An 80-year-old chronic alcoholic was diagnosed with atrial fibrillation five years ago. His son describes a stepwise decline in his father's overall memory over these years. On examination, he is having pseudobulbar affect with brisk DTR in left upper extremity and up-going plantars. What is the diagnosis?
Binswanger's disease Alzheimer's disease Multi-infarct dementia Vitamin B12 deficiency