Veterinary Medicine - November 2007 - (Page 730)

Immune-mediated neutropenia O P E E R - R E V I E W E D thrombocytopenia or bone marrow disease being the most likely causes. Multiple cytopenias increase the likelihood of bone marrow disease. Blood smear cytology may show clumping of neutrophils.3 It has been proposed that a concurrent monocy- Coombs tests are indicated. An antiplatelet antibody test in dogs with concurrent thrombocytopenia may be of interest. Evidence of concurrent immune-mediated blood cell destruction supports a diagnosis of immunemediated neutropenia. Similarly, posi- seen.5 Myeloid hyperplasia with a lack of mature neutrophils in the marrow but lots of bands would suggest peripheral destruction of the neutrophils as opposed to decreased production. DIAGNOSIS Antineutrophil antibodies To definitively diagnose immunemediated neutropenia, antineutrophil antibodies must be demonstrated. However, no validated canine and feline assays for antineutrophil antibodies exist.28,29 The difficulty of developing a reliable test in veterinary medicine is related to the inherent fragility of neutrophils and their propensity to degranulate and aggregate in vitro. Many granulocyte antibodies are likely involved. In people, multiple tests are available to detect antibodies against the five different neutrophil surface antigens that are targeted in immunemediated neutropenia. Additionally, there are tests for people for antibodies directed against lessspecific surface antigens that may be found on multiple cell types. 28 The presence of antibodies against these less-specific antigens may lead to concurrent immune-mediated diseases, such as rheumatoid arthritis, immunemediated thrombocytopenia, or immune-mediated hemolytic anemia. In veterinary medicine, IgG and complement 3 were associated with bone marrow neutrophil elements in two dogs with suspected immune-mediated neutropenia.2 More recently, IgG associated with circulating neutrophils in five of six dogs with immune-mediated neutropenia was demonstrated by using flow cytometry.30 However, it was unknown if the targets were neutrophilspecific, a shared antigen, or adsorbed surface antigen.11,30 Flow cytometry has demonstrated IgG associated with circulating neutrophils in dogs with immune-mediated neutropenia. tosis may compensate for the lack of neutrophils; this situation is seen in people. Concurrent lymphocytosis may be related to chronic antigenic stimulation and may lead to hypergammaglobulinemia. tive antinuclear antibody or rheumatoid factor test results may lend evidence of concurrent immune-mediated disease. False positive results are common if these tests are run indiscriminately (e.g. testing for rheumatoid factor in a dog without evidence of erosive polyarthritis).14 Similarly, restrict antinuclear antibody testing to those patients in which concurrent nonerosive polyarthritis is present or suspected. Cytopenia. Bone marrow aspiration or core biopsy is a useful diagnostic tool. It is indicated if there are concurrent cytopenias that cannot be explained by immune-mediated mechanisms or if these cytopenias lack a regenerative response. Bone marrow may show a neoplastic population of cells such as leukemia. Hypoplastic marrow would lend evidence to a drug-induced cytopenia, canine monocytotropic ehrlichiosis, immune-mediated neutropenia due to antibodies directed at bone marrow, or an idiopathic cause of neutropenia. Plasmacytosis may point toward Ehrlichia canis infections.27 In the case of immune-mediated neutropenia, bone marrow aspiration typically reveals hypercellular bone marrow, though hypoplasia can also be Additional diagnostic testing Ultimately, the diagnostic approach to a neutropenic dog or cat depends on whether the patient is symptomatic and how severe the neutropenia is. Febrile patients. If the patient is febrile, look for a septic focus such as a pulmonary, hepatic, or splenic infection or abscess. Use radiography and ultrasonography, and obtain blood, urine, joint fluid, and cerebrospinal fluid samples for bacterial culture. If the results of these tests are negative, consider using a technetium-99mlabeled neutrophil scan to detect neutrophil accumulation at a focus of infection. Serologic or polymerase chain reaction tests are also indicated to rule out infectious disorders such as ehrlichiosis in dogs and FeLV and FIV infections in cats. Anemic patients. With the presence of anemia, especially if it is marked, Exclusion of other causes Lacking tests to prove an immunemediated cause, the diagnosis is determined by excluding other causes and by receiving a positive response to im- 730 November 2007 VETERINARY MEDICINE

Table of Contents Feed for the Digital Edition of Veterinary Medicine - November 2007

Veterinary Medicine - November 2007 Contents Leading Off The Veterinary Medicine Interview: Dr. Lila Miller Clinical Exposures Idea Exchange A Challenging Case: Uveitis and Secondary Glaucoma in a Cat Is it Immune-Mediated Neutropenia? Pimobendan Treatment in Dogs with Congestive Heart Failure CE Form Product Preview Advertiser Index Marketplace/Classifieds Mind Over Miller Special Supplement by Lilly: Flea Bite Facts Q&A

Veterinary Medicine - November 2007

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