Chapter 111. Venous Thrombosis (Part 1) pot
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Chapter 111. Venous Thrombosis
(Part 1)
Harrison's Internal Medicine > Chapter 111. Venous Thrombosis
Venous Thrombosis: Introduction
Venous thrombosis is the result of occlusive clot formation in the veins. It
occurs mainly in the deep veins of the leg (deep vein thrombosis, DVT), from
which parts of the clot frequently embolize to the lungs (pulmonary embolism,
PE). Fewer than 5% of all venous thromboses occur at other sites (see
"Thrombosis at Rare Sites," and "Superficial Thrombophlebitis," below). Venous
thrombosis is common and often occurs spontaneously, but it also frequently
accompanies medical and surgical conditions, both in the community and the
hospital.
The symptoms of venous thrombosis are nonspecific, and therefore the
clinical diagnosis is difficult and requires objective testing by imaging. Major
complications of thrombosis include a disabling post-thrombotic syndrome and
death due to fatal PE. Treatment with anticoagulants should be prompt and
adequate.
Many risk factors for thrombosis are known, all of them related either to
immobilization or to hypercoagulability. While it has no utility to assess the risk
factor status after thrombosis has occurred, several acquired risk factors are so
strong that they warrant prophylactic anticoagulation, in both those with and
without a history of thrombosis. Detailed guidelines for primary prevention are
available.
Venous thrombosis tends to recur. The risk factors for a first venous
thrombosis are not the same as for recurrent venous thrombosis and to a large
extent are unknown. Individuals from families with inherited thrombophilia tend
to develop thrombosis at a young age and to have frequent recurrences.
Epidemiology
The incidence of a first venous thrombosis is 1–3 per 1000 persons per
year. Around two-thirds manifest as DVT of the leg, and one-third as PE. Up to
half of patients with PE have no signs of DVT. From 1–10% of venous
thromboses prove fatal, with deaths predominantly, but not exclusively, among the
elderly or in patients with severe underlying disease, notably cancer. The
incidence of venous thrombosis is exponentially related to age, where a rule of 10
applies: in children the incidence is 1 per 100,000 per year; in young adults, 1 in
10,000 per year; in the middle-aged, 1 per 1000 per year; in the elderly the
incidence is 1% per year, up to nearly 10% per year in the very oldest. The
recurrence rate of venous thrombosis is 3–10% per year.
Etiology
The causes of thrombosis can be divided into those associated with
immobilization, which are usually acquired, and those associated with
hypercoagulability, which can be either genetic or acquired (Table 111-1). Venous
thrombosis is a multicausal disease that occurs when several risk factors are
present simultaneously in a particular combination. Often, long-term risk factors,
e.g., genetic defects, are joined by short-term acquired factors (Fig. 111-1). While
many factors simply add to the risk, contributing to an individual's "thrombosis
potential," some factors may interact synergistically, when the combination adds
more to the risk than the sum of the separate contributions of the risk factors (e.g.,
factor V Leiden and oral contraceptive use).
Table 111-1 Risk Factors for Venous Thrombosis
Acquired Inherited Mixed/Unknown
Orthopedic
surgery
Antithrombin
deficiency
High levels of factor
VIII
Neurosurgery
Protein C
deficiency
High levels of factor
IX
Major abdominal
surgery
Protein S
deficiency
High levels of factor
XI
Major trauma
Factor V Leiden
(FVL)
High levels of
fibrinogen
Central
venous
catheters
Prothrombin
20210A
High levels of TAFI
Malignancy Non-
O blood
group
Low levels of TFPI
Antiphospholipid
syndrome
Dysfibrinogenemi
a
APC resistance in the
absence of FVL
Puerperium Factor XIII 34val Hyperhomocysteinemi
a
Prolonged bed
rest
High levels of PCI
(PAI-3)
Pregnancy
Obesity
Plaster cast
Oral
contraceptives
Hormonal
replacement therapy
Myeloproliferativ
e disorders
Polycythemia
vera
Long-haul travel
Age
Note: TAFI, thrombin activa
table fibrinolysis inhibitor; TFPI, tissue factor
pathway inhibitor; PCI, protein C inhibitor; PAI-
3, plasminogen activator
inhibitor-3; APC, activated protein C.
