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radiology of Alzheimer's disease

Epidemiology: - women with comparable clinical & cognitive measures with mwn have - higher beta-amyloid deposition - lower FDG glucose metabolism - lower MRI gray & white matter volumes compared to the male group - menopause accentuates these differences between men & women - hormone replacement therapy mitigates these differences Radiology: 1) neuroimaging: MRI preferable to CT - the American Academy of Neurology affirms neuroimaging is appropriate in the routine initial evaluation of patients with dementia [24] 2) computed tomography (CT) a) brain tumor b) subdural hematoma c) stroke d) normal pressure hydrocephalus 3) magnetic resonance imaging (MRI) a) more sensitive than CT to small vessel disease b) functional MRI may be able to detect changes in predementia phase (see FAD3) c) cortical atrophy, parietal, temporal & frontal cortex d) enlargement of lateral ventricles e) thinning of cortical regions spanning the temporal, parietal, & frontal heteromodal association cortices [4,6] f) diminished hippocampal volume adjusted for intracranial volume is a marker for Alzheimer's pathology [7] - CSF Abeta [1-42] is the earliest marker [7] g) functional magnetic resonance imaging (fMRI) - impaired grid cell activity (entorhinal cortex) with elevated hippocampal activity identified by fMRI in people age >= 30 years heterozygous for apoE4 [8] - apoE4 heterozygotes demonstrated deficits in test of spatial navigation [8] 4) positron-emission tomography (PET) [1,2] a) sensitivity > specificity b) may show parietal-temporal hypometabolism, a non-specific finding as also occurs in frontotemporal dementia [5] c) 11-C Pittsburgh compound B shows fibrillar amyloid - amyloid deposition by Pittsburgh compound B (PiB) is earliest sign of AD [23] - PiB Centiloid values > 40 threshold for tau formation [23] - increasing PiB Centiloid values are associated with a decline in processing speed & memory retrieval in cognitively normal elderly [23] d) imaging for amyloid & tau may be able to identify patients with mild cognitive impairment e) binding of 18F T807 in the brain during PET scanning correlates with Braak staging for Alzheimer's disease - 18F T807 binding is minimal or localized to the medial temporal lobe in the cognitively normal elderly - elevated neocortical 18F T807 binding, particularly in the inferior temporal gyrus is associated with cognitive impairment [9] see (18F T807) f) four patterns of 18F FTP tau PET [19] - limbic-predominant pattern - medial temporal lobe-sparing pattern - posterior temporal pattern resembling atypical clinical variants of AD - lateral temporal pattern resembling atypical clinical variants of AD f) 18F FTP tau PET predicts AD pathology [16] - predicts location of neurodegeneration 1 year in advance [16] - 18F FTP tau PET predicts cognitive decline in FAD3 due to PSEN1 E280A mutation [11] - [18F] Flortaucipir PET in vivo in patient with PSEN1 T116N mutation predicts post-mortem tau pathology [15] g) tau PET predicts cognitive change better than amyloid PET & MRI [20] - tau PET may support prognosis in preclinical & prodromal stages of AD - tau PET outperforms amyloid PET or brain MRI in predicting conversion of mild cognitive impairment to dementia [26] - increased 18F flortaucipir (FTP) tau PET levels associated with declines in all cognitive domains - amyloid PiB Centiloid values assume less importance in predicting cognitive decline as tau levels increase [23] h) heterogeneous cortical tau PET patterns found inpatients with preclinical AD [22] i) amyloid PET using [18F]-florbetapir - high sensitivity (0.91) & specificity (0.92) for distinguishing AD from non-AD [17] - not cost-effective [10] - both amyloid-positive & amyloid-negative results associated with changes in diagnosis & treatment [12] - age of symptom onset in sporadic AD correlated with the age an individual reaches a tipping point in amyloid accumulation [21] j) 11C-UCB-J-PET imaging (SV2A) may provide a direct measure of synaptic density [13] 5) microtubule-associated protein tau aggregation measured with 18F FTP tau PET & neurodegeneration measured with MRI are closely associated with cognitive decline in Alzheimer's disease [25] 6) SPECT not able to distinguish AD from FTD better than neuropsychiatric evaluation [3] 7) do not order dopamine transporter SPECT or PET [14]

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Alzheimer's disease (AD)

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radiology

References

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