A meta-analysis of the influence of comorbidity on treatment outcome in the anxiety disorders
Introduction
Anxiety disorders are the most common category of psychiatric disorders, with a 12-month prevalence of 18% and a lifetime prevalence of 29% (Kessler et al., 2005, Kessler et al., 2005). Anxiety disorders also exert a substantial negative impact on quality of life (Olatunji, Cisler & Tolin, 2007). For example, there is evidence of marital and financial problems in patients with panic disorder (Weissman, 1991), impairment in education and relationships in patients with social phobia (Stein & Kean, 2000), high rates of public financial assistance and diminished subjective well-being in patients with post-traumatic stress disorder (PTSD; Zatzick et al., 1997), role limitations in patients with Obsessive–Compulsive Disorder (OCD; Hollander, Kwon, Stein & Broatch, 1996), and high rates of divorce and disability in patients with Generalized Anxiety Disorder (GAD; Blazer, Hughes, George, Swartz & Boyer, 1991). Quality of life is also lower among anxiety disorder patients with higher rates of comorbidity (Lochner et al., 2003).
Comorbidity in the anxiety disorders may result in greater psychopathology and more dysfunction (Coryell et al., 1988, Lecrubier, 1998) resulting in a lower quality of life. This is an important concern given that rates of comorbidity between anxiety and other mental disorders are substantial (Lewinsohn, Zinbarg, Seeley, Lewinsohn & Sack, 1997). For example, Sanderson, DiNardo, Rapee and Barlow (1990) found that 70% of anxiety patients received at least one additional Axis I diagnosis. More recent research has shown that 92% of those with a full DSM-IV diagnosis of GAD qualify for another lifetime DSM-IV disorder (Ruscio et al., 2007). Prior research has shown that anxiety disorders tend to be highly comorbid with mood, substance, and personality disorders (Brown & Barlow, 1992), and presence of specific patterns of comorbidity (e.g., personality disorders) has been shown to be associated with more severe pathology among patients with anxiety disorders (Dreessen, Arntz, Luttels & Sallaerts, 1994).
Comorbidity may also influence treatment outcome in the anxiety disorders (Brown and Barlow, 1992, Tsao et al., 2005). Although a large body of evidence from Randomized Controlled Trials (RCTs) supports the efficacy of CBT, concern has been raised about the utility of CBT, and other empirically-based treatments that are very specific and manual-driven, in the ‘real world’ (Westen, Novotny, & Thompson, 2004). Specificity and problem focused nature of CBT has been the basis of arguments that such a treatment may not generalize to real-life “patients” who are heterogeneous and frequently present with comorbid disorders. Consistent with this notion, research has shown that comorbidity is associated with higher anxiety disorder symptom levels after CBT (Ledley et al., 2005, Weertman et al., 2005). In fact, the negative impact of comorbid major depression on CBT outcome has prompted formulations of a treatment program specifically for depressed OCD patients (Abramowitz, 2004). However, other studies have shown that comorbidity does not significantly influence outcome during CBT for anxiety disorders (e.g., Brown, Anthony, & Barlow, 1995; Dreessen et al., 1997, Tsao et al., 2002, Ollendick et al).
The present meta-analysis aims to address inconsistent findings as to the relationship between psychiatric comorbidity and treatment outcome in the anxiety disorders. Accordingly, we selected treatment outcome studies and rated them for the proportion of patients diagnosed with comorbid conditions. A secondary aim is to examine whether impact of comorbidity on treatment outcome differs according to the type of treatment being provided. Several empirically supported treatments have been identified for the anxiety disorders (see Deacon & Abramowitz, 2004 for review), most of which achieve good outcomes through cognitive (cognitive restructuring) and behavioral (e.g., exposure) interventions. However, pharmacological agents (Mitte, Noack, Steil & Hautzinger, 2005) and psychodynamic therapy (Milrod, Leon, Busch, et al. 2007) also reduce symptoms of anxiety disorders. Although these different treatments have distinct active components, the extent to which they are differentially influenced by comorbidity is unclear. Recent research suggests that outcome for comorbid conditions may vary as a function of anxiety disorder diagnosis (Hofmann & Smits, 2008). Thus, the present meta-analysis also examined the extent to which treatment outcome for different anxiety disorder diagnosis are influenced by comorbidity.
Section snippets
Selection of studies
We identified appropriate studies by conducting searches in the PsychINFO database. We conducted searches using a journal title identifier (8 different search terms; Journal of Consulting and Clinical Psychology, American Journal of Psychiatry, Behavior Therapy, Behaviour Research and Therapy, Journal of the American Academy of Child and Adolescent Psychiatry, Journal of Abnormal Child Psychology, Journal of Clinical Child Psychology, and Development and Psychopathology),1
Discussion
Although anxiety disorders commonly have comorbid diagnosis (Barlow, DiNardo, Vermilyea, Vermilyea & Blanchard, 1986), it remains unclear if such comorbidity is associated with poorer outcomes. Some have questioned the extent to which published RCTs of psychotherapy can be generalized to community outpatients. For example, Westen and Morrison (2001) report that exclusion rates for RCTs for three common disorders were 68% for depression, 64% for panic, and 65% for GAD. The investigators further
Acknowledgement
We thank Steven D. Hollon for valuable comments on a previous draft of this article.
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Indicates studies used in the meta-analysis.