Reversible Cognitive Impairment Associated With Severe Vitamin B12 Deficiency Despite Normal Hemoglobin

Vitamin B12 deficiency is a potentially treatable cause of neurological and neuropsychiatric manifestations, including cognitive impairment, and may occur in the absence of anemia¹. We report an older patient with severe vitamin B12 deficiency and progressive cognitive and functional decline who showed substantial improvement after vitamin B12 replacement. Although a direct causal relationship could not be established, this case highlights the importance of measuring serum vitamin B12 in patients with cognitive decline, even when the hemoglobin level is normal. Although the underlying cause of vitamin B12 deficiency could not be definitively established, autoimmune gastritis remained a possible etiology because intrinsic factor antibodies were positive.