Veterinary Medicine - November 2007 - (Page 726)

Immune-mediated neutropenia O P E E R - R E V I E W E D may exceed bone marrow production. Some infections, such as canine monocytotropic ehrlichiosis, impair bone marrow proliferation.15 Neutropenia may also be associated with systemic mycosis (histoplasmosis, cryptococco- 1).19 The level of cells that are targeted within the bone marrow or circulation will affect the time of onset of the cytopenia and what blood cell lines are affected. If a neutropenic patient has a history of recent drug use, suspect the Infections are the most common causes of neutropenia. sis) if myelophthisis occurs and results in subsequent cytopenias.16 In dogs, the most common infection consistently associated with neutropenia is parvovirus. In both dogs and cats, parvovirus targets tissues with high mitotic rates such as the bone marrow, leading to cytotoxic hematopoietic cell death as well as ineffective hematopoiesis. Parvovirus infection will also lead to increased neutrophil margination and consumption associated with gastrointestinal damage and endotoxemia. In cats, feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) infections are the most common infectious causes of neutropenia. FeLV infection causes the destruction of hematopoietic stem cells and ineffective maturation of neutrophils associated with an altered microenvironment. Secondary infections cause increased consumption. A cyclic neutropenia has been reported in association with FeLV infection.17 With FIV infection, neutropenia is also common but is usually mild and transient, occurring in the first few weeks after infection. Neutropenia seems to result from impaired monocyte and granulocyte differentiation.18 medication as causative and discontinue it. Chemotherapeutic agents are known to cause myelosuppression, re- lated to the suppression of cell populations with high mitotic rates. Typically, the myelosuppression is seen five to seven days after treatment. Neutrophils are commonly affected. Both exogenous (diethylstilbestrol, estradiol cypionate) and endogenous (Sertoli cell tumor) estrogens can cause bone marrow suppression, perhaps because of induction of a myelopoiesis inhibitory substance from the thymus.20 The prognosis for patients may be grave since cytopenias often do not resolve with removal of the excess estrogens. Griseofulvin may cause an idiosyncratic neutropenia in cats (particularly FIV-infected cats).21 TABLE 1 Drugs That Can Cause Neutropenia in Animals* Category Analgesics Antibiotics Anticonvulsants Antifungals Antihistamines Anti-inflammatories Antithyroid drugs Anthelmintics Cardiovascular drugs Diuretics Hypoglycemic agents Phenothiazines Sedatives and neuropharmacologic agents Miscellaneous Specific Drugs Aminopyrine, dipyrone Cephalosporins, chloramphenicol, metronidazole, penicillins, sulfonamides Mephenytoin, phenobarbital, phenytoin, primidone Griseofulvin Brompheniramine, cimetidine, trimeprazine tartrate Carprofen, gold salts, ibuprofen, indomethacin, phenylbutazone Methimazole, propylthiouracil Albendazole,** levamisole Captopril, diazoxide, hydralazine, procainamide, propranolol, quinidine Chlorothiazide Chlorpropamide, tolbutamide Chlorpromazine Diazepam, metoclopramide Allopurinol, colchicines, diethylstilbestrol, estradiol cypionate, ethanol, levodopa, mitotane, penicillamine Effects of medications Many medications can cause neutropenia either by a direct toxic effect (at the level of the bone marrow or against circulating cells) or by inducing a secondary immune-mediated disease directed against circulating neutrophils (Table *Unless otherwise noted, the source for this information is Feldman BF. Neutropenia in small animals. Vet Forum 1999;16:38-45. **Source: Stokol T, Randolph JF, Nachbar S, et al. Development of bone marrow toxicosis after albendazole administration in a dog and cat. J Am Vet Med Assoc 1997;210:1753-1756. Source: Holland M, Stobie D, Shapiro W. Pancytopenia associated with administration of captopril to a dog. J Am Vet Med Assoc 1996;208:1683-1686. 726 November 2007 VETERINARY MEDICINE

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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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