[18F]FDG-PET in patients with Alzheimer's disease: marker of disease spread

The Neuropsychological Correlates of Brain Perfusion and Gray Matter Volume in Alzheimer's Disease

BACKGROUND

Neuropsychological tests, structural neuroimaging, and functional neuroimaging are employed as diagnostic and monitoring biomarkers of patients with Alzheimer's disease (AD)Objective:We aimed to elucidate the similarities and differences in neuropsychological tests and neuroimaging with the use of the Mini-Mental State Examination (MMSE), Alzheimer's Disease Assessment Scale cognitive subscale (ADAS-cog), structural magnetic resonance image (MRI), and perfusion single photon emission computed tomography (SPECT), and parametric image analyses to understand its role in AD.

METHODS

Clinically-diagnosed AD patients (n = 155) were scanned with three-dimensional T1-weighted MRI and N-isopropyl-p-[123I] iodoamphetamine SPECT. Statistical parametric mapping 12 was used for preprocessing images, statistical analyses, and voxel-based morphometry for gray matter volume analyses. Group comparison (AD versus healthy controls), multiple regression analyses with MMSE, ADAS-cog total score, and ADAS-cog subscores as variables, were performed.

RESULTS

The AD group showed bilateral hippocampal volume reduction and hypoperfusion in the bilateral temporo-parietal lobe and posterior midline structures. Worse MMSE and ADAS-cog total score were associated with bilateral temporo-parietal volume loss and hypoperfusion. MMSE, but not ADAS-cog, was associated with the posterior midline structures. The ADAS-cog subscores were associated with the temporal volume, while perfusion analyses were linked to the left temporo-parietal region with the language function and right analogous region with the constructional praxis subscore.

CONCLUSION

MMSE and ADAS-cog are associated with temporo-parietal regions, both in volume and perfusion. The MMSE score is associated with posterior midline structures and linked to an abnormal diagnostic AD pattern. Perfusion image analyses better represents the cognitive function in AD patients.

Study of the Influence of Age in 18F-FDG PET Images Using a Data-Driven Approach and Its Evaluation in Alzheimer's Disease

Objectives

¹⁸F-FDG PET scan is one of the most frequently used neural imaging scans. However, the influence of age has proven to be the greatest interfering factor for many clinical dementia diagnoses when analyzing ¹⁸F-FDG PET images, since radiologists encounter difficulties when deciding whether the abnormalities in specific regions correlate with normal aging, disease, or both. In the present paper, the authors aimed to define specific brain regions and determine an age-correction mathematical model.

Methods

A data-driven approach was used based on 255 healthy subjects.

Results

The inferior frontal gyrus, the left medial part and the left medial orbital part of superior frontal gyrus, the right insula, the left anterior cingulate, the left median cingulate, and paracingulate gyri, and bilateral superior temporal gyri were found to have a strong negative correlation with age. For evaluation, an age-correction model was applied to 262 healthy subjects and 50 AD subjects selected from the ADNI database, and partial correlations between SUVR mean and three clinical results were carried out before and after age correction.

Conclusion

All correlation coefficients were significantly improved after the age correction. The proposed model was effective in the age correction of both healthy and AD subjects.

Difference in imaging biomarkers of neurodegeneration between early and late-onset amnestic Alzheimer's disease

Neuroimaging biomarkers differ between patients with early-onset Alzheimer's disease (EOAD) and late-onset Alzheimer's disease (LOAD). Whether these changes reflect cognitive heterogeneity or differences in disease severity is still unknown. This study aimed at investigating changes in neuroimaging biomarkers, according to the age of onset of the disease, in mild amnestic Alzheimer's disease patients with positive amyloid biomarkers in cerebrospinal fluid. Both patient groups were impaired on tasks assessing verbal and visual recognition memory. EOAD patients showed greater executive and linguistic deficits, while LOAD patients showed greater semantic memory impairment. In EOAD and LOAD, hypometabolism involved the bilateral temporoparietal junction and the posterior cingulate cortex. In EOAD, atrophy was widespread, including frontotemporoparietal areas, whereas it was limited to temporal regions in LOAD. Atrophic volumes were greater in EOAD than in LOAD. Hypometabolic volumes were similar in the 2 groups. Greater extent of atrophy in EOAD, despite similar extent of hypometabolism, could reflect different underlying pathophysiological processes, different glucose-based compensatory mechanisms or distinct level of premorbid atrophic lesions.

Data-driven identification of intensity normalization region based on longitudinal coherency of 18F-FDG metabolism in the healthy brain

OBJECTIVES

In brain ¹⁸F-FDG PET data intensity normalization is usually applied to control for unwanted factors confounding brain metabolism. However, it can be difficult to determine a proper intensity normalization region as a reference for the identification of abnormal metabolism in diseased brains. In neurodegenerative disorders, differentiating disease-related changes in brain metabolism from age-associated natural changes remains challenging. This study proposes a new data-driven method to identify proper intensity normalization regions in order to improve separation of age-associated natural changes from disease related changes in brain metabolism.

METHODS

127 female and 128 male healthy subjects (age: 20 to 79) with brain¹⁸F-FDG PET/CT in the course of a whole body cancer screening were included. Brain PET images were processed using SPM8 and were parcellated into 116 anatomical regions according to the AAL template. It is assumed that normal brain ¹⁸F-FDG metabolism has longitudinal coherency and this coherency leads to better model fitting. The coefficient of determination R² was proposed as the coherence coefficient, and the total coherence coefficient (overall fitting quality) was employed as an index to assess proper intensity normalization strategies on single subjects and age-cohort averaged data. Age-associated longitudinal changes of normal subjects were derived using the identified intensity normalization method correspondingly. In addition, 15 subjects with clinically diagnosed Parkinson's disease were assessed to evaluate the clinical potential of the proposed new method.

RESULTS

Intensity normalizations by paracentral lobule and cerebellar tonsil, both regions derived from the new data-driven coherency method, showed significantly better coherence coefficients than other intensity normalization regions, and especially better than the most widely used global mean normalization. Intensity normalization by paracentral lobule was the most consistent method within both analysis strategies (subject-based and age-cohort averaging). In addition, the proposed new intensity normalization method using the paracentral lobule generates significantly higher differentiation from the age-associated changes than other intensity normalization methods.

CONCLUSION

Proper intensity normalization can enhance the longitudinal coherency of normal brain glucose metabolism. The paracentral lobule followed by the cerebellar tonsil are shown to be the two most stable intensity normalization regions concerning age-dependent brain metabolism. This may provide the potential to better differentiate disease-related changes from age-related changes in brain metabolism, which is of relevance in the diagnosis of neurodegenerative disorders.

Drug-induced cerebral glucose metabolism resembling Alzheimer's Disease: a case study

BACKGROUND

With aging of society the absolute number and the proportion of patients with cognitive deficits increase. Multiple disorders and diseases can foster cognitive impairment, e.g., Alzheimer's disease (AD), depressive disorder, or polypharmacy.

CASE PRESENTATION

A 74 year old man presented to the Old Age Psychiatry Service with cognitive deficits while being treated for recurrent depressive episodes and essential tremor with Venlafaxine, Lithium, and Primidone. Neuropsychological testing revealed a medio-temporal pattern of deficits with pronounced impairment of episodic memory, particularly delayed recall. Likewise, cognitive flexibility, semantic fluency, and attention were impaired. Positron emission tomography (PET) with fluorodeoxyglucose was performed and revealed a pattern of glucose utilization deficit resembling AD. On cessation of treatment with Lithium and Primidone, cognitive performance improved, particularly episodic memory performance and cognitive flexibility. Likewise, glucose metabolism normalized. Despite normalization of both, clinical symptoms and glucose utilization, the patient remained worried about possible underlying Alzheimer's disease pathology. To rule this out, an amyloid-PET was performed. No cortical amyloid was observed.

CONCLUSION

Pharmacological treatment of older subjects may mimic glucose metabolism and clinical symptoms of Alzheimer's disease. In the present case both, imaging and clinical findings, reversed to normal on change of treatment. Amyloid PET is a helpful tool to additionally rule out underlying Alzheimer's disease in situations of clinical doubt even if clinical or other imaging findings are suggestive of Alzheimer's disease.

Additive scales in degenerative disease--calculation of effect sizes and clinical judgment

Background

The therapeutic efficacy of an intervention is often assessed in clinical trials by scales measuring multiple diverse activities that are added to produce a cumulative global score. Medical communities and health care systems subsequently use these data to calculate pooled effect sizes to compare treatments. This is done because major doubt has been cast over the clinical relevance of statistically significant findings relying on p values with the potential to report chance findings. Hence in an aim to overcome this pooling the results of clinical studies into a meta-analyses with a statistical calculus has been assumed to be a more definitive way of deciding of efficacy.

Methods

We simulate the therapeutic effects as measured with additive scales in patient cohorts with different disease severity and assess the limitations of an effect size calculation of additive scales which are proven mathematically.

Results

We demonstrate that the major problem, which cannot be overcome by current numerical methods, is the complex nature and neurobiological foundation of clinical psychiatric endpoints in particular and additive scales in general. This is particularly relevant for endpoints used in dementia research. 'Cognition' is composed of functions such as memory, attention, orientation and many more. These individual functions decline in varied and non-linear ways. Here we demonstrate that with progressive diseases cumulative values from multidimensional scales are subject to distortion by the limitations of the additive scale. The non-linearity of the decline of function impedes the calculation of effect sizes based on cumulative values from these multidimensional scales.

Conclusions

Statistical analysis needs to be guided by boundaries of the biological condition. Alternatively, we suggest a different approach avoiding the error imposed by over-analysis of cumulative global scores from additive scales.

The future of Alzheimer's disease: the next 10 years

Alzheimer's disease (AD) is a fast growing world-wide epidemic. AD is a genetically complex, slowly progressive, and irreversible neurodegenerative disease of the brain. During decades of asymptomatic progression multiple interactive systems, pathways and molecular mechanisms (e.g. protein processing, aberrant signaling, inflammation and immune system, lipid transport, endocytosis, apoptosis, oxidative damage and response to stress, tau pathology, neuron and synapse loss, energy metabolism), contribute to the development of the early clinical prodromal stage with episodic memory deficits and to further decline and loss of general cognitive functioning during the final syndromal dementia stage. The non-mendelian genetically complex "sporadic" AD type is the most common form of dementia affecting people usually over the age of 65. Despite considerable progress of AD research in recent years and evolving paradigm shifts in both pathophysiological concepts as well as in diagnostic criteria fundamental challenges have not yet been resolved. The strong age-related incidence, the recent failure and complete lack of disease-modifying or preventive therapy that may delay onset or substantially affect the pathophysiology of AD, result in an enormous burden posed both on individuals, their families and care givers, and the societies at large, and these call for urgent concerted worldwide measures. Based on the meeting of the German Task Force on Alzheimer's Disease (GTF-AD) in Paris on July 19th 2011, the present position paper provides an overview on the current state and future developments in epidemiology, pathophysiology, disease conceptualization, diagnostic criteria and their use in research and clinical practice, as well as preventive and symptomatic therapeutic approaches. Particular emphasis is placed on a discussion of the different approaches to diagnostics and therapy taken by preventive/public health medicine, methodologically advanced academic research propagating the use of sophisticated biomarkers, and everyday clinical practice focusing on patient-centered care. During the next 10 years, major advances both in early detection as well as in therapy and comprehensive AD care seem mandatory. These still unmet needs call for ever more concerted and focused efforts in research across the world to combat the erupting and as yet uncontrolled epidemic of AD.

Relationships between hippocampal microstructure, metabolism, and function in early Alzheimer's disease

Abnormal microstructural integrity and glucose metabolism of the hippocampus are common in subjects with Alzheimer's disease (AD) that typically manifest as episodic memory impairment. The above-tissue alterations can be captured in vivo using diffusion tensor imaging (DTI) and positron emission tomography with [18F]fluorodeoxyglucose (FDG-PET). Here, we explored relationships between the above neuroimaging and cognitive markers of early AD-specific hippocampal damage. Twenty patients with early AD (MMSE 25.7 ± 1.7) were studied using DTI and FDG-PET. Episodic memory performance was assessed using the free delayed verbal recall task (DVR). In the between-modality correlation analysis, FDG uptake was strongly associated with diffusivity in the left anterior hippocampus only (r = -0.81, p < 0.05 Bonferroni's corrected for multiple tests). Performance on DVR significantly correlated with left anterior (r = -0.80, p < 0.05) and left mean (r = -0.72, p < 0.05) hippocampal diffusivity, while the correlation with left anterior FDG uptake did not reach statistical significance (r = 0.52, n.s.). DTI-derived diffusivity of the anterior hippocampus might be a sensitive early marker of hippocampal dysfunction as reflected at the synaptic and cognitive levels. This neurobiological distinction of the anterior hippocampus might be related to the disruption of the perforant pathway that is known to occur early in the course of AD.

Correlation between cognitive deficits and glucose hypometabolism in mild cognitive impairment

BACKGROUND

In patients with mild cognitive impairment (MCI), poor performances on delayed recall and executive function are risk factors of progression to dementia. The aim of the present study was to clarify neural correlates of these neuropsychological deficits.

METHODS

Thirty patients with amnestic MCI and 15 control subjects underwent neuropsychological tests including three-word delayed recall, visual delayed recall of Rey complex figure (RCF), and two-relational reasoning of Raven's colored progressive matrices (RCPM) with a (18)F-fluorodeoxyglucose (FDG)-position emission tomography (PET) measurement of resting state. We evaluated a relationship between performance of neuropsychological tests and regional cerebral glucose metabolism using voxel-based analysis.

RESULTS

Poor performance in three-word delayed recall was related to glucose hypometabolism in the right medial temporal, right prefrontal, and left superior parietal cortices. The deficit in visual delayed recall of RCF correlated positively with hypometabolism in the bilateral posterior cingulate. The impairment in two-relational reasoning was associated with hypometabolism in the right prefrontal cortex.

CONCLUSIONS

The present findings suggest that hypometabolism in the right medial temporal cortex, right prefrontal cortex, left superior parietal cortex, and bilateral posterior cingulate reflects impairments in delayed recall while hypometabolism in the right prefrontal cortex mirrors deficits in executive function in MCI.

Cognitive estimation in aged patients with major depressive disorder

In everyday life, we often estimate rather than know. It was the goal of this study to assess the effect of depressed mood on cognitive estimation in old age. Cognitive estimation was performed in 44 subjects with major depressive disorder (MDD; DSM-IV) and 48 age-matched healthy subjects (HS). Severity of depressive symptoms was rated with the Montgomery-Asberg Depression Rating Scale (MADRS, mean=18.6+/-S.D. 4.85). Estimation tasks comprised the dimensions length (coin diameter), weight (pile of paper), quantity (number of marbles in a glass jar), and time (estimation of time it takes for a marble to roll down a marble track both before and after having observed it). Other than the procedure followed in previous tests on cognitive estimation, the tasks were performed by observing objects rather than pictures thereof. MDD patients overestimated time (before and after observation) and underestimated quantity. Cognitive estimation was not correlated to measures of frontal functioning or semantic knowledge. We conclude that MDD patients in old age are impaired to some extent in cognitive estimation and in the ability to correct themselves, deficits that are likely to affect the performance of everyday activities.

Choice of reference area in studies of Alzheimer's disease using positron emission tomography with fluorodeoxyglucose-F18

At present, there is still no consensus on the choice of the reference area in positron emission tomography (PET) studies of Alzheimer's disease (AD). In this study, PET scans with fluorodeoxyglucose-F18 were carried out in the following groups of subjects: 47 patients with probable AD, 8 patients with mild cognitive impairment, and 15 age-similar healthy subjects. Scans normalized to the cerebral global mean (CGM), cerebellum (CBL), and the primary sensorimotor cortex (SMC). We evaluated the effect of the different count normalization procedures on the accuracy of (18)F-FDG PET to detect AD-specific metabolic abnormalities (voxel-based group comparison) and to differentiate between patients and healthy subjects (ROI-based discriminant analysis) with regard to the degree of clinical deterioration. Metabolic reductions in groups of very mildly, mildly and moderate-to-severely affected patients appeared, respectively, 2.2, 2.6, and 2.7 times greater in spatial extent when tracer uptake was normalized to SMC rather than to CGM. The overall accuracy of discrimination was 94%, 91%, and 80% after normalization to SMC, CBL, and CGM, respectively. In general, normalization to SMC was somewhat superior to cerebellar normalization, allowing the detection of more pronounced metabolic deficits and the more accurate discrimination of patients from non-patients. Normalization to CGM should be used with great caution not only in advanced stages of dementia, but also in very mild AD cases.

Multi-modal imaging predicts memory performance in normal aging and cognitive decline

This study (n=161) related morphometric MR imaging, FDG-PET and APOE genotype to memory scores in normal controls (NC), mild cognitive impairment (MCI) and Alzheimer's disease (AD). Stepwise regression analyses focused on morphometric and metabolic characteristics of the episodic memory network: hippocampus, entorhinal, parahippocampal, retrosplenial, posterior cingulate, precuneus, inferior parietal, and lateral orbitofrontal cortices. In NC, hippocampal metabolism predicted learning; entorhinal metabolism predicted recognition; and hippocampal metabolism predicted recall. In MCI, thickness of the entorhinal and precuneus cortices predicted learning, while parahippocampal metabolism predicted recognition. In AD, posterior cingulate cortical thickness predicted learning, while APOE genotype predicted recognition. In the total sample, hippocampal volume and metabolism, cortical thickness of the precuneus, and inferior parietal metabolism predicted learning; hippocampal volume and metabolism, parahippocampal thickness and APOE genotype predicted recognition. Imaging methods appear complementary and differentially sensitive to memory in health and disease. Medial temporal and parietal metabolism and morphometry best explained memory variance. Medial temporal characteristics were related to learning, recall and recognition, while parietal structures only predicted learning.

CSF phosporylated TAU protein levels correlate with cerebral glucose metabolism assessed with PET in Alzheimer's disease

One major goal of drug development would be the establishment of biomarkers as objective indicators of normal biological and pathogenetic processes, or pharmacological response to a therapeutic intervention. A potential approach is to investigate proteins in CSF linked to key neuropathological features of Alzheimer's disease (AD). Recently CSF phosphorylated-Tau (p-Tau) levels have been reported to reflect neurofibrillary changes within the brain of patients with AD, however the use of serial CSF investigations in order to monitor the disease progression is not applicable. PET with FDG reveals characteristic patterns in AD patients, however so far no correlation between in vivo metabolic information and pathological features has been reported. In the present study, we tested whether CSF Tau levels correlate with metabolic rate for glucose consumption in a cohort of 28 AD patients. We found a statistically significative correlation between both CSF total and p-TAU protein and relative metabolic indexes obtained from 18FDG-PET scans in parietal, temporal and occipital lobes bilaterally. These results indicate the existence of a correlation between impairment of cerebral metabolism, estimated throughout FDG-PET, and CSF Tau protein levels.

Domain-specific improvement of cognition on memantine in patients with Alzheimer's disease treated with rivastigmine

OBJECTIVE

Cholinergic therapy is used in mild-to-moderate Alzheimer's disease (AD) and antiglutamatergic therapy in moderate-to-severe AD. Global scales, as commonly used in clinical trials, blur specifics of disease progression and drug effects. The objective was to assess combination therapy of rivastigmine plus memantine by specific neuropsychological tests in patients with mild-to-moderate AD.

METHODS

12-week-short multicenter open-label pilot study. Ninety patients with mild-to-moderate AD already on stable medication with rivastigmine (3-6 mg b.i.d.) additionally received memantine for 12 weeks. Subscales of the Alzheimer's Disease Assessment Scale (ADAS-cog), the Mini-Mental State Examination (MMSE) and additional neuropsychological tests (e.g. span tasks, semantic fluency) were assessed.

RESULTS

The scores in the ADAS-cog memory subscale, the MMSE score, and digit span and semantic fluency significantly improved on combination therapy.

CONCLUSION

Memory improvement was correlated with ADAS-cog memory score at baseline and inversely with age at onset of treatment. The data suggest that improvement on combination therapy results from an improvement of attention/executive function with secondary memory improvement, which will need to be confirmed in a subsequent double-blind study on a larger number of patients.

The neurofilament heavy chain (NfH) in the cerebrospinal fluid diagnosis of Alzheimer's disease

BACKGROUND/AIMS

Attempting to improve the cerebrospinal fluid (CSF) diagnosis of Alzheimer's disease (AD), the neurofilament heavy chain isoform, NfH(SMI35) was compared to other CSF markers [total tau, phospho-tau, amyloid beta 1-42 (Abeta42), the ratio of amyloid beta fragments Abeta42/Abeta40 (Abeta ratio)].

METHODS

CSF levels were determined in patients with AD (n = 109), mild cognitive impairment (MCI, n = 25), frontotemporal dementia (n = 15), vascular dementia (VD, n = 41), and controls (n = 58).

RESULTS

CSF NfH(SMI35) was elevated in AD and VD as compared to controls (p < 0.05). Total tau was higher in AD as compared to controls (p < 0.05). CSF phospho-tau was elevated in AD as compared to controls and VD (p < 0.05 each). CSF Abeta42 and Abeta ratios in AD were lower than in MCI and controls (p < 0.05 each).

CONCLUSION

The diagnostic potential of NfH(SMI35) is not superior to that of other CSF markers.

Screening for cognitive impairment: a triage for outpatient care

The current increase in aged individuals in number and proportion of the general population warrants dependable strategies to improve early detection of cognitive impairment. It was the goal of the present study to develop a triage for bedside testing and outpatient services. In a prospective clinical cohort study at the outpatient Memory Clinic, University of Ulm, Germany, 232 subjects were diagnosed with Alzheimer's disease [AD; NINCDS-ADRDA criteria; n = 66; age 65.9 +/- 7.3 years (mean +/- SD); Mini Mental State Examination (MMSE) score 23.4 +/- 4.1], mild cognitive impairment (MCI; criteria of Petersen et al.; n = 48; age 66.4 +/- 7.1 years; MMSE score 28.3 +/- 1.5), and major depressive disorder (DSM-IV criteria; n = 61; age 63.4 +/- 8.0 years; MMSE score 28.6 +/- 1.6). Diagnosis was secured with extensive neuropsychological, clinical, radiological, and laboratory investigations. Six brief screening tests including the Memory Impairment Screen (MIS), Letter Sorting Test (LST), Verbal Fluency (VF), and Clock Drawing Test (CDT) were assessed independently from the diagnostic procedure. We compared single items and composite scores. LST yielded a diagnostic accuracy of 0.81 and 0.62 for AD and MCI patients versus controls, respectively. With the MIS, diagnostic accuracy was 0.89 and 0.71, respectively. With a combination of LST, MIS, VF, and CDT, a sensitivity for AD and MCI patients of 1.00 and 0.83 was achieved. Thus, single-item screening (e.g. LST, VF) taking little more than 1 min and suitable for bedside testing or brief screening in the general practitioner's office yields diagnostic accuracy comparable to standard laboratory tests for other diseases. A composite of screening tests suitable for application in general outpatient care in neurological and psychiatric services reliably detects patients with AD and MCI.