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    Abstract
    Introduction
    Methods
    Results
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ORIGINAL RESEARCH PAPERS Table of Contents   
Year : 2005  |  Volume : 47  |  Issue : 3  |  Page : 139-143
Cognitive dysfunction and associated factors in patients with chronic schizophrenia


1 Hunter New England Area Health Service, Australia
2 Schizophrenia Research Foundation (India), Chennai 600101, India
3 Faculty of Health, The University of Newcastle, Callaghan, NSW 2308, Australia

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Date of Web Publication24-Sep-2009
 

   Abstract 

Background: Deficits in neurocognitive function are a hallmark of schizophrenia. They are associated with clinical manifestations and the course of the illness. A study of cognitive dysfunction in Indian patients with schizophrenia is of significance in view of a more benign course and outcome of the illness in this region.
Aim: To study cognitive deficits and associated factors in patients with chronic schizophrenia and compare them with those in the normal population.
Methods: We compared 100 patients with chronic schizophrenia with 100 matched normal controls on multiple measures of attention, executive function and memory.
Results: Compared to normal individuals, patients with schizophrenia performed poorly in all cognitive tests. Cognitive deficits in patients were related to gender, education, age, duration of illness, and presence of positive and negative symptoms.
Conclusion: The neurocognitive profile of Indian patients with chronic schizophrenia resembles those of patients in developed countries.

Keywords: Cognitive dysfunction, schizophrenia

How to cite this article:
Srinivasan L, Thara R, Tirupati S N. Cognitive dysfunction and associated factors in patients with chronic schizophrenia. Indian J Psychiatry 2005;47:139-43

How to cite this URL:
Srinivasan L, Thara R, Tirupati S N. Cognitive dysfunction and associated factors in patients with chronic schizophrenia. Indian J Psychiatry [serial online] 2005 [cited 2018 Nov 14];47:139-43. Available from: http://www.indianjpsychiatry.org/text.asp?2005/47/3/139/55936



   Introduction Top


Schizophrenia is accompanied by impairments in several domains of cognitive function. [1] Patients with schizophrenia have been found to perform more poorly than normal controls on tasks of attention, memory, executive function, language, learning and motor control. [2],[3],[4] In recent times, cognitive impairment has gained importance in terms of emerging theories on the aetiology and treatment of schizophrenia. [5]

Cognitive impairment in schizophrenia has been found to be related to measures of psychopathology [6],[7] and outcome. [8],[9] Much research on cognition in schizophrenia has been done in developed countries where the outcome was found to be poorer than that in developing countries such as India. It is of interest to know the degree and nature of cognitive dysfunction in Indian patients with schizophrenia. Studies in India have described cognitive deficits in schizophrenia. [10],[11] However, a comprehensive evaluation of deficits in all major cognitive domains, and their relation with demographic and clinical variables, has not been done. We compared cognitive deficits and associated factors in patients with chronic schizophrenia with those of a matched normal population.


   Methods Top


The case group was a consecutive sample selected from outpatients attending the treatment and rehabilitation centre of the Schizophrenia Research Foundation (India) in Chennai and comprised 100 subjects (men: 60; women: 40) fulfilling the DSM-IV criteria for chronic schizophrenia. A clinical interview and chart review established the diagnosis. All of them were on antipsychotic drug treatment at the time of evaluation. Subjects between the ages of 18 and 45 years, with at least 10 years of school education, were selected. The control group comprised 100 healthy subjects (men: 60; women: 40) with no current, past or family history of any psychiatric disorder. They were selected from among volunteers by the stratified sampling method and matched with subjects from the study group for age, sex and education. All participants gave a written informed consent after being explained the nature of the study. The cases and controls did not differ significantly in their mean age (33.6 years, SD±8.2 vs 33.9 years, SD±8.1; t=0.251) and years of formal education (14.3 years, SD±3.1 vs 13.9 years, SD±2.8; t=0.893). The patients were ill for a mean duration of 10.4 years (SD±6.8). The neuropsychological tests done are listed in [Table 1]. [11],[12],[13],[14],[1]5,[16]

Data analysis

The Statistical Package for Social Sciences (SPSS) [17] was used for data analysis. The chi-square and t tests were applied for univariate analysis. Simple correlation and partial correlation analyses were done to measure the relationship between continuous variables. The variables significant at univariate analysis were entered into classification analysis using the Mahalanobi distant statistic method to identify neuro­psychological tests that differentiated normals from patients.


   Results Top


The mean scores on the Positive and Negative Syndrome Scale (PANSS) [18] were 10.2 (SD±3.9) for the positive subscale (PS), 9.6 (SD±3.2) for the negative subscale (NS) and 23.6 (SD±5.7) for the general psychopathology subscale (GS).

Cognitive deficits

The patients performed significantly poorer than normal subjects on all tests of cognitive functions evaluated- attention, executive function, memory-except the number of perseverative responses on the Ruff Figural Fluency test for executive function, and immediate recall on the Visual Reproduction task of memory [Table 2].

The step-wise, discriminant function analysis identified 10 tests measuring tasks of attention, executive function and memory which differentiated most between patients and normal controls. The minimum D squared statistic and standardized canonical discriminant function coefficients (SCDFC) of the tests are listed in [Table 3]. A classification analysis based on the SCDFC of these 10 variables classified 92% of the study population appropriately into their original groups as patients and normal subjects.

Social and clinical factors and cognition

Women performed better than men on only one task: the Visual Paired Associate learning test (mean scores: immediate recall=12.7, SD±3.8 vs 10.7, SD±5.5, t=2.06, p<0.05; delayed recall=5.4, SD±1.0 vs 4.7, SD±1.3, t=3.03, p<0.01). The years of education did not correlate with age or clinical factors. The age and duration of illness correlated with each other (r=0.723, p<0.001) but not with PANSS subscale scores. The three PANSS subscale scores correlated positively with each other at a significance level of 0.01 or less (correlation coefficients: PS with NS=0.280; PS with GS=0.499 and NS with GS=0.461).

[Table 4] presents the significant correlations (p<0.05) among scores on cognitive tests with education, age (controlling for duration of illness), duration of illness (controlling for age) and scores on each of the subscales of PANSS (controlling for scores on the other two subscales of PANSS). Increasing age correlated with scores on the Digit Span and Digit Symbol Substitution Tests of attention, Ruff Figural Fluency Test of executive function, and verbal working memory tested by the Letter-Number Span test. More years of education correlated with better performance on tasks of attention, executive function, verbal and visual memory. A longer duration of illness correlated with indicators of executive dysfunction on the Wisconsin Card Sorting Test (WCST) and verbal memory. The positive symptom score was related to deficit on a single test of verbal memory, and negative symptoms with performance on measures of attention, executive function and visual memory. The GS score did not correlate with any cognitive deficit.


   Discussion Top


Cognitive deficits in chronic schizophrenia

We did not have any difficulty in using the neuropsychological tests developed in other cultures. The significant level of schooling of patients during which English was one of main languages taught seemed to facilitate their ability to understand and perform on tests that had numerate or verbal tasks. We feel cultural factors had little impact on performance in the neuropsychological tests.

Patients with schizophrenia performed poorly on all tests of cognitive function compared with the normal population matched with respect to gender, age and education. The classification analysis showed that patients with schizophrenia can often be clearly differentiated from the normal population based on their performance on some of the tests of attention, executive function and memory.

Factors associated with cognitive deficits

Gender differences in cognitive dysfunction have been reported. Males have been found to have more cognitive deficits than females, a trend attributed to the interplay of sex hormones, neuro-developmental and psychosocial sex differences. [19] We did not find any major gender difference except for a poorer performance of males on a memory task. Age-related decline across most neuropsychological functions has been demonstrated in schizophrenia. [20] We found that increasing age was related to poorer performance on tasks of attention, executive function and memory, which has been pointed out to be the result of an ageing brain in patients.

More years of education positively influenced performance on tasks that tested attention, executive function, memory and constructional ability. The duration of formal academic training reflected good pre-morbid functioning, intellectual level and a higher level of information-processing skills in the past. Patients with good education thus did well on cognitive tasks because of this inherent capability. A parallel can be drawn with the influence of education on cognitive changes reported in other neurological disorders. [21],[22],[23] Cognitive deficits have been found to remain relatively stable throughout the course of schizophrenia. [24] We also found that all measures, except two measures of executive function on the WCST and one of verbal memory, were stable over a range of illness duration.

We observed that negative symptoms had a strong association with cognitive dysfunction in all the domains. This finding is in agreement with the results of studies which showed that both positive and negative symptoms were associated with distinct neuropsychological deficits. [25] Heydebrand et al.[26] observed that negative symptoms were related more frequently to cognitive dysfunction than positive symptoms.


   Conclusion Top


In a group of patients with chronic schizophrenia in India, the nature and degree of cognitive deficits and their relationship to gender, age and clinical factors are comparable with observations made in developed countries. It would be of interest to explore the relationship between cognitive deficits in, and outcome of, schizophrenia among Indian patients, as they have a better outcome than patients with schizophrenia in developed countries.

 
   References Top

1.Elvevag B, Egan MF, Goldberg TE. Paired-associate learning and memory interference in schizophrenia. Neuropsychologia 2000;38:1565-75.  Back to cited text no. 1      
2.Braff DL. Psychophysiological and information processing approaches to schizophrenia. In: Charney DS, Nestler E, Bunney BS (eds). Neurobiological foundation of mental illness. New York: Oxford University Press; 1999:258-327.  Back to cited text no. 2      
3.Rund BR, Borg NE. Cognitive deficits and cognitive training in schizophrenic patients: A review. Acta Psychiatr Scand 1999;100:85-95.  Back to cited text no. 3      
4.Green MF, Kern RS, Braff DL, et al. Neurocognitive deficits and functional outcome in schizophrenia: Are we measuring the 'right stuff'? Schizophr Bull 2000;26:119-36.  Back to cited text no. 4      
5.Harvey PD, Bowie CR, Friedman JI. Cognition in schizophrenia. Curr Psychiatr Rep 2001;3:423-8.  Back to cited text no. 5      
6.Breier A, Schreiber JL, Dyer J, et al. National Institute of Mental Health longitudinal study of chronic schizophrenia. Prognosis and predictors of outcome. Arch Gen Psychiatry 1991;48:239-46.  Back to cited text no. 6      
7.Galletly CA, Clark CR, MacFarlane AC. Treating cognitive dysfunction in patients with schizophrenia. J Psychiatry Neurosci 2000;25:117-24.  Back to cited text no. 7      
8.Green MF. What are the functional consequences of neurocognitive deficits in schizophrenia? Am J Psychiatry 1996;153:321-30.  Back to cited text no. 8      
9.McGurk SR, Mueser KT, Harvey PD, et al. Cognitive and symptom predictors of work outcomes for clients with schizophrenia in supported employment. Psychiatr Serv 2003;54:1129-35.  Back to cited text no. 9      
10.Ananthanarayanan CV, Janakiramaiah N, Gangadhar BN, et al. Visual information processing deficits in clinically remitted outpatient schizophrenics. Indian J Psychiatry 1993;35:27-30.  Back to cited text no. 10      
11.John PJ, Khanna S, Mukundan CR, et al. Relationship between psychopathological dimensions and performance on frontal lobe tests in schizophrenia. Indian J Psychol Med 2001;24: 19-26.  Back to cited text no. 11      
12.Wechsler D. Wechsler Memory Scale Manual (revised). San Antonio, Texas: The Psychological Corporation; 1987.  Back to cited text no. 12      
13.Wechsler D. Wechsler Adult Intelligence Scale-revised. New York: The Psychological Corporation; 1981.  Back to cited text no. 13      
14.Baser CA, Ruff RM. Construct validity of the San Diego Neuropsychological Test Battery. Arch Clin Neuropsychol 1987;2:13-32.  Back to cited text no. 14      
15.Heaton RK. Wisconsion Card Sorting Test manual. Odessa, Florida: Psychological Assessment Resources; 1981.  Back to cited text no. 15      
16.Gold JM, Carpenter C, Randolph C, et al. Auditory working memory and Wisconsin Card Sorting Test performance in schizophrenia. Arch Gen Psychiatry 1997;54:159-65.  Back to cited text no. 16      
17.SPSS for Windows. Rel 7.5.1. Chicago: SPSS Inc.; 1996.  Back to cited text no. 17      
18.Kay SR, Fiszbein A, Opler LA. The Positive and Negative Syndrome Scale (PANSS) for schizophrenia. Schizophr Bull 1987;13:261-76.  Back to cited text no. 18      
19.Leung A, Chue P. Sex differences in schizophrenia, a review of the literature. Acta Psychiatr Scand Suppl 2000;401:3-38.  Back to cited text no. 19      
20.Fucetola R, Seidman LJ, Kremen WS, et al. Age and neuropsychologic function in schizophrenia: A decline in executive abilities beyond that observed in healthy volunteers. Biol Psychiatry 2000;48:137-46.  Back to cited text no. 20      
21.Bennett DA, Wilson RS, Schneider JA, et al. Education modifies the relation of AD pathology to level of cognitive function in older persons. Neurology 2003;60:1909-15.  Back to cited text no. 21      
22.Kesler SR, Adams HF, Blasey CM, et al. Premorbid intellectual functioning, education, and brain size in traumatic brain injury: An investigation of the cognitive reserve hypothesis. Appl Neuropsychol 2003;10:153-62.  Back to cited text no. 22      
23.Le Carret N, Lafont S, Mayo W, et al. The effect of education on cognitive performances and its implication for the constitution of the cognitive reserve. Dev Neuropsychol 2003;23:317-37.  Back to cited text no. 23      
24.Velligan DI, Miller AL. Cognitive dysfunction in schizophrenia and its importance to outcome: The place of atypical antipsychotics in treatment. J Clin Psychiatry 1999;60 (Suppl. 23):25-8.  Back to cited text no. 24      
25.Berman I, Viegner B, Merson A, et al. Differential relationships between positive and negative symptoms and neuropsychological deficits in schizophrenia. Schizophr Res 1997;25:1-10.  Back to cited text no. 25      
26.Heydebrand G, Weiser M, Rabinowitz J, et al. Correlates of cognitive deficits in first episode schizophrenia. Schizophr Res 2004;68:1-9.  Back to cited text no. 26      

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Correspondence Address:
Latha Srinivasan
Hunter New England Area Health Service, 391-393, Main Road, Cardiff, NSW 2285
Australia
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0019-5545.55936

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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]

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