The C9ORF72 hexanucleotide expansion is a
major pathological expansion pattern found in patients with
frontotemporal dementia (FTD) and amyotrophic lateral sclerosis
(C9FTD/ALS). We describe a patient in whom early clinical evaluation,
MRI and fluorodeoxyglucose (FDG) positron emission tomography (PET)
findings failed to definitively differentiate between FTD and
Alzheimer's disease (AD), whereas ¹¹C-Pittsburgh compound B (PiB) PET
was negative for amyloid pathology. He later developed ALS symptoms, and
post mortem neuropathological findings were diagnostic of FTD-ALS,
while no findings suggested AD. His sister was diagnosed with FTD, and
the C9ORF72 expansion was detected in both siblings. We conclude that ¹¹C-PiB PET imaging may help the early differential diagnosis between
AD and FTD, including C9FTD/ALS