[A case of diagnosed pernicious anemia and subacute combined degeneration of the spinal cord with abnormally elevated serum vitamin B12].

An 86-year-old male patient developed paresthesia in both hands, and six months later, pancytopenia was noted. He was diagnosed with myelodysplastic syndrome following bone marrow aspiration. Despite high serum vitamin B12 level, elevated level of serum homocysteine, positive anti-intrinsic factor antibody, and T₂-weighted hyperintense lesions on spinal cord MRI led to a diagnosis of subacute combined degeneration of the spinal cord. Treatment with intramuscular mecobalamin injections improved the pancytopenia and resolved the MRI lesions. The pancytopenia in this patient was considered to be caused by pernicious anemia. The presence of anti-intrinsic factor antibody can cause falsely normal or elevated serum vitamin B12 levels. When patients with pancytopenia report numbness, even without a decrease in serum vitamin B12 levels, pernicious anemia and subacute combined degeneration of the spinal cord should be suspected, and measurements of serum homocysteine and anti-intrinsic factor antibodies should be considered.