Objective:To compare the diagnostic performance of PET with the amyloid ligand Pittsburgh compound B (PiB-PET) to fluorodeoxyglucose (FDG-PET) in discriminating between Alzheimer disease (AD) and frontotemporal lobar degeneration (FTLD). Methods:Patients meeting clinical criteria for AD (n ϭ 62) and FTLD (n ϭ 45) underwent PiB and FDG-PET. PiB scans were classified as positive or negative by 2 visual raters blinded to clinical diagnosis, and using a quantitative threshold derived from controls (n ϭ 25). FDG scans were visually rated as consistent with AD or FTLD, and quantitatively classified based on the region of lowest metabolism relative to controls.Results: PiB visual reads had a higher sensitivity for AD (89.5% average between raters) than FDG visual reads (77.5%) with similar specificity (PiB 83%, FDG 84%). When scans were classified quantitatively, PiB had higher sensitivity (89% vs 73%) while FDG had higher specificity (83% vs 98%). On receiver operating characteristic analysis, areas under the curve for PiB (0.888) and FDG (0.910) were similar. Interrater agreement was higher for PiB ( ϭ 0.96) than FDG ( ϭ 0.72), as was agreement between visual and quantitative classification (PiB ϭ 0.88-0.92; FDG ϭ 0.64-0.68). In patients with known histopathology, overall classification accuracy (2 visual and 1 quantitative classification per patient) was 97% for PiB (n ϭ 12 patients) and 87% for FDG (n ϭ 10). Conclusions:PiB and FDG showed similar accuracy in discriminating AD and FTLD. PiB was more sensitive when interpreted qualitatively or quantitatively. FDG was more specific, but only when scans were classified quantitatively. PiB slightly outperformed FDG in patients with known histopathology. Neurology Differentiating Alzheimer disease (AD) and frontotemporal lobar degeneration (FTLD) has implications for prognosis and symptomatic treatment, 1,2 and is critical for the efforts to develop disease-specific therapies. Making an accurate diagnosis during life can be challenging given overlapping clinical features.3,4 MRI or fluorodeoxyglucose PET (FDG-PET) can improve diagnostic accuracy by demonstrating distinct topographic patterns of atrophy or hypometabolism (temporoparietal predominant in AD; frontal and anterior temporal involvement in FTLD), 5,6 but anatomic overlap between the diseases is increasingly apparent. 5,7 Consequently, many patients with pathologically confirmed FTLD are diagnosed with AD during

Patients with early age-of-onset Alzheimer's disease show more rapid progression, more generalized cognitive deficits and greater cortical atrophy and hypometabolism compared to late-onset patients at a similar disease stage. The biological mechanisms that underlie these differences are not well understood. The purpose of this study was to examine in vivo whether metabolic differences between early-onset and late-onset Alzheimer's disease are associated with differences in the distribution and burden of fibrillar amyloid-beta. Patients meeting criteria for probable Alzheimer's disease (National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer's; Disease and Related Disorders Association criteria) were divided based on estimated age at first symptom (less than or greater than 65 years) into early-onset (n = 21, mean age-at-onset 55.2 +/- 5.9 years) and late-onset (n = 18, 72.0 +/- 4.7 years) groups matched for disease duration and severity. Patients underwent positron emission tomography with the amyloid-beta-ligand [(11)C]-labelled Pittsburgh compound-B and the glucose analogue [(18)F]-labelled fluorodeoxyglucose. A group of cognitively normal controls (n = 30, mean age 73.7 +/- 6.4) was studied for comparison. [(11)C]-labelled Pittsburgh compound-B images were analysed using Logan graphical analysis (cerebellar reference) and [(18)F]-labelled fluorodeoxyglucose images were normalized to mean activity in the pons. Group differences in tracer uptake were assessed on a voxel-wise basis using statistical parametric mapping, and by comparing mean values in regions of interest. To account for brain atrophy, analyses were repeated after applying partial volume correction to positron emission tomography data. Compared to normal controls, both early-onset and late-onset Alzheimer's disease patient groups showed increased [(11)C]-labelled Pittsburgh compound-B uptake throughout frontal, parietal and lateral temporal cortices and striatum on voxel-wise and region of interest comparisons (P < 0.05). However, there were no significant differences in regional or global [(11)C]-labelled Pittsburgh compound-B binding between early-onset and late-onset patients. In contrast, early-onset patients showed significantly lower glucose metabolism than late-onset patients in precuneus/posterior cingulate, lateral temporo-parietal and occipital corticies (voxel-wise and region of interest comparisons, P < 0.05). Similar results were found for [(11)C]-labelled Pittsburgh compound-B and [(18)F]-labelled fluorodeoxyglucose using atrophy-corrected data. Age-at-onset correlated positively with glucose metabolism in precuneus, lateral parietal and occipital regions of interest (controlling for age, education and Mini Mental State Exam, P < 0.05), while no correlations were found between age-at-onset and [(11)C]-labelled Pittsburgh compound-B binding. In summary, a comparable burden of fibrillar amyloid-beta was associated with greater posterior cortical hypometabolism in early-onset Alzheimer's disease. Our d...

No abstract

We investigated relationships between glucose metabolism, amyloid load and measures of cognitive and functional impairment in Alzheimer’s disease (AD). Patients meeting criteria for probable AD underwent [11C]PIB and [18F]FDG PET imaging and were assessed on a set of clinical measures. PIB Distribution volume ratios and FDG scans were spatially normalized and average PIB counts from regions-of-interest (ROI) were used to compute a measure of global PIB uptake. Separate voxel-wise regressions explored local and global relationships between metabolism, amyloid burden and clinical measures. Regressions reflected cognitive domains assessed by individual measures, with visuospatial tests associated with more posterior metabolism, and language tests associated with metabolism in the left hemisphere. Correlating regional FDG uptake with these measures confirmed these findings. In contrast, no correlations were found between either voxel-wise or regional PIB uptake and any of the clinical measures. Finally, there were no associations between regional PIB and FDG uptake. We conclude that regional and global amyloid burden does not correlate with clinical status or glucose metabolism in AD.

Background Previous studies have demonstrated alterations in the peripheral cholinergic system in Alzheimer’s disease (AD), though results have been inconsistent and not linked to in vivo biomarkers of pathology. We examined the relationship between amyloid-beta (Aβ) plaques and plasma cholinesterase activity in a heterogeneous dementia population. Methods 29 participants with clinical AD and 35 with non-AD diagnoses underwent positron emission tomography (PET) with the amyloid ligand [11C] PIB and plasma measurements of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) activity. Multi-linear regression was used to evaluate the relationship between AChE or BChE activity and PIB binding (adjusted for age, sex, apolipoprotein E4 and vascular risk), applying voxel-wise and region of interest (ROI) approaches. AChE activity was further adjusted for cholinesterase inhibitor (ChE-I) use. Global amyloid load was measured using a PIB Index, representing mean tracer binding in frontal, parietal, lateral temporal and cingulate cortex. Results AChE activity was correlated with PIB Index (β=0.39, p<0.001) and with regional PIB binding in frontal, temporal, parietal and occipital lobes, precuneus and posterior cingulate on both voxel-wise (p<0.001 uncorrected) and ROI (β=0.26-0.41, p<0.005) analysis. Correlations remained significant after covarying clinical diagnosis (β=0.42, p=0.001), and among participants naive to ChE-I (β=0.51, p=0.005). No correlation was found between BChE activity and PIB. Among AD participants, disease severity was not correlated with AChE, BChE or PIB Index. Conclusion AChE activity in plasma is correlated with brain Aβ load. Activation of the ‘anti-inflammatory cholinergic pathway’ may provide the link between Aβ plaques and peripheral cholinergic measures.

Background Previous studies have demonstrated alterations in the peripheral cholinergic system in Alzheimer’s disease (AD), though results have been inconsistent and not linked to in vivo biomarkers of pathology. We examined the relationship between amyloid-beta (Aβ) plaques and plasma cholinesterase activity in a heterogeneous dementia population. Methods 29 participants with clinical AD and 35 with non-AD diagnoses underwent positron emission tomography (PET) with the amyloid ligand [11C] PIB and plasma measurements of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) activity. Multi-linear regression was used to evaluate the relationship between AChE or BChE activity and PIB binding (adjusted for age, sex, apolipoprotein E4 and vascular risk), applying voxel-wise and region of interest (ROI) approaches. AChE activity was further adjusted for cholinesterase inhibitor (ChE-I) use. Global amyloid load was measured using a PIB Index, representing mean tracer binding in frontal, parietal, lateral temporal and cingulate cortex. Results AChE activity was correlated with PIB Index (β=0.39, p<0.001) and with regional PIB binding in frontal, temporal, parietal and occipital lobes, precuneus and posterior cingulate on both voxel-wise (p<0.001 uncorrected) and ROI (β=0.26-0.41, p<0.005) analysis. Correlations remained significant after covarying clinical diagnosis (β=0.42, p=0.001), and among participants naive to ChE-I (β=0.51, p=0.005). No correlation was found between BChE activity and PIB. Among AD participants, disease severity was not correlated with AChE, BChE or PIB Index. Conclusion AChE activity in plasma is correlated with brain Aβ load. Activation of the ‘anti-inflammatory cholinergic pathway’ may provide the link between Aβ plaques and peripheral cholinergic measures.

No abstract

No abstract