A Simple Vitamin Deficiency With Life-Threatening Complications: A Case of B12 Deficiency and Hyperhomocysteinemia-Induced Thrombosis.

While macrocytic anemia is common in vitamin B12 deficiency, rarely, pancytopenia and hemolytic anemia can occur. Homocysteine levels are elevated in severe B12 deficiency, and this is linked to thrombus formation with potentially life-threatening complications. We present a patient with severe vitamin B12 deficiency complicated by hyperhomocysteinemia and obstructive shock from pulmonary embolism. A 56-year-old male with no medical history presented to the hospital with altered mentation. The patient's family stated he was experiencing bilateral paresthesias of his lower extremities, progressive depression, anxiety, and insomnia. Initial vitals were blood pressure of 76/36, heart rate of 70 beats per minute, respiratory rate of 14, and temperature of 36.3 degrees Celsius. He was intubated due to severe encephalopathy. Relevant labs indicated severe macrocytic anemia, thrombocytopenia, decreased B12 levels, elevated methylmalonic acid, and elevated homocysteine. Imaging demonstrated a right common femoral vein thrombosis and subsegmental pulmonary emboli. Peripheral blood smear revealed schistocytes, anisopoikilocytosis, and decreased platelet count. The patient required fluid resuscitation, antibiotics, and multiple blood products. Vitamin B12 was administered intramuscularly, which improved the anemia. Esophagogastroduodenoscopy (EGD) demonstrated gastritis. Gastric and duodenal biopsies were negative for and celiac disease. He was negative for intrinsic factor (IF) antibodies but had elevated gastrin levels. An intravenous unfractionated heparin infusion was started when the platelet count was above 50000. The patient was extubated after seven days. Heparin was transitioned to apixaban and an inferior vena cava (IVC) filter was placed. Hyperhomocysteinemia is a known pro-thrombotic factor that can lead to the development of venous thromboembolism. B12 malabsorption can stem from inflammatory bowel disease, celiac disease, gastritis, pancreatic insufficiency, gastrectomy, gastric bypass surgery, or antibodies to IF. While this case showed gastritis and negative IF antibodies, gastrin levels were elevated, indicating a mixed picture. This highlights the challenge of definitively diagnosing pernicious anemia as the cause of vitamin B12 deficiency. Vitamin B12 deficiency may lead to critical illness in which thromboembolism develops secondary to hyperhomocysteinemia.