Post-thrombotic syndrome: Short and long-term incidence and risk factors.

Background: The reported incidences of post-thrombotic syndrome (PTS) after deep vein thrombosis (DVT) vary. Further, PTS symptom development over time and its long-term incidence are unknown.
Methods: Patients included in the MEGA study were interviewed at 1 year and completed a questionnaire at 8 years of follow-up regarding symptoms and signs of PTS based on the Villalta score after a first DVT diagnosis. The cumulative incidence of PTS at 0-1 and 1-8 year, changes in PTS classification and the effect of possible clinical and laboratory risk factors were determined.
Results: After 1 year, 361 out of 1657 patients diagnosed with DVT were classified as having PTS, for a 0-1 year cumulative incidence of 21.8% (95%CI 19.9-23.8), out of whom 92 (5.6%) had severe PTS. After 8 years 633 patients without previous PTS completed the second questionnaire, of whom 44 were classified as having PTS, for a 1-8 year cumulative incidence of 7% (95%CI 5.2-9.2); of these 13 (2.1%) were classified as severe PTS. During follow-up PTS complaints improved in 69% and worsened in 7% of patients. At 1 year, risk factors were female sex (RR 1.5; 95%CI 1.2-1.9) and obesity (RR 1.5; 95%CI 1.2-7.9), with the same effect sizes at 8 years. Provoked/unprovoked DVT, thrombus location, pregnancy, hormone use and several laboratory parameters did not affect risk of PTS, either at 1 or 8 years.
Conclusion: The incidence of PTS remained substantial up to 8 years after a first DVT. Symptoms improved in a large proportion of the cases. The short and long term risks were highest in women and obese patients.
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