Academic Department, Gartnavel Royal Hospital, Glasgow, Scotland
Crichton Royal Hospital, Dumfries, Scotland
Correspondence: Professor R. G. McCreadie, Director of Clinical Research, Crichton Royal Hospital, Dumfries DGI 4TG, Scotland. Tel: 01387 244000; fax: 01387 257735; e-mail: rgmccreadie_crh{at}compuserve.com
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ABSTRACT |
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Aims To assess cognitive function in a population of patients with schizophrenia, and relate it to community functioning.
Method All patients with schizophrenia in Nithsdale, south-west Scotland, were identified (n=182). Measures of assessment were: National Adult Reading Test (NART), Mini-Mental State Examination (MMSE), Rivermead Behavioural Memory Test (RBMT), Executive Interview (EXIT), FAS Verbal Fluency and Health of the Nation Outcome Scales (HoNOS).
Results We assessed 138 patients, mean age 48 years (standard deviation (s.d.) 15). Only 14% were in-patients. The mean premorbid IQ as assessed by NART was 98 (s.d. 14); 15% of patients had significant global cognitive impairment (MMSE); 81% had impaired memory (RBMT); 25% had executive dyscontrol (EXIT); and 49% had impaired verbal fluency (FAS). Scores on the functional impairment sub-scale of HoNOS correlated with all measures of cognitive impairment.
Conclusions Cognitive dysfunction is pervasive in a community-based population of patients with schizophrenia.
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INTRODUCTION |
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METHOD |
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The ICD-10 diagnosis of schizophrenia is broad; however, a 1997 Nithsdale study (McCreadie et al, 1997) showed that 87% of patients with a clinical diagnosis of schizophrenia also fulfilled OPCRIT-derived DSM-III-R criteria (McGuffin et al, 1991).
The census identified 182 patients, 96 (53%) male and 86 (47%) female. Of these, 9% were long-stay and 5% acute inpatients, 20% were day patients, and 34% out-patients, 17% mainly had contact with the community psychiatric nurse and 15% had contact with the GP only. As a prevalence study, the population included patients whose illness varied greatly in chronicity and severity. No patients had received electroconvulsive therapy in the preceding 12 months. Informed consent was obtained for all subjects before participation.
Assessment of cognitive function
Measures were chosen for their shortness, ease of use and acceptability to
patients. Cognition was assessed using a battery of five cognitive
measures.
All cognitive measures were administered by a research nurse (V.S.), trained in the use of the scales; a session lasted about 40 minutes.
Social disability and community functioning over the preceding 2 weeks were assessed by the Health of the Nation Outcome Scales (HoNOS; Wing et al, 1998). HoNOS is a simple, brief and clinically acceptable instrument based on an interview with the keyworker.
Statistical analysis
Differences between groups were examined by t-tests and analysis
of variance (ANOVA); Pearson's r was used to examine
correlations.
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RESULTS |
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Cognitive measures
Cognition was assessed in 138 of 182 patients (response rate 76%). There
was no difference in age or gender between responders and non-responders: 52%
of responders were male; demographic and clinical variables by gender are
shown in Table 1.
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One hundred and thirty-two patients completed the NART. The mean Wechsler Adult Intelligence ScaleRevised (WAISR; Wechsler, 1981) IQ generated from the NART error score was 98 (s.d. 14, range 69-126).
On the MMSE, 15% of patients showed significant global cognitive impairment; on the RBMT, 81% showed memory impairment; on the EXIT (n=137) 25% showed executive dyscontrol; and on the FAS (n=136) 49% had reduced verbal fluency. Figure 1 shows the distribution of scores for the MMSE (n=138) and RBMT (n=135).
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Table 1 shows cognitive measures for both genders; scores were similar except in the FAS, where men scored significantly higher.
Cognition and age
Cognition scores for patients in each of six age bands are shown in
Table 2. Three women, aged 80,
89 and 90 years, were excluded from this analysis. There were no between-group
differences in the NART IQ, but there were significant between-group
differences in scores on the MMSE, RBMT, EXIT and FAS. Performance was poorest
in the over-60 age groups.
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Community status
The relationship between patients' community status (i.e., in-patient,
out-patient, etc.) and cognitive results is shown in
Table 3. There were significant
between-group differences in scores on the MMSE, RBMT and EXIT. Long-stay
in-patients scored lowest, and worse than patients of comparable age supported
only by GP care.
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HoNOS
Keyworkers of 47 of the patients were available for interview. The HoNOS
has four sub-scales which assess behaviour, functional impairment, symptoms
and social circumstances; a higher score indicates more disability. In the
functional impairment sub-scale, the keyworkers rated 27% of the patients as
having problems in the community owing to poor cognition (memory, orientation
and understanding). There were significant correlations between cognitive
measures and the functional impairment sub-scale of HoNOS; MMSE (Pearson's
r=-0.4, P<0.01), RBMT (r=-0.5,
P<0.001), EXIT (r=0.4, P<0.01) and FAS
(r=-0.4, P<0.01).
Figure 2 shows the relationship
between memory measured by RBMT and functional impairment measurement by
HoNOS; the poorer the score on memory, the worse was the functional
impairment.
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DISCUSSION |
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Cognitive dysfunction
There was a high prevalence of cognitive dysfunction in our community-based
population of patients with schizophrenia. Memory impairment was most obvious,
with 81% affected. Fifteen per cent of the patients showed significant global
cognitive impairment on the MMSE, while at least a quarter had executive
(frontal) dysfunction. This high level of current cognitive dysfunction was
present despite the fact that their premorbid IQ and schooling were
predominantly normal. Other studies (e.g.,
Crawford et al, 1992)
have found that people with schizophrenia perform similarly to control
subjects on the NART. The only gender difference was in the FAS, where the
women scored lower. This may be explained by the difference in mean age (5
years between the men and the women subjects); there is a high negative
correlation between FAS performance and age
(Crawford et al,
1993).
Our estimate of the prevalence and pervasiveness of memory problems in the Nithsdale population is almost identical to that of McKenna et al (1990), who investigated memory impairment in 60 patients with schizophrenia from acute, rehabilitation and long-stay services; in addition, similar proportions of patients in both studies are classed as having global cognitive impairment on the MMSE.
The numbers of patients with frontal dysfunction, as estimated by the FAS initial letter verbal fluency test (49%), were double those obtained using the EXIT interview (25%). Cut-off points, of course, are arbitrary. Also, the FAS is a timed test; poor performance by people with schizophrenia may be due to other factors, such as slowness or current psychotic symptoms, including thought disorder. The EXIT is designed for elderly or brain-damaged patients and allows for poor concentration and motivation.
When does cognitive decline occur?
There is much debate about when cognitive decline occurs in schizophrenia,
and whether it is progressive or static. Some studies suggest that deficits in
intellectual function are lifelong and pre-date (and may predispose to) the
onset of schizophrenia (Russell et
al, 1997). Other studies, which have examined first-episode,
drugnaïve patients, reported clear
neuropsychological deficits similar to those found in more chronic medicated
patients (Scottish Schizophrenia Research
Group, 1987). It has also been suggested that after a period of
initial deterioration early in the illness, cognitive deficits become static
(Hyde et al, 1994).
Finally, it has been suggested that as schizophrenia becomes more severe and
chronic, impairment becomes more widespread and clearly detectable, and
amounts to dementia in some individuals
(Scully et al,
1997).
While we should be cautious about making longitudinal interpretations of cross-sectional studies, the Nithsdale results suggest that older people (over 60 years of age) with schizophrenia show a poorer cognitive performance than younger patients. Our results are in direct contrast to those of Hyde et al (1994), who, in a cross-sectional study, reported no decline in cognitive function across five 10-year age cohorts (20-70 years). The apparent difference may be explained by the difference between the two groups studied: our study represents a whole population of patients, while Hyde and colleagues examined a highly selected group (522 screened to yield 74), from which patients who had conditions which might have an adverse impact on the central nervous system were excluded. In a recent shortterm (30-month) follow-up of geriatric long-stay patients with schizophrenia, cognitive and functional decline was detected (Harvey et al, 1999).
The mechanism underlying poor cognition in schizophrenia is unclear, and most work has failed to indicate a specific schizophrenic pathological process. However, many of the exclusion criteria employed by Hyde et al (1994) included comorbidity and treatments (such as substance misuse and hypertension, and electroconvulsive therapy) that are intimately associated with the schizophrenic illness process. These, as well as poor physical health and heavy cigarette smoking (Kelly & McCreadie, 1999), may contribute to a premature aging process that can lead to earlier and accelerated cognitive decline.
Cognition and community functioning
The long-stay in-patient group clearly performed worse on all cognitive
measures than did patients of a similar age in contact only with their family
doctor. This finding is in keeping with previous studies which have examined
large groups of chronic in-patients (Owens
& Johnstone, 1980).
While there has been much discussion about the range and nature of cognitive deficits, there has been less emphasis on their functional consequences. We used the HoNOS to assess community functioning. The HoNOS has recently been the subject of intensive scrutiny (British Journal of Psychiatry, 1999, 174, 380-438). It is not without its defects, but is gaining a place as another symptom and social function inventory, "better than most" (Stein, 1999). Our study showed a clear relationship between the functional impairment sub-scale of HoNOS and poor performance on current cognitive measures. The functional sub-scale is an assessment of problems in the community caused by poor cognition (memory, orientation and understanding) and physical illness or disability. The consequences of cognitive deficits were severe enough to be detected in a routine clinical setting by keyworkers, mainly community psychiatric nurses.
We conclude that cognitive dysfunction is a core disability in schizophrenia, affecting the majority of patients. Neuropsychological evaluation is rarely used in planning rehabilitation, yet cognitive deficits are likely to be a limiting factor in terms of functioning as a member of the community. If there is greater awareness of the prevalence and pervasiveness of cognitive dysfunction in schizophrenia and the ensuing disabilities, we may be able to help our patients function more effectively in the community. In Nithsdale we are now trying to engage some of our patients in cognitive remediation, a technique which, applied in schizophrenia, is in its infancy (O'Carroll et al, 1999).
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Clinical Implications and Limitations |
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LIMITATIONS
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ACKNOWLEDGMENTS |
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REFERENCES |
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Crawford, J. R., Besson, J. A. O., Bremner, M., et al (1992) Estimation of premorbid intelligence in schizophrenia. British Journal of Psychiatry, 161, 69-74.[Abstract]
Crawford, J. R., Obonsawin, M. C. & Bremner, M. (1993) Frontal lobe impairment in schizophrenia: relationship to intellectual functioning. Psychological Medicine, 23, 787-790.[Medline]
Folstein, M. F., Folstein, S. E. & McHugh, P. R. (1975) "Mini-mental State": a practical method for grading the cognitive state of patients for the clinician. Journal of Psychiatric Research, 12, 189-198.[CrossRef][Medline]
Frith, C. D., Leary, J., Cahill, C., et al (1991) IV. Performance on psychological tests: demographic and clinical correlates of the results of these tests. British Journal of Psychiatry, 159 (suppl. 13), 26-29.
Goldberg, T. E., Weinberger, D. R., Berman, K. F., et al (1987) Further evidence for dementia of prefrontal type in schizophrenia? A controlled study of teaching the Wisconsin Card Sorting Test. Archives of General Psychiatry, 44, 1008-1014.[Abstract]
Goldberg, Greenberg, R. D., Griffin, S. J., et al (1993) The effect of clozapine on cognition and psychiatric symptoms in patients with schizophrenia. British Journal of Psychiatry, 162, 43-48.[Abstract]
Green, M. F. (1996) What are the functional consequences of neurocognitive deficits in schizophrenia? American Journal of Psychiatry, 153, 321-330.[Abstract]
Harvey, P. D., White, L., Parrella, M., et al (1995) The longitudinal stability of cognitive impairment in schizophrenia. Mini-Mental State Scores at one- and two-year follow-ups in geriatric in-patients. British Journal of Psychiatry, 166, 630-633.[Abstract]
Harvey, P. D., Silverman, J. M., Mohs, R. C., et al (1999) Cognitive decline in late-life schizophrenia: a longitudinal study of geriatric chronically hospitalised patients. Biological Psychiatry, 45, 32-40.[CrossRef][Medline]
Hyde, T. M., Nawroz, S., Goldberg, T. E., et al (1994) Is there cognitive decline in schizophrenia? A cross-sectional study. British Journal of Psychiatry, 164, 494-500.[Abstract]
Kelly, C. & McCreadie, R. G. (1999) Smoking
habits, current symptoms, and premorbid characteristics of schizophrenic
patients in Nithsdale, Scotland. American Journal of
Psychiatry, 156,
1751-1757.
Kelly, C., McCreadie, R. G., MacEwan, T., et al (1998) Nithsdale Schizophrenia Surveys 17: Fifteen year review. British Journal of Psychiatry, 172, 513-517.[Abstract]
Liddle, P. F. & Crow, T. J. (1984) Age disorientation in chronic schizophrenia is associated with global intellectual impairment. British Journal of Psychiatry, 144, 193-199.[Abstract]
McCreadie, R. G. (1982) The Nithsdale Schizophrenia Survey: I. Psychiatric and social handicaps. British Journal of Psychiatry, 140, 582-586.[Abstract]
McCreadie, R. G., Leese, M., Tilak-Singh, D., et al (1997) Nithsdale, Nunhead and Norwood: similarities and differences in prevalence of schizophrenia and utilisation of services in rural and urban areas. British Journal of Psychiatry, 170, 31-36.[Abstract]
McGuffin, P., Farmer, A. E. & Harvey, I. (1991) A polydiagnostic application of operational criteria in studies of psychotic illness: development and reliability of the OPCRIT system. Archives of General Psychiatry, 48, 764-770.[CrossRef][Medline]
McKenna, P. J., Tamlyn, D., Lund, C. E., et al (1990) Amnesic syndrome in schizophrenia. Psychological Medicine, 20, 967-972.[Medline]
Nelson, H. E. (1982) National Adult Reading Test. Test Manual. Windsor, UK: NFER-Nelson.
O'Carroll, R. E., Russell, H. H., Lawrie, S. M., et al (1999) Errorless learning and the cognitive rehabilitation of memory-impaired schizophrenic patients. Psychological Medicine, 29, 105-112.[CrossRef][Medline]
Owens, D. G. C. & Johnstone, E. C. (1980) The disabilities of chronic schizophrenia their nature and the factors contributing to their development. British Journal of Psychiatry, 136, 384-395.[Abstract]
Parker, D. M. & Crawford, J. R. (1992) Assessment of frontal lobe dysfunction. In Handbook of Neuropsychological Assessment (eds J. R. Crawford, W. McKinlay & D. M. Parker), pp. 267-291. Hove: Erlbaum and Associates.
Royall, D. R., Mahurin, R. K. & Gray, K. F. (1992) Bedside assessment of executive cognitive impairment. The Executive Interview. Journal of the American Geriatric Society, 40, 1221-1226.
Russell, A. J., Munro, J. C., Jones, P. B., et al (1997) Schizophrenia and the myth of intellectual decline. American Journal of Psychiatry, 154, 635-639.[Abstract]
Saykin, A. J., Gur, R. C., Mozley, P. D., et al (1991) Neuropsychological function in schizophrenia: selective impairment in memory and learning. Archives of General Psychiatry, 48, 618-624.[Abstract]
Scottish Schizophrenia Research Group (1987) Scottish first episode schizophrenia study. III. Cognitive performance. British Journal of Psychiatry, 150, 338-340.[Abstract]
Scully, P. J., Coakley, G., Kinsella, A., et al (1997) Executive (frontal) dysfunction and negative symptoms in schizophrenia: apparent gender differences in static v. progressive profiles. British Journal of Psychiatry, 171, 154-158.[Abstract]
Stein, G. S. (1999) Usefulness of the Health of the Nation Outcome Scales. British Journal of Psychiatry, 174, 375-377.[Medline]
Wechsler, D. (1981) WAISR Manual. New York, NY: Psychological Corporation.
Wilson, B. A., Cockburn, J. M., Baddely, A. D., et al (1989) The development and validation of a test battery for detecting and monitoring everyday memory problems. Journal of Clinical and Experimental Neuropsychology, 11, 855-870.[Medline]
Wing, J. K., Beevor, A. S., Curtis, R. H., et al (1998) Health of the Nation Outcome Scales (HoNOS). Research and development. British Journal of Psychiatry, 172, 11-18.[Abstract]
World Health Organization (1992) The ICD-10 Classification of Mental and Behavioural Disorders. Geneva: World Health Organization.
Received for publication October 13, 1999. Revision received March 20, 2000. Accepted for publication April 12, 2000.