MGUS: not so benign after all

It is well appreciated that persons with multiple myeloma have an increased risk of venous thrombosis. More recently, this relative risk has been shown to be increased further in these patients while on therapy with thalidomide and its derivatives. The mechanism of this increased risk for thrombosis has traditionally been attributed to traditional neoplasia risks for thrombosis, such as decreased mobility, surgical procedures, use of chemotherapy, and/or indwelling catheters. In this study, Kristinsson et al reviewed 4 196 197 veterans who were hospitalized at least once at Veteran Affairs hospitals in the United States and identified a total of 2374 patients with monoclonal gammopathy of undetermined significance (MGUS) and 6192 multiple myeloma patients. In the whole study population, there were 39 272 persons with a deep vein thrombosis (DVT) with totals of 31 and 151 occurring among MGUS and multiple myeloma patients, respectively. Compared with the whole study population, the relative risk of DVT following a diagnosis of MGUS and multiple myeloma was 3.3 (2.3-4.7) and 9.2 (7.9-10.8), respectively. As the authors point out, it is important to realize that these data were gathered prior to the current prevalent use of thalidomide in myeloma patients.

These results have important implications. The fact that patients with MGUS have an increased risk of DVT together with the known risk of transformation to multiple myeloma suggests there may be a common underlying mechanism or etiology to the 2 conditions that is independent of cancer treatment.

Limitations of this study include the obvious facts that it is retrospective and the diagnoses are determined only by the discharge diagnostic codes. Due to the difficulty of separating patients with pulmonary embolism from other respiratory conditions, patients with isolated pulmonary embolism were not identified and so we don't know if there is an increased risk for that. Nonetheless, this study should point the way to identifying the underlying pathogenesis of DVT in patients with plasma cell dysplasia and may ultimately help to identify those patients who should have thromboprophylaxis.