Medicine (Austin & Northern Health) - Research Publications
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ItemTau imaging with [18F]THK-5351 in progressive supranuclear palsy(WILEY-BLACKWELL, 2017-01)BACKGROUND AND PURPOSE: Visualization of pathogenic protein aggregates is crucial to elucidate pathomechanisms and to make an accurate diagnosis in many neurodegenerative conditions. Aggregates of the microtubule-binding protein, tau, are one of the most important pathogenic molecules in neurodegenerative disorders. Progressive supranuclear palsy (PSP) is characterized by the deposition of tau proteins in some specific area such as the basal ganglia and brainstem. We tried to detect tau lesions in the brains of living patients with PSP with a novel positron emission tomography (PET) tracer, [18 F]THK-5351, which we have recently developed. METHODS: Paraffin-embedded brain sections of the patients with PSP were used for autoradiography with [3 H]THK-5351 and immunohistochemistry. Nine healthy controls, 13 patients with Alzheimer's disease and three patients with PSP participated in this PET study with [18 F]THK-5351. To detect amyloid-β deposition, PET imaging with Pittsburgh compound B was also performed. RESULTS: Autoradiography in the brain sections of patients with PSP demonstrated [3 H]THK-5351 binding to tau deposits with a high selectivity. Although patients with PSP exhibited no remarkable [18 F]THK-5351 retention in the temporal cortex, significantly higher tracer retention was observed in the globus pallidus and midbrain. In contrast, amyloid imaging with Pittsburgh compound B showed no remarkable accumulation in the cerebral cortex of PSP. CONCLUSIONS: We conclude that [18 F]THK-5351 PET can potentially be used to detect the regional brain distribution of tau lesions in PSP, thereby facilitating the differential diagnosis of neurodegenerative disorders associated with tau protein.
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ItemCerebrovascular disease, Alzheimer's disease biomarkers and longitudinal cognitive decline(WILEY-BLACKWELL, 2016-06)
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ItemPrevalence of amyloid-β pathology in distinct variants of primary progressive aphasia(WILEY, 2018-11)OBJECTIVE: To estimate the prevalence of amyloid positivity, defined by positron emission tomography (PET)/cerebrospinal fluid (CSF) biomarkers and/or neuropathological examination, in primary progressive aphasia (PPA) variants. METHODS: We conducted a meta-analysis with individual participant data from 1,251 patients diagnosed with PPA (including logopenic [lvPPA, n = 443], nonfluent [nfvPPA, n = 333], semantic [svPPA, n = 401], and mixed/unclassifiable [n = 74] variants of PPA) from 36 centers, with a measure of amyloid-β pathology (CSF [n = 600], PET [n = 366], and/or autopsy [n = 378]) available. The estimated prevalence of amyloid positivity according to PPA variant, age, and apolipoprotein E (ApoE) ε4 status was determined using generalized estimating equation models. RESULTS: Amyloid-β positivity was more prevalent in lvPPA (86%) than in nfvPPA (20%) or svPPA (16%; p < 0.001). Prevalence of amyloid-β positivity increased with age in nfvPPA (from 10% at age 50 years to 27% at age 80 years, p < 0.01) and svPPA (from 6% at age 50 years to 32% at age 80 years, p < 0.001), but not in lvPPA (p = 0.94). Across PPA variants, ApoE ε4 carriers were more often amyloid-β positive (58.0%) than noncarriers (35.0%, p < 0.001). Autopsy data revealed Alzheimer disease pathology as the most common pathologic diagnosis in lvPPA (76%), frontotemporal lobar degeneration-TDP-43 in svPPA (80%), and frontotemporal lobar degeneration-TDP-43/tau in nfvPPA (64%). INTERPRETATION: This study shows that the current PPA classification system helps to predict underlying pathology across different cohorts and clinical settings, and suggests that age and ApoE genotype should be considered when interpreting amyloid-β biomarkers in PPA patients. Ann Neurol 2018;84:737-748.
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ItemSensitivity of composite scores to amyloid burden in preclinical Alzheimer's disease: Introducing the Z-scores of Attention, Verbal fluency, and Episodic memory for Nondemented older adults composite score.(Wiley, 2016)INTRODUCTION: Cognitive composite scores developed for preclinical Alzheimer's disease (AD) often consist of multiple cognitive domains as they may provide greater sensitivity to detect β-amyloid (Aβ)-related cognitive decline than episodic memory (EM) composite scores alone. However, this has never been empirically tested. We compared the rate of cognitive decline associated with high Aβ (Aβ+) and very high Aβ (Aβ++) in cognitively normal (CN) older adults on three multidomain cognitive composite scores and one single-domain (EM) composite score. METHODS: CN older adults (n = 423) underwent Aβ neuroimaging and completed neuropsychological assessments at baseline, and at 18-, 36-, 54-, and 72-month follow-ups. Four cognitive composite scores were computed: the ADCS-PACC (ADCS-Preclinical Alzheimer Cognitive Composite), ADCS-PACC without the inclusion of the mini-mental state examination (MMSE), an EM composite, and the Z-scores of Attention, Verbal fluency, and Episodic memory for Nondemented older adults (ZAVEN) composite. RESULTS: Compared with Aβ+ CN older adults, Aβ++ CN older adults showed faster rates of decline across all cognitive composites, with the largest decline observed for ZAVEN composite (d = 1.07). Similarly, compared with Aβ- CN older adults, Aβ+ CN older adults also showed faster rates of cognitive decline, but only for the ADCS-PACC no MMSE (d = 0.43), EM (d = 0.53), and ZAVEN (d = 0.50) composites. DISCUSSION: Aβ-related cognitive decline is best detected using validated neuropsychological instruments. Removal of the MMSE from the ADCS-PACC and replacing it with a test of executive function (verbal fluency; i.e., the ZAVEN) rendered this composite more sensitive even in detecting Aβ-related cognitive decline between Aβ+ and Aβ++ CN older adults.
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ItemQuantitative Amyloid Imaging in Autosomal Dominant Alzheimer's Disease: Results from the DIAN Study Group(PUBLIC LIBRARY SCIENCE, 2016-03-24)Amyloid imaging plays an important role in the research and diagnosis of dementing disorders. Substantial variation in quantitative methods to measure brain amyloid burden exists in the field. The aim of this work is to investigate the impact of methodological variations to the quantification of amyloid burden using data from the Dominantly Inherited Alzheimer's Network (DIAN), an autosomal dominant Alzheimer's disease population. Cross-sectional and longitudinal [11C]-Pittsburgh Compound B (PiB) PET imaging data from the DIAN study were analyzed. Four candidate reference regions were investigated for estimation of brain amyloid burden. A regional spread function based technique was also investigated for the correction of partial volume effects. Cerebellar cortex, brain-stem, and white matter regions all had stable tracer retention during the course of disease. Partial volume correction consistently improves sensitivity to group differences and longitudinal changes over time. White matter referencing improved statistical power in the detecting longitudinal changes in relative tracer retention; however, the reason for this improvement is unclear and requires further investigation. Full dynamic acquisition and kinetic modeling improved statistical power although it may add cost and time. Several technical variations to amyloid burden quantification were examined in this study. Partial volume correction emerged as the strategy that most consistently improved statistical power for the detection of both longitudinal changes and across-group differences. For the autosomal dominant Alzheimer's disease population with PiB imaging, utilizing brainstem as a reference region with partial volume correction may be optimal for current interventional trials. Further investigation of technical issues in quantitative amyloid imaging in different study populations using different amyloid imaging tracers is warranted.
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ItemAssessment of amyloid β in pathologically confirmed frontotemporal dementia syndromes.(Wiley, 2017)INTRODUCTION: The diagnostic utility of in vivo amyloid β (Aβ) imaging to aid in the clinical distinction between frontotemporal dementia (FTD) and Alzheimer's disease remains unclear without data on the prevalence and severity of Aβ in pathologically confirmed FTD syndromes. METHODS: Aβ was assessed in 98 autopsy-confirmed FTD and 36 control cases, and the pathological accuracy of 11C-Pittsburgh compound B (PiB)-positron emission tomography imaging was assessed in a subset of FTD cases (n = 15). RESULTS: Aβ was identified in a similar proportion of FTD syndromes and age-matched controls and increases with age. Alzheimer's disease pathology was identified in all cases with high PiB retention and in one case with low PiB retention. We further demonstrate a strong regional correlation between volume fraction of histological Aβ with PiB standard uptake value ratio scaled to the white matter. DISCUSSION: The present study provides a pathologic reference to assist in the interpretation of in vivo assessments in FTD syndromes.
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ItemA 'Disease Severity Index' to identify individuals with Subjective Memory Decline who will progress to mild cognitive impairment or dementia(NATURE PORTFOLIO, 2017-03-13)Subjective memory decline (SMD) is a heterogeneous condition. While SMD might be the earliest sign of Alzheimer's disease (AD), it also occurs in aging and various neurological, medical, and psychiatric conditions. Identifying those with higher risk to develop dementia is thus a major challenge. We tested a novel disease severity index generated by multivariate data analysis with numerous structural MRI measures as input. The index was used to identify SMD individuals with high risk of progression to mild cognitive impairment (MCI) or AD. A total of 69 healthy controls, 86 SMD, 45 MCI, and 38 AD patients were included. Subjects were followed up for 7.5 years. Clinical, cognitive, PET amyloid imaging and APOE ε4 data were used as outcome variables. The results showed that SMD evidenced cognitive performance intermediate between healthy controls and MCI. The disease severity index identified eleven (13%) SMD individuals with an AD-like pattern of brain atrophy. These individuals showed lower cognitive performance, increased CDR-SOB, higher amyloid burden and worse clinical progression (6.2 times higher likelihood to develop MCI, dementia or die than healthy controls). The current disease severity index may have relevance for clinical practice, as well as for selecting appropriate individuals for clinical trials.