To present clinical features, brain imaging and postmortem findings in a 90-year-old woman with TDP-43 positive behavioral variant frontotemporal degeneration (BvFTD).

Frontotemporal degeneration has been reported only rarely and without autopsy confirmation in the oldest-old and is often not considered in the differential diagnosis in this age group. Further, the reliability of advanced brain imaging to identify FTD in this age group is in question.

A 90-year-old woman first sought medical advice when she developed aphasia and memory loss. The initial clinical impression was AD with remote cerebral infarct; however, symptoms progressed rapidly over 6-months to mutism, ADL impairment, and parkinsonism. On further questioning, the family endorsed insidious onset of personality changes, delusions and disinhibited behavior over several years. Evaluation included MRI, EEG and spinal fluid examination. FDG-PET was performed to differentiate FTD from AD.

Brain MRI indicated profound bitemporal and frontal atrophy. Similarly, FDG-PET/CT found bilateral moderate/severe anterior temporal, anterior cingulate and frontal hypometabolism consistent with BvFTD. In addition, there was mild/moderate hypometabolism in the parietal, posterior cingulate and precuneus cortex bilaterally making it impossible to unequivocally exclude AD.  The patient died 4 months later and brain autopsy was performed. There were low/intermediate pathologic changes of AD with neuritic plaques but a low Braak stage (A1, B1, C3 by NIA-AA criteria). This level of AD pathology is insufficient to account for dementia. Immunohistochemistry demonstrated numerous ubiquitin neuronal and glial inclusions that did not co-localize with tau pathology. Immunohistochemistry for TDP-43 was subsequently performed revealing intraneuronal cytoplasmic inclusions. Genetic testing found a tau variant associated with both AD and FTD.

Advanced age does not exclude FTD and should be considered in the differential diagnosis, even in the oldest-old. Further, multiple pathologies are common in the oldest old. Advanced brain imaging including MRI, FDG-PET can help identify non-AD dementias in elderly.