Veterinary Medicine - November 2007 - (Page 729)

Immune-mediated neutropenia O P E E R - R E V I E W E D Antithyroid medications, such as methimazole, can cause severe neutropenia. In 1.5% of cats, this occurs within the first three months of therapy. The neutropenia typically resolves within a week of discontinuing methimazole therapy.22 In dogs, anticonvulsants, such as phenobarbital and primidone, can induce neutropenia (as well as thrombocytopenia and anemia) as an idiosyncratic reaction. Phenobarbital can also lead to bone marrow necrosis with long-term use.23 Chediak-Higashi syndrome, a form of albinism seen in cats as well as other species, may have a concurrent neutropenia. DIAGNOSTIC APPROACH Signalment and clinical signs No breed, sex, or size predisposition has been identified for immune-mediated neutropenia. However, dogs younger infections such as FeLV or parvovirus. Physical examinations need to be directed at detecting any nidus of infection. Careful auscultation for murmurs (endocarditis), abdominal palpation, spinal palpation (discospondylitis), and palpation of the lymph nodes are vital. Persistent fever is the most frequently reported physical examination finding in dogs and cats with immune-mediated neutropenia. 6 In Bone marrow disorders Neutropenia can also be the result of disorders that affect the bone marrow. Myeloproliferative and lymphoproliferative diseases and myelophthisis are not infrequently encountered and can result in crowding of the bone marrow space with their respective populations and subsequent cytopenias. Bone marrow necrosis and myelofibrosis with resultant cytopenias can be caused by numerous primary disorders (sepsis, lymphoma, drug toxicosis, or systemic lupus erythematosus), or they may be idiopathic.23 Persistent fever is frequently reported in dogs and cats with immune-mediated neutropenia. than 4 years old may be 4.1 times as likely to develop idiopathic neutropenia as are dogs older than 4 years.16 Dogs may be asymptomatic or may be presented for nonspecific clinical signs. How long dogs or cats might be neutropenic before showing clinical signs is unknown, but the duration from the onset of illness to the time of referral ranged from three to 180 days (median = 46 days) in one retrospective case series.5 Commonly reported clinical signs include lethargy, lameness (possibly shifting), and anorexia.16 Less commonly reported signs include diarrhea, vomiting, and hypersalivation.2,3,11 case reports, joint effusion, conjunctivitis, facial edema, oral ulcerations, epistaxis, pyoderma, abscessation of a digit with local lymphadenomegaly, abdominal pain, mucoid vaginal discharge, and scrotal inflammation have all been reported.2,3,5,11 Genetic disorders Infrequently, genetic disorders can also result in neutropenia. Cyclic stem cell proliferations are noted to occur in graycolored rough collies.24 The neutrophils disappear from peripheral blood at 10to 12-day intervals, during which time dogs are clinically ill. The syndrome results from a stem cell defect leading to abnormal responses to growth factors or accelerated cell loss through apoptosis. Malabsorption of vitamin B 12 in young giant schnauzers causes neutropenia that is accompanied by anemia and methylmalonic aciduria. 25 This disorder responds to parenteral vitamin B12 therapy. Border collies may present with neutropenia due to a rare disease that causes failure of segmented neutrophils to enter peripheral circulation (myelokathexis).26 Complete blood count On a complete blood cell count (CBC), dogs with immune-mediated neutropenia have a lower neutrophil count than do dogs with neutropenia attributed to other causes.6 Severe neutropenia (< 500/µl) with a lack of toxic change is common,14 although reports in the literature are limited. Similarly, some reports of immune-mediated neutropenia in cats reveal that the cats commonly have a marked lymphocytosis and mild thrombocytopenia.14 Toxic change of neutrophils strongly indicates concurrent secondary infection and should resolve with appropriate antibiotic therapy. Concurrent anemia, which can be immune-mediated or from chronic inflammation or bone marrow disease, may be noted. Thrombocytopenia may also be noted, with immune-mediated History taking and physical examination Given that infections and drug administration are the most common causes of neutropenia, history taking and physical examinations need to be directed at gathering information relevant to these areas. A thorough drug history should include over-the-counter products and supplements that the owners might not consider drugs. A vaccine history is essential to assess the possibility of VETERINARY MEDICINE November 2007 729

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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