The authors report a case of subacute combined degeneration of the cervicothoracic spinal cord involving the dorsal and lateral spinal columns, extending to the brainstem, due to cobalamin deficiency in an elderly patient. Symptoms of this subacute myelopathy are potentially reversible with early diagnosis. Presenting symptoms of this myelopathy, involvement of the lateral columns and brainstem have rarely been documented by magnetic resonance imaging (MRI) studies. MRI showed increased T2-weighted signal in the spinal cord. The patient's background and history and the posterior location of the abnormalities increased the specificity of MRI, and the resolution of clinical symptoms with vitamin supplementation confirmed the diagnosis.