Vitamin B12 Deficiency Presenting as Pseudothrombotic Microangiopathy and Intestinal Pseudo-Obstruction

Vitamin B12 deficiency is a common and reversible cause of megaloblastic anemia, but in severe cases, it may mimic thrombotic microangiopathy (TMA), a presentation known as pseudothrombotic microangiopathy (pseudo-TMA). This rare entity is frequently underrecognized and may lead to inappropriate therapies if not promptly identified. We report the case of a 62-year-old man who presented with abdominal pain, distension, and constipation, initially raising concern for intestinal obstruction or malignancy. Laboratory evaluation revealed macrocytic anemia, thrombocytopenia, elevated lactate dehydrogenase, and indirect hyperbilirubinemia. Further assessment demonstrated a low reticulocyte count, absence of significant schistocytosis, markedly reduced vitamin B12 levels, and elevated ferritin. Autoimmune testing confirmed pernicious anemia as the underlying etiology. Treatment with intramuscular hydroxocobalamin resulted in complete clinical and hematologic recovery. This case demonstrates the value of recognizing pseudo-TMA and considering vitamin B12 deficiency in patients with TMA-like features and unexplained gastrointestinal symptoms.