When the diagnosis is difficult to digest: severe vitamin B₁₂ deficiency secondary to pernicious anemia mimicking life-threatening thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) is an uncommon yet life-threatening condition, usually marked by a classic pentad of microangiopathic hemolytic anemia (MAHA), thrombocytopenia, acute kidney injury (AKI), neurological disturbances, and fevers. Prompt recognition and treatment is essential to reduce morbidity and mortality. The rarity and variability of presentations, however, makes this a difficult diagnosis to make reliably, and in many cases, treatment is initiated empirically before the appropriate diagnostic testing is completed. After TTP and other common causes of thrombotic microangiopathy (TMA) have been excluded, evaluation for causes of “pseudo”-thrombotic microangiopathy (“pseudo”-TMA) should be pursued. Herein, we present a case of a young man with a history of previously treated hepatitis C virus (HCV) infection presenting with a syndrome concerning for TTP: MAHA, thrombocytopenia, and dizziness with gait ataxia. Disseminated intravascular coagulation (DIC) and autoimmune hemolysis were quickly ruled out, and plasma exchange was emergently initiated. Further workup identified an undetectably low vitamin B₁₂ level with profound elevations in both homocysteine and methylmalonic acid (MMA) levels. Folate and vitamin B₁₂ were replenished, with a rapid resolution of hemolysis and improvement in both the platelet count and hemoglobin that allowed for plasma exchange to be permanently discontinued. Further workup identified positivity of both intrinsic factor and parietal cell autoantibodies, suggesting a diagnosis of pernicious anemia. He was determined to have “pseudo”-TMA secondary to critical vitamin B₁₂ deficiency. The patient was safely discharged home with scheduled subcutaneous vitamin B₁₂ injections along with outpatient follow-up with both Hematology and Gastroenterology.