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Thrombosis, defined as excessive clotting,
has three main causes: reduced blood flow (stasis), increase in
blood coagulation factors (hypercoagulability), and abnormalities
in the vessel wall. Once the endothelium is injured, platelet adhesion
is accompanied by platelet aggregation and thrombin formation. This
process is usually tightly regulated in order to prevent excessive
bleeding or clotting. However, at times, the process is uncontrolled,
and a thrombus can form in excessive amounts or in an unusual place,
causing harm.
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Thrombosis and thrombophilia in childhood is of increasing concern. Although
symptomatic thrombotic disease in children is rare when compared
with adults, its occurrence can lead to mortality or life-long sequelae.
The reported rate of thrombosis is 5.3 per 10,000 hospitalized patients,
with a bimodal peak in incidence in the neonatal and adolescent
age groups.1-4 Less than 10% of events
in children are idiopathic.1-4 Thrombosis during
childhood is a multifactorial event caused by both genetic and acquired
risk factors. Three or 4 different thrombotic risk factors are identified
in most cases.1,4,5,6 Most children with thrombosis have
an underlying medical condition that alters the hemostatic system
to induce activation of coagulation and/or to prevent the inhibition
of coagulation. The majority of conditions are related to inflammation
or to abnormal blood flow (Table 438-1).
In addition to the hemostatic changes secondary to underlying illness,
many children also have the additional risk factor of a central
venous catheter inserted to facilitate therapy for the underlying illness.1-3,7,8 The
use of central venous catheter constitutes the most common acquired
risk factor for thrombosis.5,7,8 As many as 60% of
children with thrombosis will also have an inherited prothrombotic
abnormality (Table 438-2), but the clinical
relevance of congenital thrombophilia in asymptomatic children or
in the presence of an acquired risk factor (eg, the presence of
a central venous catheter) in childhood is still uncertain.1,9,10 There
is debate about which children to screen, as well as when and how,
for these genetic states. Families should be counseled about the significance
of a prothrombotic state before testing is performed, especially
in asymptomatic children. The pediatric community needs to be able
to educate families about the signs and symptoms of thromboembolic
disease, medical treatments and their potential adverse effects, and
types of inherited and acquired thrombophilias.
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