Vitamin B12 Deficiency Mimicking Thrombotic Microangiopathy: A Case of Pseudo-Thrombotic Microangiopathy.

Introduction: Vitamin B12 deficiency may rarely present with hemolysis and schistocytosis, mimicking thrombotic microangiopathy (TMA). This pseudo-TMA variant is clinically significant, as delayed recognition may lead to unnecessary treatments and adverse outcomes. Case presentation: A 44-year-old male with no significant medical history or dietary restrictions presented with progressive lightheadedness, epigastric discomfort, and unintentional weight loss. Laboratory evaluation revealed macrocytic anemia with evidence of hemolysis and reticulocytopenia. A negative Coombs test made autoimmune hemolytic anemia less likely. Further workup demonstrated low serum vitamin B12 and elevated methylmalonic acid, consistent with B12 deficiency. Upper endoscopy with gastric biopsy revealed atrophic mucosa lacking parietal cells, and serology was positive for anti-parietal cell and intrinsic factor antibodies, confirming pernicious anemia. The patient was treated with intramuscular vitamin B12, resulting in rapid hematologic recovery and complete resolution of symptoms. Conclusion: This case illustrates a rare presentation of pernicious anemia as pseudo-TMA, emphasizing the importance of recognizing macrocytosis and reticulocytopenia as distinguishing features from true TMA. Early identification of vitamin B12 deficiency can prevent unnecessary invasive interventions and allows for rapid clinical improvement with supplementation.