Incidental discovery of acquired factor X deficiency in a patient with multiple myeloma.

Factor X deficiency is a very rare coagulopathy caused by a constitutional or acquired deficiency of factor X, or by the presence of a circulating anticoagulant in the blood. Factor X deficiency has already been described in patients with AL amyloidosis, the pathophysiological mechanism being related to factor X trapping in amyloid deposits. We report the case of a patient with multiple myeloma and acquired factor X deficiency, in whom the diagnosis of amyloidosis was excluded by all investigations. Factor X deficiency is exceptionally reported in the context of multiple myeloma, where the deficiency is related to plasma cell dyscrasia responsible for the production of monocolonal immunoglobulins of the light chain type. This case report reviews the procedures to be followed by clinicians and biologists in multiple myeloma hemopathy, and systematically includes a hemostasis work-up in the initial management of the disease. Acquired factor X deficiency can cause life-threatening bleeding if not properly managed.