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Neurocase. 2016;22(2):161-7. doi: 10.1080/13554794.2015.1080283. Epub 2015 Aug 25.

Early-onset Alzheimer's disease versus frontotemporal dementia: resolution with genetic diagnoses?

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a Department of Neurology and Neurological Sciences , Stanford University , Stanford , CA , USA.
b Department of Neurology, Memory and Aging Center , University of California , San Francisco , CA , USA.
c Helen Wills Neuroscience Institute, University of California , Berkeley , CA , USA.
d Departments of Psychiatry and Neurology , Semel Institute for Neuroscience and Human Behavior, University of California , Los Angeles , CA , USA.
e Department of Radiology, Lawrence Berkeley National Laboratory , University of California , Berkeley , CA , USA.


We report a diagnostically challenging case of a 64-year-old man with a history of remote head trauma who developed mild behavioral changes and dyscalculia. He was diagnosed with clinical Alzheimer's disease (AD), with additional features consistent with behavioral variant frontotemporal dementia. Structural magnetic resonance imaging revealed atrophy in bilateral frontal and parietal cortices and hippocampi on visual inspection and left frontal pole and bilateral anterior temporal encephalomalacia, suspected to be due to head trauma. Consistent with the diagnosis of Alzheimer's pathology, positron emission tomography (PET) with Pittsburgh compound B suggested the presence of beta-amyloid. Fluorodeoxyglucose PET demonstrated hypometabolism in bilateral frontal and temporoparietal cortices. Voxel-based morphometry showed atrophy predominant in ventral frontal regions (bilateral orbitofrontal cortex, pregenual anterior cingulate/medial superior frontal gyrus), bilateral mid cingulate, bilateral lateral temporal cortex, and posterior insula. Bilateral caudate, thalamus, hippocampi, and cerebellum were prominently atrophied. Unexpectedly, a pathologic hexanucleotide repeat expansion in C9ORF72 was identified in this patient. This report underscores the clinical variability in C9ORF72 expansion carriers and the need to consider mixed pathologies, particularly when imaging studies are inconsistent with a single syndrome or pathology.


Alzheimer’s disease; Frontotemporal dementia

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