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Clinical Investigations |
1 Department of Neurology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
2 Department of Nuclear Medicine, Seoul National University College of Medicine, Seoul, Korea
3 Department of Nuclear Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
| ABSTRACT |
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Key Words: frontotemporal dementia glucose metabolism 18F-FDG PET statistical parametric mapping hemispheric asymmetry
| INTRODUCTION |
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Patients with progressive nonfluent aphasia and semantic dementia usually experience language disturbances and thus are easily distinguished from individuals with other dementing disorders. However, patients with FTD, the most common form of frontotemporal lobar degeneration, may experience forgetfulness or a variety of behavioral abnormalities and are often misdiagnosed as having Alzheimers disease, vascular dementia, or psychiatric illnesses. Thus, an accurate differentiation of FTD from other dementing disorders should be important from the diagnostic and therapeutic points of view. Accurate diagnoses of dementias have become more important since the advent of new drugs, such as cholinesterase inhibitors, for treatment of Alzheimers disease.
The degeneration of the frontal and anterior parts of the temporal areas in FTD results in atrophy seen on brain CT or MR imaging and hypoperfusion or hypometabolism seen on SPECT or PET (3,4). Most previous SPECT and PET studies that investigated functional changes in the brain regions of patients with FTD used the region-of-interest (ROI) method. The ROI method, however, selects only those brain regions that are expected to have functional changes, whereas recently developed voxel-wise analysis, such as the statistical parametric mapping (SPM) method, can detect any brain region with functional changes, without an a priori hypothesis.
The aim of the current study was 2-fold: first, to delineate the brain regions with reduction of glucose metabolism in FTD using SPM analysis of 18F-FDG PET images; and second, to investigate the hemispheric asymmetry of glucose metabolism in FTD, which has not been systematically studied.
| MATERIALS AND METHODS |
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PET Data Analysis
SPM Analysis of Regional Glucose Metabolism.
Before statistical analysis, using SPM99 (Wellcome Department of Cognitive Neurology, Institute of Neurology, University College London) implanted in a Matlab 5.3 environment (MathWorks, Inc.), all images were preprocessed for spatial normalization into the Montreal Neurological Institute (MNI) template to remove intersubject anatomic variability, then smoothed with a FWHM 16-mm Gaussian kernel to increase the signal-to-noise ratio and to account for subtle variations in anatomic structures (5). The count of each voxel was normalized to the average count of cerebellum using a customized program, because cerebellum is known to be one of the least affected regions in FTD. Images of patients with FTD were compared with those of healthy controls in a voxel-wise manner using SPM99 both for between-group analysis and for individual-to-group analysis (P < 0.001, uncorrected; extent threshold, k = 200). For the group analysis, a 2-sample t test was used to detect differences between the FTD and healthy control groups. For the individual analyses, a 2-sample t test was performed for each patient, so that each patient as 1 group (n = 1) was compared with the same healthy control group (n = 11). For the group analysis, 2 different statistical criteria were used: P < 0.01 (T = 5.18), corrected for multiple comparison (extent threshold, k = 50); and P < 0.0005 (T = 6.29), corrected (extent threshold, k = 50). Even if the former statistical criterion (P < 0.01, corrected) was stringent enough for imaging research, areas with significant group differences in the current study were far too extensive to identify and localize the peak coordinates for each brain region. Therefore, we applied an additional criterion that was more stringent (P < 0.0005, corrected). For display, green was used for the lower threshold (T = 5.18) and red for the higher threshold (T = 6.29) (Fig. 1). However, the table of local maxima (Table 3) was composed based on the lower threshold.
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Analysis of Hemispheric Asymmetry of Glucose Metabolism.
To evaluate the hemispheric asymmetry of glucose metabolism in FTD, we obtained asymmetry indices (AIs) of metabolism between the hemispheres using ROI and SPM analyses of 18F-FDG PET images in each patient with FTD. From the preprocessed PET images, including cerebellar normalization (mean 18F-FDG activity of cerebellum = 50) as described previously, the average 18F-FDG activity of each hemisphere was counted using the ROI method and an AI between the hemispheres was computed using the following equation: AIROI = (average 18F-FDG activity of left hemisphere average 18F-FDG activity of right hemisphere)/(average 18F-FDG activity of left hemisphere + average 18F-FDG activity of right hemisphere) x 200. The brain-mask image given in SPM software was divided into the left and right hemispheres according to the x-coordinate of each voxel to define the ROIs. On an SPM{t} map of each patient, the number of voxels with significant (P < 0.001, uncorrected) hypometabolism compared with the healthy control group was counted in each hemisphere, and an AI between the hemispheres was calculated using the following equation: AISPM = (number of hypometabolic voxels in right hemisphere number of hypometabolic voxels in left hemisphere)/(number of hypometabolic voxels in right hemisphere + number of hypometabolic voxels in left hemisphere) x 200. Positive AIROI and AISPM values indicate that the right hemisphere is more hypometabolic (in terms of extent and/or intensity) than the left hemisphere; negative values indicate the opposite.
Statistical Analysis
Data are expressed as mean ± SD. A difference between unpaired data was analyzed by an unpaired Student t test. Correlation between AIROI and AISPM was evaluated by calculating the Pearson linear correlation coefficient. Except for SPM analysis, P < 0.05 was considered significant.
| RESULTS |
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| DISCUSSION |
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We found additional hypometabolic brain regions that have not been reported in prior studies. These areas were the insula and uncus. The insula, with its connection with cerebral cortex, basal ganglia, thalamus, and limbic structures such as amygdala and entorhinal cortex, is known to be involved in a variety of brain activities, including somatosensory, swallowing, gustatory, vestibular, cardiovascular, and language functions (14). It has also been reported that damage to the insula produces subjective feelings of anergia, underactivity, and tiredness (15). Thus, it may be possible that insular lesions in our patients may partly contribute to such symptoms as lack of energy and reduced speech and activities. Also, the insula is one of the brain structures involved in a network recruited during memory testing. Its activity level may show a compensatory change with aging in healthy old individuals (16). Failure of this compensatory change may be associated with cognitive impairment in patients with FTD. No functional imaging studies have reported insular involvement in FTD. Rosen et al. (17) reported an atrophy of the insula in FTD using voxel-based morphometry of MR images. They suggested the possibility of a role for the insula in social behavior. Hypometabolism in the uncus may be associated with a dysfunction in the amygdala. The amygdala has strong links with emotional processing. Removal of the amygdala and surrounding structures resulted in profound social disturbances in primates (18). Also, the uncus is a part of brain regions reported to be involved in emotional expression and visual processing of emotions (19). Metabolic impairment of the uncus as revealed in this study may be associated with disturbances in emotional processing and social behavior in patients with FTD.
It has been suggested that asymmetric hemispheric degeneration is common in patients with FTD (11,2022). However, no systematic analysis has been performed. Furthermore, those studies included patients with progressive nonfluent aphasia and semantic dementia, which are known to preferentially affect the left hemisphere. We evaluated the hemispheric asymmetry of metabolism only in patients with FTD. We found that hemispheric metabolic asymmetry was common (90%) and intense in FTD, even after patients with progressive nonfluent aphasia and semantic dementia were excluded. Thus, it can be suggested that FTD is a disorder that causes an asymmetric degeneration of cerebral hemispheres. According to our definition, 29 patients with FTD recruited in this study were classified into left-dominant (hypometabolism more severe in the left hemisphere; n = 18), right-dominant (n = 8), or bilateral groups (n = 3). The clinical significance of the metabolic asymmetry is unknown. The right-dominant group appeared to be heterogeneous in clinical manifestations. On the other hand, patients who presented with naming difficulty (patients 1, 3, 23, and 26) or had naming difficulty at initial examination (patient 15) all belonged to the left-dominant group. This correlation does not seem to be specific, however, because a large portion of the left-dominant group (13/18) did not have such language disturbancepredominant profiles. The reason for the overrepresentation of the left-dominant group remains speculative. One possible explanation is that FTD may preferentially affect the left hemisphere. A pathology study demonstrated greater left- than right-sided atrophic changes in most cases of FTD (13). Alternatively, this may be caused by a sampling bias. Left-dominant patients can show language disturbances even in early stages. Thus, it is more likely that these patients are brought to neurology clinics. On the other hand, right-dominant patients may present predominantly with behavioral or psychiatric abnormalities, and so are first seen at psychiatric clinics and potentially are misdiagnosed as having psychiatric illnesses.
A potential limitation of this study is that brain PET images were corrected for attenuation using a calculated instead of a measured method. In our previous study, however, there was a strong linear correlation (r = 0.99) between regional brain counts on 18F-FDG PET images corrected for attenuation using calculated and measured methods (23). In the present study, before the performance of SPM analysis, brain activity values were normalized to average cerebellar activity (i.e., cerebellar normalization) instead of average whole brain activity (i.e., global normalization), because cerebellum is known to be one of the least affected regions in FTD. In patients with FTD as well as Alzheimers disease, average whole brain activity may be abnormally low, resulting in a relatively high value for certain voxels relative to whole brain activity. This would compromise test sensitivity and might even lead to results indicating that certain areas of the brain were showing higher activity in those patients than in controls (24). In this study, partial-volume correction of PET data was not performed. To our knowledge, systematic investigation of the influence of brain atrophy on 18F-FDG PET findings in patients with FTD has not been reported. However, there are consistent reports on the persistence of hypometabolism after partial-volume correction in neurodegenerative diseases and in healthy aging (2527). Nevertheless, studies are needed to investigate to what extent the partial-volume effect as a result of brain atrophy influences 18F-FDG PET findings in FTD.
| CONCLUSION |
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| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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For correspondence or reprints contact: Sang Eun Kim, MD, PhD, Department of Nuclear Medicine, Seoul National University Bundang Hospital, 300 Gumi-dong, Bundang-gu, Seongnam-si, Gyeonggi-do, 463-707, Korea.
E-mail: kse{at}snu.ac.kr
| REFERENCES |
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