Journal of Affective Disorders 162 (2014) 61–66

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Research report

The effect of comorbid major depressive disorder or bipolar disorder on cognitive behavioral therapy for social anxiety disorder Katie Fracalanza a, Randi E. McCabe b,c,n, Valerie H. Taylor d, Martin M. Antony a a

Department of Psychology, Ryerson University, Toronto, ON, Canada Department of Psychiatry and Behavioural Neurosciences, McMaster University, Hamilton, ON, Canada c Anxiety Treatment and Research Centre, St. Joseph's Healthcare Hamilton, ON, Canada d Department of Psychiatry, Women's College Hospital, Toronto, ON, Canada b

art ic l e i nf o

a b s t r a c t

Article history: Received 26 November 2013 Received in revised form 6 March 2014 Accepted 7 March 2014 Available online 24 March 2014

Background: Major depressive disorder (MDD) and bipolar disorder (BD) commonly co-occur in individuals with social anxiety disorder (SAD), yet whether these comorbidities influence the outcomes of cognitive behavioral therapy (CBT) for SAD is unclear. Methods: The present study examined the degree to which individuals with SAD and comorbid MDD (SADþ MDD; n ¼ 76), comorbid BD (SADþBD; n ¼ 19), a comorbid anxiety disorder (SADþANX; n ¼ 27), or no comorbid diagnoses (SADþNCO; n ¼41) benefitted from CBT for SAD. Individuals were screened using the Structured Clinical Interview for DSM-IV and then completed the Social Phobia Inventory and the Depression Anxiety Stress Scales before and after 12-weeks of group CBT for SAD. Results: At pretreatment the SADþMDD and SADþBD groups reported higher social anxiety symptoms than the SADþANX and SADþ NCO groups. All groups reported large and significant improvement in social anxiety with CBT. However, at posttreatment the SADþMDD and SADþ BD groups continued to have higher social anxiety symptoms than the SADþNCO group, and the SADþANX group did not differ in social anxiety symptoms from any group. The sample also showed small and statistically significant improvement in depressive symptoms with CBT for SAD. Limitations: Information about medication was not collected in the present study, and we did not assess the long-term effects of CBT. Conclusion: Our results suggest that CBT for SAD is an effective treatment even in the presence of comorbid mood disorders in the short-term, although extending the course of treatment may be helpful for this population and should be investigated in future research. & 2014 Elsevier B.V. All rights reserved.

Keywords: Social anxiety disorder Major depressive disorder Bipolar disorder Comorbidity Cognitive behavioral therapy

1. Introduction Social anxiety disorder (SAD) is characterized by excessive and persistent fear in social or performance situations (American Psychiatric Association, 2013). It is one of the most common psychological disorders, with an estimated lifetime prevalence rate of 12.1% (Kessler et al., 2005). SAD is also associated with low quality of life and functional impairment in the domains of work, education, and relationships (Aderka et al., 2012; Antony et al., 1998b). Furthermore, mood disorders occur at high rates in individuals with SAD. Specifically, 19.5–32% of individuals with SAD have co-occurring major depressive disorder (MDD; Huppert, 2009; Ohayon and n Corresponding author at: Anxiety Treatment and Research Centre, St. Joseph's Healthcare Hamilton, 50 Charlton Avenue East, Hamilton, Ontario, Canada L8N 4A6. Tel.: þ 1 905 522 1155x33695; fax: þ1 905 521 6120. E-mail address: [email protected] (R.E. McCabe).

http://dx.doi.org/10.1016/j.jad.2014.03.015 0165-0327/& 2014 Elsevier B.V. All rights reserved.

Schatzberg, 2010) and 3–21.1% of outpatients with SAD have comorbid bipolar disorder (Koyuncu et al., 2014; Perugi et al., 1999; Van Ameringen et al., 1991). This is concerning in light of prior research demonstrating that comorbid mood disorders are associated with more severe social anxiety symptoms and functional impairment in individuals with SAD (Aderka et al., 2012; Fracalanza et al., 2011; Koyuncu et al., 2014). Given these findings, it is important to understand the impact of comorbid MDD and bipolar disorder on the outcomes of cognitive behavioral therapy (CBT) for SAD, especially since CBT is recommended as part of first line treatment for these populations (Swinson et al., 2006). Only a handful of prior studies have investigated the degree to which comorbid depressive symptoms influence the outcomes of psychological treatment for SAD, and the results have been conflicting. Some studies have found that individuals with more severe depressive symptoms are less likely to benefit from CBT for SAD in the short term (Chambless et al., 1997; Ledley et al., 2005),

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or to maintain their gains in the longer term (Marom et al., 2009), while other studies have suggested that depressive symptoms do not have a detrimental effect on the outcomes of SAD treatment. For example, Erwin et al. (2002) found that although socially anxious people with comorbid MDD or dysthymic disorder reported more severe social anxiety and depressive symptoms prior to and following treatment, they improved with CBT to the same extent as socially anxious individuals without a comorbid depressive disorder. Furthermore, there are studies that have found that comorbid MDD affects neither the initial severity of anxiety symptoms nor improvement during CBT for SAD (Joormann et al., 2005; Van Velzen et al., 1997). Therefore, the impact of depressive symptoms on CBT for SAD is unclear (see Bauer et al., 2012 for a detailed review), and further research in this area is needed. In addition, to the best of our knowledge, there have been no prior empirical investigations on the degree to which CBT for SAD is an effective treatment in the presence of comorbid bipolar disorder, characterized by depressive and manic or hypomanic episodes (American Psychiatric Association, 2013). Studies that address this question are sorely needed, as CBT for social anxiety is commonly provided to individuals with comorbid bipolar disorder in practice, despite the lack of data on how helpful this is. Examining how bipolar disorder impacts CBT for SAD is of particular interest as social anxiety disorder was found to be the most common anxiety disorder in a sample of anxious individuals with comorbid bipolar disorder (Fracalanza et al., 2011). Overall, investigating the degree to which comorbid MDD or bipolar disorder impact the outcomes of CBT for SAD is an essential step in determining how to optimally address social anxiety symptoms when mood disorders are present. The primary goal of the present study was to investigate changes in social anxiety symptoms with CBT for SAD in individuals with comorbid MDD or bipolar disorder relative to two comparison groups – individuals with one or more comorbid anxiety disorder and individuals with no comorbid diagnoses. Hypotheses about whether these groups would report differential levels of improvement in SAD symptoms with CBT were not proposed, since findings on the effect of comorbid MDD on CBT for SAD have been mixed, and no prior study has examined the impact of comorbid bipolar disorder on CBT for SAD. The present study also sought to determine the impact of CBT for SAD on depressive symptoms and the degree to which initial depressive symptom severity is associated with improvement in social anxiety with CBT.

2. Method 2.1. Participants A total of 214 individuals completed group CBT for SAD at the Anxiety Treatment and Research Centre (ATRC), an outpatient clinic in a large community hospital located in Hamilton, Ontario, Canada between 2001 and 2011. Individuals were included in the present study if they had a current principal diagnosis of SAD, as determined by the Structured Clinical Interview for DSM-IV (SCIDIV) and: comorbid MDD (SADþMDD group; n¼ 76); comorbid bipolar disorder (SADþBD group; n ¼19); one or more comorbid anxiety disorder (SADþANX group; n ¼27); or no comorbid diagnoses (SADþ NCO group; n ¼41). Within the SAD þBD group, 53% had bipolar I disorder, and 47% had bipolar II disorder, and the results of the SCID-IV indicated that there were no manic or hypomanic symptoms present at the time of the assessment. There were 51 individuals excluded from the present study. Three individuals were excluded because their SPIN scores were 2.5 or more standard deviations below the sample mean and were considered outliers (King et al., 2011). Individuals were also

excluded from the current study if diagnostic criteria were met for: MDD in partial or full remission (n ¼19); a comorbid disorder other than MDD, bipolar disorder or an anxiety disorder (e.g., comorbid substance use disorder; n ¼12); dysthymic disorder (n ¼9); depressive disorder not otherwise specified (n ¼5); schizoaffective disorder (n ¼2); or a mood disorder due to a general medical condition (n ¼1). The present sample was comprised of 77 males and 86 females, most of whom (85%) identified as Caucasian. The average age of participants was 35 (SD¼ 12.02). In terms of marital status, 60% of participants were single, 34% were married or co-habiting, and 6% were divorced or widowed. Most participants (64%) had started or completed college or university. The average age of SAD onset in the present sample was 12 (SD¼7.99), and the mean number of comorbid diagnoses was 1.91 (SD¼1.67). More information about demographics by group can be found in Table 1, and information about demographic differences between groups can be found in the results section. 2.2. Measures 2.2.1. SCID-IV (First et al., 1996) The SCID-IV is a clinician-administered semistructured interview that assesses the DSM-IV criteria for Axis I disorders. Earlier versions of the SCID have demonstrated good interrater reliability (Segal et al., 1994; Williams et al., 1992), adequate test–retest reliability (Williams et al., 1992), and high criterion-related validity for most disorders in clinical samples. 2.2.2. Social Phobia Inventory (SPIN; Connor et al., 2000) The SPIN is a 17-item measure comprised of items that assess various aspects of social anxiety, including fear, avoidance, and physiological arousal. Respondents indicate the degree to which they have been bothered by these symptoms in various types of social or performance situations over the past week on a 5-point Likert scale ranging from 0 (not at all) to 4 (extremely). Examples of items are: “Parties and social events scare me” and “I avoid having to give speeches.” The SPIN has high internal consistency (α ¼.92), good test–retest reliability (r¼ .86), and good convergent and discriminant validity (Antony et al., 2006). The SPIN has also demonstrated sensitivity to changes following group CBT for SAD (Antony et al., 2006). It is of note that a score of 19 or greater on the SPIN has been used to identify individuals with SAD in previous research (Connor et al., 2000), and 95% of the present sample produced SPIN scores above this cutoff. 2.2.3. Depression Anxiety Stress Scales, 21-item version (DASS-21; Lovibond and Lovibond, 1995a) The DASS-21 is comprised of three 7-item subscales that assess symptoms of depression, anxiety, and stress. For the purpose of the present study, only the depression subscale (DASS-D) was used. On the DASS-D respondents indicate the degree to which each statement about depressive symptoms applied to them over the past week on a 4-point Likert scale ranging from 0 (did not apply to me at all) to 3 (applied to me very much). Examples of items are: “I couldn't seem to experience any positive feeling at all” and “I felt down-hearted and blue.” The subscales of the DASS21 have high internal consistency (αs ¼ .89 to .96), good test–retest reliability (rs ¼.71 to .81), and high convergent and discriminant validity in both community and clinical samples (Antony et al., 1998a; Crawford and Henry, 2003; Lovibond and Lovibond, 1995b). 2.3. Procedure Prior to treatment, each individual completed the SCID-IV, which was administered by a psychologist or a clinician with training in diagnostic assessment who was supervised by a

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Table 1 Demographic profile of the sample by group. Demographic variable

SADþ MDD group (n¼ 76)

SADþ BD group (n¼ 19)

SADþANX group (n¼ 27)

SADþ NCO group (n ¼41)

35 (46%) 41 (54%)

4 (21%) 15 (79%)

14 (52%) 13 (48%)

24 (59%) 17 (41%)

63 (85%) 1 (1%) 6 (8%) – 2 (3%) 2 (3%) 315.67a,b (12.57) 12.95 (8.62) 2.86 (1.52)a

19 (100%) – – – – 40.21a (11.15) 9.75 (5.04) 2.68 (1.16)a

22 (81%) – 5 (19%) – – – 32.85b,c (11.17) 10.60 (8.27) 1.63 (0.97)b

33 (80%) – 5 (12%) 1 (3%) – 2 (5%) 31.76c (11.13) 10.44 (7.34) 0.00c

Marital status1 Single Married or cohabitating Divorced or separated

48 (64%) 22 (29%) 5 (7%)

8 (42%) 9 (47%) 2 (11%)

17 (63%) 10 (37%) –

25 (61%) 14 (34%) 2 (5%)

Education High school College/university Graduate school

26 (34%) 49 (65%) 1 (1%)

5 (26%) 12 (63%) 2 (11%)

7 (26%) 18 (67%) 2 (7%)

13 (32%) 26 (63%) 2 (5%)

Household Income1 4$60000 $60000 þ

40 (67%) 20 (33%)

8 (57%) 6 (43%)

14 (64%) 8 (36%)

15 (44%) 19 (56%)

Sex Male Female Ethnicity1 White Aboriginal Asian Black Hispanic Other (an ethnicity not listed) Mean age in years (SD) Mean age at onset of SAD (SD)1 Mean number of additional diagnoses2

Statistical test value

p

χ2(3)¼ 7.60

.06

χ2(15) ¼ 13.54

.56

F (3, 159) ¼ 2.61 F (3, 150) ¼ 1.42 F (3, 159) ¼ 55.19

.05 .24 .00

χ2(6)¼ 5.34

.50

χ2(6)¼ 4.57

.60

χ2(3)¼ 4.79

.19

Note: SADþ MDD¼ social anxiety disorder and comorbid major depressive disorder; SADþBD ¼social anxiety disorder and comorbid bipolar disorder (bipolar I disorder or bipolar II disorder); SADþANX ¼social anxiety disorder and one or more comorbid anxiety disorder; SADþ NCO¼ social anxiety disorder and no comorbid disorder. Values with different subscripts differ at the p o .05 level. 1 2

Missing data. Total number of diagnoses excluding social anxiety disorder.

psychologist. Diagnoses were determined by participant responses to the SCID-IV, and when multiple disorders were present, the disorder causing the most distress or impairment was considered the principal diagnosis and other disorders were considered comorbid. Interrater reliability (n ¼13 cases; 2 raters) on diagnoses determined by the SCID-IV was high (Cohen's kappa¼ .89). Next, individuals completed a demographic questionnaire, the SPIN, and the DASS-D. Following this, all individuals received twelve 2-hour sessions of manualized group CBT for SAD based on manuals by Heimberg and Becker (2002) and Antony and Swinson (2008). The main components of treatment were psychoeducation, cognitive restructuring, exposure to feared social situations, and social skills training. All groups were run by two therapists trained in CBT for SAD. Therapists were psychologists, master's level psychology practitioners, social workers, or graduate students supervised by psychologists. There were five to eight individuals with SAD in each group. Immediately following treatment, individuals completed the SPIN and the DASS-D again.

3. Results 3.1. Preliminary analyses and data analytic strategy In order to determine if there were significant differences in the demographic characteristics between groups, one-way Analyses of Variance (ANOVAs) were conducted on continuous variables and chi-square tests were conducted on categorical variables. These tests showed that there was a statistically significant difference in the age of participants between groups, F(3, 159)¼2.61, p¼ .05, η2p ¼.05. Individuals in the SADþBD group were significantly older

than individuals in the SADþANX and SADþNCO groups (pso.04), with no other differences in age between groups. Thus, age was controlled for in all subsequent analyses. There was also a significant difference in the total number of comorbid disorders between groups, F(3, 159)¼55.19, po.001, η2p ¼.51. As expected, individuals in the SADþMDD, SADþ BD and SADþANX groups all had a significantly greater number of comorbid diagnoses than individuals in the SADþ NCO group (pso.001). In addition, individuals in the SADþMDD and SADþBD groups presented with significantly more comorbid disorders than individuals in the SADþANX group (pso.01), and there was no significant difference in the number of comorbid disorders between the SADþMDD and SADþBD groups. To explore whether the number of comorbid disorders was related to depressive symptom severity, a 2-tailed Pearson correlation was run on the number of comorbid disorders and DASS-D scores at pretreatment. This test showed a significant positive association between overall comorbidity level and initial depressive symptom severity, r¼ .44, po.001. Given the significant statistical overlap between comorbidity level and depressive symptoms, and the fact that the presence or absence of comorbid disorders was a central and intentional between-group difference in the present study, the total number of comorbid disorders was not controlled for in subsequent statistical analyses. There were no other statistically significant differences on demographic characteristics between groups. See Table 1 for group means and standard deviations on demographic variables. The assumptions of normality and homogeneity of variance were tested and found to be upheld in this dataset. Mixed 2 (time: pretreatment, posttreatment) by 4 (group: SAD þMDD, SAD þBD, SAD þANX, SADþNCO) Analyses of Covariance (ANCOVAs) were conducted to examine differences between groups before and

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Table 2 Scores on the symptom measures by group.

SPIN pretreatment SPIN posttreatment DASS-D pretreatment DASS-D posttreatment

SADþMDD group (n¼ 76)

SADþBD group (n ¼19)

SADþ ANX group (n¼ 27)

SADþNCO group (n¼ 41)

M

SD

M

SD

M

SD

M

SD

45.56 34.55 12.87 10.31

12.63 13.13 6.26 6.34

49.16 33.79 9.26 7.84

9.27 12.53 4.75 5.57

40.74 30.52 7.85 6.56

9.86 14.42 5.10 5.81

40.27 23.10 6.04 4.24

11.46 12.65 5.06 4.03

Note: SADþ MDD¼ social anxiety disorder and comorbid major depressive disorder; SADþBD ¼social anxiety disorder and comorbid bipolar disorder (bipolar I disorder or bipolar II disorder); SADþANX ¼social anxiety disorder and one or more comorbid anxiety disorder; SADþ NCO¼ social anxiety disorder and no comorbid disorder; SPIN¼ Social Phobia Inventory; DASS-D ¼Depression Anxiety Stress Scales-Depression Subscale.

after CBT on social anxiety and depressive symptoms controlling for age. Tukey's least significant difference (LSD) posthoc tests were used to examine all omnibus effects in the present study. Table 2 displays SPIN and DASS-D means and standard deviations at pretreatment and posttreatment by group. 3.2. Effect of CBT on social anxiety symptoms The ANCOVA on SPIN scores showed a significant main effect of time, F(1, 158)¼ 35.87, po.01, η2p ¼.19, Cohen's d¼1.01, Power¼1.00, and a significant main effect of group, F(3, 158)¼6.57, po.001, η2p ¼.11, Power¼.97, but no significant time  group interaction effect, F(3, 158)¼2.57, p¼.06, η2p ¼.05, Power¼.62. Posthoc tests showed that at pretreatment individuals in the SADþMDD and SADþ BD groups reported comparable social anxiety symptoms (p¼.18) that were significantly higher than the social anxiety symptoms of individuals in the SADþANX and SADþ NCO groups (pso.05), whose scores did not differ significantly (p¼ .84). Despite these baseline differences, all groups reported a statistically significant reduction in social anxiety symptoms from pretreatment to posttreatment (pso.001). However, at posttreatment individuals in the SADþ MDD, SADþBD, and SADþANX groups had comparable social anxiety symptom levels (ps4.19) that were higher than the social anxiety symptom levels of individuals in the SADþNCO group (pso.03). 3.3. Effect of CBT on depressive symptoms The ANCOVA on DASS-D scores showed a significant main effect of time, F(1, 158)¼6.51, p¼ .01, η2p ¼ .04, Cohen's d¼0.32, Power¼.72, and a significant main effect of group, F(3, 158)¼15.82, po.001, η2p ¼.23, Power¼1.00, but no significant time  group interaction effect, F(3, 158)¼0.55, p¼ .65, η2p ¼ .01, Power¼.16. Posthoc tests showed that at pretreatment individuals in the SADþMDD group reported significantly higher depressive symptoms than individuals in all other groups (pso.02). At pretreatment individuals in the SADþBD group also reported significantly higher depressive symptoms than individuals in the SADþ NCO group (p¼ .05), and individuals in the SADþANX group reported depressive symptoms that did not differ significantly from those of individuals in the SADþBD or SADþNCO groups (ps4.20). Collapsed across groups, the present sample reported a reduction in depressive symptoms from pretreatment to posttreatment (po.01). At posttreatment, although individuals in the SADþMDD group continued to have elevated depressive symptoms relative to individuals in the SADþANX and SADþNCO groups (pso.01), individuals in the SADþ MDD group no longer reported significantly higher depressive symptoms than individuals in the SADþBD group (p¼.06). In addition, at posttreatment individuals in the SADþ BD group no longer reported significantly higher depressive symptoms than individuals in the SADþNCO group (p¼ .06).

3.4. Effect of depressive symptom severity on social anxiety symptoms It was also of interest to directly examine whether initial depressive symptom severity was associated with the degree to which individuals showed improvement in social anxiety symptoms from pretreatment to posttreatment. This was examined using two analyses. First, 2-tailed Pearson correlations were run between DASS-D scores at pretreatment and change scores on the SPIN.1 This analysis revealed no significant association between initial depressive symptom severity and social anxiety symptom reduction with CBT, r ¼ .04, p ¼.61. Second, the sample was separated into five groups of differing depression severity levels based on Connor et al.'s (2000) guidelines for interpreting DASS-D scores. The depression severity groups were: normal (score of 0–4; n¼ 35), mild (score of 5–6; n ¼24), moderate (score of 7–9; n¼ 32), severe (score of 10–13; n¼ 26), and very severe (score of 14þ ; n¼ 46). A mixed 2 (time: pretreatment, posttreatment) by 5 (depression severity: normal, mild, moderate, severe, very severe) ANCOVA on SPIN scores controlling for age was conducted to examine the impact of depressive symptoms severity on social anxiety symptom change with CBT for SAD. The ANCOVA revealed a significant main effect of time, F(1, 157) ¼ 35.49, p o.01, η2p ¼ .18, Cohen's d¼ 1.01, Power ¼1.00, and a significant main effect of depression severity, F(4, 157) ¼9.18, p o.001, η2p ¼ .19, Power¼.99, but no significant time  depression severity interaction effect, F(4, 157) ¼0.15, p¼ .96, η2p o.01, Power¼ .08. Posthoc tests showed that at pretreatment individuals in the very severe depression group reported significantly higher social anxiety symptoms than individuals with all other depression levels (ps o.05), and individuals in the mild and moderate depression groups reported significantly higher social anxiety symptoms than individuals in the normal group (ps o.04). Individuals in all depression severity groups reported a significant reduction in social anxiety symptoms from pretreatment to posttreatment (ps o.01). At posttreatment, individuals in the very severe depression group continued to report higher social anxiety symptoms than individuals in all other depression severity groups (ps o.03), and there were no other differences between groups. Of note, most individuals (80%) with very severe depression belonged to the SADþMDD group, and 6.5% belonged to the SADþBD group. 4. Discussion The main goal of the present study was to examine the impact of comorbid mood disorders on the outcomes of group CBT for SAD. Specifically, the present study compared the degree to which social anxiety and depressive symptoms changed with manualized 1 Calculated by subtracting each participant's SPIN score at posttreatment from their SPIN score at pretreatment.

K. Fracalanza et al. / Journal of Affective Disorders 162 (2014) 61–66

group CBT for SAD in individuals with comorbid MDD, comorbid bipolar disorder, a comorbid anxiety disorder, or no comorbid disorder. We also examined the degree to which initial depressive symptom severity was related to improvement in social anxiety with CBT. To the best of our knowledge, the current study represents the first investigation of the impact of comorbid bipolar disorder on the effectiveness of CBT for SAD. The results showed that regardless of mood disorder comorbidity, individuals reported large and statistically significant improvement in social anxiety symptoms with treatment. In addition, individuals reported small to moderate and statistically significant improvement in depressive symptoms with CBT for SAD. Despite these gains, individuals with SAD and a comorbid mood disorder started treatment with more severe social anxiety symptoms than individuals with SAD and a comorbid anxiety disorder or no comorbid disorder. Individuals with a comorbid mood disorder also ended treatment with elevated social anxiety symptoms compared to individuals with no comorbid disorder, but no longer differed in social anxiety severity compared to individuals with a comorbid anxiety disorder at posttreatment. In addition, individuals with comorbid depression began and ended treatment with more severe depressive symptoms than individuals with a comorbid anxiety disorder or no co-occurring disorder. Similarly, individuals with comorbid bipolar disorder started treatment with more severe depressive symptoms than individuals without a comorbid disorder, but finished treatment with depressive symptoms that were comparable to all other groups. We found no statistically significant correlation between initial depressive symptom severity and the degree to which social anxiety symptoms improved with CBT. When individuals were divided into groups based on initial depressive symptom severity, the results mirrored the findings from when individuals were separated based on presenting comorbid diagnosis. That is, we found that all individuals reported improvement in social anxiety symptoms with CBT, although individuals with very severe depressive symptoms began and finished treatment with worse social anxiety symptoms than those with less severe depressive symptoms. Our findings are in line with several prior studies reporting that depressive symptoms do not hinder the effectiveness of CBT for SAD (Erwin et al., 2002; Joormann et al., 2005; Turner et al., 1996; Van Velzen et al., 1997). Similarly, the current results are consistent with the findings of a large randomized controlled trial (N ¼ 1004) which showed that although comorbid depression was associated with starting and ending treatment with more severe anxiety symptoms in a sample of individuals with mixed anxiety disorders2, co-occurring depression did not interfere with the magnitude of gains from computerized CBT, medication management, or both (Campbell-Sills et al., 2012). The present findings are also in agreement with the results of previous studies on the impact of comorbid depression on CBT for panic disorder (Allen et al., 2010) and obsessive–compulsive disorder (Storch et al., 2010), which found that comorbid depression did not interfere with anxiety symptom reduction. Further, our results are in line with those of Bowen and D'Arcy (2003), who found that in a sample of individuals with panic disorder, hypomanic symptoms did not have a negative effect on response to CBT. Despite the evidence that individuals can benefit from CBT for anxiety when comorbid depression or bipolar spectrum symptoms are present, the findings in this literature are inconsistent (e.g., Chambless et al., 1997; Ledley et al., 2005; Marom et al., 2009). Given the mixed findings, it is important that research continue to clarify how and when comorbid mood disorders interfere with anxiety symptom reduction with CBT.

2 Including SAD, generalized anxiety disorder, panic disorder, and posttraumatic stress disorder.

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Our finding that individuals with SAD and comorbid depression or bipolar disorder began treatment with more severe social anxiety symptoms than individuals with SAD and a comorbid anxiety disorder or no additional disorder is in line with prior studies that have linked co-occurring mood disorders to more severe initial clinical presentations (Fracalanza et al., 2011; Joormann et al., 2005; Koyuncu et al., 2014; Perugi et al., 2001). The higher pretreatment SAD severity of individuals with comorbid mood disorders is likely the reason that these individuals continued to have elevated SAD symptoms after treatment. In addition to more severe baseline social anxiety symptoms, the mood disorder groups in our study presented with greater overall comorbidity than the comparison groups. We considered the possibility that having a greater degree of comorbidity, as opposed to having a mood disorder specifically, contributed to elevated SAD symptoms in those with a co-occurring mood disorder. However, given that greater overall comorbidity was significantly associated with higher depressive symptoms in the present study, these factors cannot be considered independent in our investigation. Despite the more severe initial clinical presentations of individuals with a comorbid mood disorder, individuals with either a comorbid mood or anxiety disorder finished treatment with greater residual symptoms than those without co-occurring problems. Thus, additional sessions following a standard course of CBT may be helpful in facilitating further symptom remission for those with SAD and comorbid difficulties. Future research should test the degree to which additional CBT sessions produce further improvement in this population, and whether additional sessions should address social anxiety or symptoms of a co-occurring condition. A few other aspects of our findings are worthy of mention. The result that depressive symptoms decreased in our sample even though they were not directly targeted in treatment lends further support to the notion that CBT for an individual's principal disorder can result in an overall improvement in psychopathology. Indeed, prior studies have also found that CBT for SAD leads to improved depressive symptoms (see Deacon and Abramowitz, 2004; Olatunji et al., 2010 for reviews of outcomes of CBT for SAD). Separately, there have been limited investigations of the prevalence of co-occurring bipolar disorder in individuals with SAD. In our sample of outpatients with SAD we found that approximately 12% had comorbid bipolar I or II disorder. The rate of bipolar disorder co-occurrence found in the present study fell in between the rates of bipolar disorder comorbidity reported in prior SAD samples (3–21.1%; Koyuncu et al., 2014; Perugi et al., 1999; Van Ameringen et al., 1991). The varying rates of bipolar disorder in SAD samples may be partially explained by methodological differences between studies. Higher rates of bipolar disorder co-occurrence are reported when patients' retrospective recall of symptoms is used to determine the presence of bipolar disorder (e.g., Perugi et al., 1999), and more modest rates are reported when studies determine the presence of bipolar disorder using a semistructured diagnostic interview (e.g., Koyuncu et al., 2014; Van Ameringen et al., 1991). More research is required to understand how frequently individuals with SAD present for treatment with bipolar disorder. The present study had several strengths, including examining a novel research question about bipolar disorder comorbidity, using a treatment-seeking sample, and examining two different comparison groups. However, the present study also had several limitations. First, although individuals with comorbid bipolar disorder who complete treatment at the ATRC typically take medication to control bipolar disorder symptoms, the present study did not specifically control for the dose or types of medications used by participants, and doing so in future research would represent an important extension of the current study. In addition, this study did not assess symptoms at a follow-up period, thus it is

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unknown whether individuals maintained the gains that they reported at posttreatment. Further, the present study assessed the outcomes of CBT for SAD using self-report measures of social anxiety and depressive symptoms, and this could be expanded on in future work by using multimodal assessments of symptoms as well as additional outcome measures (e.g., cognitive factors, functional impairment, quality of life). Lastly, although this study had high power to detect main effects, power to detect interaction effects was lower, and it is possible that interaction effects would be detected in a larger sample. In sum, the current study showed that group CBT for SAD is a feasible and beneficial treatment for individuals with SAD and comorbid MDD or bipolar disorder. In our SAD sample we found that individuals with a comorbid mood disorder presented for treatment with more severe social anxiety symptoms than individuals with a comorbid anxiety disorder or no comorbid disorder; and individuals with either mood or anxiety disorder comorbidity finished treatment with higher social anxiety symptoms than those with no comorbid disorders. Overall these findings support the use of group CBT for individuals with SAD and a comorbid mood disorder, although additional treatment sessions may be helpful to people with SAD and co-occurring difficulties. Given the paucity of research on individuals with a principal anxiety disorder and comorbid bipolar disorder, more empirical work is needed to determine whether treatments that are being used in practice are effective for this population, and how existing treatments might be adapted to best help this group of individuals. Conflicts of interest No conflicts of interest to declare.

Role of funding source This study was supported by an Undergraduate Student Research Award from McMaster University. The funding source did not have a role in the study design; the collection, analysis or interpretation of the data; the writing of the report; or the decision to submit the paper for publication.

Acknowledgments We would like to thank Lisa Young for her assistance with data management and all of the individuals who participated in this study.

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