Megaloblastic Anemia

In a survey of 500 patients with megaloblastic anemia in India, vitamin B12 deficiency was identified as the cause in 280 patients. Among these 280 patients, what is the most common etiology of B12 deficiency?

A 58-year-old Indian vegetarian man presents with progressive dyspnea and paresthesias. Laboratory findings show macrocytic anemia with hypersegmented neutrophils and a serum B12 level of 85 pg/mL (normal >200). What is the most common cause of megaloblastic anemia in this patient?

A 65-year-old man on methotrexate for rheumatoid arthritis develops macrocytic anemia with megaloblastic changes on bone marrow. B12 and folate levels are low-normal. Which is the drug of choice to prevent and treat methotrexate-induced megaloblastic anemia?

A 52-year-old vegetarian woman from rural India presents with progressive fatigue, glossitis, and paresthesias in both feet. Blood smear shows macrocytic RBCs with hypersegmented neutrophils. Serum B12 is 180 pg/mL (normal >200) and folate is normal. What is the drug of choice for her anemia?

A 45-year-old woman with pernicious anemia is started on intramuscular vitamin B12 therapy. Which of the following is NOT a recognized hematologic or neurologic complication that may develop if B12 deficiency is left untreated?