Risk factors for post-thrombotic syndrome in patients with a first deep venous thrombosis.

Background: Post-thrombotic syndrome (PTS) is a chronic complication of deep venous thrombosis (DVT).
Objectives: To determine the risk of PTS after DVT and to assess risk factors for PTS.
Methods: Patients were recruited from the Multiple Environmental and Genetic Assessment (MEGA) study of risk factors for venous thrombosis. Consecutive patients who suffered a first DVT of the leg were included in a follow-up study. All patients completed a questionnaire and DNA was obtained. PTS was ascertained in a structured interview using a clinical classification score.
Results: The 1-year cumulative incidence of PTS was 25% and 7% for severe PTS. Elastic compression stockings were prescribed in 1412 (85%) patients. The majority used their stockings every day. Women were at an increased risk compared with men [risk ratio (RR) 1.5, 95% confidence interval (CI) 1.3-1.8]. Similarly, obese patients had a 1.5-fold increased risk of PTS compared with normal weight patients (RR 1.5, 95% CI 1.2-1.9), with a 1-year cumulative incidence of 34% compared with 22%. Patients who already had varicose veins had an increased risk (RR 1.5, 95% CI 1.2-1.8) of PTS. DVT in the femoral and iliac vein was associated with a 1.3-fold increased risk of PTS compared with popliteal vein thrombosis (RR 1.3, 95% CI 1.1-1.6). Patients over 60 years were less likely to develop PTS than patients below the age of 30 (RR 0.6, 95% CI 0.4-0.9). Malignancy, surgery, minor injury, plaster cast, pregnancy or hormone use did not influence the risk of PTS neither did factor (F)V Leiden nor the prothrombin 20210A mutation.
Conclusions: PTS is a frequent complication of DVT, despite the widespread use of elastic compression stockings. Women, obese patients, patients with proximal DVT and those with varicose veins have an increased risk of PTS, whereas the elderly appeared to have a decreased risk.