Cognitive deficits have been shown to be a strong and reliable clinical predictor of functional impairment in schizophrenia.1
Several meta-analyses have indicated that when examined cross-sectionally, patients show moderate to large effect sizes across a variety of neuropsychological domains with effect sizes, ranging from −0.46 to −1.57, with memory and executive dysfunction representing the more robust impairments.2–8
The trajectory of the disorder with aging has been less clear, with ongoing debate about whether schizophrenia follows a neurodevelopmental or neurodegenerative course or some combination thereof. Early descriptions of schizophrenia by Emil Kraepelin as “dementia praecox” led to the contention that cognitive deterioration occurs beyond that found in the initial stages of the illness. Some early studies indicated progressive decline in neurocognitive function with age9,10
but this has been disputed with indications that deficits later in life are typical of normal aging.11–13
(Irani, et al., unpublished data) Furthermore, postmortem data from elderly patients with schizophrenia has not shown excess of those neuropathological abnormalities found in typical neurodegenerative disorders such as Alzheimer’s disease,14
yet chemical markers such as cortical amines and neuropeptides deficits have been associated with more severe cognitive dysfunction in some patients.15
Reviews of longitudinal studies have indicated either stability in cognitive impairment over a year16
or no evidence of deterioration among community-dwelling adults.17
A recent examination of an epidemiological first-episode cohort followed over 10–12 years showed that some aspects of cognition are compromised at initial onset (executive function) and do not deteriorate, while others (visuospatial functions) are spared during the first episode but deteriorate with time.18
Recently a meta-analysis showed improvement in some tasks or no difference for others over 12 months due to cognitive remediation or neuropsychological test practice effects.19
These conflicting findings continue to raise questions about the longitudinal course of the disorder.
Additionally, most studies have focused on younger populations. The nature and magnitude of cognitive impairments in older patients has received comparatively less attention. In fact the term “older” has been used variably in various studies and reviews. For the current study, we relied on the consensus statement by members of the International Late-Onset Schizophrenia Group and operationally defined it as schizophrenia in an individual over the age of 50 years. Older individuals with schizophrenia continue to constitute a high proportion of hospitalizations and institutionalizations, making the issue of late-life trajectory of schizophrenia an important public health concern. Geriatric schizophrenia has been found to be the most expensive among all medical disorders based on per capita Medicare and Medicaid expenses.20
Given the substantial personal and economic cost of aging-related cognitive and functional impairments, further clarification of cognitive functioning in older individuals with schizophrenia is needed. Furthermore, a better understanding of the cognitive course of schizophrenia over the life span can also advance our understanding of the neurobiology of the disorder and aid in ongoing efforts focused on early detection and intervention of this complex disorder.
A recent review focused on the nature and course of cognition in late-life schizophrenia in individuals over 50 years of age.21
This qualitative review suggested that cross-sectional studies show impairments in executive function, visuospatial ability, and verbal fluency, with less consistent deficits in memory, attention, and working memory. Longitudinal findings were interpreted as indicating the presence of cognitive decline around age 65, with early deficits in visuospatial abilities. While this review was conducted thoroughly, it was limited to a qualitative description of the observed deficits, thus lacking important information on the magnitude of the effect.
Here, we extended this line of work by conducting a quantitative meta-analysis of existing studies in older patients with schizophrenia. A meta-analytic approach allowed us to combine the results of several studies to examine synthesized effect sizes, which provide more powerful estimates of true population differences than those derived from a single study. We examined the impact of both global cognitive measures as well as specific neuropsychological domains in older samples of schizophrenia patients as compared with age-matched comparison groups. A separate analysis of longitudinal data was also conducted to more closely examine the course of the disorder. We further sought to clarify the impact of potential moderators such as various methodological, demographic, and clinical variables that have been previously linked to differences between patients and healthy comparison groups.