Page 13 - index
P. 13

immune-mediated neutropenia (part 1)
➤ Continued from Page 12

ated with an altered microenvironment. Genetic disorders
Secondary infections cause increased Infrequently, genetic disorders can
consumption. A cyclic neutropenia has also result in neutropenia. Cyclic stem
been reported in association with FeLV cell proliferations are noted to occur in
infection. With FIV infection, neutrope- gray-colored rough collies (Figure 3).
nia is also common but is usually mild The neutrophils disappear from periph-
and transient, occurring in the frst few eral blood at 10 to 12-day intervals, dur-
weeks after infection. Neutropenia seems ing which time dogs are clinically ill.
to result from impaired monocyte and The syndrome results from a stem cell
granulocyte differentiation. defect leading to abnormal responses
to growth factors or accelerated cell
Effects of medications loss through apoptosis.
Many medications can cause neutropenia Malabsorption of vitamin B12 in
either by a direct toxic effect (at the level young giant schnauzers causes neu-
of the bone marrow or against circulating tropenia that is accompanied by ane-
cells) or by inducing a secondary immune- mia and methylmalonic aciduria. This
mediated disease directed against circu- disorder responds to parenteral vitamin
lating neutrophils. The level of cells that B12 therapy.
are targeted within the bone marrow or Border collies may present with
circulation will affect the time of onset of neutropenia due to a rare disease that
the cytopenia and what blood cell lines are causes failure of segmented neutro-
affected. If a neutropenic patient has a his- phils to enter peripheral circulation
tory of recent drug use, suspect the medi- (myelokathexis).
cation as causative and discontinue it. Chediak-Higashi syndrome, a form
Chemotherapeutic agents are known of albinism seen in cats as well as other
to cause myelosuppression, related to the species, may have a concurrent neu-
suppression of cell populations with high Figure 3 Gray-colored rough Collie tropenia. o
mitotic rates. Typically, the myelosuppres-
sion is seen fve to seven days after treatment. Antithyroid medications, such as methima-
Neutrophils are commonly affected. zole, can cause severe neutropenia. In 1.5% of
Both exogenous (diethylstilbestrol, estra- cats, this occurs within the frst three months
diol cypionate) and endogenous (Sertoli cell of therapy. The neutropenia typically resolves
tumor) estrogens can cause bone marrow sup- within a week of discontinuing methimazole
pression, perhaps because of induction of a therapy.
myelopoiesis inhibitory substance from the In dogs, anticonvulsants, such as phenobar-
thymus. The prognosis for patients may be bital and primidone, can induce neutropenia
grave since cytopenias often do not resolve (as well as thrombocytopenia and anemia)
with removal of the excess estrogens. as an idiosyncratic reaction. Phenobarbital
Griseofulvin may cause an idiosyncratic can also lead to bone marrow necrosis with
neutropenia in cats (particularly FIV-infected long-term use.
Bone marrow disorders
Neutropenia can also be the
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