Atypical Presentations of Alzheimer’s Disease: Beyond Amnestic Dementia

Neuropathological and biomarker-based studies indicate that Alzheimer’s disease may sometimes present not with the typical amnestic dementia syndrome of the hippocampal type but with atypical clinical pictures. Atypical presentations include frontal dementia sometimes with additional behavioural component mimicking frontotemporal dementia, logopenic primary progressive aphasia and posterior cortical atrophy, while mixed presentations include patients with additional vascular or Lewy body pathology. More atypical presentations include non-logopenic (semantic, non-fluent agrammatic and unclassifiable) primary progressive aphasia, corticobasal syndrome and cases mixed with normal pressure hydrocephalus. Atypical clinical presentations of Alzheimer’s disease may be more common than previously thought. Cerebrospinal fluid levels of biomarkers such as amyloid beta peptide, hyperphosphorylated tau protein and total tau protein, may offer a useful tool for correct ante mortem identification of such patients, which is likely to affect therapeutic decisions.