GAD: Comorbidity with Other Disorders
Despite different methodological approaches in early studies, the available studies report a high prevalence of psychiatric comor-bidity in patients with GAD. For example, in some studies more than 90% of GAD patients had additional symptoms that fulfilled criteria for at least one or more concurrent disorders (range of 45–91%). An examination of the relative frequencies of various comorbid diagnoses in patients with GAD obtained from the available studies reveals that other anxiety and mood disorders frequently complicate the course of GAD (see diagnostic deci-sion tree for GAD: Figure 53.1).
The National Comorbidity Survey showed 90% of re-spondents with lifetime GAD had at least one other lifetime dis-order and of those with current GAD, 66% had at least one other current disorder. The most common comorbidities (specifically that criteria for both disorders were met) were found for mood disorders (major depression and dysthymia), panic disorder and (for current comorbidity only) agoraphobia. High 12 month rates for comorbidity for GAD and major depression were reaffirmed in the NCS-R (Kessler et al., 2005). Other studies have also found that the highest comorbidities were with depressive disor-ders and panic disorders. GAD usually has an earlier onset than other anxiety and depressive disorders when comorbid disorders are present. Brawman-Mintzer and associates (1993) found that GAD had an onset before dysthymia and panic disorder, and af-ter simple and social phobia. Further, onset of major depression seemed to follow the onset of anxiety. Similar findings have been reported by other investigators.
As in adult GAD, childhood GAD (or overanxious anxiety disorder as it was earlier labeled) is also characterized by an unu-sual degree of comorbidity. Kashani and coworkers (1990) observed that over 50% of children with overanxious disorder had symptoms that met criteria for at least one additional psychiatric diagnosis. Among the most prevalent current comorbid diagnoses are social phobia (16–59%), simple phobia (21–55%), panic disorder (3–27%) and depression (8–39%). Furthermore, Masi and coworkers (1999) found, in those children and adolescents they sampled, that 87% had a comorbid disorder. In particular, high rates of separation anxiety, social anxiety and depressive disorders were found.
Alcoholism also complicates the clinical course of GAD for some patients; however, the available literature suggests that the diagnosis of alcohol abuse is not as prevalent in GAD as in other anxiety disorders, and the pattern of abuse is often a brief and nonpersistent one. GAD onset is usually later than that of the alcohol use disorder. Personality disorders have been observed to co-occur in approximately 50% of patients with GAD. For exam-ple, rates of GAD and personality disorders in clinical popula-tions have ranged from 31 to 46%. Cluster C personality disorders, specifically avoidant personality disorder, dependent personality disorder and obsessive–compulsive personality disorder are com-mon. Interestingly, Cluster A personality traits, in particular sus-piciousness and mistrust, may be prominent in GAD as well.
Comorbid GAD is associated with increased severity of comorbid disorders (Kessler, 2000; Kessler et al., 2005). Ad-ditionally, the presence of comorbid disorders in GAD patients is related to increased rates of negative outcomes such as dis-ability, impairment and cost of care. Rates of relapse for GAD patients with comorbid depression appear higher than in nonco-morbid GAD patients. Further, comorbidity is also associated with greater treatment seeking. Unsurprisingly, data indicate that patients with comorbid GAD and depression may have poorer response to treatment than patients with either disorder only.