More Atypical than Atypical Alzheimer's Disease Phenotypes: A Treviso Dementia (TREDEM) Registry Case Report

Background: A 57-year-old right-handed man was admitted to the Treviso Memory Clinic due to the presence of memory forgetfulness, repetition of the same questions, episodes of confusion, initial difficulties in performing complex tasks and easy distraction over the past two years, as well as recurrent and never-happened-before car accidents. Objective: We report a peculiar case of an early onset Alzheimer's disease (AD) with an unusual symptomatology, apparently not fitting in any of the categorized atypical forms of AD nor being representative of a typical amnestic AD. Methods: The patient underwent a neuropsychological, structural, and metabolic cerebral evaluation by MRI and 18F-FDG PET, together with the search for cerebral amyloid (amyloid PET), a genetic testing for dementia related genes and the dosage of CSF protein biomarkers of neurodegenerative conditions. Results: We observed a convergence of predominant frontal (dysexecutive, verbal disinhibition) and posterior (visuospatial) features of cognitive impairment. Structural MRI sequences showed subarachnoid spaces of the vault enlarged in the fronto-parietal region with anterior and posterior cortical atrophy. The hippocampus appeared preserved. The 18F-FDG PET scans showed hypometabolism in the prefrontal, lateral temporal, posterior parietal, and occipital regions bilaterally. The 18F-Flutemetamol scan showed a diffused uptake of the amyloid tracer at the cerebral cortex. CSF biomarkers were compatible with Alzheimer's disease (AD). Conclusion: This case report presented with clinical phenotypic aspects atypical of AD, both frontal and posterior, never described as concomitant in the most accredited criteria for atypical AD, and appeared therefore more atypical than each of the atypical AD phenotypes already reported.