MRI of hippocampus and entorhinal cortex in mild cognitive impairment: A follow-up study

Neurobiology of Aging 29 (2008) 31–38

MRI of hippocampus and entorhinal cortex in mild cognitive impairment: A follow-up study Tero Tapiola a,b,∗ , Corina Pennanen a,b,d , Mia Tapiola a , Susanna Tervo a , Miia Kivipelto a , Tuomo H¨anninen a,b , Maija Pihlajam¨aki a,b , Mikko P. Laakso a,d , Merja Hallikainen a , Anne H¨am¨al¨ainen a , Matti Vanhanen a , Eeva-Liisa Helkala c , Ritva Vanninen d , Aulikki Nissinen e , Roberta Rossi f , Giovanni B. Frisoni f , Hilkka Soininen a,b a

Department of Neuroscience and Neurology, University of Kuopio, Brain Research Unit, Clinical Research Center, Mediteknia, 70211 Kuopio, Finland b Department of Neurology, Kuopio University Hospital, 70211 Kuopio, Finland c Department of Public Health, University of Kuopio, 70211 Kuopio, Finland d Department of Clinical Radiology, Kuopio University Hospital, 70211 Kuopio, Finland e National Institute of Public Health, Mannerheimintie 116, 00300 Helsinki, Finland f LENITEM, IRCCS San Giovanni di Dio-FBF, Brescia, Italy Received 13 April 2006; received in revised form 16 August 2006; accepted 15 September 2006 Available online 13 November 2006

Abstract The concept of mild cognitive impairment (MCI) has been proposed to represent a transitional stage between normal aging and dementia. We studied the predictive value of the MRI-derived volumes of medial temporal lobe (MTL) structures, white matter lesions (WML), neuropsychological tests, and Apolipoprotein E (APOE) genotype on conversion of MCI to dementia and AD. The study included 60 subjects with MCI identified from population cohorts. During the mean follow-up period of 34 months, 13 patients had progressed to dementia (9 to Alzheimer’s disease (AD)). In Cox regression analysis the baseline volumes of the right hippocampus, the right entorhinal cortex and CDR sum of boxes predicted the progression of MCI to dementia during the follow-up. In a bivariate analysis, only the baseline volumes of entorhinal cortex predicted conversion of MCI to AD. The Mini-Mental State Examination (MMSE) score at baseline, WML load, or APOE genotype were not significant predictors of progression. The MTL volumetry helps in identifying among the MCI subjects a group, which is at high risk for developing AD. © 2006 Elsevier Inc. All rights reserved. Keywords: Alzheimer’s disease; Entorhinal cortex; Hippocampus; MRI; Memory; Mild cognitive impairment; White matter lesions; Volumetry; Follow-up study; APOE

1. Introduction An important public health concern in developed countries is aging of the population and increase in the prevalence

∗ Corresponding author at: Department of Neurology, Kuopio University Hospital, P.O. Box 1777, FIN 70211 Kuopio, Finland. Tel.: +358 44 7113135; fax: +358 17 173019. E-mail address: [email protected] (T. Tapiola).

0197-4580/$ – see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.neurobiolaging.2006.09.007

of various dementias, particularly Alzheimer’s disease (AD). The concept of mild cognitive impairment (MCI) is considered a transitional stage between normal aging and very early AD [30,31]. Although various criteria for MCI were used in different studies, an annual conversion rate of 6–25% from MCI to AD has been estimated [32], which greatly exceeds that seen in the normal population. The current challenge is to define from the MCI population the subjects having progressive disease, and extract them of those having stable MCI, which never turn to dementia. This provides a basis for trials

32

T. Tapiola et al. / Neurobiology of Aging 29 (2008) 31–38

of interventions targeted to prevent the conversion of MCI to dementia. The formation of long-term cognitive memory is dependent on the medial temporal lobe (MTL) structures, which consist of the hippocampus, the entorhinal, perirhinal, and parahippocampal cortices. These structures are known to be critical for successful encoding of new events and facts into long-term memory [36]. In AD these structures show the first pathologic findings, which can be found already in the MCI state [4,11,21,39,40]. Apolipoprotein E (APOE) ␧4 allele is a well-known risk factor for AD. The APOE ␧4 has been associated with the development of AD among the persons with MCI [30], and it is also associated with amnestic MCI [27]. In AD the ␧4 carriers show earlier age of onset and enhanced AD related pathology [26], and more pronounced atrophy in the MTL structures [9,10,16] compared to non-carriers. Presence of ␧4 allele has been associated with smaller hippocampal volume in AD and vascular dementia within just 1 year of disease onset [3]. Information of an individual’s APOE genotype of those already symptomatic for dementia may not improve knowledge about the patient’s prognosis, but information about the APOE status of patients with MCI might have the potential to offer insight into the likelihood of conversion to clinical dementia. Longitudinal studies are needed to explore putative markers that are the most effective ones in predicting the conversion of normal aging to MCI and further to dementia. So far, MRI studies, providing a window to the brain in vivo, have shown to be among the most reliable of the putative markers of incipient dementia. A few studies [5,7,8,15,17,18,29] have focused on MRI-based volumetric measurements of different brain regions in cognitive impairment suggesting that particularly the MTL structures, the entorhinal cortex and the hippocampus, show atrophy even in the preclinical stage of AD. However, there exists no consensus, which of these structures best predict conversion from MCI to AD. In the present longitudinal, population-based study we examined the predictive value of the hippocampal and entorhinal cortical volumes, white matter lesions (WML), neuropsychological tests, and APOE polymorphism on conversion from MCI to dementia and AD.

2. Methods 2.1. Subjects The present follow-up study included 60 subjects with MCI aged 63–81 years. The study subjects were derived from large, population-based random samples of persons living in Kuopio region, Eastern Finland [13,19,37]. The baseline visit included a high resolution structural MRI scan. The three follow-up visits were performed in 1999–2004 in the Department of Neurology, Kuopio University Hospital, Finland, and they included neuropsychological tests and clinical neuro-

logical examination. Finally, the medical history (hospital records) was obtained for those participants who did not participate in all study visits to detect the possible conversion to dementia. The conversion to dementia was considered as the end-point of the follow-up. The Local Ethics Committee approved the study, and all the participants gave informed consent for their participation in the study. 2.2. Diagnosis of dementia Diagnostic evaluations for patients included medical history, physical and neurological examinations performed by a physician, and a detailed neuropsychological evaluation administered by a neuropsychologist. The severity of cognitive decline was graded according to the Clinical Dementia Rating (CDR) Scale. Furthermore, brain MRI scan, cerebrospinal fluid analysis, EKG, chest radiography and blood tests were performed. These were not used in the diagnostic phase except for excluding other possible pathologies underlying the symptoms. The diagnosis of dementia was based on the criteria of the Diagnostic and statistical manual of mental disorders, 4th ed. (DSM-IV) [2] and the diagnosis of AD on the National Institute of Neurologic and Communicative Disorders and Stroke and Alzheimer’s Disease and Related Disorders Association (NINCDS-ADRDA) criteria [28]. 2.3. Diagnosis of MCI The subjects with MCI were identified from two different population cohorts. In both the cohorts, the evaluation consisted of a structured interview including CDR scale and a comprehensive neuropsychological assessment. The scoring of the CDR was independent of the scores obtained from neuropsychological tests. MCI was diagnosed using the criteria proposed by Mayo Clinic Alzheimer’s Disease Research Center. These criteria have been modified later, but at the time this study was conducted the criteria required: (1) memory complaint by patient, family, or physician; (2) normal activities of daily living; (3) normal global cognitive function; (4) objective impairment in memory or in one other area of cognitive function as evident by scores >1.5 S.D. below the age-appropriate mean; (5) CDR score of 0.5; and (6) absence of dementia [30,35]. In the first cohort, the following test battery was used for a comprehensive neuropsychological evaluation of different cognitive domains—memory: Visual Reproduction Test (immediate and delayed recall) from Wechsler Memory Scale, Logical Memory Test (immediate and delayed recall) from Wechsler Memory Scale-Revised, Word List Recall (immediate and delayed recall) from the Consortium to Establish a Registry for Alzheimer’s Disease (CERAD) Neuropsychological Assessment Battery, delayed recall of the Constructional Praxis from CERAD, New York University Paragraph Recall (immediate and delayed recall); language: Abbreviated (15 items) Boston Naming Test, vocabulary subtest from the Wechsler Adult Intelligence Scale-Revised

T. Tapiola et al. / Neurobiology of Aging 29 (2008) 31–38

33

(WAIS-R); attention and executive function: Verbal Fluency Test, Trail Making Test parts A and B; visuospatial skills: Constructional Praxis from CERAD, Block Design from the WAIS-R; global functioning: Mini-Mental State Examination (MMSE), Clock Drawing Test (the CERAD version). In this cohort, however, two memory test scores only were used as the objective psychometric criteria of memory impairment in MCI diagnosis: according to the normative data in delayed recall in the Logical Memory Test from the WMS-R or in the Visual Reproduction Test from the WMS. The detailed neuropsychological evaluation in the second cohort [19] included the Buschke Selective Reminding Test, the Logical Memory Test from the Wechsler Memory Scale-Revised, the Boston Naming Test, the Vocabulary subtest of the Wechsler Adult Intelligence Scale, the Verbal Fluency Test, the Copy a Cube Test, the Clock Setting Test, the Block Design subtest of the Wechsler Adult Intelligence Scale, the Wisconsin Card Sorting Test using Nelson’s version, and the Trail Making Test. All the MCI subjects included in the present study had memory impairment and most of them (72%) had multiple domain amnestic MCI.

nial area according to the formula: (volume/intracranial area) × 100.

2.4. MRI acquisition and volumetric assessment

APOE genotype was determined from blood leukocytes. DNA was extracted by a standard phenol-chloroform extraction, and APOE genotypes were analyzed by polymerase chain reaction and HhaI digestion as described previously [38].

The subjects were scanned with a 1.5 T Vision (Siemens, Erlangen, Germany) using a three-dimensional magnetization prepared rapid acquisition gradient echo sequence (TR/TE 9.7/4 and 13.5/5.7, matrix 256 × 192, 1 acquisition). The images were re-aligned to correct the undesirable effects for the head tilt and rotation. Standard neuroanatomical landmarks (such as the orbits, sulci and the commissures) were used to correct for possible deviations in any of the three orthogonal planes and the scans were reconstructed into 2.0 mm thick contiguous coronal slices, oriented perpendicular to the intercommissural line. The hippocampi and entorhinal cortices were manually traced by a single tracer (C.P.), blinded to the clinical data, using custom-made software for a standard Siemens work console. Tracing of the hippocampus started rostrally where the hippocampus first appears below the amygdala and ended posteriorly in the section where the crura of the fornices depart from the lateral wall of the lateral ventricles. The entorhinal cortex volumes were traced according to the histology-based criteria designed for MRI volumetric measurements [14,29]. In brief, the most anterior slice measured was the one after the appearance of the temporal stem, and the last slice was the one where the uncus and gyrus intralimbicus were no longer separable. Once the ROI has been traced, the software calculates the volume for every structure by computing the number of voxels for each traced image. The intraclass correlation coefficients for intrarater reliability were 0.96 for the hippocampus and 0.95 for the entorhinal cortex measured from 10 subjects. The coronal intracranial area at the level of the anterior commissure was measured and used for normalization of the volumetric data. For the purpose of data presentations, the volumes were normalized to the intracra-

2.5. White matter lesions The WML were evaluated by a single rater (R.R.) on MRI images on computer screen with either proton density (PD) and T2 weighted images or with T2 weighted and FLAIR images by using the rating scale by Wahlund et al. [41]. The WMLs were defined as bright lesions ≥5 mm on T2, PD or FLAIR images. In frontal, temporal, parieto-occipital, and infratentorial regions WMLs were scored: 0 = no lesions (including symmetrical, well-defined caps or bands), 1 = focal lesions, 2 = beginning of confluence of lesions, 3 = diffuse involvement of the entire region; and in the basal ganglia: 0 = no lesions, 1 = one focal lesion (≥5 mm), 2 = >1 focal lesion, 3 = confluent lesions. The sum score of frontal, temporal, parieto-occipital, basal ganglia, and infratentorial regions were used in the analysis. 2.6. APOE genotyping

2.7. Statistical analyses The statistical software SPSS for Windows V11.5 (SPSS Inc., Chicago, IL) was used to analyze the data. In all statistical analyses of the volumetric data, we used volumes normalized for the intracranial area. T-test was used to find group differences. The effect of side (within-group variable) and outcome (between-group variable) on volumes of hippocampus and entorhinal cortex was assessed by ANOVA. Interaction terms were included in the model as needed. Because of variability in follow-up length, the predictive accuracy of volumetry for dementia was assessed by Cox regression analysis with follow-up time as time variable and conversion to dementia or AD as status variable. The hazard ratios (HR) with 95% CI and significance (p-value) are presented. The level of statistical significance of differences was set at p < 0.05.

3. Results 3.1. Descriptive characteristics The mean follow-up time of subjects was 34 (S.D. 8.7, range 10–54) months. During this period, 13 (21.7%) patients had progressed to dementia (progressive MCI). Nine patients in this group had a clinical diagnosis of probable AD, 3 had vascular dementia and 1 had dementia of mixed type. In the

34

T. Tapiola et al. / Neurobiology of Aging 29 (2008) 31–38

Table 1 Descriptive characteristics

N Age (years) Female/male Follow-up (months) Education (years) MMSE at baseline CDR sum of boxes WML load APOE ␧4+/␧4−

Table 2 Volumes of hippocampus and entorhinal cortex Stable MCI

Progressive MCI

47 72.9 (4.2) 33/14 35.2 (8.2) 6.7 (1.5) 24.1 (2.6) 1.2 (0.5), n = 45 4.2 (4.5) 21/26

13 72.1 (4.2) 8/5 30.7 (9.9) 6.6 (1.9) 23.3 (2.3) 2.1 (1.1), n = 12* 4.5 (2.9) 8/5

Results are mean (S.D.). MMSE: Mini-Mental State Examination; CDR: Clinical Dementia Rating Scale; WML: white matter lesions; APOE ␧4+/␧4−: at least one APOE ␧4 allele/no APOE ␧4 allele. * p < 0.05.

stable MCI group, 7 subjects had a neuropsychological profile of control subjects in the last follow-up visit. At baseline, there were no differences between the outcome groups in follow-up time, education, age, WML load or the MMSE score (Table 1). Patients with stable MCI had lower CDR sum of boxes (p < 0.05) compared to patients with progressive MCI (Table 1). The progressive MCI group included eight patients with at least one APOE ␧4 allele. Three patients were heterozygous for the APOE ␧ allele (␧3/␧4) and five homozygous (␧4/␧4). Five patients with the progressive MCI were ␧4 non-carriers (␧3/␧3). The stable MCI group consisted of 21 APOE ␧4 allele carriers. Eighteen of them were heterozygous for the APOE ␧4 allele (17 ␧3/␧4, 1 ␧2/␧4), and 3 were homozygous. Twenty-six subjects in the stable MCI group were ␧4 noncarriers (25 ␧3/␧3, 1 ␧2/␧3). 3.2. Volumetric measurements At baseline, the total volume (sum of the right and left side) of hippocampi and the entorhinal cortices were significantly reduced (p < 0.05) in the progressive MCI group compared to stable MCI (Table 2). In an ANOVA model that included side as within-group variable and outcome as between-group variable there was a significant effect of side (F(1, 58) = 19.98, p < 0.001) and outcome (F(1, 58) = 5.89, p < 0.05) on hippocampal volumes. There were no statistically significant interactions between the outcome groups or brain hemispheres. Subjects with progressing MCI had reduced volumes of the hippocampi and the volume of the left hippocampus was smaller in both stable and progressing MCI. The ANOVA model of the entorhinal cortex showed a significant effect of side (F(1, 58) = 13.66, p < 0.001) and outcome (F(1, 58) = 4.54, p < 0.05). There was a significant side by outcome group interaction ((F(1, 58) = 5.45, p < 0.05) and pairwise comparison showed a significant reduction in the volumes of the right entorhinal cortex in progressive MCI (p = 0.01). The lowest volumes were found in patients with progression of MCI to AD (right hippocampus: 12.9 ± 2.4 (mean ± S.D.), left hippocampus: 12.2 ± 2.7, right entorhinal cortex: 6.1 ± 1.3, left entorhinal cortex: 5.8 ± 0.6). The

Stable MCI

Progressive MCI

Right HC APOE ␧4+ APOE ␧4−

15.52 (2.36) 14.99 (2.48) 15.96 (2.20)

13.53 (2.26) 12.75 (2.38) 14.79 (1.51)

Left HC APOE ␧4+ APOE ␧4−

14.19 (2.25) 13.96 (2.02) 14.38 (2.43)

12.80 (2.68) 11.26 (2.03) 15.27 (1.42)

Total HC APOE ␧4+ APOE ␧4−

29.71 (4.42) 28.94 (4.39) 30.34 (4.42)

26.33 (4.54)* 24.01 (3.83) 30.06 (2.81)

Right EC APOE ␧4+ APOE ␧4−

7.91 (1.56) 7.96 (1.73) 7.87 (1.44)

6.62 (1.44) 6.11 (0.95) 7.42 (1.82)

Left EC APOE ␧4+ APOE ␧4−

7.11 (1.53) 7.22 (1.37) 7.02 (1.68)

6.44 (1.45) 5.88 (0.75) 7.34 (1.91)

Total EC APOE ␧4+ APOE ␧4−

15.02 (2.98) 15.17 (3.00) 14.90 (3.02)

13.06 (2.74)* 12.00 (1.59) 14.76 (3.50)

Results are mean (S.D.). HC: normalized volume of the hippocampus; EC: normalized volume of the entorhinal cortex; total: sum of the right plus left side volumes; APOE ␧4+/␧4−: at least one APOE ␧4 allele/no APOE ␧4 allele. Bold values are significant at p < 0.05. * p < 0.05.

ANOVA models showed significantly reduced volumes in subjects with progression of MCI to AD (hippocampus: F(1, 54) = 7.82, p < 0.01; entorhinal cortex: F(1, 54) = 9.39, p < 0.005) and in the right hemisphere in the two outcome groups (hippocampus: F(1, 54) = 17.16, p < 0.001; entorhinal cortex: F(1, 54) = 14.14, p < 0.001). The APOE groups (at least one ␧4 allele, no ␧4 allele) did not differ in age, education, follow-up time, baseline MMSE score, WML load, or CDR sum of boxes in progressive MCI. In subjects with stable MCI, the only statistically significant difference was found in the follow-up time as subjects without the APOE ␧4 allele had a longer follow-up time compared to subjects with ␧4 allele (mean ± S.D.: 37.9 ± 5.46 versus 31.7 ± 9.79, p < 0.05). In the progressive MCI group there was a tendency of decreased volumes in patients with at least one APOE ␧4 allele compared to those without the ␧4 allele, and difference in total volume of the hippocampi between APOE ␧4 carriers and non-carriers did reach statistical significance (p < 0.05) (Table 2, Fig. 1). Furthermore, progressive MCI patients with at least one ␧4 allele had significantly reduced volumes of the hippocampi and entorhinal cortices (p < 0.05) compared to stable MCI subjects with at least one ␧4 allele (Table 2, Fig. 1). However, in subjects without the APOE ␧4 allele, there were no differences in the MTL volumes between the stable and progressive MCI groups (Fig. 1). 3.3. Cox regression analysis In the univariate Cox regression analysis, the volumes of the hippocampus and entorhinal cortex on the right side, the

T. Tapiola et al. / Neurobiology of Aging 29 (2008) 31–38

35

Table 4 Bivariate Cox regression analysis (MTL structures and CDR sum of boxes) with follow-up (months) as time variable and outcome (Dementia, AD) as status variable Dementia

AD

Right HC CDR sum of boxes

0.805 (0.61–1.07) 2.627 (1.43–4.84)#

0.731 (0.52–1.03) 1.685 (0.71–4.00)

Left HC CDR sum of boxes

0.952 (0.73–1.24) 2.721 (1.53–4.83)##

0.812 (0.59–1.11) 1.829 (0.80–4.17)

Total HC CDR sum of boxes

0.932 (0.81–1.07) 2.675 (1.48–4.84)##

0.864 (0.72–1.03) 1.723 (0.73–4.05)

Right EC CDR sum of boxes

0.577 (0.35–0.94)* 3.124 (1.67–5.86)##

0.448 (0.24–0.83)# 2.222 (0.93–5.33)

Left EC CDR sum of boxes

0.787 (0.50–1.24) 3.001 (1.60–5.64)##

0.542 (0.30–0.97)* 2.268 (0.93–5.50)

Total EC CDR sum of boxes

0.799 (0.62–1.02) 3.175 (1.67–6.05)##

0.658 (0.47–0.92)* 2.285 (0.93–5.60)

Results are expressed as hazard ratio (95% confidence interval). HC: normalized volume of the hippocampus; EC: normalized volume of the entorhinal cortex; total: sum of the right plus left side volumes; AD: conversion of MCI to Alzheimer’s disease; CDR: Clinical Dementia Rating Scale. * p < 0.05. # p < 0.01. ## p < 0.001. Fig. 1. Total volumes of the hippocampi and entorhinal cortices in stable and progressive MCI in subjects with at least one APOE ␧4 allele or without ␧4 allele. Filled circles represent patients with conversion of MCI to AD during the follow-up period.

Table 3 Univariate Cox regression analysis with follow-up (months) as time variable and outcome (Dementia, AD) as status variable Dementia (0.58–0.94)*

AD

Right HC Left HC

0.738 0.866 (0.68–1.10)

0.668 (0.49–0.91)# 0.739 (0.55–1.00)**

Total HC

0.881 (0.77–1.00)**

0.815 (0.69–0.97)*

Right EC Left EC

0.597 (0.38–0.93)* 0.836 (0.56–1.24)

0.439 (0.25–0.77)# 0.568 (0.34–0.95)*

Total EC

0.824 (0.65–1.04)

0.651 (0.47–0.90)#

Age Gender MMSE at baseline CDR sum of boxes Education APOE ␧4 allele WML load

0.991 (0.87–1.12) 0.625 (0.20–1.98) 0.919 (0.73–1.16) 2.730 (1.55–4.81)## 0.979 (0.68–1.42) 0.534 (0.17–1.69) 1.007 (0.89–1.14)

0.972 (0.84–1.12) 0.543 (0.15–2.04) 0.918 (0.70–1.20) 1.948 (0.90–4.21) 1.198 (0.78–1.84) 0.359 (0.89–1.44) 1.016 (0.88–1.17)

Results are expressed as hazard ratio (95% confidence interval). HC: normalized volume of the hippocampus; EC: normalized volume of the entorhinal cortex; total: sum of the right plus left side volumes; AD: conversion of MCI to Alzheimer’s disease; MMSE: Mini-Mental State Examination; CDR: Clinical Dementia Rating Scale; WML: white matter lesions. * p < 0.05. ** p = 0.05. # p < 0.01. ## p < 0.001.

total volume of the hippocampi, and the CDR sum of boxes significantly predicted the progression of MCI to dementia (Table 3). The baseline MMSE score, WML burden, or the APOE ␧4 allele were not significant predictors of progression. When patients with non-AD dementia were excluded, the right, left and total hippocampal and entorhinal cortex volumes significantly predicted the progression to AD (Table 3). In this analysis CDR sum of boxes, MMSE scores or APOE ␧4 allele were not significant predictors for AD. In bivariate Cox regression analysis the CDR sum of boxes and the volumes of the right entorhinal cortex remained significantly associated with progression of MCI to dementia, whereas progression of MCI to AD was significantly associated only with the baseline volumes of the entorhinal cortices (Table 4).

4. Discussion Clinically relevant measures for predicting dementia in elderly subjects suffering from memory disorders are needed. Some previous studies have shown promising results on evaluation of the MTL structures in the prediction of conversion of MCI to AD [7,15,17,18]. The strength of the present study is the large sample size of MCI deriving from population-based cohorts with a mean follow-up time of 34 months. However, during this follow-up period only 13 subjects (21.7%) converted to dementia, with the annual conversion rate being 7.7% suggesting the heterogeneity of MCI. In the study by Larrieu et al. [23], an annual conversion rate of 8.3% was found, and more than 40% of cases

36

T. Tapiola et al. / Neurobiology of Aging 29 (2008) 31–38

reverted to normal during 5 years of follow-up. In our study, 7 out of 60 MCI subjects (12%) who entered the follow-up showed improvement of cognition in the last evaluation also indicating instability to some degree in MCI category as a diagnostic entity. Although the conversion rate and the number of subjects with progression of MCI to AD were low in our population-based study, atrophy of the entorhinal cortex and hippocampus in the beginning of the follow-up had a significant prognostic value in detecting subjects with progressive MCI. It is well known that the entorhinal cortex occupies the key position for the communications between the hippocampus and the rest of the brain. Accordingly, the degeneration of the neuronal architecture of the entorhinal cortex destroys a large functional hippocampal pathway, respectively, causing memory impairment and cognitive deficits associated with AD [12]. In our previous cross-sectional study, volumetric MRI analysis of the entorhinal cortex and hippocampus provided in vivo evidence that entorhinal atrophy precedes hippocampal atrophy in AD [29]. We showed that the most efficient overall classification between controls and individuals with MCI subjects was achieved with entorhinal cortex (65.9%), whereas the best overall classification between controls and AD patients (90.7%) and between individuals with MCI and AD patients (82.3%) was achieved with hippocampal volumes. These results suggested that the entorhinal atrophy precedes hippocampal atrophy in AD. The entorhinal volume loss was dominant over the hippocampal volume loss in MCI, whereas more pronounced hippocampal volume loss appeared in mild AD. In the present study the MTL atrophy on the right side predicted the conversion of MCI to dementia, though if considering the prediction to AD, both hemispheres were predictors for conversion. These results remind the previous study showing greater atrophy of the right entorhinal cortex in subjects with progression of MCI to AD [6]. The hemispheric differences in the volumes might be related to alternations in left–right asymmetry in the progressive MCI, but in the interpretation of the results the heterogeneity of the MCI and dementia should be emphasized. MRI volumetric data in combination with neuropsychological data and APOE ␧4 allele have shown a significant role in predicting the risk of AD [1,30]. In the present study, we found that the unilateral analysis the volumes of the hippocampus and the entorhinal cortex on the right side and CDR sum of boxes significantly predicted the progression of MCI to dementia. Instead the MMSE score, WML burden, or APOE genotype were not significant predictors of progression. If patients who developed non-AD dementia were excluded, volumes of hippocampi and entorhinal cortex predicted the progression to AD, but in this analysis CDR sum of boxes did not reach significance. These findings are well in line with data reported by Korf et al. [22] showing that visual assessment of MTL structures on MRI using a standardized rating scale is a predictor of dementia in

MCI subjects independently of, e.g. age, gender, education, MMSE, CDR sum of boxes, APOE genotype, and WML burden. The APOE ␧4 allele is a well-established risk factor for AD. Some previous studies have shown a strong effect of the APOE ␧4 allele on the degree of atrophy of the MTL structures, and also on brain metabolism measured by PET [9,10,16,25,33,34]. Also in the present study the effect of ␧4 allele was seen. In the progressive MCI group, patients with at least one ␧4 allele had significantly reduced hippocampus compared to those without ␧4 allele, and volumes of MTL structures were significantly decreased in progressive MCI patients with ␧4 allele compared to stable MCI subjects. On the other hand, there were no differences in volumes between the stable and progressive MCI groups without ␧4 allele. However, APOE ␧4 allele did not predict progression in Cox regression analysis. This is probably explained by low number of converters and consequently small number of subjects in each APOE strata. It has been proposed that the WML burden is associated with cerebrovascular or vascular phenomena [24]. Although vascular factors are recognized as risk factors for AD and MCI [19,20,37], we found no association between WMLs and progression of MCI to dementia in this population-based cohort. The extent of WML burden was relatively modest in this cohort that may be explained by the criteria of MCI used in this study emphasizing the memory loss. However, also other studies have indicated that MTL atrophy is a stronger predictor of dementia than the amount of WMLs [22]. In conclusion, we observed in our present study an annual conversion rate of 7.7% from MCI to dementia. Atrophy was seen in MTL in the baseline, mostly on the right side, which predicted the conversion to dementia over follow-up of 34 months. Atrophy of MTL was significantly present in progressive MCI group versus stable MCI group in carriers of at least one ␧4 allele, and not significantly present in noncarriers. In our study, the neuropsychological testing, WML load or APOE genotyping provided no additional value in prediction of progression of MCI to AD. MCI subjects are of major interest for preventive pharmaceutical and nonpharmaceutical interventions and MTL volumetry helps in identifying among the MCI subjects a group that is at high risk for developing AD.

Acknowledgements The study was supported by the EVO grant 5772720 from the Kuopio University Hospital, Nordic Center of Excellence in Neurodegeneration, the Sigrid Jus´elius Foundation, the North-Savo Regional Fund of the Finnish Cultural Foundation, and the Academy of Finland. Disclosure statement: The manuscript has been approved by all the authors, and there are no conflicts of interest, or any other kind of conflicts regarding it.

T. Tapiola et al. / Neurobiology of Aging 29 (2008) 31–38

References [1] Albert MS. Cognitive and neurobiologic markers of early Alzheimer disease. Proc Natl Acad Sci USA 1996;93(24):13547–51. [2] American Psychiatric Association. Diagnostic and statistical manual of mental disorders. 4th ed. Washington, DC: American Psychiatric Association; 1994. [3] Bigler ED, Lowry CM, Anderson CV, Johnson SC, Terry J, Steed M. Dementia, quantitative neuroimaging, and apolipoprotein E genotype. AJNR Am J Neuroradiol 2000;21(10):1857–68. [4] Braak H, Braak E. Neuropathological staging of Alzheimer-related changes. Acta Neuropathol (Berl) 1991;82(4):239–59. [5] De Santi S, de Leon MJ, Rusinek H, Convit A, Tarshish CY, Roche A, et al. Hippocampal formation glucose metabolism and volume losses in MCI and AD. Neurobiol Aging 2001;22(4):529–39. [6] deToledo-Morrell L, Stoub TR, Bulgakova M, Wilson RS, Bennett DA, Leurgans S, et al. MRI-derived entorhinal volume is a good predictor of conversion from MCI to AD. Neurobiol Aging 2004;25:1197–203. [7] Dickerson BC, Goncharova I, Sullivan MP, Forchetti C, Wilson RS, Bennett DA, et al. MRI-derived entorhinal and hippocampal atrophy in incipient and very mild Alzheimer’s disease. Neurobiol Aging 2001;22(5):747–54. [8] Du AT, Schuff N, Amend D, Laakso MP, Hsu YY, Jagust WJ, et al. Magnetic resonance imaging of the entorhinal cortex and hippocampus in mild cognitive impairment and Alzheimer’s disease. J Neurol Neurosurg Psychiatry 2001;71(4):441–7. [9] Geroldi C, Pihlajam¨aki M, Laakso MP, DeCarli C, Beltramello A, Bianchetti A, et al. ApoE-epsilon4 is associated with less frontal and more medial temporal lobe atrophy in AD. Neurology 1999;53(8): 1825–32. [10] Geroldi C, Laakso MP, DeCarli C, Beltramello A, Bianchetti A, Soininen H, et al. Apolipoprotein E genotype and hippocampal asymmetry in Alzheimer’s disease. A volumetric MRI study. J Neurol Neurosurg Psychiatry 2000;68(1):93–6. [11] Huesgen CT, Burger PC, Crain BJ, Johnson GA. In vitro MR microscopy of the hippocampus in Alzheimer’s disease. Neurology 1993;43(1):145–52. [12] Hyman BT, Van Hoesen GW, Damasio AR, Barnes CL. Alzheimer’s disease: cell-specific pathology isolates the hippocampal formation. Science 1984;225(4667):1168–70. [13] H¨anninen T, Hallikainen M, Murtolahti R, Vanhanen M, Soininen H. Prevalence of mild cognitive impairment: a population-based study in elderly subjects. Acta Neurol Scand 2002;106(3):148–54. [14] Insausti R, Juottonen K, Soininen H, Insausti AM, Partanen K, Vainio P, et al. MR volumetric analysis of the human entorhinal, perirhinal, and temporopolar cortices. Am J Neuroradiol 1998;19(4):659–71. [15] Jack Jr CR, Petersen RC, Xu YC, O’Brien PC, Smith GE, Ivnik RJ, et al. Prediction of AD with MRI-based hippocampal volume in mild cognitive impairment. Neurology 1999;52(7):1397–403. [16] Juottonen K, Lehtovirta M, Helisalmi S, Riekkinen Sr PJ, Soininen H. Major decrease in the volume of the entorhinal cortex in patients with Alzheimer’s disease carrying the apolipoprotein E ␧4 allele. J Neurol Neurosurg Psychiatry 1998;65(3):322–7. [17] Killiany RJ, Gomez-Isla T, Moss M, Kikinis R, Sandor T, Jolesz F, et al. Use of structural magnetic resonance imaging to predict who will get Alzheimer’s disease. Ann Neurol 2000;47(4):430–9. [18] Killiany RJ, Hyman BT, Gomez-Isla T, Moss MB, Kikinis R, Jolesz F, et al. MRI measures of entorhinal cortex vs. hippocampus in preclinical AD. Neurology 2002;58(8):1188–96. [19] Kivipelto M, Helkala E-L, H¨anninen T, Laakso MP, Hallikainen M, Alhainen K, et al. Midlife vascular risk factors and late-life mild cognitive impairment. A population based study. Neurology 2001;56(12): 1683–9. [20] Kivipelto M, Helkala EL, Laakso MP, Hanninen T, Hallikainen M, Alhainen K, et al. Apolipoprotein E ␧4 allele, elevated midlife cholesterol and systolic blood pressure are independent risk factors for late-life Alzheimer’s disease. Ann Intern Med 2002;137(3):149–55.

37

[21] Kordower JH, Chu Y, Stebbins GT, DeKosky ST, Cochran EJ, Bennett D, et al. Loss and atrophy of layer II entorhinal cortex neurons in elderly people with mild cognitive impairment. Ann Neurol 2001;49(2):202–13. [22] Korf ES, Wahlund LO, Visser PJ, Scheltens P. Medial temporal lobe atrophy on MRI predicts dementia in patients with mild cognitive impairment. Neurology 2004;63(1):94–100. [23] Larrieu S, Letenneur L, Orgogozo JM, Fabrigoule C, Amieva H, Le Carret N, et al. Incidence and outcome of mild cognitive impairment in a population-based prospective cohort. Neurology 2002;59(10):1594–9. [24] Launer LJ. Epidemiology of white-matter lesions. Int Psychogeriatr 2003;15(Suppl. 1):99–103. [25] Lehtovirta M, Soininen H, Laakso MP, Partanen K, Helisalmi S, Mannermaa A, et al. SPECT and MRI analysis in Alzheimer’s disease: relation to apolipoprotein E epsilon 4 allele. J Neurol Neurosurg Psychiatry 1996;60(6):644–9. [26] Lehtovirta M, Laakso MP, Frisoni GB, Soininen H. How does the apolipoprotein E genotype modulate the brain in aging and in Alzheimer’s disease? A review of neuroimaging studies. Neurobiol Aging 2000;21(2):293–300. [27] Lopez OL, Jagust WJ, Dulberg C, Becker JT, DeKosky ST, Fitzpatrick A, et al. Risk factors for mild cognitive impairment in the Cardiovascular Health Study Cognition Study: part 2. Arch Neurol 2003;60(10): 1394–9. [28] McKhann G, Drachman D, Folstein M, Katzman R, Price D, Stadlan EM. Clinical diagnosis of Alzheimer’s disease: report of the NINCDSADRDA Work Group under the auspices of Department of Health and Human Services Task Force on Alzheimer’s Disease. Neurology 1984;34(7):939–44. [29] Pennanen C, Kivipelto M, Tuomainen S, Hartikainen P, H¨anninen T, Laakso MP, et al. Hippocampus and entorhinal cortex in mild cognitive impairment and early AD. Neurobiol Aging 2004;25(3):303– 10. [30] Petersen RC, Smith GE, Ivnik RJ, Tangalos EG, Schaid DJ, Thibodeau SN, et al. Apolipoprotein E status as a predictor of the development of Alzheimer’s disease in memory-impaired individuals. JAMA 1995;273(16):1274–8. [31] Petersen RC, Smith GE, Waring SC, Ivnik RJ, Tangalos EG, Kokmen E. Mild cognitive impairment: clinical characterization and outcome. Arch Neurol 1999;56(3):303–8. [32] Petersen RC, Stevens JC, Ganguli M, Tangalos EG, Cummings JL, DeKosky ST. Practice parameter: early detection of dementia—mild cognitive impairment (an evidence-based review). Report of the Quality Standards Subcommittee of the American Academy of Neurology. Neurology 2001;56(9):1133–42. [33] Reiman EM, Caselli RJ, Yun LS, Chen K, Bandy D, Minoshima S, et al. Preclinical evidence of Alzheimer’s disease in persons homozygous for the e4 allele for apolipoprotein E. N Engl J Med 1996;334(12):752– 8. [34] Reiman EM, Caselli RJ, Chen K, Alexander GE, Bandy D, Frost J. Declining brain activity in cognitively normal apolipoprotein E epsilon 4 heterozygotes: a foundation for using positron emission tomography to efficiently test treatments to prevent Alzheimer’s disease. Proc Natl Acad Sci USA 2001;98(6):3334–9. [35] Smith GE, Petersen RC, Parisi JE, Ivnik RJ, Kokmen E, Tangalos EG, et al. Definition, course, and outcome of mild cognitive impairment. Aging Neuropsychol Cogn 1996;3:141–7. [36] Squire LR, Zola-Morgan S. The medial temporal lobe memory system. Science 1991;253(5026):1380–6. [37] Tervo S, Kivipelto M, H¨anninen T, Vanhanen M, Hallikainen M, Mannermaa A, et al. Incidence and risk factors for mild cognitive impairment: a population-based three year follow-up study of cognitively healthy elderly subjects. Dement Geriatr Cogn Disord 2004;17(3):196–203. [38] Tsukamoto K, Watanabe T, Matsushima T, Kinoshita M, Kato H, Hashimoto Y, et al. Determination by PCR-RFLP of apo E genotype in a Japanese population. J Lab Clin Med 1993;121(4):598–602.

38

T. Tapiola et al. / Neurobiology of Aging 29 (2008) 31–38

[39] Van Hoesen GW, Hyman BT. Hippocampal formation: anatomy and the patterns of pathology in Alzheimer’s disease. Prog Brain Res 1990;83:445–57. [40] Van Hoesen GW, Hyman BT, Damasio AR. Entorhinal cortex pathology in Alzheimer’s disease. Hippocampus 1991;1(1):1–8.

[41] Wahlund LO, Barkhof F, Fazekas F, Bronge L, Augustin M, Sjogren M, et al. European Task Force on Age-related White Matter Changes. A new rating scale for age-related white matter changes applicable to MRI and CT. Stroke 2001;32(6):1318–22.