C. J. Herold et al.: Cognitive Performance in Schizophrenia
Longitudinally, the extent of progressive brain tissue decrease in patients with schizophrenia is found to be twice that of healthy subjects and particularly affects frontal areas (Hulshoff Pol & Kahn, 2008; Olabi et al., 2011). Similar significant reductions in superior frontal gyrus and orbitofrontal regions were observed in a small male sample of young patients with schizophrenia and older healthy subjects in comparison to a young healthy control group (Convit et al., 2001). Moreover, gray matter decreases in frontal cortex were greater in chronic than in first-episode schizophrenia (Chan, Di, McAlonan, & Gong, 2011; Ellison-Wright, Glahn, Laird, Thelen, & Bullmore, 2008). Except for cognitive flexibility, our pattern of findings with rather stable deficits across different groups is consistent with the results of previous studies. Mockler et al. (1997) confirmed widespread cognitive deficits, but did not report any significant age effects on cognitive functioning in 62 patients with chronic schizophrenia between 18 and 69 years of age. However, the majority of patients were below 50 years, and just 6 patients formed the oldest group (60 to 69 years). Moreover, executive functions were not specifically addressed. Similarly, Hijman et al. (2003) who compared performance on four subtests of the Wechsler Adult Intelligence Test between 112 patients with chronic schizophrenia and 70 healthy controls (age range: 16 to 56 years) did not describe a significant interaction effect of age with group, while patients performed worse on all subtests. The oldest group (46 to 56 years) comprised 17 patients; the majority of patients were below 46 years of age. Performance on the subtest picture arrangement, which shares aspects of executive functioning, decreased with age, a process which appeared to be slightly more pronounced in the patient group. Bowie and colleagues (2008) also reported deficits in a number of important neuropsychological domains including psychomotor speed and cognitive flexibility. Performance levels compare to the “middle-aged” and “older” patient subgroups investigated in the present study. However, Bowie et al. (2008) recruited a group of old patients (50–85 years), but did not include younger patients with chronic schizophrenia. In light of the reduced life expectancy of patients with chronic schizophrenia (Laursen, 2011), the subgroup of old patients (70–85 years) may represent a number of survivors who either had a more favorable course of the disorder or were less vulnerable to its consequences during the aging process. The study showed evidence for age-associated cognitive decline on the more complex components of an information-processing test, which Bowie et al. (2008) alternatively referred to “the course of illness and the processing demands of the cognitive measure of interest.” However, their results mirror our findings because they did not only show a significant age-associated decline in the TMT A, but also a similar although nonsignificant trend toward for the TMT B in the patients. In the present study, executive functions were only addressed by using the TMT, while other tests such as the Wisconsin Card Sorting Test were not applied. Because of reduced © 2017 Hogrefe
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cognitive capacity of especially the older patients, we restricted our cognitive assessment to a few tests. While groups were carefully matched for age and sex, in the patients years of education were significantly reduced, which may be expected in a group of patients with a chronic course of the disease, of whom 20–60% were hospitalized. For this reason years of education were controlled for in the MANOVA. Negative symptoms differed nonsignificantly between the patient groups, while positive symptoms (trend-level only) and BPRS total score were lower in older than younger patients. These differences correspond to the amelioration of acute schizophrenic symptoms with increasing age (Schmid et al., 2011), already described by Bleuler (1949). That the older patients are nonetheless severely affected is indicated by their dwelling status, illustrating that older patients are more often institutionalized. Given that age and duration of illness coincide because of onset of the disease in early adulthood and the exclusion of patients with late onset schizophrenia, the three age groups differed significantly with respect to illness duration. The marginal, albeit significant group difference of age at illness onset, determined on basis of the patients’ history and case notes, may well be explained by the fact that the youngest group per definitionem does not comprise patients with a later onset, which is also reflected by the respective standard deviations. Data concerning the predominant treatment of the patients in the past were unfortunately not available. At the time of assessment the majority of the patients were receiving atypical antipsychotics only or typical and atypical antipsychotic medication in combination. Potential medication effects cannot be entirely excluded as patients were examined cross-sectionally, although the three patient groups showed only marginally, nonsignificant differences with respect to CPZ equivalents. Similarly, significant medication effects were not identified in the large meta-analysis by Irani and colleagues (2011). In contrast, other studies indicate a beneficial impact of atypical (Guilera, Pino, Gómez-Benito, & Rojo, 2009; Thornton, Van Snellenberg, Sepehry, & Honer, 2006; Woodward, Purdon, Meltzer, & Zald, 2005) and typical (Davidson et al., 2009; Mishara & Goldberg, 2004; Schröder, Tittel et al., 1996) antipsychotic medication on cognition in schizophrenia. Especially the latter findings are important given that particularly the older patients of our sample might have received mainly classical antipsychotics in the past. Additional factors other than age are likely to affect cognitive flexibility: The large meta-analysis cited above (Irani et al., 2011) revealed a significant role for both demographic (age, sex, education, race) and clinical factors (living status, age of onset, duration of illness, clinical symptoms). From a clinical standpoint, co-morbid somatic conditions and other life-style factors should also be added in longitudinal studies, as physical illnesses like the metabolic syndrome, which increases in incidence with rising age and is associated with cognitive deterioration (Schröder & Pantel, 2011), are more common in patients GeroPsych (2017), 30 (1), 35–44