Bone marrow cytological findings in 4 dogs and a cat with hemophagocytic syndrome

A case of nerve sheath tumor followed by multicentric high-grade T-cell lymphoma in an African pygmy hedgehog (Atelerix albiventris)

A 3-year-old intact male African pygmy hedgehog was presented at the Teaching Hospital of the Faculty of Veterinary Medicine, University of Belgrade, with a growth on the left side of its abdomen. After clinical examination, the mass was surgically removed, and histopathological findings indicated a nerve sheath tumor. The hedgehog fully recovered after surgery and was euthanized eight months later due to the appearance of multicentric changes in the internal organs. Further necropsy and macroscopic, cytologic, histopathologic, and immunohistochemical findings revealed that the tumor was a multicentric high-grade T-cell lymphoma. This is an unusual case of an African pygmy hedgehog with two different neoplasms-a nerve sheath tumor followed by lymphoma.

Clinical and Pathological Findings in Fatal Cases of Severe Fever With Thrombocytopenia Syndrome With High Viremia in Cats

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging zoonotic disease caused by the SFTS virus (SFTSV). SFTSV causes severe symptoms both in humans and cats. In this study, we report the clinical and pathological findings of 4 fatal cases of cats with high SFTS viremia levels. These cats showed an acute onset of fever, leukopenia, thrombocytopenia, and increased serum amyloid A and pro-inflammatory cytokine levels. A high viral copy number was detected in the blood, oral swabs, rectal swabs, conjunctiva swabs, and urine. Histopathologically, necrotizing lymphadenitis, splenitis with lymphoblastoid cell proliferation, and hemophagocytosis were observed in all 4 cats. Immunohistochemistry revealed the presence of SFTSV antigen on lymphoblastoid B cells. SFTSV-RNA was detected in systemic tissues, including the brain. The present findings provide useful information for understanding the features of fatal SFTS in cats. To elucidate the mechanisms of severe progress of SFTS cats, as well as its role as a source of human infection, further research is needed.

Hemophagocytic syndrome associated with large granular lymphoma in an adult dog

Hemophagocytic syndrome (HPS) is a rare disorder characterized by dysregulation of the immune response resulting in uncontrolled activation of macrophages with exacerbated phagocytosis of host cells. In dogs, the criteria for diagnosis include the presence of pancytopenia or bicytopenia in the peripheral blood and >2% hemophagocytic macrophages in bone marrow aspirates. When HPS is associated with lymphoma, it is called lymphoma-associated hemophagocytic syndrome (LAHS). Here, we present a case of a 4 ½-year-old female spayed Old English Mastiff that presented with severe thrombocytopenia, mild anemia, mild to moderate leukopenia, and large granular lymphocytes (LGLs) in the peripheral blood. The patient had enlarged lymph nodes with many LGLs seen cytologically, leading to the interpretation of LGL lymphoma. Bone marrow displayed numerous LGLs that stained strongly for CD3 but did not show immunoreactivity to CD4 or CD8, and PCR for antigen receptor rearrangement analysis confirmed a clonal T-cell receptor gamma gene rearrangement. The presence of ~3.5% hemophagocytes present on the bone marrow evaluation raised concern for HPS and, more specifically, LAHS. HPS and LAHS are challenging to diagnose and require many criteria to be fulfilled before a definitive diagnosis can be made; the low number of cases in the literature makes this even more challenging in dogs. This case represents secondary LAHS due to LGL lymphoma in a dog.

International Harmonization of Nomenclature and Diagnostic Criteria (INHAND): Non-proliferative and Proliferative Lesions of the Non-human Primate (M. fascicularis)

The INHAND (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions Project (www.toxpath.org/inhand.asp) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP) and North America (STP) to develop an internationally accepted nomenclature for proliferative and nonproliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying microscopic lesions observed in most tissues and organs from the nonhuman primate used in nonclinical safety studies. Some of the lesions are illustrated by color photomicrographs. The standardized nomenclature presented in this document is also available electronically on the internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous lesions as well as lesions induced by exposure to test materials. Relevant infectious and parasitic lesions are included as well. A widely accepted and utilized international harmonization of nomenclature for lesions in laboratory animals will provide a common language among regulatory and scientific research organizations in different countries and increase and enrich international exchanges of information among toxicologists and pathologists.

Presumptive hemophagocytic syndrome associated with immune-mediated anemia in two Miniature Dachshunds

This report describes the cases of two Miniature Dachshunds who were suspected to have immune-mediated hemolytic anemia (IMHA) and were treated with immunosuppressive therapy. However, progression of anemia, increases in C-reactive protein (CRP) and total-bilirubin (T-Bil) levels, splenomegaly, transition to nonregenerative anemia, and thrombocytopenia occurred after the treatment. Splenectomy and bone-marrow aspirations were performed subsequently. Both dogs were diagnosed with hemophagocytic syndrome (HPS) associated with IMHA. Unfortunately, they died 9 and 6 days later. These findings indicate that some cases of refractory IMHA have the pathogenicity of HPS. HPS should be included as a differential diagnosis of refractory IMHA concurrent with thrombocytopenia. Continuously elevated CRP and T-Bil levels may be helpful indicators in the detection of HPS associated with IMHA.

Severe Fever with Thrombocytopenia Syndrome Phlebovirus causes lethal viral hemorrhagic fever in cats

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging hemorrhagic fever caused by the SFTS phlebovirus (SFTSV). SFTS patients were first reported in China, followed by Japan and South Korea. In 2017, cats were diagnosed with SFTS for the first time, suggesting that these animals are susceptible to SFTSV. To confirm whether or not cats were indeed susceptible to SFTSV, animal subjects were experimentally infected with SFTSV. Four of the six cats infected with the SPL010 strain of SFTSV died, all showing similar or more severe symptoms than human SFTS patients, such as a fever, leukocytopenia, thrombocytopenia, weight loss, anorexia, jaundice and depression. High levels of SFTSV RNA loads were detected in the serum, eye swab, saliva, rectal swab and urine, indicating a risk of direct human infection from SFTS-infected animals. Histopathologically, acute necrotizing lymphadenitis and hemophagocytosis were prominent in the lymph nodes and spleen. Severe hemorrhaging was observed throughout the gastrointestinal tract. B cell lineage cells with MUM-1 and CD20, but not Pax-5 in the lesions were predominantly infected with SFTSV. The present study demonstrated that cats were highly susceptible to SFTSV. The risk of direct infection from SFTS-infected cats to humans should therefore be considered.

Feline non-regenerative anemia: Diagnostic and treatment recommendations

PRACTICAL RELEVANCE

Non-regenerative anemia, or anemia with reticulocytopenia, is a daily diagnosis in feline practice.

CLINICAL CHALLENGES

The disease processes underlying non-regenerative anemia are many and diverse. A major diagnostic evaluation may be required to correctly diagnose and treat the underlying cause.

AUDIENCE

All veterinarians caring for cats will face the diagnostic and therapeutic challenge of non-regenerative anemia. Readers will benefit from the review of diagnostic testing and therapeutic options for non-regenerative anemia.

EVIDENCE BASE

This review summarizes the currently available literature informing diagnostic and treatment recommendations related to non-regenerative anemia. The evidence available to support the recommendations in this review is graded as low and includes predominantly expert opinion, case reports and cases series, on which the authors' interpretation/consensus is based.

Hemophagocytosis and Histoplasma-like fungal infection in 32 cats

Histoplasmosis is one of the most common systemic fungal diseases in cats from the United States. It commonly causes respiratory or disseminated disease and is often associated with one or more cytopenias. Here, we describe 32 cats in which a Histoplasma-like fungal infection was associated with concurrent hemophagia in at least one sample site, commonly spleen, bone marrow, liver, and/or lymph node. The degree of hemophagia was characterized as moderate or marked in the majority of cases, and in all cases, there was a predominance of phagocytized mature erythrocytes. A few cases also had macrophages with phagocytized erythroid precursors, platelets, and/or neutrophils. Complete blood count results were available for 25 cats, and cytopenias were common (20/25), including solitary anemia (10), anemia and thrombocytopenia (5), solitary neutropenia (2), pancytopenia (2), and anemia and neutropenia (1). Bone marrow samples were only available in a small subset of cases, preventing the further assessment of the causes of the cytopenias. Hemophagocytosis has been previously reported in cats with neoplastic diseases and a cat with calicivirus infection, and likely occurs with other conditions as well, such as hemorrhage or hemolysis. Results of this report suggest that systemic fungal disease is an additional differential to consider when there is hemophagia in a feline cytology sample.

A case of hemophagocytic syndrome progressing into large granular lymphoma in a dog

A 12-year-old castrated male mixed breed dog was presented with anorexia, lethargy, intermittent vomiting, diarrhea, and weight loss. Clinicopathologic and imaging abnormalities included pancytopenia, icterus, and splenomegaly with multiple minute hypoechogenic nodules. Bone marrow (BM) smears revealed 2.5% hemophagocytic macrophages. In addition, an increased number of small to intermediate lymphocytes (16.3%) and plasma cells (3.2%) were recognized in the BM smears. More than 80% of the lymphocytes contained multiple small intracytoplasmic magenta granules. Histopathologic findings of the spleen revealed hemophagocytosis. Large granular lymphocytes (LGLs) were not found on the liver cytology or splenic histopathology at this time. PCR for antigen receptor rearrangement (PARR) analysis showed a clonal reaction in the T-cell receptor ɤ (TCRɤ) gene in the BM sample. The dog was diagnosed with hemophagocytic syndrome (HPS). The dog was maintained in good condition with immunosuppressive therapy. However, the dog developed hepatic LGL lymphoma 7 months later. At this time, PARR analysis showed a clonal TCRɤ gene rearrangement in the hepatic LGL lymphoma samples. The BM and liver sample clonal rearrangements showed 100% homology, indicating that the small to intermediate granular lymphocytes in the BM at the HPS stage had progressed to hepatic LGL lymphoma. To our knowledge, this is the first report of canine secondary HPS caused by the occurrence of a BM LGL lymphoma clone that progressed to hepatic LGL lymphoma.

Hemophagocytic syndrome in a cat

Case summary

A 12-year-old male castrated domestic shorthair cat was evaluated for a 10 month history of weight loss. Thin body condition and a grade II/VI systolic parasternal heart murmur was noted during examination. Moderate-to-severe anemia and intermittent thrombocytopenia were identified on serial complete blood counts. Antibodies against feline immunodeficiency virus (FIV) were detected, but vaccination for FIV occurred previously. Echocardiography revealed biatrial and biventricular enlargement, left ventricular hypertrophy and pericardial effusion. Splenomegaly was present on abdominal ultrasound and cytological evaluation revealed macrophagic infiltration with erythrophagocytosis. Cytological evaluation of the bone marrow revealed similar findings. Histopathology of the spleen confirmed hemophagocytosis with no evidence of malignancy. A presumptive diagnosis of hemophagocytic syndrome was made. PCR testing for FIV on the splenic tissue was negative. The cat was treated with lomustine. Disease progression occurred approximately 6 months after diagnosis and the cat was euthanized.

Relevance and novel information

To our knowledge, this is one of the few reports describing the diagnosis of hemophagocytic syndrome in a cat.

Lymphoma-associated hemophagocytic syndrome in six dogs

Hemophagocytic syndrome (HPS) is a clinicopathological entity characterized by histiocytic proliferation, with marked hemophagocytosis in the reticuloendothelial organs. HPS caused by lymphoma is termed lymphoma-associated hemophagocytic syndrome (LAHS), and there are few reports on canine and feline LAHS. The objective of this study was to examine the clinical, diagnostic, and clinicopathologic features of LAHS in six dogs. The diagnostic criteria of LAHS consisted of lymphoma, bicytopenia or pancytopenia in the blood, and increased hemophagocytosis in the reticuloendothelial organs. In one dog, an ocular form of lymphoma was recognized. A splenic form was recognized in two dogs, and a hepatosplenic form was recognized in three dogs. Immunophenotyping revealed T-cell origin in five dogs and B-cell origin in one dog by polymerase chain reaction for antigen receptor rearrangement analysis. Nonspecific esterase stain was performed to differentiate between neoplastic lymphocytes and hemophagocytes. All five dogs with T-cell lymphoma were diagnosed with large granular lymphocyte (LGL) lymphoma. In three cases, palliative therapy with glucocorticoids was conducted, while the other three cases received chemotherapy as well. The survival times for the three dogs with glucocorticoids only were 6, 6, and 10 days and were 30, 54, and 68 days for the three treated with anticancer therapy. The median survival time for the dogs was 20 days. This report indicates that canine LAHS is likely to be caused by LGL lymphoma, and it has an aggressive behavior and poor general prognosis, as seen in humans.

Evaluation of blood and bone marrow in selected canine vector-borne diseases

BACKGROUND

Bone marrow (BM) is a major hematopoietic organ that can harbour a variety of vector-borne pathogens; however, knowledge of BM pathological changes in dogs infected with vector-borne pathogens is limited. Thus, the aim of the present study was to assess the pathological changes in canine BM associated with natural infections by four vector-borne pathogens, as well as to determine the relationships between such changes and abnormalities of the peripheral blood.

METHODS

Cytological disorders and pathological changes of the BM of 83 dogs naturally-infected with one or more of four vector-borne pathogens (i.e., Anaplasma platys, Leishmania infantum, Babesia vogeli and Hepatozoon canis) were evaluated and compared with the corresponding hematological findings.

RESULTS

Dysgranulopoiesis and dysmegakaryocytopoiesis were the most frequently observed BM abnormalities in infected dogs. Erythroid suppression, and lymphocytic, monocytic and macrophage hyperplasia were also observed. Interestingly, associations between suppression and hyperplasia of specific cell lines in the marrow and corresponding changes in numbers of circulating peripheral blood cells were not observed.

CONCLUSIONS

Infections with one or more of the vector-borne pathogens examined in this study should be considered as differential diagnoses for secondary dysmyelopoiesis.

Nonregenerative anemia: mechanisms of decreased or ineffective erythropoiesis

In veterinary medicine, anemia without an appropriate compensatory hematopoietic response is termed nonregenerative. Nonregenerative anemia is a common clinical entity, occurring as a result of diminished or ineffective erythropoiesis in association with many types of pathology. This article reviews nonregenerative anemia in domestic animals, emphasizing mechanisms of disease, and also covers other conditions associated with nonregenerative anemia in people. Many aspects of nonregenerative anemia in animals are worthy of further investigation, from molecular mechanisms of disease to epidemiologic impacts.

Hemophagocytic Syndrome in a Pancytopenic Simian Retrovirus–Infected Male Rhesus Macaque (Macaca mulatta)

Hemophagocytic syndrome (HPS) is a macrophage hyperactivation disorder triggered by disrupted T–cell macrophage cytokine interaction. HPS has been reported in humans, dogs, cats, and cattle, and it is infrequent and poorly characterized in animals. A 16-year-old male rhesus macaque was euthanized because of severe pancytopenia, including nonregenerative anemia (hematocrit = 5.5%), neutropenia (0.29 K/μl), and thrombocytopenia (21 K/μl). Bone marrow was hypocellular with normal maturation, myeloid hypoplasia, and few megakaryocytes. There were numerous morphologically normal macrophages (12% of nucleated cells), with 6% of nucleated cells being hemophagocytic macrophages in the bone marrow. Serology was negative, but polymerase chain reaction and immunohistochemistry were positive for simian retrovirus type 2. Blood and bone marrow findings were consistent with HPS. Cytopenias are common in simian retrovirus–infected macaques, but HPS has not been reported. An association between simian retrovirus infection and HPS is undetermined, but retrovirus-associated HPS has been observed in humans.

Hemophagocytic syndrome in dogs: 24 cases (1996-2005)

OBJECTIVE

To determine the frequency, potential causes, and clinical and clinicopathologic features of hemophagocytic syndrome in dogs.

DESIGN

Retrospective study.

ANIMALS

24 client-owned dogs.

PROCEDURES

Records for dogs in which diagnostic bone marrow specimens (including an aspiration smear and core biopsy material) were obtained from 1996 to 2005 were reviewed. Inclusion criteria were presence of bicytopenia or pancytopenia in the blood and > 2% hemophagocytic macrophages in the bone marrow aspirate.

RESULTS

Of 617 bone marrow specimens evaluated, evidence of hemophagocytic syndrome was detected in 24 (3.9%). The Tibetan Terrier breed was overrepresented among dogs with hemophagocytic syndrome. Clinical signs associated with hemophagocytic syndrome included fever, icterus, splenomegaly, hepatomegaly, and diarrhea. Hemophagocytic syndrome was associated with immune-mediated, infectious, and neoplastic-myelodysplastic conditions and also occurred as an idiopathic condition. Overall, dogs with infection-associated hemophagocytic syndrome had better 1-month survival rates than dogs with immune-associated and idiopathic hemophagocytic syndrome.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that hemophagocytic syndrome may occur more frequently in dogs than has previously been suspected on the basis of the paucity of reported cases. Although most dogs had definable underlying disease conditions, idiopathic hemophagocytic syndrome was also identified. Hemophagocytic syndrome of any cause is potentially life-threatening; however, the prognosis should be adjusted on the basis of the associated disease process and potential for successful treatment.

Canine hemophagocytic histiocytic sarcoma: a proliferative disorder of CD11d+ macrophages

Histiocytic disorders of dogs include histiocytoma, localized histiocytic sarcoma (HS), disseminated HS (malignant histocytosis), and the reactive histiocytoses: cutaneous and systemic. A common element to these diseases is proliferation of dendritic cells (DC) of either Langerhans cell (epithelial DC) or interstitial DC lineage. In this report, 17 dogs with hemophagocytic HS are described. Breeds affected included Bernese Mountain Dog (6), Golden Retriever (4), Rottweiler (3), Labrador Retriever (2), a mixed-breed dog, and a Schnauzer, which were from 2.5 to 13 years old. The dogs presented with Coombs negative responsive anemia in 16/17 dogs (94%), thrombocytopenia in 15/17 dogs (88%), hypoalbuminemia in 16/17 dogs (94%), and hypocholesterolemia in 11/16 dogs (69%). All dogs died or were euthanized. The clinical course ranged from 2 to 32 weeks (mean 7.1 weeks). Diffuse splenomegaly with ill-defined masses was consistently present. Microscopic lesions were prevalent in spleen, liver, lung, and bone marrow. Metastasis occurred by insidious intravascular invasion with minimal mass formation. Histiocytes were markedly erythrophagocytic and accompanied by foci of extramedullary hemopoiesis. Cytologically, the histiocytes varied from well differentiated to atypical, with atypia more prevalent in spleen than bone marrow. These tumors arose from splenic red pulp and bone marrow macrophages, which expressed major histocompatibility complex class II and the beta2 integrin, CD11d. They had low and/or inconsistent expression of CD1 and CD11c, which are dominantly expressed by canine nonhemophagocytic HS of DC origin. Canine histiocytic proliferative diseases now encompass proliferation of all members of the myeloid histiocytic lineage: Langerhans cells, interstitial DC, and macrophages.

Malignant histiocytosis in a domestic cat: cytomorphologic and immunohistochemical features

Malignant histiocytosis (MH) was diagnosed in a 13-year-old neutered male Domestic Shorthair cat on the basis of light microscopic and immunohistochemical findings. Thoracic fluid analysis showed a modified transudate which contained a very few atypical discrete cells. Cytologic and histologic evaluation of mediastinal and splenic masses revealed a pleomorphic population of large, discrete, round cells 10 to 30 micrometers in diameter with marked cellular atypia. Nuclei were oval to reniform, often with prominent, bizarre nucleoli. Multinucleated cells and mitotic figures were commonly seen. Erythro- and leucocytophagia were noted. Immunohistochemistry indicated a scattered positive staining pattern with the histiocytic antigenic marker Mac387 and a minor population of cells showing positive reactivity for lysozyme. This report describes the characterization of MH in a cat and emphasizes that MH should be considered as a differential diagnosis in proliferative disorders of discrete-cells in this species.

Cytology of the spleen

Fine-needle aspiration of the spleen is a useful method for evaluation of reactive, inflammatory, and neoplastic disorders, particularly those that involve the hematopoietic system. Interpretation of splenic aspirates is enhanced by concurrent evaluation of blood and other hemic tissues.

Flow cytometric evaluation of hemophagocytic disorders in canine

BACKGROUND

Hemophagocytic macrophages in canine bone marrow are observed in malignant histiocytosis as well as benign hemophagocytic histiocytosis. Cytomorphologic evaluation alone may be inadequate to consistently differentiate between benign and malignant forms of hemophagocytic disorders.

OBJECTIVE

The purpose of this study was to evaluate the ability of flow cytometry and immunophenotyping to differentiate between benign and malignant types of hemophagocytic disorders in dogs.

METHODS

Blood smears and bone marrow differential cell counts were evaluated for 10 dogs with hemophagocytic disorders. Bone marrow samples were labeled with monoclonal antibodies to CD18, MCH class-II, Thy-1, CD14, CD3, and CD21. Using flow cytometry, forward-angle versus side-angle light scatter plots were analyzed and immunophenotypes were determined.

RESULTS

Scatter plots from 3 dogs with a necropsy diagnosis of malignant histiocytosis revealed 2 atypical cell clusters. One cluster contained cells of similar size or larger than immature myeloid cells and metamyelocytes. Cells in the other cluster were highly granular, with granularity similar to or greater than that of metamyelocytes. In bone marrow from dogs with malignant histiocytosis that was labeled with anti-CD14 antibody, macrophages represented 29-48% of nucleated cells. Seven dogs had a clinical or histopathologic diagnosis of benign hemophagocytic syndrome. Three of the dogs had normal cell distribution in scatter plots. Two dogs had 2 abnormal cell clusters: 1 within the immature myeloid and metamyelocyte gates and the other with granularity similar to or greater than that of metamyelocytes. The remaining 2 dogs had an atypical cell population, mostly within the immature myeloid gate. For dogs with benign hemophagocytic syndromes, 6-17% of cells in the bone marrow were CD14 positive.

CONCLUSIONS

The cellular distribution in scatter plots and the total number of macrophages in bone marrow may be useful in differentiating malignant histiocytosis from benign hemophagocytic syndromes in dogs.

A retrospective study of canine pancytopenia

To better define the incidence and causes of canine pancytopenia, we retrospectively evaluated the results of complete blood counts submitted to the University of Minnesota Veterinary Teaching Hospital during a 1-year period. Pancytopenia was defined as packed cell volume < 36%, total leukocyte count < 6,000/microliter or total segmented neutrophil count < 3,000/microliter, and platelet count < 200,000/microliter. Of 4,560 complete blood counts, 110 (2.4%) samples from 51 dogs met the criteria for pancytopenia. Eleven different disease processes were identified. These included chemotherapy-associated pancytopenia (n=22), parvovirus infection (n=5), malignant histiocytosis (n=5), idiopathic aplastic anemia (n=3), sepsis (n=3), myelodysplastic syndrome (n=3), immune-mediated hematologic disease (n=3), lymphoblastic leukemia (n=2), ehrlichiosis (n=2), estrogen toxicity (n=2), and multiple myeloma (n=1). Malignant histiocytosis and idiopathic aplastic anemia occurred more frequently than was expected. Doxoruicin was the chemotherapeutic agent associated with pancytopenia. Hematologic recovery and patient survival time varied with the cause of pancytopenia; therefore, a specific diagnosis was essential for establishing prognosis. Differentiation among causes of pancytopenia requires a systemic approach that includes elimination of infectious and drug-induced causes, and examination of bone marrow aspiration and core biopsy specimens.

Cytologic evaluation of benign and malignant hemophagocytic disorders in canine bone marrow

Canine hemophagocytic disorders were studied to better understand the cytologic features that differentiate benign and malignant disease. Of 286 canine clinical bone marrow reports evaluated retrospectively, 13 (4.5%) noted at least 3% hemophagocytic macrophages. Macrophages comprised between 6% and 44% of nucleated bone marrow cells. Clinical diagnoses for dogs with hemophagocytic disorders included malignant histiocytosis (n = 2), myelodysplastic syndromes (n = 4), round cell neoplasia (n = 2), immune-mediated disorders (n = 2), and idiopathic hemophagocytic syndrome (n = 3). Differentiation of benign and malignant forms of histiocytosis was problematic. Two dogs with a diagnosis of hemophagocytic syndrome had macrophages with atypical features similar to those described for malignant histiocytosis. Furthermore, only 2 of 11 dogs with presumably benign hemophagocytic disorders had exclusively mature macrophages in bone marrow. Other dogs had variable numbers of large reticular-type cells characterized by lacy chromatin, anisocytosis, anisokaryosis, and prominent and/or multiple nucleoli. On the basis of these results, cytomorphologic evaluation of bone marrow alone may not be adequate to consistently differentiate benign and malignant forms of hemophagocytic disorders.

Evaluation of proliferative disorders in canine bone marrow by use of flow cytometric scatter plots and monoclonal antibodies

The combination of flow cytometric scatterplot analysis and specific monoclonal antibodies was used to evaluate the lineage of cells from six dogs with proliferative disorders of bone marrow. Scatterplot analysis was used to identify mature and immature myeloid and erythroid cells. The immunophenotype of cells in the immature myeloid gate was determined by labeling cells with four monoclonal antibodies. These results were compared to results of cytologic and cytochemical evaluation. The immunophenotype of a dog with a diagnosis of myelogenous leukemia was a cluster of differentiation-18 (CD-18) positive, CD-14 negative, Thy-1 negative, and a major histocompatibility complex (MHC) class II negative. The immunophenotype of a dog with a diagnosis of myelomonocytic leukemia was CD-18 positive, CD-14 positive, Thy-1 positive, and MHC class II positive. Although this phenotype clearly differentiated myelomonocytic leukemia from myelogenous leukemia, it was similar to the immunophenotype of dogs with a diagnosis of malignant histiocytosis or hemophagocytic syndrome. The immunophenotype of two dogs with myelodysplastic syndrome was CD-18 positive and CD-14 negative. Results for Thy-1 and MHC class II were variable. As additional lineage-specific monoclonal antibodies become available, immunophenotyping should become a valuable tool for determination of the lineage of cells in canine myeloproliferative disorders.

Haemophagocytic syndrome with disseminated intravascular coagulation in a dog

Clinical signs and haematological abnormalities of haemophagocytic syndrome of unknown origin are described for a male, nine-year-old rottweiler referred because of weakness, depression, mild weight loss and relapsing fever. Mucous membranes were pale and the spleen was enlarged. Ultrasonography revealed diffuse irregular structures in the enlarged spleen, and cytological examination of multiple fine needle aspirates of the spleen demonstrated extramedullary haematopoiesis. Haematological examination revealed pancytopenia and disseminated intravascular coagulation. A bone marrow smear contained numerous marrow macrophages with a cytologically benign appearance, containing phagocytosed haematopoietic cells. The dog died one week after referral. The differential diagnosis is discussed.