Unusual bleeding manifestations in a case of primary amyloidosis with factor X deficiency but elevations of in vivo markers of thrombin formation and activity

We describe a case of primary amyloidosis (AL) with severe factor X (FX) deficiency in an amateur cyclist presenting with muscular pain at rest and ecchymoses in his legs. No circulating inhibitor of FX was found by mixing studies and there was no deficiency of other vitamin K-dependent coagulation factors and inhibitors or of α₂-antiplasmin. Thrombin-time and reptilase time were abnormally prolonged and were not corrected by mixing with normal plasma. Administration of plasma or prothrombin complex concentrate (PCC) were unsuccessful in controlling bleeding: the apparent half-life of transfused FX was 6 minutes. Resting resulted in cessation of muscular pain and bleeding. Renal and cardiac deterioration led the patient to death 3 years after presentation. No further bleeding manifestations did occur during this period. FX levels remained consistently below 3%, but prothrombin fragment 1.2 and thrombin-antithrombin complex - measured at distance from PCC administration and prior to deterioration of renal and cardiac function - were markedly elevated. At autopsy, disseminated amyloidosis was found with sparing of the skeletal muscles and of the skin. This is the first report of increased in vivo prothrombin activation and activity in AL-associated FX deficiency.