Josephs, Keith A.

AbstractINTRODUCTIONAlzheimer's disease (AD) pathology causes corticobasal syndrome (CBS) in 21%–50% of patients. Studies have assessed hypometabolism in CBS according to β‐amyloid (A) positron emission tomography (PET), but the understanding of the association of both AD‐tau (T) and A with hypometabolism is incomplete.METHODSThirty‐three CBS patients and 45 controls underwent fluorodeoxyglucose (FDG), flortaucipir, and Pittsburgh compound‐B PET and were classified as A± and T±. FDG‐PET uptake was extracted for 12 regions‐of‐interest in dominant (most affected) and non‐dominant hemispheres and compared across A/T groups.RESULTSA+T+ patients had greater hypometabolism in temporo‐parieto‐occipital cortices than A+T‐ and A‐T‐ groups, with no differences observed between the A+T‐ and A‐T‐ groups. FDG asymmetry was more accentuated in A+T+ patients. Medial temporal and basal ganglia metabolism were similar across AT groups.DISCUSSIONAmyloid and tau positivity contribute synergistically to hypometabolism and asymmetry in temporo‐parieto‐occipital cortices in CBS, with AD‐like patterns of hypometabolism observed only in A+T+ patients.Highlights Amyloid (A) and tau PET (T) status can be used to stratify CBS patients. A+T+ CBS patients show more hypometabolism in temporo‐parieto‐occipital cortices. Medial temporal metabolism (typical AD pattern) is similar across AT groups. Parieto‐occipital cortices should be assessed when investigating AT pathology in CBS. Amyloid and tau positivity contribute synergistically to hypometabolism and asymmetry in CBS.

ABSTRACT Alzheimer's disease (AD) is the leading cause of dementia in the elderly, marked by abnormal protein buildup (beta‐amyloid and tau) resulting in neuronal loss, especially in the medial temporal lobe and other limbic regions. The presence of transactive response DNA binding protein 43 (TDP‐43) immunoreactive inclusions in medial temporal lobe regions has also been associated with neuroimaging changes in limbic regions. It has been proposed that hypometabolism in limbic regions on [ 18 F] fluorodeoxyglucose positron emission tomography (FDG‐PET) in a patient with a slowly evolving amnestic syndrome may be a signature of the presence of TDP‐43. In this context, we observed an 86‐year‐old Caucasian female with dementia characterized by a slowly evolving amnestic syndrome, along with focal medial temporal atrophy evident on MRI and hypometabolism in limbic regions on FDG‐PET. The patient subsequently died and underwent an autopsy. We performed detailed neuroimaging and digital neuropathological analyses of the hippocampal subfields to better understand the relationship between clinico‐imaging findings and histopathology. In addition to TDP‐43, we identified three other pathological processes in the medial temporal lobe: sequestosome‐1/p62, argyrophilic grain disease (AGD), and primary age‐related tauopathy (PART). Hippocampal subfield volumes and rates of atrophy were no different from those of matched healthy controls, except for the atrophy rate in cornu ammonis 1 (CA1). Digital histopathology revealed the relative highest burden of pathology for p62, followed by TDP‐43, AGD, and PART in CA1. Multiple pathological processes appear to have contributed to the hippocampal atrophy and hypometabolism in our patient with a slowly progressive amnestic syndrome.