Multiple sclerosis and risk of venous thromboembolism: a population-based cohort study.

Background: Multiple sclerosis (MS) patients may be at increased risk of venous thromboembolism (VTE), but evidence is limited.
Objectives: To examine long-term risk of VTE among MS patients.
Patients and Methods: We conducted a population-based cohort study among 17,418 Danish MS patients and 87,090 comparison cohort members from the general population. Data on MS, VTE and comorbidities were obtained from the Danish National Registry of Patients including all admissions to Danish hospitals since 1977. We computed cumulative risks for VTE and adjusted incidence rate ratios (IRRs).
Results: A total of 34 (0.2%) MS patients and 36 (0.04%) comparison cohort members had a deep venous thrombosis (DVT) within 1 year following the date of initial MS diagnosis/index date [adjusted IRR = 3.02 (95% CI: 2.14-4.27)]. During this period, 16 (0.09%) MS patients and 26 (0.03%) comparison cohort members had a documented pulmonary embolism (PE) [adjusted IRR = 2.85 (95% CI: 1.72-4.70)]. During the subsequent up to 29 years, 315 (1.9% of MS patients alive at year 1) MS patients had a record of a DVT [adjusted IRR = 2.28 (95% CI: 2.01-2.59)] and 129 (0.8%) had PE [IRR = 1.58 (95% CI: 1.31-1.92].
Conclusion: MS is a risk factor for VTE, but the absolute risk is low.
(Copyright © 2012 S. Karger AG, Basel.)