Amnesia in Frontotemporal Dementia with Amyotrophic Lateral Sclerosis, Masquerading Alzheimer's Disease

A 68-year-old man with a clinical diagnosis of Alzheimer's disease (AD) later developed amyotrophic lateral sclerosis (ALS), which was confirmed at autopsy at age 72 years. Because neuronal loss and AD-type pathologies (Braak stage II for neurofibrillary tangles) were scant, TDP-43-positive intracytoplasmic inclusions in hippocampal dentate granular cells and in neurons in the subiculum and amygdala, even though small in amount, may represent the earliest lesions of ALS-related dementia and could be the cause of dementia in this patient. Although the persistent elevation of creatine kinase from the onset could be a pointer to the presence of motor involvement, more accurate characterization of dementia, which may differentiate ALS-related dementia and AD, is necessary.