Amyloid Imaging in Dementia and Neurodegenerative Disease

Alzheimer’s disease (AD) accounts for 70% of dementia cases. Neuropsychological testing has limited sensitivity and specificity compared with the gold standard of histological examination postmortem. The neuropathological hallmarks of AD are β-amyloid peptide aggregates and hyperphosphorylated tau protein. Imaging using amyloid PET tracers allows the detection of amyloid deposition in vivo, serving as an important diagnostic tool. Several approved amyloid PET tracers are available with equivalent performance in clinical practice and vendor-specific image interpretation methodologies. In addition, amyloid PET imaging can play a role in discriminating between the various etiologic forms of neurodegeneration, particularly in the setting of mixed pathologies. Amyloid co-pathology has been reported with other neurodegenerative diseases such as dementia of Lewy bodies or associated with other pathologies that can contribute to patient symptoms, such as vascular dementia. The presence of multiple comorbid neuropathologies can erroneously lead to the diagnosis of and treatment of AD when the cause of the symptoms is related to mixed dementia, limiting therapeutic efficacy in this group. More importantly, β-amyloid imaging has a clinical impact in 60–63% of cases, changing the suspected etiology from AD to non-AD in 25% of the patients. Several ongoing trials are evaluating the role of amyloid deposition in AD pathophysiology and assessing anti-amyloid therapy efficacy.