Is it immune-mediated neutropenia? - Veterinary Medicine
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Is it immune-mediated neutropenia?
Since no test definitively identifies an immune-mediated neutropenia in dogs and cats, diagnosing this condition and treating it appropriately rely on your excluding thecommon causes of neutropenia, such as infections and drug reactions.


VETERINARY MEDICINE


Effects of medications


Table 1: Drugs That Can Cause Neutropenia in Animals*
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 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 medication as causative and discontinue it.

Chemotherapeutic agents are known to cause myelosuppression, related 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

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

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

Genetic disorders

Infrequently, genetic disorders can also result in neutropenia. Cyclic stem cell proliferations are noted to occur in gray-colored rough collies.24 The neutrophils disappear from peripheral blood at 10 to 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 B12 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

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 than 4 years old may be 4.1 times as likely to develop idiopathic neutropenia as are dogs older than 4 years.16


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Source: VETERINARY MEDICINE,
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