively with periodic acid–Schiff and alcian blue, and a diagnosis of gelatinous transformation of the bone marrow (GTBM, serous atrophy of fat) was made. Although its precise prevalence remains to be determined, GTBM should be suspected in rabbits with persistent cytopenias following prolonged starvation or gastrointestinal disease.     

A case of hypercalcemia in a heifer presumably due to mammary carcinoma bovine hypercalcemia of malignancy

Mammary carcinoma is rare in cattle with only a handful of cases found in the literature, and none have reported an associated hypercalcemia. An 8‐year‐old Holstein‐Friesian heifer was presented to the Purdue University Veterinary Teaching Hospital's Large Animal Hospital with a 3‐month history of lethargy. Laboratory abnormalities included ionized hypercalcemia and hypophosphatemia (2.28 mmol/L and 1.8 mg/dL, respectively). Physical examination revealed a mammary mass that was cytologically described as a suspected mammary carcinoma, which was later confirmed by histologic evaluation. On surgical removal of the mass, calcium initially decreased rapidly, and within a few days was within the RI, further supporting a diagnosis of hypercalcemia of malignancy in a heifer. However, attempts to confirm this using hormone profiles (parathyroid hormone [PTH], parathyroid hormone‐related protein [PTHrp], and calcitriol) were inconclusive due to the lack of validated assays and RIs for cattle. Immunohistochemical staining for PTHrP showed scattered cytoplasmic staining among the neoplastic cells, suggesting PTHrP production by these cells.     

Hypercalcemia and high serum parathyroid hormone-related protein concentration in a horse with multiple myeloma

A 13-year-old gelding was examined because of weight loss, hyperglobulinemia, and hypercalcemia. Possible causes of hypercalcemia that were considered included renal failure, primary hyperparathyroidism, vitamin D toxicosis, and malignancy. There was no history of vitamin D ingestion, and serum creatinine and parathyroid hormone concentrations were normal, making renal failure and primary hyperparathyroidism unlikely. The hypercalcemia was suspected to be a result of malignancy, but thorough testing did not reveal any neoplastic disease. Eight months later, serum parathyroid hormone-related protein (PTHrP) concentration was high, supporting the suggestion that hypercalcemia was a result of malignancy. In addition, radial immunodiffusion confirmed a selective 300-fold increase in serum IgA concentration. The horse was euthanatized, and postmortem examination revealed neoplastic infiltrates in the kidneys, lymph nodes, liver, and bone marrow. Neoplastic cells had morphologic characteristics of plasma cells, and immunohistochemical staining confirmed that neoplastic cells were expressing PTHrP and IgA. The final diagnosis was multiple myeloma with expression of IgA paraprotein.     

Subleukaemic acute myeloid leukaemia with myelodysplasia in a horse

Acute myeloid leukaemia (AML) is rarely reported in horses and myelodysplastic syndrome (MDS) has been described only in one case. Acute myeloid leukaemia is defined as the presence of at least 20% blasts in the marrow or blood. On the other hand, MDS is characterised by morphologic abnormalities in one or more cell lineages with hypercellular marrow and peripheral cytopenias due to ineffective haematopoiesis. We report a case of acute myelomonocytic leukaemia with myelodysplasia-related features in a horse. A supposed diagnosis was based on abnormal morphology of circulating neoplastic cells and bone marrow cytology. A final diagnosis was made by using flow cytometry (FC) in conjunction with cytochemistry (CC) rarely reported in the haematopoietic neoplasms of the horse.     

Diagnosis and treatment of chronic T-lymphocytic leukemia in a spotted hyena (Crocuta crocuta).

Physical examination of an asymptomatic 20-yr-old intact female spotted hyena (Crocuta crocuta) revealed a midabdominal mass. A complete blood count (CBC) revealed peripheral lymphocytosis. Abdominal ultrasonography and laparoscopy confirmed severe splenomegaly. Cytologic examination of a bone-marrow core and histologic examination of spleen and liver biopsy samples revealed neoplastic small lymphocytes. Immunohistochemical staining of liver and spleen samples with the use of leukocyte-specific monoclonal antibodies showed that the neoplastic lymphocytes were immunoreactive to T-lymphocyte CD3 receptor and immunonegative to B-lymphocyte CD79a receptor. The morphology and distribution of neoplastic T-lymphocytes within the spleen, liver, peripheral blood, and bone marrow was most consistent with chronic T-lymphocytic leukemia. Treatment with chlorambucil and prednisone effectively decreased the lymphocyte count, but was associated with thrombocytopenia, which resolved after chlorambucil treatment was temporarily discontinued. Chemotherapy was resumed with a single dose of L-asparaginase, followed by a lower dosage of chlorambucil and continued prednisone. Two years after initial diagnosis, the hyena developed a hemoabdomen and was euthanized. Neoplastic T-lymphocytes were present in spleen, liver, visceral and peripheral lymph nodes, lungs, heart, kidney, adrenal glands, mesentery, intestines, pancreas, brain, and bone marrow.     

Extreme lymphocytosis with myelomonocytic morphology in a horse with diffuse large B‐cell lymphoma

An 11‐year‐old, 443‐kg Haflinger mare was presented to the North Carolina State University Veterinary Teaching Hospital with a 2‐week history of lethargy and a 3‐day duration of anorexia, pyrexia, tachycardia, and ventral edema. Severe pitting edema, peripheral lymphadenopathy, and a caudal abdominal mass were noted on physical examination. An extreme leukocytosis (154.3 × 10³/μL) and microscopic hematologic findings suggestive of myelomonocytic leukemia were observed. Serum protein electrophoresis revealed a monoclonal gammopathy and urine protein electrophoresis revealed a monoclonal light chain proteinuria. Necropsy and histopathology confirmed widespread neoplastic infiltration in many organs with a heterogenous population of cells; there was no apparent evidence of bone marrow involvement. Immunohistochemistry confirmed presence of a majority of B cells with a limited antigen expression, admixed with a lower number of T cells. Molecular clonality analysis of IgH2, IgH3, and kappa‐deleting element (KDE, B cell) on whole blood and KDE on infiltrated tissues revealed clonal rearrangements, and the KDE intron clones that amplified in blood and in infiltrated tissue were identical. In contrast, the clonality analysis of T‐cell receptor γ revealed no clonality on blood cells and infiltrated tissues. In conjunction with the histopathologic changes, the lesion was interpreted to be composed of neoplastic B cells with a reactive T‐cell population. Polymerase chain reaction testing for equine herpes virus 5 was negative. The final diagnosis was diffuse large B‐cell lymphoma with a marked hematogenous component.     

Development of prednisone resistance in naïve canine lymphoma: Longitudinal evaluation of NR3C1α, ABCB1, and 11β-HSD mRNA expression

Prednisone resistance develops rapidly and essentially universally when dogs with lymphoma are treated with corticosteroids. We investigated naturally occurring mechanisms of prednisone resistance in seven dogs with naïve multicentric lymphoma, treated with oral prednisone; four dogs were administered concurrent cytotoxic chemotherapy. Expression of NR3C1α, ABCB1 (formerly MDR1), 11β-HSD1, and 11β-HSD2 mRNA was evaluated in neoplastic lymph nodes by real-time RT-PCR. Changes of expression levels at diagnosis and at time of clinical resistance to prednisone were compared longitudinally using a Wilcoxon signed-rank test. Clinical resistance to prednisone was observed after a median of 68 days (range: 7–348 days) after initiation of treatment. Relative to pretreatment samples, prednisone resistance was associated with decreased NR3C1α expression in biopsies of all dogs with high-grade lymphoma (six dogs, p=.031); one dog with indolent T-zone lymphoma had increased expression of NR3C1α. Resistance was not consistently associated with changes in ABCB1, 11β-HSD1, or 11β-HSD2 expression. Decreased expression of the glucocorticoid receptor (NR3C1α) may play a role in conferring resistance to prednisone in dogs with lymphoma. Results do not indicate a broad role for changes in expression of ABCB1, 11β-HSD1, and 11β-HSD2 in the emergence of prednisone resistance in lymphoma-bearing dogs.     

Role of Latent Feline Leukemia Virus Infection in Nonregenerative Cytopenias of Cats

Background: Nonregenerative cytopenias such as nonregenerative anemia, neutropenia, and thrombocytopenia in cats with feline leukemia virus (FeLV) antigen are assumed to be caused by the underlying FeLV infection. In addition, cats with negative FeLV antigen-test results that have cytopenias of unknown etiology often are suspected to suffer from latent FeLV infection that is responsible for the nonregenerative cytopenias.
Objective: The purpose of this study was to assess the role of latent FeLV infection by polymerase chain reaction (PCR) in bone marrow of cats with nonregenerative cytopenias that had negative FeLV antigen test results in blood.
Animals: Thirty-seven cats were included in the patient group. Inclusion criteria were (1) nonregenerative cytopenia of unknown origin and (2) negative FeLV antigen test result. Antigenemia was determined by detection of free FeLV p27 antigen by ELISA in serum. Furthermore, 7 cats with positive antigen test results with nonregenerative cytopenia were included as control group I, and 30 cats with negative antigen test results without nonregenerative cytopenia were included as control group II.
Methods: Whole blood and bone marrow samples were tested by 2 different PCR assays detecting sequences of the envelope or long terminal repeat genes. FeLV immunohistochemistry was performed in bone marrow samples.
Results: Two of the 37 cats (5.4%) in the patient group were positive on the bone marrow PCR results and thus were latently infected with FeLV.
Conclusions and Clinical Importance: The findings of this study suggest that FeLV latency is rare in cats with nonregenerative cytopenias.