The Great Hematologic Mimic: A Case Report of Vitamin B12 Deficiency Presenting as Thrombotic Microangiopathy

Introduction: Vitamin B12 deficiency often manifests with hematological symptoms such as fatigue, pallor, glossitis, and neurological issues including paresthesias and cognitive impairments. Laboratory results typically indicate macrocytic anemia, hypersegmented neutrophils, and elevated serum methylmalonic acid and homocysteine levels. Approximately 3.6% of adults aged 19 and older experience this deficiency. In rare instances, vitamin B12 deficiency may present as microangiopathic hemolytic anemia (MAHA), mimicking thrombotic thrombocytopenic purpura (TTP), characterized by hemolysis and thrombocytopenia, termed pseudo-thrombotic microangiopathy (TMA). This misdiagnosis frequently occurs in the presence of associated thrombocytopenia, leading to ineffective and costly treatments such as plasma exchange. Case Presentation: A 40-year-old African American woman with GERD presented with several days of epigastric pain, fatigue, weakness, and exertional dyspnea. Examination revealed conjunctival pallor and mild epigastric tenderness. Laboratory studies showed macrocytic anemia, thrombocytopenia, elevated ferritin, undetectable vitamin B12, and low folate with a markedly decreased reticulocyte count, indicating ineffective erythropoiesis. Intravascular hemolysis was evidenced by indirect hyperbilirubinemia, elevated LDH, undetectable haptoglobin, and hemoglobinuria. The patient improved clinically with notable improvement of her hematological markers following vitamin B12 replacement with daily cyanocobalamin injections. The Coombs test was negative and ADAMTS13 activity was normal, excluding autoimmune hemolysis and TTP. EGD demonstrated atrophic gastritis, and serology was positive for anti–intrinsic factor and antiparietal cell antibodies, confirming pernicious anemia. Conclusion: This case underscores the significance of considering vitamin B12 deficiency in the differential diagnosis of microangiopathic hemolytic anemia to prevent unnecessary treatments and ensure appropriate management.