Relationship between clock drawing test performance and regional cerebral blood flow in Alzheimer's disease: a single photon emission computed tomography study

The clock drawing test (CDT) is a useful tool for screening cognitive impairment. Previous neuropsychological studies have revealed that CDT performance requires several cognitive functions including semantic memory, visuospatial function and executive function. However, the neural substrates involved remain to be elucidated. The aim of the present study was to identify the brain regions responsible for CDT performance in patients with Alzheimer's disease (AD). Twenty-six patients satisfying the National Institute of Neurological and Communicative Disease and Stroke-Alzheimer's Disease and Related Disorders Association criteria for probable AD underwent the CDT and the Mini-Mental State Examination (MMSE), together with a N-isopropyl-p-[123I] iodoamphetamine (IMP) single photon emission computed tomography measurements of the resting regional cerebral blood flow (rCBF). The CDT score correlated significantly with the MMSE score (r=0.582; P < 0.05). Stepwise multiple regression analysis revealed that the MMSE score and the left posterior temporal rCBF were major predictors of CDT score. These findings suggest that the CDT score may reflect the severity of dementia, and that it has a close relationship with the left posterior temporal function. Our findings provide the first functional neuroimaging evidence for the neural substrates involved in CDT performance.     

Regional cerebral blood flow measured by99mTc-HMPAO SPECT differs in subgroups of Alzheimer's disease

Summary Alzheimer's disease (AD) is a heterogeneous entity. Identifying AD subtypes might have impact in patients' response to different treatment strategies. We designed a study to examine regional cerebral blood flow (rCBF) in AD subtypes. To identify AD subtypes, we performed a cluster analysis including performance on memory, language, visuospatial, praxis, and executive functions. The rCBF measured by^99mTc-HMPAO SPECT was referred to the cerebellum. We examined 35 patients fulfilling the NINCDS-ADRDA criteria of probable AD and 13 age and sex-matched healthy cognitively intact controls. AD patients were at the early stage of the disease, their mean Mini-Mental Status (MMS) score (S.D.) was 22.5 (3.6). The cluster analysis revealed two AD subgroups: AD1 (N=12) and AD2 (N=23). The subgroups did not differ in age, sex, or global clinical severity as assessed by MMS and Brief Cognitive Rating Scale (BCRS). Both subgroups had equally impaired memory. The AD2 group was inferior to the AD1 group on verbal, visuospatial, praxic, and executive functions. The AD1 group showed reduced rCBF ratios in the temporal and parietal cortices and the amygdala compared to controls. The AD2 group differed from controls in the rCBF ratios of frontal, temporal, parietal, occipital, basal ganglia, and amygdaloid regions bilateral and from AD1 in the rCBF ratios of frontal and temporal cortices. In AD patients, the rCBF ratios did not correlate with MMS or BCRS scores. In contrast, several significant correlations were found between decreases rCBF ratios and impairment of memory and other cognitive functions. In conclusion, a cluster analysis on neuropsychological test performance identified two AD subgroups that differed on the neuropsychological profile and on the rCBF in spite of similar global clinical severity.     

Relationship between blood flow kinetics and severity of Alzheimer's disease: assessment of severity using a questionnaire-type examination, Alzheimer's disease assessment scale, cognitive sub-scale (ADAS(cog)).

We assessed hemokinetics associated with changes in Alzheimer's disease (AD) severity in 90 AD patients by researching the relationship between AD Assessment Scale, cognitive sub-scale (ADAS(cog)) scores and regional cerebral blood flow (rCBF). In the present study, we employed the questionnaire-type ADAS(cog) examination to accurately assess the severity of AD. Between five groups classified on the basis of ADAS(cog) score, significant differences were observed in parietal, lateral temporal and superior frontal rCBF. In addition, in parietal and lateral temporal regions, significant correlations were also observed between ADAS(cog) score and rCBF. In superior frontal rCBF, significant differences were noted only between group 5 (> or =40 ADAS(cog) points) and each of the other groups; there was no significant correlation between rCBF and ADAS(cog) score. Thus, we propose the following mechanism for blood flow kinetics associated with changed severity: In an early stage of AD, blood flow in the medial temporal cortex is impaired, and gradually involves the temporoparietal regions. While the medial temporal impairment of blood flow reaches a plateau, temporoparietal blood flow continues to be impaired well into a severe stage, at which point blood flow impairment in the frontal region is initiated.     

The investigation of Alzheimer''s disease with single photon emission tomography.

Twenty patients satisfying standard clinical criteria for Alzheimer's disease (AD) and six age-matched normal controls were studied using 99mTc hexamethyl-propyleneamine oxime and single photon emission tomography. The AD patients had lower regional cerebral blood flow (rCBF) in the temporal and posterior parietal lobes compared to controls. AD patients with apraxia and aphasia had lower rCBF in the lateral temporal and posterior parietal lobes than AD patients without these features. Within the AD group, correlations were found between neuropsychological tests and rCBF: praxis correlated with posterior parietal activity, memory with left temporal lobe activity and language with activity throughout the left hemisphere.     

A SPECT study of apathy in Alzheimer's disease

BACKGROUND/AIMS: To assess the association between regional cerebral blood flow (rCBF) and apathy in Alzheimer's Disease (AD). METHODS: SPECT and MRI scans were obtained from 51 nondepressed outpatients meeting criteria for probable AD (age 77.6 +/- 6.6 years; MMSE 22.3 +/- 5.1; 23 apathetic, 28 nonapathetic) and 23 healthy elderly (75.6 +/- 3.8 years) controls. The following regions of interest (ROIs) were compared between apathetic and nonapathetic AD patients and then referenced against aged controls: anterior cingulate, orbitofrontal cortex, middle medial temporal cortex, hippocampus, medial superior temporal cortex, thalamus/hypothalamus and pons. RESULTS: Apathetic and nonapathetic patients had significant differences in rCBF. Relative to nonapathetic AD patients, apathetic AD patients had lower perfusion in 2 ROIs (right orbitofrontal cortex and left anterior cingulate) and higher perfusion in 5 ROIs (right and left hippocampi, left medial superior temporal gyrus, and right and left middle medial temporal cortex). Comparison of rCBF in these 7 ROIs to healthy elderly controls confirmed hypoperfusion in the left anterior cingulate and right orbitofrontal cortex and suggested a relative sparing of perfusion among apathetic AD patients in the remaining 5 ROIs. CONCLUSIONS: In this group of nondepressed patients with AD, apathetic subjects displayed significant perfusion differences compared to nonapathetic subjects.     

Neural substrates for writing impairments in Japanese patients with mild Alzheimer's disease: a SPECT study

Language is fairly well preserved in most patients with mild Alzheimer's disease, but writing ability seems to be impaired even in the early stages of the disease. To investigate the neural bases of writing impairments in Alzheimer's disease (AD), we examined the correlation between writing ability and regional cerebral blood flow (rCBF) in 52 Japanese patients with mild AD compared to 22 controls, using single photon emission computed tomography (SPECT). We found that, compared with control subjects, Kana writing to dictation and copying Kanji words were preserved in AD patients, but writing to dictating Kanji words was impaired. We classified the errors in the Kanji dictation task into four types to investigate the correlation between rCBF and the error type, as follows: non-response errors, phonologically plausible errors, non-phonologically plausible errors, and peripheral errors. Non-response errors, which indicated difficulty with retrieving Kanji graphic images, were the most frequent. When controlled for confounding factors, the number of non-response errors negatively correlated with rCBF in the left inferior parietal lobule, the posterior middle and inferior temporal gyri, and the posterior middle frontal gyrus. Thus, the impaired recall of Kanji in early Alzheimer's disease is related to dysfunctional cortical activity, which appears to be predominant in the left frontal, parietal, and temporal regions.     

Single-Photon Emission Computed Tomography Studies of Regional Cerebral Blood Flow in Multiple Infarct Dementia

Multiinfarct dementia (MID) and Alzheimer's disease (AD), both characterized by a decline in cognitive function, are often difficult to differentiate and may coexist. This study reports the findings of single-photon emission computed tomography (SPECT) using [²³¹]N-isopropyl-p-iodoamphetamine to determine cerebral blood flow patterns in patients with MID (n = 11 ), as compared with patients with AD (n = 22) and nondemented control subjects (n = 12). Data were acquired at two tomographic levels for dorsolateral frontal, parietal, orbitofrontal, and temporal areas of the cortex. Analyses of variance revealed that the blood flow pattern for the MID group was very similar to that in the AD patients, with both groups showing hypoperfusion in the temporal area, although blood flow in the left parietal region was lower for the patients with AD. When normal regional cerebral blood flow (rCBF) was defined as within 2 standard deviations of control values, most of the patients with MID had normal rCBF, while a few patients showed abnormal rCBF in all regions. In contrast, the majority of AD patients showed abnormal rCBF in the temporal part of the cortex. This suggests that while AD is characterized by hypoperfusion in the temporal and parietal areas, there is no characteristic rCBF pattern in MID. These findings emphasize the need to use multiple modalities when clinically evaluating patients with MID.     

Quantitative analysis of brain perfusion SPECT in Alzheimer's disease using a fully automated regional cerebral blood flow quantification software, 3DSRT

PURPOSE: The clinical symptoms of Alzheimer's disease (AD) show great diversity depending on the clinical stage. We investigated the correlation of regional cerebral blood flow (rCBF) changes and the clinical severity of AD patients. METHODS: Thirty-nine AD patients and 16 normal subjects participated in this study. AD patients were divided into three subgroups by clinical severity. Quantitative brain perfusion SPECT analyses were performed using a rCBF quantification software, 3DSRT. RESULTS: In mild AD, significant decreases of rCBF were detected in the bilateral parietal, angular gyrus, pericallosal, thalamus, right temporal and left hippocampal regions. Moderate AD patients showed significantly lower blood flow than those with mild AD only to the right hippocampus. Analysis of the severe AD group revealed a nearly diffuse decrease of rCBF throughout the cerebral cortex except for part of the frontal lobe compared with moderate patients. CONCLUSIONS: These results were consistent with previous findings demonstrated by qualitative analysis of CBF. The decreased thalamic blood flow was noteworthy as this finding has rarely been reported. In consideration of the structure and function of the Papez circuit, which connects the medial temporal lobe and thalamus, a remote metabolic effect might be the cause of lower rCBF in the thalamus.     

SPECT检测利培酮对精神分裂症患者脑血流灌注的影响

目的探讨利培酮对局部脑血流灌注(rCBF)的影响及疗效与rCBF之间的关系。方法研究组为24例未用过药的精神分裂症患者。男10例,女14例。正常对照组26例,男12例,女14例。用利培酮(3～6mg/d)治疗8周。患者在治疗前后进行基础状态及认知激活状态脑SPECT显像。结果与正常对照组相比,治疗前基础状态时,24例患者左右颞叶后下部血流灌注增加;激活状态时,左额叶外侧中部血流灌注显著下降。治疗后与治疗前相比,右颞叶外侧部、左右颞叶后上部基础状态的血流灌注显著下降;左右额叶中下部、左额叶外侧下部、左额颞上部及左额外侧上部认知激活状态的血流灌注显著增加。PANSS减分率与脑血流灌注的变化有关。结论利培酮治疗精神分裂症后,右颞外侧部、左右颞叶后上部、左右额叶中下部及左额叶外侧上下部的血流灌注变化显著。疗效与血流灌注变化有关。提示脑血流灌注对预测药物疗效具有重要意义。     

A high-resolution single photon emission computed tomography study of verbal recognition memory in Alzheimer's disease

BACKGROUND: In view of the recent technological advances and its ease of availability, we used single photon emission computed tomography (SPECT) to examine the performance of early Alzheimer's disease (AD) subjects on a verbal recognition memory task. METHODS: Eighteen early AD and 10 matched healthy control subjects underwent split-dose (99m)Tc-HMPAO (Ceretec) SPECT using a verbal recognition memory and control task. SPECT images co-registered with MRI scans were used to determine relative regional cerebral blood flow (rCBF) changes in regions of interest. RESULTS: In healthy control subjects, verbal recognition increased rCBF in the right occipital region, thalamus, left prefrontal pole, posterior parietal region and cerebellum, and decreased rCBF in the right hippocampus. AD subjects showed bilateral prefrontal, posterior parietal and occipital increases, unilateral increase in the left posterior temporal region, and bilateral reductions in the hippocampus. Although activation was significantly different between the two groups in the right thalamus and left medial prefrontal region, the verbal recognition task did not enhance discrimination between groups. CONCLUSIONS: Compared with controls, AD subjects activate a similar but more extensive bilateral network during verbal recognition, possibly reflecting an attempt to compensate for impaired processing.     

The relevance of hippocampal subfield integrity and clock drawing test performance for the diagnosis of Alzheimer’s disease and mild cognitive impairment

Objectives: The clock drawing test (CDT) is one of the worldwide most used screening tests for Alzheimer’s disease (AD). MRI studies have identified temporo-parietal regions being involved in CDT impairment. However, the contributions of specific hippocampal subfields and adjacent extrahippocampal structures to CDT performance in AD and mild cognitive impairment (MCI) have not been investigated so far. It is unclear whether morphological alterations or CDT score, or a combination of both, are able to predict AD.

Methods: 38 AD patients, 38?MCI individuals and 31 healthy controls underwent neuropsychological assessment and MRI at 3 Tesla. FreeSurfer 5.3 was used to perform hippocampal parcellation. We used a collection of statistical methods to better understand the relationship between CDT and hippocampal formation. We also tested the clinical feasibility of this relationship when predicting AD.

Results: Impaired CDT performance in AD was associated with widespread atrophy of the cornu ammonis, presubiculum, and subiculum, whereas MCI subjects showed CDT-related alterations of the CA4-dentate gyrus and subiculum. CDT correlates in AD and MCI showed regional and quantitative overlap. Importantly, CDT score was the best predictor of AD.

Conclusions: Our findings lend support for an involvement of different hippocampal subfields in impaired CDT performance in AD and MCI. CDT seems to be more efficient than subfield imaging for predicting AD.     

Cortical signature of clock drawing performance in Alzheimer's disease and mild cognitive impairment

It is unclear whether clock drawing test (CDT) performance relies on a widely distributed cortical network, or whether this test predominantly taps into parietal cortex function. So far, associations between cortical integrity and CDT impairment in Alzheimer's disease (AD) and mild cognitive impairment (MCI) largely stem from cortical volume analyses. Given that volume is a product of thickness and surface area, investigation of the relationship between CDT and these two cortical measures might contribute to better understanding of this cognitive screening tool for AD. 38 patients with AD, 38 individuals with MCI and 31 healthy controls (HC) underwent CDT assessment and MRI at 3 Tesla. The surface-based analysis via Freesurfer enabled calculation of cortical thickness and surface area. CDT was scored according to the method proposed by Shulman and related to the two distinct cortical measurements. Higher CDT scores across the entire sample were associated with cortical thickness in bilateral temporal gyrus, the right supramarginal gyrus, and the bilateral parietal gyrus, respectively (p < 0.001 CWP corr.). Significant associations between CDT and cortical thickness reduction in the parietal lobe remained significant when analyses were restricted to AD individuals. There was no statistically significant association between CDT scores and surface area (p < 0.001 CWP corr.). In conclusion, CDT performance may be driven by cortical thickness alterations in regions previously identified as “AD vulnerable”, i.e. regions predominantly including temporal and parietal lobes. Our results suggest that cortical features of distinct evolutionary and genetic origin differently contribute to CDT performance.     

Brain structural and cognitive correlates of clock drawing performance in Alzheimer's disease.

The Clock Drawing Test (CDT) is widely used in the assessment of dementia and is known to be sensitive to the detection of deficits in neurodegenerative disorders such as Alzheimer's disease (AD). CDT performance is dependent not only on visuospatial and constructional abilities, but also on conceptual and executive functioning; therefore, it is likely to be mediated by multiple brain regions. The purpose of the present study was to identify component cognitive processes and regional cortical volumes that contribute to CDT performance in AD. In 29 patients with probable AD, CDT performance was significantly related to right-, but not left-hemisphere, regional gray matter volume. Specifically, CDT score correlated significantly with the right anterior and posterior superior temporal lobe volumes. CDT scores showed significant relationships with tests of semantic knowledge, executive function, and visuoconstruction, and receptive language. These results suggest that in AD patients, CDT performance is attributable to impairment in multiple cognitive domains but is related specifically to regional volume loss of right temporal cortex.     

Relationship between regional cerebral blood flow and verbal fluency in Alzheimer's disease

Category and letter verbal fluency tests are widely used for dementia detection and severity measure. Performances of these tasks have been regarded to be mainly associated with the left frontal lobe function. However, some recent studies suggest that there are different neuropsychological bases between these two tasks, and the brain region which contributes to these performances still remains unclear in Alzheimer's disease (AD). To clarify the neural basis of verbal fluency in AD, we examined the relationship between performances of these tasks and regional cerebral blood flow (rCBF). Twenty-five AD patients were administered verbal fluency tasks and single photon emission computed tomography (SPECT) scans. Thirteen cortical regions of interest were symmetrically defined in each hemisphere. Letter fluency scores were correlated significantly only with the left prefrontal (Brodmann's area (BA) 10-46) regional cerebral blood flow (rCBF). In contrast, category fluency scores were correlated most strongly with the left temporal rCBF and also with the left prefrontal (BA 10-46) rCBF. In conclusion, the present study suggests that left prefrontal (BA 10-46) dysfunction contributes to decline in both letter and category fluency scores in AD, while typical posterior dysfunction of AD has a closer relationship with decline in category fluency scores.     

Cerebral blood flow patterns underlying the differential impairment in category vs letter fluency in Alzheimer's disease.

Verbal fluency tasks are used to assess language functioning in Alzheimer's disease (AD), and performance typically declines as the disease progresses. However, several studies have shown that Category Fluency performance (produce words from a category) declines faster than Letter Fluency performance (produce words beginning with a certain letter), which is not the case for other dementias. The purpose of this study was to determine if each of these two types of fluency tasks was associated with different patterns of cerebral blood flow abnormality in AD. A resting, Xenon-inhalation regional cerebral blood flow measurement (133Xe rCBF) and neuropsychological evaluation was administered to 25 patients with probable AD and 24 healthy elderly controls. Stepwise regression using rCBF measures as predictor variables was used to predict Category and Letter Fluency performance, in both a combined group of patients and controls, and in the patient group alone. Correlations were also computed between rCBF variables and the difference between normatively corrected scores on each task for each subject, which characterized the extent of the discrepancy between them. In full sample regressions, both Category and Letter Fluency were predicted by education and the decline in left inferior parietal flow, a focal AD-related deficit. Additional variance in Category fluency, however, was predicted by global mean flow, while additional variance in Letter Fluency was predicted by frontal flow. Within the patient sample, in turn, the primary predictor of Category Fluency was mean flow; the primary predictor of Letter Fluency was left-sided frontal flow. Analysis of the fluency difference score revealed that relatively greater impairment of Category Fluency was associated with more typical, AD-related deficits in posterior temporal and parietal perfusion. When the two were equivalently impaired, typical AD-related deficits were accompanied by marked deficits in frontal perfusion. These findings are consistent with the underlying neuropsychology of these tasks, and suggest that Category Fluency's stronger association to the most typical CBF deficits of AD account for its greater sensitivity to this disease. Letter Fluency deficits, on the other hand, carry significant information about the degree to which perfusion deficits have spread to frontal cortex.     

Regional cerebral blood flow abnormalities associated with apathy and depression in Alzheimer disease

The aim of this study was to identify brain areas related to apathy or depression in patients with Alzheimer disease (AD). Eighty-one AD patients were enrolled in this prospective study. (99m)Tc-HMPAO single photon emission computed tomography was performed to evaluate regional cerebral blood flow (rCBF). According to the Neuropsychiatric Inventory subscores of apathy and depression, 9 patients were classified as clinically significant (cs) depressed and non-cs-apathetic (D+) groups and 9 were classified as cs-apathetic and non-cs-depressed (A+) groups. In addition, 18 patients were classified as age-matched and Mini-Mental State Examination-matched disease control groups (D-, A-). The significance of rCBF differences between groups and the correlation between rCBF and subscores in 81 AD patients were estimated by SPM (uncorrected P < 0.005) analysis. D+ patients had significantly lower perfusion in the right orbitofrontal and inferior frontal gyri than D- patients, whereas A+ patients had this in the right amygdala, temporal, posterior cingulate, right superior frontal, postcentral, and left superior temporal gyri than A- patients. The negatively correlated areas with depression subscores included the left inferior frontal and the right middle frontal gyri and those with apathy subscores included the right temporal and right medial frontal gyri. We suggest that this finding may indicate that apathy and depression in AD patients involve distinct functional circuits.     

Comparison of brain perfusion in corticobasal degeneration and Alzheimer's disease

To compare brain perfusion between corticobasal degeneration (CBD) and Alzheimer's disease (AD), we measured regional cerebral blood flow (rCBF) semiquantitatively with single-photon emission computed tomography in 10 patients with CBD and 16 with AD. There was no significant difference in age or illness duration between the patients with CBD and AD. Mini-Mental State Examination scores were significantly lower in the AD patients than in the CBD patients. All CBD patients showed asymmetric akinetic-rigid syndrome and limb apraxia. Four CBD patients were demented, and 1 AD patient had parkinsonism. Compared with 12 age-matched control subjects, the average of the left and right rCBF values for the CBD patients was significantly reduced in the prefrontal, anterior cingulate (AC), medial premotor, sensorimotor (SM), posterior parietal (PP) and superior temporal (ST) cortices as well as in the basal ganglia (BG) and thalamus (Th), while the prefrontal, PP and ST cortices were significantly hypoperfused in the AD patients. In the CBD patients, rCBF was significantly less in the AC and SM cortices, and in the Th and BG, and significantly greater in the PP cortex than in the AD patients. Interhemispheric differences of rCBF in the inferior prefrontal and SM cortices were significantly greater in the CBD patients than the AD patients. It is concluded that rCBF comparison may aid in differentiating CBD from AD.     

Effects of long-term Donepezil therapy on rCBF of Alzheimer's patients.

BACKGROUND: The recent introduction of acetylcholinesterase inhibitors (AChEIs) therapy for Alzheimer's Disease (AD) has led to the need to assess the brain's response to the therapy on an objective, neurophysiological basis. Brain perfusion single photon emission computed tomography (SPECT) was used in an open-label study to evaluate the effect of chronic Donepezil administration to a group of patients affected by mild to moderate AD, compared to a group of AD patients not receiving AChEIs and kept under observation for a similar period. METHODS: Twenty-five consecutive patients with probable AD (National Institute of Neurological and Communicative Disorders and Stroke-Alzheimer's Disease and Related Disorders Association criteria) (19 women, 6 men; mean age: 74.2+/-7.2; mean Mini-Mental State Examination score, MMSE: 19.8+/-3.5) underwent (t0) brain SPECT with 99mTc-hexamethylpropylene-amine-oxime by a brain-dedicated, high-resolution camera and were re-evaluated (t1) after 11+/-2.6 months of chronic Donepezil administration (5mg/day) (treated group). Thirteen AD patients (9 women, 4 men, mean age: 71.4+/-5.7, MMSE score: 20.6+/-3.5) were not treated with AChEIs and served as controls (untreated group). They were subjected to the same evaluation after 13+/-1.4 months as the treated group. Statistical parametric mapping (SPM) was employed to analyse SPECT findings. RESULTS: The MMSE score declined significantly (P<0.01) from t0 to t1 both in untreated (from 20.6+/-3.5 to 17.8+/-4.4) and in treated (from 19.8+/-3.5 to 17.8+/-4.1) group. At t(0), the untreated group showed higher regional cerebral blood flow (rCBF) than the treated group in a frontal and a frontal-parietal region of the left hemisphere. Between t0 and t1, significant rCBF reduction was observed in the temporal lobe and occipital-temporal cortex of the left hemisphere in the untreated group, whereas no significant change was observed in the treated group. The rCBF of the two groups did not significantly differ at t1. By covariate SPM analysis between t0 and t1 in treated patients, MMSE score changes correlated significantly with rCBF changes in a large left frontal-temporal region. CONCLUSIONS: Brain perfusion is preserved in AD patients undergoing chronic Donepezil therapy while it is reduced in untreated patients. SPECT is a promising tool with which to assess the impact of AChEI therapy on brain functioning of AD patients.     

Functional connectivity during language processing in acute cocaine withdrawal: A pilot study

The performance of two groups of patients with semantic dementia (SD), with predominant right (SDR) and left temporal lobe atrophy (SDL), was contrasted with that of cases with probable Alzheimer's disease (AD) on a range of standard episodic memory tasks. While the SDL group achieved a good score on a composite visual, but not a verbal, episodic memory measure, the AD and SDR groups were equivalently impaired at visual and verbal memory. The SD, but not the AD, groups were, by definition, impaired on simple tests of semantic memory. Standard verbal episodic memory tests, therefore, failed to discriminate patients with SD from those with probable AD and even visual memory tests may result in misclassification of SDR cases.     

Can episodic memory tasks differentiate semantic dementia from Alzheimer's disease?

The performance of two groups of patients with semantic dementia (SD), with predominant right (SDR) and left temporal lobe atrophy (SDL), was contrasted with that of cases with probable Alzheimer's disease (AD) on a range of standard episodic memory tasks. While the SDL group achieved a good score on a composite visual, but not a verbal, episodic memory measure, the AD and SDR groups were equivalently impaired at visual and verbal memory. The SD, but not the AD, groups were, by definition, impaired on simple tests of semantic memory. Standard verbal episodic memory tests, therefore, failed to discriminate patients with SD from those with probable AD and even visual memory tests may result in misclassification of SDR cases.