Chapter 111. Venous Thrombosis (Part 3) potx
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Chapter 111. Venous Thrombosis
(Part 3)
Thrombophilia Testing
Testing for prothrombotic abnormalities outside the setting of abundant
familial thrombophilia serves no purpose. A positive test does not help in the
diagnosis of thrombosis, nor does it predict the risk of recurrent thrombosis, nor,
therefore, does it affect long-term preventive strategies.
Hereditary Thrombophilia
Individuals from families with a hereditary tendency for venous thrombosis
generally have a more severe thrombotic tendency than individuals not from such
families. Even when the genetic defect is the same in the two groups, those with
hereditary thrombophilia from affected families have their first thrombosis at a
young age (20–35 years), few fail to develop thrombosis in their lifetime, and
many have recurrent disease. Early studies on thrombotic risk associated with
prothrombotic defects were based on such families and overestimated risks for all
patients with thrombophilic defects. Generally, individuals from such families
need not be treated differently than others, except (1) oral contraceptives
containing estrogens should be discouraged in all, and (2) postpartum
anticoagulant prophylaxis should be considered in those with prothrombotic
defects. Long-term treatment can be considered after a first episode of thrombosis,
but only in high-risk families, particularly those with antithrombin deficiency.
Thrombosis at Rare Sites
One in 25 venous thromboses occurs in the arm, while other, even more
rare locations are the brain (cerebral vein thrombosis), the digestive system
(mesenteric vein thrombosis), and the liver (portal vein thrombosis, and hepatic
vein thrombosis, also known as Budd-Chiari syndrome). Thrombosis of the arm is
almost invariably associated with central venous catheters. Deteriorating liver
function and portal hypertension may point to thrombosis in the hepatic or portal
veins, neurologic defects to cerebral vein thrombosis, and severe abdominal
complaints to mesenteric vein thrombosis. In rare cases, DVT may be associated
with embolic stroke, when a patent foramen ovale is present (paradoxical stroke).
Although local abnormalities often play a role, a procoagulant state due to cancer
or hereditary abnormalities increases the incidence of thrombosis in rare locations.
In all these cases diagnosis is based on imaging, and treatment should consist of
anticoagulation similar to that of more common forms of thrombosis, as well as
treatment of local causes and consequences.
Superficial Thrombophlebitis
A painful red string is a clear sign of superficial thrombophlebitis. This is
the only type of venous thrombosis that can reliably be diagnosed without imaging
techniques. Although research is limited, the causes of superficial
thrombophlebitis appear similar to those of other forms of venous thrombosis, and
extension to the deep vein occurs. Treatment options are a matter of debate and
vary from anticoagulants to an expectant approach.
Global Data
Venous thrombosis occurs in all ethnic groups, with possibly a somewhat
higher incidence in Africans than in whites and Asians. Whereas acquired risk
factors are largely identical in these large ethnic groups, the two most common
genetic risk factors (factor V Leiden and prothrombin 20210A) are found only in
whites. These are unique gain-of-function mutations with a very low mutation rate
(i.e., they occurred only once). Loss-of-function mutations leading to deficiencies
of antithrombin, protein C, and protein S do not differ much by ethnic group. Due
to founder effects, prevalences of factor V Leiden and prothrombin 20210A may
vary widely in ethnic subpopulations, i.e., in various European populations the
prevalence of factor V Leiden varies between 1% (Italy) and 15% (southern
Sweden). Acquired risk factors may vary by local circumstances, e.g.,
hyperhomocysteinemia due to differences in diet, reproductive factors due to
number of pregnancies, and use of oral contraceptives. The literature on Africans
and Asians is sparse.
Diagnosis
The true prevalence of thrombosis in patients presenting with either
clinically suspected DVT of the leg or PE is ~15–25%. Therefore, the diagnostic
workup for both these diseases has two objectives: (1) to exclude the disease
quickly and safely in as many patients as possible, preferably with noninvasive
and easy-to-use and cost-effective methods; and (2) to confirm the presence of
thrombosis in the remaining patients with an accurate imaging technique. The
purpose of the first step is to withhold both unnecessary further diagnostic testing
and anticoagulant treatment. Although the diagnostic workup of DVT and PE have
much in common, they will be discussed separately.
