The International Journal of Psychosocial Rehabilitation
Prevalence and Correlates of Cognitive Impairment in
 Stroke Patients in a Rehabilitation Setting

 
Sanjiv K Saxena
 
Staff Clinical Researcher
National
University of Singapore, Singapore

   Citation:
Saxena, S K. (2006). Prevalence and Correlates of Cognitive Impairment in Stroke Patients in a
Rehabilitation Setting.
  International Journal of Psychosocial Rehabilitation.
10 (2) 37-47.

 

 
Corresponding Address:
Dr Sanjiv K Saxena
National University of Singapore,
E-mail: sanjiv@alumni.nus.edu.sg
Ph: (65) 91018190
 
Acknowledgement : 
This study was conducted as an MSc thesis project in the Medical Faculty Graduate Studies Programme at National University of Singapore . I am thankful to my Thesis Supervisors, A/Prof Ng Tze Pin and Dr Fong and also to the staff of Ang Mo Kio Community Hospital and St Luke’s Hospital for their help and support in this study

 


Abstract:

Background: Stroke is associated with considerable physical and psychological impairment. Cognitive impairment in stroke patients is associated with adverse outcomes during their rehabilitative process.  Identifying the baseline factors associated with cognitive impairment in stroke patients would help the multidisciplinary team involved in the rehabilitative process to maximize the functional recovery of stroke patients.  
Aim: The aim of the study was to ascertain the prevalence of cognitive impairment and its baseline determinants in the rehabilitation settings.  
Methodology: A cross- sectional study of 200 stroke patients was conducted in two community (rehabilitation) hospitals. Assessments were made on admission to the hospitals which besides including information on sociodemographic, clinical and neurological variables also included assessment of functional and neurological impairment, depression and cognitive impairment.   Validated tools of assessment were used in the study, viz. NIHS for neurological impairment, Barthel Index for functional assessment. AMT for cognitive impairment and GDS for depression.  
Results: On admission 54.5 % of the patients were with cognitive impairment. In multivariate analyses, the independent significant predictors of cognitive impairment were age more than 81 years (OR=6.78, 95% C.I. 2.34, 19.64), lesser education (OR=4.73, 95% C.I. 1.41, 13.11), severe neurological impairment on admission (OR=5.00, 95% C.I. 1.70, 14.67) and depression on admission (OR=3.19, 95% C.I. 1.61, 6.30).
 
Conclusion: Considerable proportion of stroke patients present with cognitive impairment during their rehabilitation which in turn is significantly determined by modifiable baseline factors like depression. Judicious identification of this group of patients would maximize the recovery of stroke patients.

 


Introduction
 
Stroke is a disease with considerabe physical 1,2 and psychosocial impairments. 3-7
 
Dementia and cognitive impairment are such psychological impairments in stroke patients which besides having as high a prevalence of and 17-38% 3-7 respectively are also associated with many short and long term poorer outcomes including poorer functional recovery in stroke patients. 8-10
Adopting clinical diagnostic criteria like DSM-1V for dementia may miss out the cases among the stroke patients who are cognitively impaired but not demented known as “cognitive impairment, no dementia” (CIND), 11 which besides being an important challenge in dementia epidemiology also has consistently been reported as  a correlate of poorer functional recovery in stroke patients.8-10  Low et al 11 in their cross-sectional survey observed that 33.3% were cognitively impaired but not demented (CIND) 2.4% had possible dementia and 64.3% of the subjects were cognitively normal.
Though the prevalence of cognitive impairment in stroke patients is high and is associated with adverse effects on the rehabilitative outcomes still there is a lack of consensual agreement regarding  determinants  of cognitive impairment  e.g. increasing age was  found to be a significant correlate of post stroke cognitive impairment by Allan et al. 12 but T.K. Tatemichi 13 did not  find increasing age to be significantly associated with post  stroke cognitive impairment. Likewise R.M. Parekh et al 14 did not find significant relationship between depression and cognitive impairment but R.G. Robinson et al 15 found a significant relationship between cognitive deficits and depression in stroke patients.
Knowledge about such baseline modifiable and non-modifiable determinants of cognitive impairment in stroke patients would help the multidisciplinary team involved in the rehabilitative process of stroke patients to adopt an appropriate treatment modality to reduce the burden of cognitively impaired stroke patients which in turn will help maximize the functional recovery of stroke patients during their rehabilitation.
The aim of the study was to ascertain the prevalence and baseline determinants of cognitive impairment in stroke patients.

Methods and Materials
Methods
Patients
A cross-sectional study was conducted on 252 stroke patients who were consecutively admitted into two rehabilitation hospitals in Singapore during the period from April 2002 to September 2002. The patients satisfied the WHO criteria for defining stroke (defined as a condition characterised by rapidly developed clinical signs of focal disturbance of cerebral function lasting more than 24 hours with no apparent cause other than vascular origin). All the patients in the study gave informed consent for participation in the study. We excluded 48 patients with severe dysphasia because the measurement tools used in the study required participants to be able to communicate. Another four patients refused participation, hence 200 patients fulfilled the inclusion criteria for enrolment into the study. 

Measurements
Information obtained on admission for 200 patients included socio-demographic variables (age, gender, ethnicity, marital status, education level, living arrangement , presence of caregiver). Clinical variables extracted from clinical case records included presence of cardiovascular risk factors, viz. smoking, hypertension, hyperlipidaemia, diabetes, ischemic heart disease and atrial fibrillation, visual impairment and hearing impairment. Neurological variables included stroke lesion type (ischemic vs haemorrhagic), location of stroke (cortical versus non-cortical), side (left or right sided) and distribution (unifocal or multi-focal) based on CT head reports, and whether the stroke was recurrent. Post-stroke urinary incontinence (defined as involuntary loss of urine in a post-stroke patient), dysphagia (as diagnosed by a swallowing therapist), aspiration pneumonia (as diagnosed by a clinician) and post-stroke seizures (excluding those with pre-existing epilepsy), on-admission Ryle’s tube and urinary catheterization.

On admission the patients were assessed on neurological, depressive symtoms, cognitive status, and physical functioning using the National Institute of Health Stroke Scale (NIHSS), Geriatric Depression Scale (GDS-15), Abbreviated Mental Test (AMT) and  Barthel Index (BI).
Neurological and functional assessment was performed by a physician (SKS) and questionnaire interviews were performed by a trained research nurse, with translations for non-English speaking patients.

NIHSS: Assesses level of consciousness, horizontal gaze, visual fields, facial palsy, motor strength, ataxia, sensory system, language, dysarthria and extinction or inattention. The scale scores range from 0 to 42, with 42 denoting the most severe neurological impairment. The NIHSS has been shown to have high intra and inter-rater reliability 16, and predict long-term stroke outcome17, and post-acute care disposition among stroke patients18.  Three categories of neurological impairment, namely mild, moderate and severe, were defined with the following cut-off values: mild impairment = 1-6, moderate impairment = 7-12 and severe impairment = 13-42.

GDS: The 15-item short form version of the Geriatric Depression Scale (GDS-15) was used to assess depressive symptoms. The short-GDS has been found to be a suitable instrument to screen for depression in the general population 19 and validated for use in the elderly Chinese population locally20.  It has scores ranging from 0 to15, with a score of 5 to 10 indicating mild depression and a score of 11 to 15 indicating severe depression.

Abbreviated Mental Test (AMT) : was used to assess cognitive impairment.  In elderly patients, AMT has been shown to give good predictive validity of cognitive impairment and dementia21 and has been validated in local settings by Sahadevan et al.22   The 10-item scale gives scores ranging from 0 to10 with a score of 7 or less indicating cognitive impairment. 

Barthel Index: Physical functioning and disability was assessed by the Barthel Index (BI) 23 for independence in activities of daily living (grooming, transfer, walking, bladder and bowel control, dressing, climbing stairs, feeding and bathing) which has been validated and is widely used in stroke patients24. The scores of the scale range from 0 to 100, with a score of 100 denoting complete independence.  Three ordinal categories of functional disability were defined using the following cut-off values: (1) severe: 0-50; (2) moderate: 51-75; (3) mild to no impairment: 76-100.  ADL dependence upon admission, upon planned discaharge and at six months after stroke onset was defined as Barthel Index score ≤ 50.

Statistical Analysis:
Besides ascertaining the prevalence, the baseline factors predicting post stroke cognitive impairment were ascertained and modeled using Logistic Regression analyses. Significant baseline variables identified from univariate analyses were included in the final regression model using forward selection procedures for entry at p=0.05 and removal at p=0.10. The strengths of association of the predictors were expressed as the odds ratios and their 95% confidence intervals.
 
Results:
Patient characterstics
The patients in the study were aged between 40 and 96, mean 71.5 (S.D. = 10.5); 54% were males; 88% were Chinese, 7% Malays, and 5% Indians; 50% were married, 7% were unmarried and 43% were either widowed or divorced. Among them, 10% were living alone, 12.5% did not have an identifiable care giver.
Visual and hearing impairment were present in 10% and 5% of the patients. The prevalence of cardiovascular risk factors and co-morbidities were: hypertension: 87%; diabetes: 47%; smokers: 45%; ischemic heart disease: 22%; atrial fibrillation: 7%; hyperlipidaemia: 72%. The stroke lesions were hemorrhagic in 12.5% of the patients, and cortical in 28%; 47% had left sided lesion; multifocal 49%; 42% had recurrent stroke.  Among the patients, 25% had post-stroke dysphagia, 59% urinary incontinence, 5% aspiration pneumonia; 2% epilepsy. Neurological impairment was assessed according to the NIH scale as mild in 47% of the patients, moderate in 36% and severe in 16% of the patients. On admission, 60% of the patients were with depressive symptoms and 54% were cognitively impaired.

Prevalence of cognitive impairment:
On admission 109/200 (54.5%) of the patients were cognitively impaired.

Univariate analysis of factors associated with cognitive impairment on admission
On univariate logistic regression the factors significantly associated with cognitive impairment on admission were (Ref. Table 1): Socio-Demographic variables:
(a) Age: 66-80 years (O.R.-2.03,   95%C.I.-1.06, 3.81); < = 81 years (O.R.-6.09   95%C.I.-2.42, 15.42);  (b) Gender: Females (O.R.-1.83,    95%C.I.-1.04, 3.23) (c) Marital Status: Widow/er, Divorced/ee: (O.R.-1.88,   95%C.I.-1.04, 3.32). (d) Educational Level:  < = secondary level (O.R.-4.52,   95%C.I.-1.91, 10.66)

Clinical Variable: (a) Depression (O.R.-4.23, 95%C.I.-2.31, 7.73).  (b) Severe functional impairment: Severe (O.R.15.72, 95%C.I.-1.89, 130.44)
Neurological variable: (a) Moderate Neurological impairment (O.R.-2.96,  95%C.I.-1.57, 5.58)   (b) Severe Neurological impairment (O.R.-7.10,   95%C.I.-2.66, 18.91) (c) On admission Ryle`s tube: (O.R.-5.81, 95%C.I.-1.93, 17.51) (d) Urinary incontinence:  (O.R.-3.51, 95%C.I.-1.94, 6.33) (e) Post stroke aspiration pneumonia: (O.R.-8.06,   95%C.I.-1.002, 64.66)

Table 1:  Univariate Analysis of the factors associated with cognitive impairment on admission:
Socio Demographic Variables Cognitively Impaired
No: 109(54.5%)
 
Normal Cognition
No: 91(45.5%)
p O.R. 95%C.I.
Age: > = 65 yrs. 24 (22.0) 39 (42.8)   1.00  
  66-80 yrs. 55 (50.4) 44 (48.3) <0.05 2.03 1.06,3.81
 
 
< = 81 yrs.
 
30 (27.5)   8 ( 8.7) <0.01 6.09 2.42,15.42
Gender: Male 52 (47.7) 57 (62.6)   1.00  
 
 
Female
 
57 (52.2) 34 (37.3) <0.05 1.83 1.04, 3.24
Ethnicity: Chinese: 95 (87.1) 82 (90.1)   1.00  
  Malay   9 (8.2)   5 (5.4) NS 1.55 0.50, 4.8
 
 
Indian
 
  5 (4.5)   4 (4.3) NS 1.07 0.28, 4.1
Marital Status: Married: 49 (44.9) 52 (57.1)   1.00  
  Unmarried   5 (4.5)   8 (8.7) NS 0.66 0.20, 2.1
 
 
Widow/Divorced
 
55 (50.4) 31 (34.0) <0.05 1.88 1.04, 3.3
Educational Level: > Secondary: 8 (7.3) 24 (26.3)   1.00  
 
 
< = Secondary
 
101(92.6) 67 (73.6) <0.01 4.52 1.91,10.66
Living Arrangement: Living with            
someone:       
 
101 (92.6)
 
79 (86.8)
   
1.00
 
 
 
Living Alone
 
    8 (7.3) 12 (13.1) NS 0.52 0.20, 1.33
Care Giver: Present: 99 (90.8) 76 (83.5)   1.00  
  Absent: 10 (9.1) 15 (16.4) NS 0.51 0.21, 1.20
 
Clinical Variables          
Visual Impairment: Present: 12 (11.0) 8   (8.7) NS 1.28 0.50,3.29
 
 
Absent:
 
97 (88.9) 83 (91.2)   1.00  
Hearing Impairment: Present: 4 (36.6) 6   (6.5) NS 0.54 0.14, 1.97
 
 
Absent:
 
105 (96.3) 85 (93.4)   1.00  
Hypertension: Present 97 (88.9) 78 (85.7) NS 1.34 0.58, 3.11
 
 
Absent:
 
12 (11.0) 13 (14.2)   1.00  
Diabetes Mellitus: Present 54 (49.5) 40 (43.9) NS 1.25 0.71, 2.18
 
 
Absent:
 
55 (50.4) 51 (56.0)
 
  1.00  
Smoking: Present 49 (44.9) 42 (46.1) NS 0.95 0.54, 1.66
  Absent:
 
60 (55.0) 49 (53.8)   1.00  
Ischemic Heart Disease: Present 30 (27.5) 15 (16.4) NS 1.92 0.96, 3.85
 
 
Absent:
 
79 (72.4) 76 (83.5)   1.00  
Atrial Fibrillation: Present 10 (9.1) 4   (4.3) NS 2.19 0.66 ,7.25
 
 
Absent:
 
99 (90.8) 87 (95.6)   1.00  
Hyperlipidaemia: Present 78 (71.5) 66 (72.5) NS 0.95 0.51, 1.77
 
 
Absent:
 
31 (28.4) 25 (27.4)   1.00  
Depression: Present: 82 (75.2) 38 (41.7) <0.01 4.23 2.31, 7.73
  Absent: 27 (24.7)
 
53 (58.2)   1.00  
Functional Impairment: Mild: 1 (0.9) 8 (8.7)   1.00  
  Moderate 37 (33.9) 47 (51.6) NS 6.28 0.75, 52.37
 
 
Severe:
 
71 (65.1) 36 (39.5) <0.05 15.7 1.89 ,130.44
 
Neurological Variables          
Lesion Type: Hemorrhage 12 (9.1) 13 (14.2)   1.00  
 
 
Infarction:
 
97 (88.9) 78 (85.7) NS 1.34 0.58, 3.11
Lesion Location: Cortical: 37 (33.9) 20 (21.9)   1.00  
 
 
Non Cortical
 
66 (60.5) 61 (67.0) NS 0.58 0.30, 1.11
Lesion Distribution: Focal: 49 (44.9) 36 (39.5)   1.00  
 
 
Multifocal:
 
53 (48.6) 46 (50.5) NS 0.84 0.47, 1.51
Recurrent CVA: Yes: 18 (16.5) 18 (19.7) NS 0.79 0.38, 1.64
 
 
No:
 
89 (81.6) 71 (78.0)   1.00  
Neurological Impairment: Mild: 36 (33.1) 59 (64.8)   1.00  
  Mod.: 47 (43.1) 26 (28.5) <0.01 2.96 1.57, 5.58
  Severe:
 
26 (23.8)   6 (6.5) <0.01 7.10 2.66, 18.91
On Adm. Ryle`s Tube: Present: 23 (21.1) 4 (4.3) <0.01 5.81 1.93, 17.51
  Absent:
 
86 ( 78.8) 87 (95.6)   1.00  
Dysphagia: Present 32 (29.3) 18 (19.7) NS 1.68 0.87, 3.26
 
 
Absent:
 
77 (70.6) 73 (80.2)   1.00  
Urinary Incontinence:
 
 
Present:
 
79 (72.4)
 
39 (42.8)
 
<0.01
 
3.51
 
1.94, 6.33
 
 
Absent:
 
39 (35.7) 52 (57.1)   1.00  
Aspiration Pneumonia: Present: 9 (8.2) 1 (1.0) <0.05 8.06 1.00, 64.6
 
 
Absent:
 
100 (91.7) 90 (98.9)   1.00  
Epilepsy: Present:  1 (0.9) 3 (3.2) NS 0.27 0.02, 2.66
  Absent: 108 (99.0) 88 (96.7)   1.00  
   

Multivariate analysis of the factors associated cognitive Impairment in stroke patients on admission: (Ref. Table 2)
The significant predictors were: (a) Age more than 81 years (O.R. - 6.78,   C.I. - 2.34, 19.64) (b) Education less than equal to secondary level (O.R.-4.73, C.I. - 1.41, 13.11)  (c)Severe neurological impairment (O.R.-5.00, C.I. - 1.70, 14.67) (d) Depression   (O.R.-3.19; C.I.-1.61, 6.30)

Table 2: Multiple forward logistic regression of cognitive impairment on admission in stroke patients*
                        
Variables Beta p O.R. 95% C.I.
 
Age:
 
 
> = 81 years
 
 
1.91
 
<0.01
 
6.78
 
2.34, 19.64
Education:
 
Less than equal to Sec. Level
 
1.55 <0.01 4.73 1.41 , 13.11
Neurological Impairment:
 
Severe
 
1.61 <0.01 5.00 1.70, 14.67
Depression: Present:
 
1.16 <0.01 3.19 1.61,  6.30
* at probability of entry at 0 .05 and removal at 0.10
 
Discussion
In this study we have been able to identify the group of stroke patients who upon their admission to rehabilitation settings are cognitively impaired and their baseline correlates. This group of patients is likely to make lesser functional recovery.
One of the main aims of the study was to ascertain the significant determinants of cognitive impairment in stroke patients.
We observed that increasing age, lesser education, severe neurological impairment and depression were significant determinants of cognitive impairment in stroke patients.
Severe stroke at onset has been consistently reported to be a significant correlate of post stroke cognitive impairment. 25, 26 This suggests that stroke induced brain injury affects cognition as well. However the domains of neurological impairment affecting the cognition in stroke patients should be identified so that more concerted efforts can be mounted for better recovery from neurological and cognitive impairment. 
Likewise consistent with previous observations we found increasing age and lower educational level 13, 27 to be significant correlates of post stroke cognitive impairment. The probable reasons for this could be because with the increasing age there may be a concomitant degenerative process setting in and the lower educational level may be associated with lesser mental reserve.

  In our study we found depression to be a significant correlate of cognitive impairment. Till to date the intricate relationship between cognitive impairment and depression remains largely unclear. Hence an independent long-term longitudinal study to evaluate a temporal relationship between the two would help understand the topic better as more concerted efforts may then be applied to identify and treat the entity which is causative of the other outcome.
            Lack of association between functional disability and post stroke cognitive impairment has also been reported previously28 which suggests that post stroke cognitive impairment is mainly the result of stroke induced neurological injury.

Post stroke ryles tube insertion and urinary incontinence were a significant correlates of cognitive impairment in univariate analysis but given the presence of barthel index scale, were not independent correlates as each of these domains are measured separately on the barthel index scale. Likewise vascular risk factors were not a significant correlate of post stroke cognitive impairment in our study as has also been reported previously. 29

            In conclusion considerable proportion of stroke patients present with cognitive impairment in the rehabilitation settings and that cognitive impairment in stroke patients is determined by modifiable factors like depression. Hence by judiciously identifying this group of patient the functional recovery of stroke patients can be maximized. 
 
 

 
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