[A case of vitamin B12 deficiency with involuntary movements and bilateral basal ganglia lesions].

An 86-year-old woman with a one-year history of dementia was admitted to our hospital complaining of loss of appetite, hallucinations, and disturbance of consciousness. She gradually presented with chorea-like involuntary movements of the extremities. Diffusion-weighted magnetic resonance imaging (MRI) showed bilateral symmetrical hyperintense signals in the basal ganglia. The serum vitamin B12 level was below the lower detection limit of 50 pg/ml. The homocysteine level was markedly elevated at 115.8 nmol/ml. Anti-intrinsic factor and anti-parietal cell antibody tests were positive. Gastrointestinal endoscopy revealed atrophic gastritis. The patient was diagnosed with encephalopathy due to vitamin B12 deficiency caused by pernicious anemia. Involuntary movements and MRI abnormalities improved with parenteral vitamin B12 supplementation. Bilateral basal ganglia lesions are rare manifestations of adult vitamin B12 deficiency. The present case is considered valuable in identifying the pathophysiology of involuntary movement due to vitamin B12 deficiency.