Arterial and venous thrombosis in patients with monoclonal gammopathy of undetermined significance: incidence and risk factors in a cohort of 1491 patients.

Monoclonal gammopathy of undetermined significance (MGUS) has been associated with an increased risk of thrombosis. We carried out a retrospective multicentre cohort study on 1491 patients with MGUS. In 49 patients (3.3%) MGUS was diagnosed after a thrombotic event. Follow-up details for a period of at least 12 months after diagnosis of MGUS were obtained in 1238 patients who had no recent history of thrombosis (<2 years) prior to diagnosis, for a total of 7334 years. During the follow-up, 33 of 1238 patients (2.7%) experienced thrombosis, with an incidence of 2.5 arterial events and 1.9 venous events per 1000 patient-years. Multivariate analysis showed increased risks of arterial thrombosis in patients with cardiovascular risk factors [hazard ratio (HR) 4.92, 95%confidence interval (CI) 1.42-17.04], and of venous thrombosis in patients with a serum monoclonal (M)-protein level >16 g/l at diagnosis (HR 3.08, 95%CI 1.01-9.36). No thrombosis was recorded in patients who developed multiple myeloma (n = 50) or other neoplastic diseases (n = 21). The incidence of arterial or venous thrombosis in patients with MGUS did not increase relative to that reported in the general population for similarly aged members. Finally, the risk of venous thrombosis did increase when the M-protein concentration exceeded >16 g/l.