The influence of medical burden severity and cognition on functional competence in older community-dwelling individuals with schizophrenia

https://doi.org/10.1016/j.schres.2015.12.009Get rights and content

Abstract

Objective

Cognition predicts functional competence among individuals with schizophrenia across the lifespan. However, as these individuals age, increasing levels of medical burden may also contribute to functional deficits both directly and indirectly through cognition. Thus, we assessed the relationship among, cognition, medical burden, and functional competence in older individuals with schizophrenia.

Methods

We analyzed data obtained from 60 community-dwelling participants with schizophrenia and 30 control participants aged 50 or above. Cognition was assessed using the MATRICS Consensus Cognitive Battery (MCCB), functional competence was assessed using the USCD Performance-Based Skills Assessment (UPSA), and medical burden was assessed using the Cumulative Illness Rating Scale for Geriatrics (CIRS-G). Group differences were assessed using independent samples t-tests or chi-square tests. Mediation analyses using bootstrapping techniques were used to assess whether cognition mediated the effects of medical burden on functional competence.

Results

Participants with schizophrenia had higher levels of medical burden, cognitive deficits, and functional impairments. In participants with schizophrenia, cognition, but not medical burden, predicted functional competence after adjusting for age, education, gender, clinical symptoms, and anticholinergic burden of medications. In control participants, cognition and medical burden both predicted functional competence after adjusting for age, education, and gender. Further, cognition was found to fully mediate the association between medical burden and functional competence in control participants.

Conclusion

Cognition is a robust predictor of functional competence among older individuals with schizophrenia, regardless of medical burden. Cognitive deficits associated with schizophrenia may mask any further cognitive impairment associated with medical burden and its impact on function.

Introduction

Cognitive deficits are a core feature in schizophrenia and are among the strongest predictors of functional status (Bowie and Harvey, 2006, Green et al., 2000, Green et al., 2004). The severity of cognitive deficits in community-dwelling individuals with schizophrenia remains stable into the 7th decade (Heaton et al., 2001, Rajji et al., 2013) and may worsen later in life (Loewenstein et al. 2012). Further, the impact of these deficits on function is relatively stable in older individuals with schizophrenia (Kalache et al. 2015). While cognitive function also determines functional abilities in healthy older individuals (Aguero-Torres et al., 2002, Beland and Zunzunegui, 1999, Hebert et al., 1999), other factors, e.g., medical burden, are also powerful predictors of function in late life (Aguero-Torres et al., 2002, Cavanaugh and Wettstein, 1983, Guccione et al., 1994). Thus, with the growing number of older individuals with schizophrenia (Carney et al., 2006, Goeree et al., 2005, Lafeuille et al., 2014, Schoepf et al., 2014) characterizing cognitive and non-cognitive factors that impact functional status is critical for the development of effective rehabilitation strategies for this population.

Schizophrenia is associated with considerable medical comorbidity (Carney et al., 2006, Jeste et al., 1996, Lafeuille et al., 2014, Nasrallah et al., 2006, Schoepf et al., 2014). Compared to the general population, medical illnesses in individuals with schizophrenia tend to be more severe (Dixon et al., 1999, Jeste et al., 1996, Sokal et al., 2004) and result in higher rates of hospital admissions (Schoepf et al. 2014), health care costs (Goeree et al., 2005, Lafeuille et al., 2014), and mortality (Schoepf et al. 2014). In addition to contributing to functional impairment, chronic medical conditions such as cardiovascular disease, (Gildengers et al., 2010, Zuccala et al., 2005), diabetes (Gregg et al. 2000), and pulmonary disorders (Liesker et al. 2004) adversely affect cognition. Significant associations have been observed between medical burden and cognition in older individuals with (Gildengers et al., 2010, Mariani et al., 2008, Solomon et al., 2011) and without psychiatric disorders (Duff et al., 2007, Gregg et al., 2000, Liesker et al., 2004, Zuccala et al., 2005). Given the high prevalence of chronic medical conditions in individuals with schizophrenia (Carney et al., 2006, Lafeuille et al., 2014, Schoepf et al., 2014), we must also consider the possibility of medical burden having not only a direct effect on functional status, but also an indirect effect through its influence on cognition.

To our knowledge, only two published studies have investigated the relationship between medical burden and functional status in individuals with schizophrenia. In one longitudinal study of 124 older and institutionalized patients with schizophrenia, neither the number of baseline medical diagnoses nor an increased number of medical diagnoses over a four-year period contributed to change in functional status (Friedman et al. 2002). The functional abilities that are typically assessed in institutionalized patients consist of self-care skills or the ability to carry out activities of daily living (e.g., dressing, toileting, feeding etc.) (Friedman et al. 2002). Thus, these findings may not generalize to community-dwelling individuals who typically have higher-order functional abilities (e.g., managing medications, preparing meals, utilizing transportation within the community, etc.) (Auslander et al. 2001). This is important because 80% of older individuals with schizophrenia live in the community (Gurland and Cross 1982).

In a second study based on cross-sectional baseline data from 1460 individuals with schizophrenia who participated in the CATIE trial, medical comorbidity was a weaker correlate of psychosocial functioning and employment status than neurocognitive impairment and clinical symptoms (Chwastiak et al. 2006). However, in the CATIE trial, most individuals with cardiovascular disease were deemed too medically unstable to participate in a clinical trial and were excluded (Stroup et al. 2003). Thus, the medical burden of the CATIE study group may underestimate the true medical burden of this population. Furthermore, the mean (SD) age of patients in this study was 40.6 (11.1) years, limiting the generalizability of the findings to older individuals with schizophrenia.

To address these limitations in the literature on the relationship between medical burden and functional status in older individuals with schizophrenia, we conducted a study including older community-dwelling individuals with schizophrenia aged 50 or above. We aimed to (1) quantify medical burden and assess its direct impact on functional competence, and (2) characterize the relationships among medical burden, clinical symptoms, cognition, and function.

Section snippets

Participants

Sixty participants with schizophrenia were recruited at the Centre for Addition and Mental Health (CAMH) in Toronto, Canada using advertisements and physician referrals. Thirty community-dwelling age and gender-matched control participants without a psychiatric disorder were additionally recruited from the Greater Toronto Area using advertisements. The study was approved by the CAMH Research Ethics Board and all participants provided written informed consent.

Eligibility criteria for

Results

Participants with schizophrenia and control participants did not differ in age or gender. However, participants with schizophrenia had significantly lower level of education, higher ACB Total Scores, higher CIRS-G Total Scores, higher CIRSG-SI scores, lower MCCB Global Scores, and lower UPSA Total Scores (Table 1). No group differences were observed between individual CIRS-G organ systems (Fig. 1). A summary of the medications that all participants were on at the time of assessment is presented

Discussion

To our knowledge, this is the first published study to investigate the relationships among functional competence and clinical symptoms, cognition, and medical burden in a sample of older community-dwelling individuals with schizophrenia. Our results showed that while the types of medical conditions present in both groups of participants were similar, participants with schizophrenia experienced higher levels of medical burden, cognitive deficits, and functional impairment than control

Funding

Canadian Institutes of Health Research (CIHR 200017 to BHM, and CIHR 180087 to TKR).

Contributors

CT contributed to the study design and conception, performed literature search, statistical analyses, and wrote the first draft of the manuscript. BHM contributed to the study design and conception. SMK, SK, and ZG contributed to the study design and data extraction. ANV, MAB, and MN contributed to the study design and interpretation of the clinical and neuropsychological assessments. TKR supervised CT in the study design and conception, literature search, statistical analysis, interpretation

Conflict of interest

Dr. Mulsant received within the past three years research support from Bristol-Myers Squibb (medications for a NIH-funded clinical trial), Pfizer (medications for a NIH-funded clinical trial), and Eli-Lilly (medications for a NIH funded clinical trial). He directly own stocks of General Electric (less than $5000). Dr. Butters has received remuneration for providing neuropsychological assessment services for GlaxoSmithKline and received salary support from NIH R01 MH072947 and MH080240. The

Acknowledgments

The authors would like to acknowledge all participants and their families for their contribution to this work.

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