Diagnostic Challenge in Frontal Variant Alzheimer's Disease With Low Amyloid-β PET Retention.

Diagnosing frontal variant Alzheimer's disease (fvAD) is difficult and could be even more difficult when amyloid-beta (Aβ) PET retention is low. A 63-year-old woman presenting with a 3-year history of apathy and memory impairment showed executive dysfunction, memory impairment, and severe bilateral frontotemporal atrophy on MRI. Aβ PET showed only equivocal findings in the right frontal lobe and was negative. However, CSF showed a severely decreased Aβ42/40 ratio and increased phospho-tau181. AD-tau-specific (18F)-MK6240 PET revealed increased tracer retention predominantly in the bilateral frontal lobes, confirming the fvAD diagnosis. (18F)-MK6240 PET can be valuable in resolving diagnostic uncertainties in atypical patients with low Aβ retention.