Functional Interactions of the Entorhinal Cortex: An 18F-FDG PET Study on Normal Aging and Alzheimer’s Disease Lisa Mosconi, MD1; Alberto Pupi, MD1; M. Teresa R. De Cristofaro, MD1; Mozghan Fayyaz, MD1; Sandro Sorbi, MD2; and Karl Herholz, MD3 1Department of Clinical Pathophysiology, Nuclear Medicine Unit, University of Florence, Italy; 2Department of Neurological and Psychiatric Sciences, University of Florence, Italy; and 3Neurological Clinic and Max-Planck-Institute for Neurological Research, University of Cologne, Germany Alzheimer’s disease (AD) is a brain disorder characterized by Alzheimer’s disease (AD) is a neurodegenerative clini- reduced cerebral glucose metabolism (CMRgl) in several corti- copathologic syndrome leading to progressive, irreversible cal regions. Evidence from neuropathology studies, animal 18 loss of memory and behavioral function and is associated models of AD, and F-FDG PET studies on cognitive impair- ␤ ment suggest that disrupted connections with the entorhinal with a pathologic neuronal loss and accumulation of -amy- cortex (EC) could be implicated in the emergence of the cortical loid plaques and neurofibrillary tangles and threads (NFT). hypometabolism. This 18F-FDG PET study assessed the func- Neuroimaging studies with PET and SPECT techniques tional interactions—that is, the intercorrelations between the EC have largely investigated AD, showing cerebral metabolic and the whole brain in vivo—in normal aging and AD. Methods: (CMRgl) and blood flow (CBF) reductions in the temporal, Eighty-seven consecutive clinical AD patients underwent 18F- parietal, posterior cingulate, and prefrontal regions (1). On FDG PET scanning at rest. Thirty-five sex- and age-matched the other hand, neuropathology and neurochemical studies healthy elderly subjects were studied as controls (NC). A voxel- have shown that the limbic entorhinal cortex (EC) is the based correlation analysis was performed with statistical para- metric mapping to assess significant correlations between rel- brain area preferentially affected by the early deposition of ative CMRgl (rCMRgl) in the EC and the rest of the brain, for NC NFT (2,3) and neuronal loss (4), which increase in the later and AD patients. Results were considered significant at P Ͻ stages of AD (2). 0.001. Results: The pattern of EC functional interactions varies Although there is evidence that the EC is anatomically between normal aging and AD patients. In NC, the left and right connected with the brain areas typically characterized by EC were bilaterally correlated with several cortical and limbic functional impairment in AD (5), its role in the onset of such regions, in accord with the major anatomic pathways identified a functional disruption is still uncertain. Important insights in nonhuman primates. Alternatively, in AD patients, the EC correlations with the contralateral hemisphere were entirely lost, about the involvement of the EC in the cortical hypometab- 18 whereas those within the ipsilateral hemisphere were preserved olism associated with AD derived from F-FDG PET stud- only with the inferior temporooccipital (T–O) areas. Conclusion: ies on animal models of AD. Indeed, Meguro et al. (6) This 18F-FDG PET correlation study indicates that AD-related provided evidence that lesions of the rhinal cortex of non- processes lead to an altered functional relationship between the human primates cause a long-lasting CMRgl decline in the EC and several cortical and limbic regions, with respect to parietal, temporal, and occipital associative cortices, the normal aging. Our results suggest that the assessment of cou- posterior cingulate, and the hippocampal regions. Addition- pled rCMRgl reductions between the EC and the ipsilateral T–O ally, EC lesions in rats were shown to induce CMRgl cortex, besides the typical pattern of cortical reduction, could increase 18F-FDG PET diagnostic sensitivity and further moti- decreases in the frontal, parietal, and temporal regions ip- vate its inclusion in the clinical assessment of AD. silateral to the lesion (7). These studies showed that the Key Words: PET; 18F-FDG; Alzheimer’s disease; entorhinal cor- parietotemporal hypometabolism found in AD may result tex; functional interactions; connectivity; aging partly from neuroanatomic disconnection with the EC. J Nucl Med 2004; 45:382–392 On the other hand, little is known about the functional connections between the EC and the rest of the brain in living human beings. A recent 18F-FDG PET study by de Leon et al. (8) showed that reduced baseline levels of CMRgl in the EC are reliable predictors of future neocor- Received Jun. 27, 2003; revision accepted Oct. 7, 2003. For correspondence contact: Alberto Pupi, MD, Department of Clinical tical hypometabolism as well as of cognitive decline in Pathophysiology, Nuclear Medicine Unit, University of Florence, viale Mor- gagni 85, 50134 Florence, Italy. normal elderly subjects. However, to our knowledge, no E-mail: [email protected]fi.it study has been performed so far in vivo in humans with 382 THE JOURNAL OF NUCLEAR MEDICINE • Vol. 45 • No. 3 • March 2004 neuroimaging techniques to specifically explore the func- Control Subjects. Controls (NC) were 35 healthy and unmedi- tional interconnections of the EC in normal aging and AD. cated sex- and age-matched subjects (19 men, 16 women; mean In this 18F-FDG PET study a voxel-based correlation age, 69.3 Ϯ 5.6 y; age range, 64–81 y; educational level, 10.3 Ϯ Ն analysis was performed to assess the functional interactions 3.2 y; Mini-Mental State Examination [MMSE] score, 26) from between the EC and the whole brain in both healthy elderly the NEST-DD database. With their informed consent and approval by local ethics committees, they were studied with PET under the subjects and clinical AD patients. Our hypothesis was that same conditions and using the same scanning protocol at 3 col- in the control subjects the EC correlates with a widely laborating laboratories (see below). As described in Herholz et al. distributed functional system, in accord with the major (1), brain disease or cognitive disorders had been excluded by MRI anatomic pathways identified in nonhuman primates (5). and detailed clinical and neuropsychologic examination. With regard to AD patients, we hypothesized that the patho- 18F-FDG PET Scanning Procedures logic involvement of the EC in AD could lead to modifica- The detailed 18F-FDG PET scanning procedure used is de- tions of its connectivity, resulting in lost or weakened cor- scribed in Herholz et al. (1). AD patients scans were acquired at relations with the rest of the brain. our center using a General Electric Advance PET device. Emission scans were acquired in 2-dimensional mode with an axial field of MATERIALS AND METHODS view (FOV) of 152 mm, an in-plane full width at half maximum Participants (FWHM) of 4.6 mm, and a slice thickness of 4.25 mm. NC scans AD Patients. Subjects were recruited in the context of the were acquired at Cologne, Liege, and Dresden centers using ECAT ϩ Network for Efficiency and Standardization of Dementia Diagno- EXACT, ECAT 951, and ECAT EXACT HR scanners, with an sis (NEST-DD) research project funded by the European Commis- axial FOV of 162, 108, and 155 mm, an in-plane FWHM of 6, 8.5, sion (http://www.nest-dd.org) and were studied for cerebral glu- and 3.6 mm, and a slice thickness of 3.375, 3.37, and 2.46 mm, cose metabolism with PET between November 2000 and respectively (1). 18 November 2002 at the Florence University Center. Eighty-seven Subjects were injected with a dose of 110–370 MBq F-FDG consecutive AD patients were included in the study after having at a resting state with eyes closed and ears unplugged in a dimly provided informed consent. All subjects were diagnosed according lighted room with minimal background noise. A polycarbonate to the National Institute for Neurological Disorders and Stroke and head holder was used to reduce head movement during the scan. the Alzheimer’s Disease and Related Disorders Association crite- The required minimum time interval between injection and starting Ϯ ria (9). The study procedures included examinations by neurolo- the scan was 30 min. On average, scans were started 42 19 min gists and psychiatrists, routine laboratory tests, neuropsychologic after injection. The required minimum scan duration was 10 min. Ϯ examinations, electroencephalograms, MRI and PET scans, and On average, scan duration was 19 3 min. Images were recon- blood samples for genetic analysis. Patients were excluded in the structed using filtered backprojection including correction for at- case of (a) complications of other medical illnesses possibly caus- tenuation, measured by a transmission scan for NC images and ing cognitive impairment, such as thyroid disease, vitamin defi- according to Chang’s method (10) for AD patients because of its ciencies, and malignant disease; (b) mental disease, substance robustness in case of movements, and scatter using standard soft- abuse, or significant neurologic antecedents (e.g., brain trauma, ware as supplied by scanner manufacturers. Further details can be tumors, epilepsy, vascular dementia, other dementing illnesses, found in Herholz et al. (1). and inflammatory disease); (c) evidence of focal brain lesions on 18F-FDG PET Image Transformation MRI. Clinical and demographic characteristics of the patients An MS-DOS version of NEUROSTAT (kindly provided by under study are reported in Table 1. Prof. Satoshi Minoshima, Department of Internal Medicine, Uni- versity of Michigan, Ann Arbor, MI) running on a WindowsMe (Microsoft) system was used to realign PET images relative to the TABLE 1 anterior–posterior commissural line (AC–PC) and to normalize Clinical and Demographic Characteristics them onto the 18F-FDG PET template provided by NEUROSTAT of AD Patients Under Study (11). This procedure involves both a 9-parameter linear affine transformation and a nonlinear warping deformation to match the Characteristic AD patients standard stereotactic Talairach and Tournoux space (12). It was n 87 shown to be particularly effective in accounting for eventual Sex cortical atrophy and ventricular enlargement (11).