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The Effects of Age on Cognitive Deficits in Schizophrenia: Page 2 of 2

The Effects of Age on Cognitive Deficits in Schizophrenia: Page 2 of 2

Longitudinal Studies

In a longitudinal study of older ambulatory patients, Heaton et al. (2001) found no evidence of change over an average of 60 months on a comprehensive neuropsychological battery. However, only 22 of the 142 patients were over age 65 at entry into the study. Another longitudinal study reported that older patients had selectively greater impairments in abstraction abilities than younger patients, with no increased age-related differences in other aspects of cognitive functioning (Fucetola et al., 2000). Further, Granholm et al. (2000) reported that older patients had a reduced ability to process complex information, as shown by increased utilization of information-processing resources while performing an attentional task. There is some evidence of age-related changes in the ability to perform complex and resource-demanding tasks even in ambulatory patients.

In a study of hospitalized patients with chronic schizophrenia (age>65) with MMSE scores >17, 30% declined over a 30-month period (Harvey et al., 1999b). The best two predictors of cognitive decline were lower education and greater severity of positive symptoms at baseline. A follow-up study of geriatric patients with schizophrenia who entered the study while hospitalized and who were reassessed after they were discharged to nursing homes also demonstrated cognitive decline over an average of 2.5 years (Harvey et al., 1999a).

Additional support for age-related cognitive decline comes from a study of chronically institutionalized patients ranging in age from 25 to 85 who were followed for six years and compared to healthy individuals and patients with AD (Friedman et al., 2001). This study found that the patients with schizophrenia had an age-associated risk of cognitive decline not found in the patients with AD or the healthy controls. The oldest patients with schizophrenia (ages 75 to 80 at baseline) dropped by six MMSE points in six years, while those under the age of 65 did not change in their functioning over the follow-up period. Furthermore, patients with AD declined by 12 or more MMSE points, regardless of age at entry into the study. This suggests that chronicity alone is not a sufficient determinant of cognitive decline until patients cross a certain age threshold. Later studies have indicated that newly incident medical conditions predict risk for cognitive decline (Friedman et al., 2002) and have sug-gested more recently that declines in cognitive functioning over time in poor-outcome patients predict the course of functional decline as well (Harvey and Davidson, 2002).

Conclusions

While a number of studies on cognition in older patients with schizophrenia have been published in the past decade, the specific effect of aging remains unclear. It appears that cognitive decline with aging in schizophrenia is multi-determined. While the decline does not appear to occur at all in younger patients, even those with a chronic course of illness, it is also not likely to be a pattern found in all older individuals with schizophrenia.

It appears that certain risk factors-possibly a chronic course of illness, less education, higher levels of positive symptoms and poor baseline cognitive functioning-are associated with the age-related cognitive decline observed in some patients. Ambulatory patients may also decline in late life on particularly complex tasks. However, the timing and severity of the decline may differ from poor-outcome patients.

Complicating the identification of those at risk for cognitive decline are the different research designs employed by various groups of researchers. This leads to the difficulty of parsing out the effects on cognition of life-long institutionalization, chronic psychosis, long-term antipsychotic medication administration and other factors. The Figure illustrates that longitudinal studies of chronically ill patients universally find global cognitive decline, while the only cross-sectional studies that failed to find age-related differences in cognition assessed only one specific domain and excluded low-functioning patients. In addition, a longitudinal study that failed to observe cognitive decline was of somewhat younger ambulatory patients. Since expected declines in cognition for healthy individuals only become substantial after age 65, it stands to reason that examination of patients with schizophrenia who are younger than 65 may be insufficient to detect decline.

Future longitudinal studies will assist in determining why cognitive decline occurs in late life for some patients with schizophrenia, but not for others. Consequently, treatment strategies for those at highest risk for decline may be developed in the near future. In turn, functional outcome, by way of improving or at least preserving cognitive functions, may be improved for the large number of elderly patients with schizophrenia.

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References

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