A Rare Case of Hereditary Factor XI Deficiency Accompanied by Lupus Anticoagulant in an Adult Patient with Monoclonal Gammopathy of Undetermined Significance.

Acquired coagulopathy, particularly bleeding due to factor X deficiency, is a rare but not unusual phenomenon in patients with plasma cell dyscrasias such as amyloidosis. We herein report a rare case of a Han Chinese man with recurrent scattered skin ecchymosis on the forearms due to factor XI (FXI) deficiency and lupus anticoagulant who was diagnosed with monoclonal gammopathy of undetermined significance (MGUS) and confirmed to have a heterozygous mutation p.L190P (c.T569C) in the FXI gene. To our knowledge, this is the first case report of MGUS concurrent with a FXI missense mutation and lupus anticoagulant.