Incidence, Timing of Onset and Severity of Post-Thrombotic Syndrome after Acute Symptomatic Deep Vein Thrombosis: Two-Year Results from a Canadian Multicenter Prospective Cohort Study (The VETO Study).

Background and Objectives: The post thrombotic syndrome (PTS) is a chronic complication of deep venous thrombosis (DVT). It is difficult to provide DVT patients with long-term prognostic information as there is little longitudinal data on the occurrence of PTS after DVT. We performed a prospective multicenter study of long-term outcomes after DVT (the Venous Thrombosis Outcomes [VETO] Study) to determine the incidence, timing of onset and severity of PTS.

Methods: Consecutive patients with objectively diagnosed acute DVT were recruited at 7 participating hospital centres from April 2001-July 2002. Patients attended study visits at Baseline, 4, 8, 12 and 24 months. Clinical data were recorded and standardized assessments for PTS (using Villalta scale) were performed by trained study personnel at each follow-up visit. Patients were classified as having developed PTS if the ipsilateral Villalta score was ≥ 5 on at least 2 visits or at the final follow-up visit, and having severe PTS if a score of >14 or a venous ulcer was documented on any one occasion. The Kaplan-Meier survival method was used to estimate the cumulative probability of PTS and of severe PTS over time.

Results: The study cohort consisted of 359 patients. The mean age was 56 years, 50% were male, 2/3 were outpatients, 55% had proximal DVT and 20% had previous DVT. The Kaplan-Meier estimates of cumulative risk of PTS were 29% at 4 months, 33% at 8 months, 35% at 12 months and 37% at 24 months. Corresponding risks of severe PTS were 6.6%, 6.9%, 6.9% and 6.9%, respectively. When the analysis was stratified according to history of DVT, the cumulative incidence of PTS in patients without previous DVT was 25%, 28%, 30% and 31% at 4, 8, 12 and 24 months. Corresponding rates of PTS in patients with previous DVT were 45%, 51%, 53% and 57%.

Conclusions: More than one third of patients in our cohort developed PTS within 2 years of DVT, and of these, 1 in 6 was classified as severe. Most cases of PTS and of severe PTS were apparent by 4 months after DVT. Patients with previous DVT had a higher frequency of PTS and of late onset PTS. Our study provides longitudinal data on prognosis that is relevant both to patients with DVT and their treating physicians.