Chapter 112. 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. . Chapter 112. Venous Thrombosis (Part 1) Harrison's Internal Medicine > Chapter 111. Venous Thrombosis Venous Thrombosis: Introduction Venous thrombosis is the. 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. 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