Psychiatric comorbidity among adults with schizophrenia: A latent class analysis
Introduction
Psychiatric comorbidity is recognized as an important clinical problem in the diagnosis, treatment, and prevention of mental illness. Among adults with schizophrenia, numerous studies have shown an increased prevalence of anxiety, depressive, and substance use disorders greater than that found in the general population (Buckley et al., 2009). Most studies have focused on individual comorbid diagnoses with schizophrenia even though comorbidities are often far more complex than single dualities (Kessler et al., 1994, Ginzburg et al., 2010, Weich et al., 2011). There have been few efforts to characterize patterns of psychiatric comorbidity beyond pairwise examination of individual diagnoses among adults with schizophrenia.
For adults with schizophrenia, psychiatric comorbidity has most often been conceptualized in terms of “dual diagnoses”, referring to a co-occurring substance use disorder (RachBeisel et al., 1999, Drake et al., 2007). Epidemiological and clinical studies have consistently found that nearly half of all adults with schizophrenia have a lifetime substance use disorder (Regier et al., 1990, Kessler et al., 1997, O'Daly et al., 2005). Alcohol and drug use disorders have long been recognized to interfere with schizophrenia as comorbid substance abuse is related to greater positive symptoms, higher rate of relapse, and worse physical and mental health in schizophrenia (Buckley et al., 2009). One prominent hypothesis to account for comorbid substance abuse among those with schizophrenia is the “self-medication” hypothesis, which postulates that individuals abuse substances to help relieve painful affects, emotions, states of distress, or other mental health symptoms (Khantzian, 1997), although the theory remains debatable (Mueser et al., 1992).
Depression is another psychiatric disorder that often co-occurs with schizophrenia. An estimated 23–57% of adults with schizophrenia have comorbid depression (Buckley et al., 2009). Schizophrenia with comorbid depression imports a poorer clinical outcome and lower overall quality of life than those with no depression (Sim et al., 2004, Buckley et al., 2009). Yet interestingly, adults with schizophrenia with comorbid depression have been found to have greater awareness of their mental illness than those with no comorbid depression, suggesting comorbidity may be related to a greater degree of insight but a poorer quality of life (Sim et al., 2004).
Anxiety disorders are a third category of psychiatric diagnoses that have been examined in schizophrenia. The prevalence of different anxiety disorders among adults with schizophrenia vary from an estimated 10–15% with a comorbid panic disorder to an estimated 12–29% with a comorbid posttraumatic stress disorder, and an estimated 12–23% with comorbid obsessive compulsive disorder (Buckley et al., 2009, Achim et al., 2011). Studies have shown that adults with schizophrenia and a comorbid anxiety disorder report greater general psychopathology, but few other clinical differences (Tibbo et al., 2003) and some have even found more positive outcomes associated with comorbidity (Garvey et al., 1991, Emsley et al., 1999). Particular attention has been given to schizophrenia with a comorbid obsessive compulsive disorder as considerable evidence suggests a “schizo-obessive” subtype (Poyurovsky et al., 2003, Bottas et al., 2005, Buckley et al., 2009).
In the current study, we used latent class analysis to examine patterns of psychiatric comorbidity among a national sample of U.S. adults diagnosed with schizophrenia using data from the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE) study. The comorbid psychiatric diagnoses examined included depression, anxiety disorders, and substance use disorders. Latent class analysis represents a unique analytic approach to examine multiple comorbidities. Unlike simple descriptive or cluster analytic approaches, latent class analysis characterizes individuals based on probabilistic models of subgroup membership (which is more reflective of reality) instead of needing to specify subgroups beforehand and allows quantitative comparison models of fit across several possible diagnostic combinations (of which there are a possible 32 combinations in this study). This study aimed to use this advanced statistical technique to not only characterize common patterns of comorbidity among adults with schizophrenia, but relate them to differences in symptomatology, illness and treatment insight, and quality of life as these have been identified as important outcomes in schizophrenia (Andreasen et al., 1990, Pini et al., 2001, Hofer et al., 2004).
Section snippets
Sample
Baseline data from a total of 1446 adults participating in CATIE (Lieberman et al., 2005) were reanalyzed for this study. CATIE was conducted between January 2001 and December 2004 at 57 U.S. sites (16 university clinics, 10 state mental health agencies, seven Veterans Affairs medical centers, six private nonprofit agencies, four private-practice sites, and 14 mixed system sites) and is one of the largest randomized controlled drug trials of adults with schizophrenia to date. Details of CATIE
Results
Of a sample of 1446 adults with schizophrenia, 400 (27.7%) had comorbid major depression, 355 (24.6%) had comorbid alcohol abuse/dependency, 419 (29.0%) had comorbid drug abuse/dependency, 73 (5.0%) had comorbid obsessive compulsive disorder, and 197 (13.6%) had some other comorbid anxiety disorder in the past 5 years. Overall, 810 (56.0%) of the total sample had at least one comorbid mental health disorder with schizophrenia.
As shown in Table 1, latent class analysis revealed that three
Discussion
Among a national sample of adults with schizophrenia, the majority (56%) had a comorbid anxiety, depression, or substance use disorder diagnosis in the past 5 years, consistent with previous studies on people with severe mental illness (RachBeisel et al., 1999, Drake et al., 2007, Buckley et al., 2009, Achim et al., 2011). It appears there are three distinct latent profiles of psychiatric comorbidity among adults with schizophrenia: those without any comorbidity, those with comorbid anxiety and
Acknowledgments
The funding for CATIE was provided by the NIMH Grant# N01MH90001. The NIMH had no further role in study design, data collection, analysis, interpretation, writing, or decision to submit the paper for publication.
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