The optimal duration of oral anticoagulant therapy for a first episode of DVT varies and depends on whether risk factors are transient or persistent. A comparison of 6 weeks versus 6 months of oral anticoagulant therapy found an increased risk of recurrent venous thromboembolism in the 6-week group. The risk decreased from 18.1% with 6 weeks of treatment to 9.5% with 6 months; 12 patients would have to be treated for 6 months instead of 6 weeks to prevent 1 episode of recurrent venous thromboembolism (NNT=12; LOE=1b).20 A subsequent comparison of 3 months of anticoagulation with extended oral anticoagulation for approximately 10 months found a reduction in the risk of recurrent venous thromboembolism (ARR=26%; NNT=4) but an increased risk of major bleeding (ARI=3.8%; NNH=26) in the extended therapy group over a period of 2 years (LOE=1b).21 In general, a longer duration of oral anticoagulant therapy is not surprisingly associated with a decreased risk of venous thromboembolic recurrence and an increased risk of bleeding complications. Using the data from the previously mentioned study, for every 100 patients given extended therapy instead of the traditional 3 months there will be 4 additional major bleeds and 25 fewer episodes of recurrent venous thromboembolism. A recent Cochrane review of 1500 patients in 4 studies similarly found a decreased risk of recurrent venous thromboembolism with prolonged warfarin therapy (0.9% vs 12%, ARR=11.1; NNT=9) but an increased incidence of major bleeding (2.1% vs 0%, ARI=2.1%; NNH=48; LOE=1a).22 In the case of recurrent DVT, lifetime anticoagulant therapy should be considered in the absence of risk factors for bleeding. The specific recommendations for duration of oral anticoagulation have been adapted from the American College of Chest Physicians (LOE=5)15 and are included in Figure 1.
Compression Stockings
The addition of compression stockings to standard oral anticoagulant therapy is supported by a study of 194 patients comparing the use of knee-high 30 to 40 mm Hg custom-fitted graded compression stockings over a 2-year period and a median follow-up of 76 months. The development of mild-moderate postphlebitic syndrome was decreased by 58% (ARR=27.1%; NNT=3.7), and the incidence of severe postphlebitic syndrome was decreased by 51% (ARR=12%; NNT=8.3). Although there was not a significant difference in the rate of recurrent venous thromboembolism, extended use of compression stockings improved the long-term clinical course and should be considered a valuable addition in the long-term management of DVT (LOE=1b).23
Investigation for possible malignancy or coagulation defect
Although there is an increased incidence of cancer at the time of presentation in patients with idiopathic DVT (ie, no clear predisposing cause such as bed rest), a complete medical evaluation including history, physical examination, and basic laboratory studies has been shown to adequately detect malignancy in this setting. A retrospective study of 986 consecutive patients found no difference in cancer incidence over the next 34 months among the 142 DVT patients and 844 patients with DVT ruled out by the clinical evaluation outlined in Table 4 (LOE=4).24 A prospective cohort study of 260 patients with DVT provided 2 years of regular follow-up visits and found that all subsequent cancers were diagnosed because the patient became symptomatic and sought care from a general practitioner (LOE=2b).25 Beyond initial and age-appropriate cancer screening, there is no evidence that an aggressive search for an underlying malignancy is warranted.
Inherited thrombophilias are associated with an increased risk for venous thromboembolic disease, yet the diagnosis of one of these defects does not substantially change the clinical management of initial or recurrent DVT. Likewise, counseling regarding the increased risk associated with prolonged immobilization, surgery, pregnancy, and exogenous estrogen therapy would be unchanged. A sensible approach may be to screen for hereditary thrombophilias (factor V Leiden, protein C deficiency, protein S deficiency, antithrombin III deficiency, antiphospholipid antibodies, and hyperhomocysteinuria) in the case of recurrent DVT, a younger patient, or a family history of thromboembolic disease. In the event that an inherited thrombophilia is diagnosed, further screening and possible identification of other family members could lead to avoidance of known secondary risk factors and subsequent thromboembolic events. The typical patient with an initial episode of DVT will not benefit from the investigation for an inherited coagulation defect.
Conclusions
The clinical and economic outcomes associated with DVT can be improved with a simple evidence-based approach to therapy Figure 1. Management of a first episode of DVT should begin with immediate anticoagulation with LMWH, preferably at home if there are no contraindications to outpatient management. Oral anticoagulation should be instituted at initial presentation and continued for a period of 3 to 6 months depending on individual risk factors for bleeding. The addition of compression stockings provides symptomatic relief and decreases the incidence of symptomatic postphlebitic syndrome. Extensive evaluation for malignancy or an inherited thrombophilia is not warranted in most cases of DVT.