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April2011 Vol.48 Issue:      2 Table of Contents
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Assessment of Cognitive Functions in Asymptomatic Carotid Artery Disease

Omar A. El-Serafy1, Foad A. Abd Allah1, Mona AF. Nada1, Waleed A. Ammar2, Mohamed Nasr I. El-Sirafy3, Ahmed A. Imam4, Amany H. Abou Al-Magd1

Departments of Neurology1, Cardiology2, Cairo University; Diagnostic Radiology3,

Alexandria University; National Heart Institute4; Egypt

 



ABSTRACT

Background: Carotid artery disease is an important cause of cognitive impairment in patients with stroke. Detection of a relation between carotid stenosis in asymptomatic subjects and cognitive dysfunction can open new scoop for early treatment. Objective: To assess the relation between cognitive function and asymptomatic carotid disease and to detect the relation between asymptomatic carotid stenosis and brain MRI. Methods: Ten asymptomatic subjects with moderate to severe carotid stenosis and 10 healthy control subjects were included. All subjects were subjected to: complete neurovascular examination, laboratory investigations, carotid and transcranial duplex, MRI brain and cognitive assessment using tests for global and specific cognitive functions. Results: In comparison to the control group, subjects with carotid stenosis had significantly lower levels of performance in tests of memory, language, executive functions, verbal memory and visuospatial functions, independent of MRI lesions. White matter hyperintensities were more prevalent than lacunar infarction in the carotid stenosis group. A statistically significant correlation was found between the degree of carotid stenosis and performance on tests of memory and executive functions. Subjects with bilateral carotid stenosis performed worse than those with unilateral stenosis in attention, memory and executive functions tests. Conclusion: Carotid artery stenosis was associated with poor neuropsychological performance in neurologically asymptomatic subjects. This could not be explained by a higher proportion of silent MRI lesions in asymptomatic subjects, making it less likely caused by silent emboli. [Egypt J Neurol Psychiat Neurosurg.  2011; 48(2): 95-102]

 

Key Words: Asymptomatic carotid artery stenosis, carotid duplex, cognition, MRI brain.

 

 

Correspondence to Mona Abd el Fatah Nada, Department of Neurology, Cairo University.

Tel.: +20189288848. Email: mona_A_nada@yahoo.com





INTRODUCTION

 

Cerebrovascular disease is an important cause of cognitive impairment and dementia1. Cognitive impairment itself is a risk factor for future ischemic stroke2. Carotid artery (CA) stenosis is an important risk factor for stroke and could be therefore possibly a risk factor for cognitive declinement3.

Most previous studies on the relationship between CA stenosis and cognitive impairment have been on symptomatic patients3 while few studies have been made on cognitive impairment in asymptomatic CA stenosis5,6. The possible mechanisms for cognitive impairment with CA stenosis are microembolization, white matter disease, and hypoperfusion6.

The aim of this work is to assess the relation between cognitive function and asymptomatic CA disease and to detect the relation between asymptomatic CA stenosis and MRI brain findings.

 

SUBJECTS AND METHODS

 

Subjects:

The current study is a Cross Sectional Study for twenty subjects (11 males and 9 females) with their age ranging from 50-70 years (Mean age 58.55±5.97 SD) recruited from neurology department and outpatient clinic, Cairo University Hospitals and the National Heart Institute in the period from September 2008 to October 2009. All persons gave their informed consent prior to their inclusion in the study. Our subjects were divided into 2 groups:

-        Group I: Included 10 subjects having asymptomatic moderate to severe (≥50%) CA stenosis by duplex ultrasound, Group II: Included 10 apparently healthy volunteers matched in age and sex, recruited from patient relatives and workers in Cairo University Hospital.

-        In group I, subjects have been selected according to the following criteria: 1- Age between 50 and 70 years. 2 - Patients with moderate and severe extracranial CA stenosis (≥50%). 3- No clinical history of cerebrovascular manifestations (either stroke or TIAs), and no positive neurological findings in clinical examination.4- Patients not presenting with pre–existing dementia or scores on Mini-mental Status Examintion (MMSE)< 247. 5- Patients not presenting with depression assessed by Beck’s inventory questionnaire. 6- No evidence of cardiac diseases which can cause cardio-embolic ischemic infarctions. 7. No evidence of medical systemic disease that can affect the cognitive function. 8. Absence of significant intracranial arterial stenosis (>50%). 9. No history of drug intake that may affect the cognitive function.

 

Both group I and II were subjected to the following battery of assessment:

a-      Full clinical assessment including: Complete neurological history and examination stressing on the level of education, blood pressure measurement (supine and standing), and pulsations (carotid and peripheral) assessed by palpation and auscultation.

b-     Neuropsychological tests: Tests screening for cognitive functions are divided into: global cognitive function tests (MMSE7 and Addenbrookes Cognitive test (ACE)8 and specific cognitive functions tests (Paired Associate Learning Test9,10 and Block Design Subtest11), and Beck’s inventory questionnaire to exclude depression12, 13.

c-      Routine laboratory tests: They were  performed to assess risk factors for cognitive dysfunction and to exclude associated medical illnesses that may induce cognitive dysfunction including: FBS, PPBS, CBC, ESR, urea, creatinine, serum uric acid, liver function tests (serum albumin, PT, PC and  INR), Na+, K+ and Ca++, lipid profile and thyroid function tests.

d-     Duplex Ultrasonography: 

1.      Extracranial Carotid Duplex Scan: Carotid duplex scanning for screening and quantification of extracranial CA disease was performed by qualified vascular operator using Philips HDI 5000 machines at the Neurovascular Laboratory of Neurology Department of Cairo-University hospitals. A high frequency (7-10MHz) linear array transducer was employed to scan the CA from the most proximal CCA to the ICA as far as the mandible permitted. The intima-media complex thickness (IMT) was measured at the far wall. Carotid arteries were considered normal if the IMT was <1.0 mm, no plaque detectable and Peak systolic velocity (PSV) ICA was <125 cm/s. Carotid atherosclerotic disease was considered present if the IMT showed diffuse thickening (≥ 1.0 mm) or carotid plaques were detected. Pulsed Doppler signals were routinely recorded from CCA just proximal to the bifurcation, origin of ECA, proximal, mid and if accessible distal ICA. They were recorded in longitudinal view with < 60 degree insonation angle. PSV and end-diastolic velocities (EDV) were recorded at the proximal ICA, distal CCA and PSV ICA/CCA ratio were calculated14. The degree of stenosis was primarily assessed by using the Doppler information. Hemodynamically insignificant plaque (< 50% stenosis) was diagnosed if plaque was detected on B-mode image and PSV was < 125 cm/s. Moderate ICA stenosis (≥ 50%) was diagnosed by PSV ICA > 125 cm/s and PSV ICA/CCA ratio > 2, severe ICA stenosis (≥ 70%) according to NASCET criteria by PSV ICA > 230 cm/s and PSV ICA/CCA ratio >4, and critical ICA stenosis (>80%) by EDV > 140 cm/s. ICA occlusion was diagnosed when occluding material was visualized in B-mode, color and pulsed Doppler signal was absent and diastolic velocity in the ipsilateral CCA was low or absent15.

2.      Transcranial Color Coded Duplex Ultrasonography: Using phased array transducer with multifrequency of 2-4 (MHZ) of Phillips HDI 5000 machine through temporal bone window as a “road map”, for the presence of stenosis, occlusions of major intracranial vasculature where cases with intracranial stenosis more than 50% were excluded from the study using Baumgartner criteria for quantification of intracranial stenosis16.

e-      Brain MRI without contrast: Performed in department of radio-diagnosis, Cairo University Hospital and other private centers on 1.5 T MRI machine.

f-      ECG and Trans-Thoracic ECHO Cardiography: To assess heart condition and possible sources of emboli.

 

Statistical Methods

Analysis of data was done by IBM computer using SPSS (statistical program for social science version 12). Chi-square test, Fisher exact test, Spearman correlation, unpaired t-test and Mann Whitney Wilcoxon U test were used.

 

RESULTS

 

Regarding comparison of risk factors in the two studied groups, cardiovascular risk factors were more prevalent in group I than in group II (Table 1).

Detailed Neuropsychological assessment tests showed significant difference between the two groups in the global cognitive functions measured by Addenbrookes Cognitive test (ACE) and specifically in the subtests of memory, language and executive function.

Also, a statistically significant difference between the two groups was found in visuospatial functions measured by the block design subtest of (WAIS)'s and verbal memory measured by PALT (Table 2 and 3).

Moderate to severe CA stenosis was detected in all subjects of group I where five subjects were found to have bilateral significant CA stenosis, three subjects with right CA stenosis and two subjects with left sided CA stenosis.

In group II, two subjects only showed right carotid bulb plaques 25% and 35% non significant stenosis.                                                                                  

A statistical correlation had been found between the degree of CA stenosis and neuropsychological tests where subjects in group I who had bilateral CA stenosis showed a sharp decrease in performance in tests of attention, memory (measured by anterograde memory and delayed recall) and executive function (measured by verbal fluency letter) compared to subjects with unilateral carotid stenosis (Table 4).

Regarding MRI finding, a statistically significant difference was found between group I and group II as regards the presence or absence of abnormal signal intensities (white matter hyperintensities or lacunar infarcts). No statistically significant difference was found when comparing  detailed MRI findings in both groups. The abnormal signal intensities in MRI were not significantly associated with poor performance in cognitive tests (Table 5).

Subjects with abnormal signal intensities in MRI were found to have higher degree of CA stenosis compared to subjects without abnormal MRI signal intensity (Table 6). Patients with bilateral CA stenosis showed significant cognitive impairment than patients with unilateral carotid stenosis.


 

Table 1. Risk Factors in Group I and Group II.

 

 

Group I (No.=10)

Group II (No.=10)

P value

No.

%

No.

%

Education

  • Illiterate

  • School graduated                      

  • University graduated

Hypertension

Diabetes Mellitus

Dyslipidemia

Hyperuricemia

Smoking

Alcohol

Ischemic Heart Disease

Peripheral Vascular Disease

 

6

1

3

9

7

7

3

6

3

7

3

 

60

10

30

90

70

70

30

60

30

70

30

 

5

4

2

4

1

4

1

4

1

0

0

 

50

40

20

40

10

40

10

40

10

0

0

 

>0.05 S

 

 

<0.05 HS

<0.05 HS

>0.05 S

>0.05 S

>0.05 S

>0.05 S

<0.05 HS

>0.05 S

S = significant, HS= Highly Significant

 

Table 2. Comparison between Group I and II as Regards Cognitive Function Tests.

 

P Value

t

Group II (No.=10)

Group I (No.=10)

Cognitive functions

<0.05 S

2

98±2.5

95±5.5

MMSE

<0.01 HS

3

91.8±4.1

80±10

ACE

<0.05 S

2.1

7.2±3

2.6±2.3

Block design

<0.05  S

2.4

14.6±2.6

12±2.7

PALT

<0.05  S

2.1

3.3±3

2.3±2.1

Beck Inventory test

MMSE = Mini-mental Status Examination, ACE = Addenbrocke’s Cognitive Examination,

PALT = Paired Associated Learning Test, S = significant, HS = Highly Significant

Table 3. Comparison between Group I and II as Regards Cognitive Subtests.

 

P Value

t

Group II (No.=10)

Group I (No.=10)

Cognitive functions

>0.05 NS

1.5

10±0.00

9.7±0.4

Orientation

>0.05 NS

1.6

5±0.0

4.1±1.8

Attention

>0.05 NS

1.1

2.8±0.4

2.2±0.9

Recall

>0.05 NS

1.4

20.8±0.9

19.7±1.7

Anterograde memory

<0.01 HS

3.6

6.4±0.8

3.8±2

Delayed recall

>0.05 NS

1.7

4±0.0

3.7±0.5

Retrograde memory

<0.01  HS

4.2

3.9±0.1

1.5±0.9

Verbal Fluency (Lettoral)

<0.01 HS

4

4.7±0.7

2.8±1.03

Verbal Fluency(Categoral)

<0.05  S

2.2

11.6±0.8

10±1.9

Naming

>0.05 NS

1.9

4.1±0.9

3.3±1.8

Visuospatial

NS= Non- Significant S =significant, HS= Highly Significant

 

Table 4. Relation between Unilateral & Bilateral Carotid Stenosis as Regards Cognitive Tests in Group I.

 

P Value

t

Stenosis

Cognitive tests

Bilateral

(No=5),  50%

Unilateral

(No=5), 50%

>0.05  NS

1.8

75±10

79±11

ACE test

>0.05 NS

0.8

1.7±1.4

2.2±1.8

Block design test

>0.05  NS

1.6

9±4

11±3

PALT

>0.05  NS

1.9

8.9±0.8

9.9±0.4

Orientation

<0.05 S

2.2

2.6±1.2

3.4±1.5

Attention

>0.05 NS

0.9

1.7±0.4

2±1.3

Immediate recall

<0.05 S

2.1

9±1.1

11±1.3

Anterograde memory

<0.05 S

2.6

2.5±2

3.9±2

Delayed recall

>0.05  NS

1.9

2.7±0.9

3.6±1.2

Retrograde memory

<0.05 S

2.2

1.6±0.4

2.7±1.1

Verbal fluency (letter)

>0.05 NS

1.5

1.9±0.3

2.8±1

Verbal fluency (category)

>0.05  NS

1.9

8±1.9

10±2.1

Naming

>0.05  NS

1.4

1.3±0.7

2.2±1.4

Visuospatial

ACE= Addenbrocke’s Cognitive Examination, PALT= Paired Associated Learning Test ,NS= Non- Significant S=significant

 

Table 5. Relation between MRI Findings and Cognitive Tests in Group I.

 

P Value

t

Magnetic Resonance Imaging

Cognitive tests

Abnormal signal intensities (No=6)

No abnormal signal intensity (No=4)

>0.05  NS

1.8

84±10

79±10

ACE test

>0.05 NS

0.2

1.8±1.6

2.3±1.9

Block design test

>0.05  NS

1.2

12±2

11.6±3

PALT

>0.05  NS

0.09

9.8±0.5

9.7±0.5

Orientation

>0.05  NS

1.2

4.4±1.3

3.7±2

Attention

>0.05  NS

0.07

2.4±0.9

2±1.1

Immediate recall 

>0.05  NS

1.2

20±1.6

19±1.8

Anterograde memory

>0.05  NS

1.7

4.3±2

3±2

Delayed recall

>0.05  NS

0.6

3.8±0.8

3.5±0.6

Retrograde memory 

>0.05  NS

1.8

1.6±0.8

1.3±1.2

Verbal fluency (letter)

>0.05  NS

0.08

2.8±0.7

2.7±0.9

Verbal fluency (category)

>0.05  NS

1.7

10±1.6

9±2.1

Naming

>0.05  NS

1.4

4±1.5

2.2±1.9

Visuospatial

ACE= Addenbrocke’s Cognitive Examination, PALT= Paired Associated Learning Test, NS= Non-significant

 

Table 6. Comparison between Mean Degree of Carotid Stenosis versus MRI Findings in Group I.

 

P

t

Stenosis%

Mean±SD

MRI  Findings ( No = 10)

<0.05 S

2.1

10±54

No abnormal signal intensity ( No=4)

11±65

Abnormal signal intensities (No=6)

 


DISCUSSION

 

 Most previous studies on the relationship between CA stenosis and cognitive impairment have been on symptomatic patients3,42,43. On the other hand, few studies have been conducted on cognitive impairment in asymptomatic CA stenosis5,6. Results of the current study showed that subjects with asymptomatic CA stenosis had significantly lower level of performance in cognitive tests both globally manifested in ACE test and specifically in block design test and PALT compared to the control group. In group I, as regards the ACE subtests, memory, language and executive function were significantly affected. Executive dysfunction indicates frontal lobe involvement, episodic memory dysfunction indicates medial temporal lobe involvement and left inferolateral temporal lobe is important in naming by which semantic memory is assessed44.

Our study revealed a statistically significant poor performance in the visuospatial function when measured by block design test in group I compared to control group, however the difference in performance in the visuospatial function when measured by the ACE test was not statistically significant between both groups. So, we assumed that the block design test is more sensitive than the ACE test in assessment of visuospatial functions.

Mathiesen and his colleagues in (2004)18 reported that subjects with asymptomatic CA stenosis showed a significantly poor performance specifically in tests of attention, sustained attention, and psychomotor speed with less significant poor performance in tests of memory and motor functioning, and this was not correlated with MRI findings.

According to previous studies20,45, frontal executive function was the most common cognitive dysfunction in patients with asymptomatic CA stenosis. Other studies found no significant difference in cognitive functioning between patients with CA stenosis & controls23,24.

As regards carotid duplex results in the current study, subjects who had bilateral CA stenosis showed a significant decrease in performance in tests of attention, memory (measured by anterograde memory and delayed recall) and executive function (measured by verbal fluency letter) compared to subjects with unilateral carotid stenosis.

Silvestrini et al.28 reported that subjects with left sided stenosis had significantly lower performances at verbal fluency, while subjects with right sided stenosis had significantly lower performances at non verbal cognitive tasks and visuospatial functions. On the contrary, Romero et al. in (2009)19 did not find a different relation between left and right side CA stenosis and cognitive performance. The number of subjects in the present study who had only right or only left carotid artery stenosis was too small to make a comparison in the cognitive function between the two groups.

We found that the degree of CA stenosis was significantly related to cognitive impairment especially in memory and executive function tests. This goes in concordance with previous studies18,19, who found that the more severe the CA stenosis, the poorer the cognitive performance.

As regards MRI findings, the present study showed that asymptomatic CA stenosis was associated with positive brain MRI findings (lacunar infarcts or increased in WMH). In the presence of CA stenosis, these MRI findings could be possibly explained by: 1. Microembolization from the carotid plaques producing silent lacunar infarctions. 2. Carotid stenosis is a marker for underlying risk factors for vascular disease as microangiopathy leading to microcirculatory disturbances. 3. Reduction in cerebral perfusion due to carotid stenosis6,28,46.

Four of our subjects out of ten with cognitive impairment showed no signal abnormalities in MRI. This goes in concordance with previous studies5,18. The absence of MRI findings in some of our patients can be explained by the likelihood that the neuropsychological tests were more sensitive to early changes in cerebral functioning due to atherosclerosis than MRI and a possible reason for this may be that early impairment of cortical functioning is better reflected in neuropsychological test performance than MRI, which is particularly sensitive to changes in white matter18,22. Another explanation is that we did not perform other MRI modalities such as spin echo gradient T2 or MRI with higher Tesla which is more sensitive than conventional MRI in detecting minor ischemic cortical or subcortical lesions.

In the present study, MRI findings were positively correlated with the mean degree of CA stenosis. This goes in concordance with a previous study19, who reported that the increased in the severity of CA stenosis was associated with an increased prevalence of MRI lesions.

Presence of periventricular WMH at baseline was found to double the risk of future dementia47. There is also evidence that progression of WM disease is accompanied by a decline in cognitive performance, supporting an etiological link between the WM changes and cognitive decline48. Also, silent lacunar infarctions can produce cognitive impairment22.

 

Conclusion

Early screening for CA stenosis and early detection of mild cognitive impairment is essential to avoid further complications e.g. vascular dementia and for early medical or surgical intervention.

 

[Disclosure: Authors report no conflict of interest]

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الملخص العربى

 

تقييم الوظائف المعرفية فى مرضى ضيق الشريان السباتى غير المصحوب بأعراض

 

ﺇن مرض ضيق الشريان السباتى المتقدم (نسبة الضيق ٥٠%) غير المصحوب بأعراض الناتج عن تصلب الشرايين، من الأمراض الشائعة لدى كبار السن و المسئول عن حوالى ٩-١٨% من اﻹحتشاءات المخية الناتجة عن القصور فى الدورة الدموية الأمامية للمخ، وهو أيضا سبب هام للتدهور فى الوظائف المعرفية والعته المخى.

وقد أجرى هذا العمل لدراسة العلاقة بين ضيق الشريان السباتى المتقدم غير المصحوب بأعراض والتدهور فى الوظائف المعرفية، ولدراسة ﺇن كانت هذه العلاقة ناتجة بسبب ومصاحبة بتغيرات فى أشعة الرنين المغناطيسى للمخ، وما ﺇذا كان هناك علاقة بين ضيق الشريان السباتى غير المصحوب بأعراض المتقدم والتغيرات فى أشعة الرنين المغناطيسى للمخ. وقد اشتملت الدراسة على عشرين شخصا، ١١ ذكر و ٩ إناث، عشرة مصابون وعشرة غير مصابين كمجموعة ضابطة للمقارنة، يختلفون بدرجات متفاوتة فى التعليم، مدخنين وغير مدخنين، وبعض عوامل خطورة مثل (ارتفاع ضغط الدم – مرض البول السكرى - ارتفاع نسبة حمض البوليك فى الدم – ارتفاع نسبة الدهون فى الدم – مرض قصور الشرايين التاجية – مرض قصور الشرايين الطرفية) وقد تم تقسيم هؤلاء الأشخاص إلى مجموعتين: المجموعة الأولى اشتملت على ١٠ مصابين بمرض ضيق الشريان السباتى غير المصاحب بأعراض المتقدم. المجموعة الثانية  اشتملت على ١٠ غير مصابين كمجموعة ضابطة للمقارنة وقد أجرى لهؤلاء الأشخاص ما يلى: فحص إكلينيكي للجهاز العصبى – الأبحاث المعملية الروتينية ووظائف الغدة الدرقية - اختبارات نفسية عصبية لقياس الوظائف المعرفية - فحص بالموجات فوق الصوتية على شرايين الرقبة والمخ - رسم قلب وفحص بالموجات فوق الصوتية على القلب- أشعة رنين مغناطيسى على المخ. وقد لوحظ وجود فروق ذات دلالة ﺇحصائية بين المجموعة الأولى والمجموعة الثانية فى الاختبارات المعرفية الآتية: (اختبار أدينبروك لقياس القدرات المعرفية العامة وبالأخص فى الأجزاء المتعلقة بالذاكرة واللغة والوظائف التنفيذية – وأيضا فى اﻹختبارات المعرفية الخاصة مثل اختبار رسوم المكعبات لقياس وظيفة الحس الفراغى – واختبار الأزواج المترابطة لقياس الذاكرة اللفظية). وجد أيضا وجود فرق ذى دلالة ﺇحصائية بين المجموعة الأولى والمجموعة الثانية من حيث زيادة سمك بطانة الشريان السباتى بالنسبة للمجموعة الأولى. كما وجد فى المجموعة الأولى خمسة أشخاص مصابين بمرض ضيق الشريان السباتى المتقدم غير المصحوب بأعراض على الجانبين، وفى ثلاث أشخاص على الجانب الأيمن فقط، وفى شخصين على الجانب الأيسر فقط، أما فى المجموعة الثانية فقد وجد شخصين مصابين بضيق بسيط فى الشريان السباتى بنسبة ۲٥%، ٣٥%. كما وجدت علاقة سلبية ذات دلالة ﺇحصائية بين درجة ضيق الشريان السباتى ونتائج اﻹختبارات الآتية (الذاكرة الحاضرة – الذاكرة الرجوعية - الوظائف التنفيذية المتمثلة فى الطلاقة اللفظية بنوعيها الحروف والطوائف). كما وجد أن أداء الأشخاص المصابين بمرض ضيق الشريان السباتى المتقدم غير المصحوب بأعراض على الجانبين كان أسواء من أقرانهم المصابين بالمرض على جانب واحد فى اﻹختبارات الآتية (اﻹنتباه - الذاكرة الحاضرة - اﻹسترجاع المؤخر - الوظائف التنفيذية المتمثلة فى الطلاقة اللفظية للحروف). أما فيما يختص بنتائج الرنين المغناطيسى على المخ، فقد وجد فرق ذى دلالة إحصائية بين المجموعة الأولى والمجموعة الثانية بالنسبة لوجود ﺇحتشاءات فجوية أو تصلب بالمادة البيضاء المحيطة ببطين المخ. كما وجد علاقة طردية ذات دلالة إحصائية بين درجة ضيق الشريان السباتى ونتائج الرنين المغناطيسى على المخ، ولكن لم تظهر علاقة ذات دلالة إحصائية بين نتائج اﻹختبارات المعرفية ونتائج الرنين المغناطيسى على المخ. مما تقدم نستخلص خطورة مرض ضيق الشريان السباتى المتقدم غير المصحوب بأعراض على الوظائف المعرفية وضرورة التشخيص المبكر حيث أن اﻹصابة بهذا المرض تكون مصحوبة بسوء الأداء فى اﻹختبارات النفسية العصبية خاصة فى اختبارات الذاكرة، اللغة، الحس الفراغى، والوظائف التنفيذية. اﻹختبارات النفسية العصبية كانت أكثر حساسية من الرنين المغناطيسى لقياس مدى التدهور فى الوظائف المعرفية.



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