Monoclonal gammopathy of undetermined significance and risk of venous thromboembolism.

BACKGROUND: Patients with multiple myeloma are at increased risk of venous thromboembolism (VTE), but little information is available on VTE risk in patients with the precursor condition monoclonal gammopathy of undetermined significance (MGUS). OBJECTIVE: To evaluate the risk of VTE and its impact on mortality in patients with MGUS. PATIENTS AND METHODS: We identified 1610 patients with MGUS and no prior diagnosis of VTE during the 1978-2005 period in North Jutland County, Denmark. We used the Danish Central Population Registry to select 16,100 general population comparison cohort members with no prior VTE diagnosis, matched with the MGUS patients by age, sex, and comorbidity. Follow-up data on VTE incidence in the two groups were obtained from the Danish National Patient Registry covering all Danish hospitals. Time-varying Cox regression analysis was used to compute the incidence rate ratio (IRR) of VTE and the mortality rate ratio (MRR) for MGUS patients who developed VTE compared to MGUS patients without VTE. RESULTS: In the MGUS cohort, 50 VTE events were identified during 12,594 person-years (PY) of follow-up, corresponding to an incidence rate of 4.0 VTEs/1000 PY. The IRR for VTE among MGUS patients compared to the comparison cohort was 1.37 (95% confidence interval (CI): 1.00-1.88). Of the 50 MGUS patients with VTE, one was later diagnosed with malignant transformation. The adjusted MRR for MGUS patients with VTE compared to MGUS patients without VTE was 1.94 (95% CI: 1.36-2.77). CONCLUSIONS: MGUS is a risk factor for VTE, and VTE is a marker for increased mortality among MGUS patients.