Pernicious Anemia Presenting as Pseudo-Thrombotic Microangiopathy: A Case Report.

Thrombotic thrombocytopenic purpura (TTP) is a rare, life-threatening thrombotic microangiopathy (TMA) characterized by microangiopathic hemolytic anemia, thrombocytopenia, and end-organ dysfunction, with high untreated mortality that can be effectively reduced with timely plasma exchange (PLEX) and immunosuppressive therapy. However, several conditions can produce a clinically similar pseudo-TMA picture, among which severe vitamin B12 deficiency is an underrecognized and potentially treatable mimic that occurs due to ineffective intramedullary erythropoiesis, megaloblastic fragmentation of structurally abnormal erythrocytes, and pancytopenia in the absence of true endothelial injury or ADAMTS13 deficiency. We present a 74-year-old female patient who presented with altered mental status, bradycardia, and severe hemolytic anemia, in whom PLEX was initiated for suspected TTP but failed to improve platelet counts despite four sessions, ultimately prompting a workup that showed B12 deficiency due to pernicious anemia, confirmed by an elevated methylmalonic acid (MMA) and low serum B12, with complete hematologic recovery following cyanocobalamin repletion.