G
eneralized anxiety disorder (GAD) is a disabling, chronic condition that is common in many medical set- tings. However, it remains one of the least researched anxiety disorders, for numerous reasons. First, because the diagnostic category of GAD was first introduced in DSM-III in 1980, studies conducted before that date have limited relevance and questionable validity; sub- stantive revisions of the diagnostic criteria in later edi- tions of DSM (see “Diagnosis” subsection of this chap- ter) made longitudinal data collection challenging. Second, because treatment resistance in GAD is not uncommon, patients and therapists are reluctant to en- gage in the prolonged and frequently unsuccessful ther- apeutic process that could yield much-needed informa- tion. Third, because the diverse symptoms of GAD can mimic a variety of medical conditions, GAD patients are usually seen by non–mental health specialists. Psy- chiatric referral, if made, is frequently delayed. Finally, because “pure” GAD without comorbid conditions is uncommon, the interpretation of studies with heteroge- neous comorbid samples is difficult.Collecting information on GAD in populations with special needs, such as children, women, and older pa- tients, is especially challenging. A possible explanation
is the reluctance of both investigators and relatives to “expose” the elderly, children, and women of childbear- ing potential to research. However, regulatory agencies, yielding to public demands, have begun to emphasize the need to include these patient groups in research studies. The recognition that GAD accounts for a very sizable proportion of all mental illness, that comorbid GAD complicates more than half of all psychiatric and medical conditions, and that GAD is associated with substantially increased disability and medical cost (Judd et al. 1998; Maser 1998; Olfson and Gameroff 2007; Olfson et al. 1997) should mobilize the field.
Epidemiology
The diagnostic criteria for GAD in DSM-IV (retained in DSM-IV-TR; American Psychiatric Association 1994, 2000) are more inclusive than those in previous editions of DSM. As a result, prevalence rates of GAD have been revised upward. Although rates remain highly dependent on the method of interviewing used to obtain them (e.g., family history, first- or second- degree relatives or index-pair informants, direct inter- viewing, training and experience of the interviewers
Supported in part by National Institute of Mental Health grants MH53582, MH30906, and MH077156 and by Independent Scientist Award MH01397 (L.A. Papp).
[Rougemont-Buecking et al. 2008]), the more recently reported rates seem to reflect clinical reality.
The largest survey of DSM-III GAD was conducted in 1983–1984 as part of the Epidemiologic Catchment Area (ECA) study (Blazer et al. 1991b). The 1-year prev- alence rate for GAD, excluding other disorders, was 3.8%. Given the high rate of comorbidity in GAD, the rate dropped to 2.7% when comorbid depression and panic were excluded, and to 1.7% when all other comor- bid conditions were excluded. The ECA data also showed that GAD was about twice as prevalent in women as in men. Without comorbid panic and depres- sion, GAD was found to be more prevalent among Afri- can Americans. When no exclusions were made, preva- lence was highest in people younger than age 30 years.
Five other community-based studies examined the prevalence of DSM-III GAD. In the United States, the point, 1-year, and lifetime prevalence rates were 2.5%, 4%, and 6.4%, respectively (Uhlenhuth et al. 1983; Weissman et al. 1978). Current prevalence of 1.5% and 1-year prevalence of 5.2% were reported from Europe (Angst and Dobler-Mikola 1985), whereas two studies conducted in Asia (Hwu et al. 1989; Lee et al. 1990a, 1990b) found that the 1-year prevalence of GAD ranged from 3.4% to 8.6%, and the lifetime prevalence ranged from 2.9% to 10.5%; rates were lowest among city dwellers. As in the ECA study, Asian women with GAD outnumbered men 2 to 1. In contrast to the U.S. study, however, age comparisons in the Asian samples showed increasing rates of prevalence over time (2.9% for ages 18–24 years vs. 4.3% for ages 45–65 years).
In Florence, Italy, Faravelli et al. (1989) assessed a community sample of 1,110 adults for both DSM-III and DSM-III-R (American Psychiatric Association 1987) anxiety disorders. GAD was the most frequently reported disorder, but prevalence rates declined signifi- cantly when the more stringent DSM-III-R criteria were used. The lifetime prevalence rates for DSM-III and DSM-III-R GAD were 5.4% and 3.9%, and the point prevalence rates were 2.8% and 2.0%, respectively. Overall, rates were lower than those reported in other surveys. Possible explanations include the use of psychi- atrists, rather than lay interviewers, as diagnosticians and the use of a hierarchical diagnostic model, which allowed only one possible diagnosis per case. Wacker et al. (1992) used both DSM-III-R and ICD-10 criteria to compare the prevalence of GAD in a survey of residents in Basel, Switzerland. They found that the lifetime prev- alence of DSM-III-R GAD was 1.9%; the ICD-10 prevalence rate was 9.2%, more than four times greater.
The largest study of DSM-III-R GAD was con- ducted by Wittchen et al. (1994). They used data col- lected from the U.S. National Comorbidity Survey, which included 8,098 community-based respondents between ages 15 and 54 years. The current prevalence of GAD was 1.6%, the 1-year prevalence was 3.1%, and the lifetime prevalence was 5.1%. Consistent with previous surveys, GAD was twice as common in women as in men. In addition, GAD was more common in those who were unemployed, separated, divorced, widowed, and older than 24 years. Of those with lifetime GAD, 90% reported at least one other lifetime DSM disorder (most often, depression and panic), and of those with current GAD, 65% reported current comorbid disorders (most commonly, depression, panic, and agoraphobia). Similar to the percentage reported by Wacker et al. (1992), life- time prevalence of GAD according to ICD-10 criteria was significantly higher (8.9%). The discrepancy may be attributed, in part, to the higher symptom thresholds re- quired by DSM-III-R for diagnosis. The ICD-10 sys- tem requires only four symptoms (as opposed to six in DSM-III-R) and does not stipulate that worries must be excessive or unrealistic.
Rates of DSM-IV-defined GAD, although varying significantly among the few surveys, are more compara- ble with those based on ICD-10 criteria. Some argue that the two diagnostic systems identify different groups of patients with GAD (Slade and Andrews 2001). This may explain the similar prevalence in spite of significantly discrepant diagnostic criteria. For instance, unlike DSM- IV, the ICD-10 diagnosis of GAD requires symptoms of autonomic arousal and does not allow comorbid panic/ agoraphobia, social phobia, or obsessive-compulsive dis- order. DSM-IV sets a higher threshold of severity than ICD-10 by requiring excessive worry, significant distress or impairment, and 6 months of duration.
An Australian household survey of 10,641 adults, us- ing the Composite International Diagnostic Interview to identify GAD as defined by DSM-IV, revealed a 1-month prevalence of 2.8% and a 12-month prevalence of a whopping 36% (Hunt et al. 2002). The differences in rating instrument used and the training of the inter- viewers might explain this highly discrepant percentage. In the group with 1-month DSM-IV GAD, comorbid- ity was 68%. In a sample of 2,847 households in Sin- gapore, the General Health Questionnaire and Schedules for Clinical Assessment in Neuropsychiatry were used to generate DSM-IV GAD diagnoses (Lim et al. 2005). Lifetime prevalence of GAD was 3.3%, and current prevalence was 3.0%. Female-to-male ratio was 3.6:1. As
expected, high comorbidity was reported for major de- pression, dysthymia, panic disorder, and social phobia.
The U.S. National Comorbidity Survey Replication study (NCS-R; Kessler et al. 2005) reported a DSM-IV GAD lifetime prevalence rate of 5.6% and a 12-month prevalence rate of 3.0%. With a required minimum symptom duration of at least 1 month (compared with the 6 months required by DSM-IV ), the respective rates increased to 9.1% and 4.5%. When subjects with a 1-month minimum symptom duration were included and the “excessiveness” criterion was not included, the rates in this study were even higher (12.8% and 6.2%, respectively). Claiming improved validity, the authors advocated lowering the duration and eliminating the controversial term “excessive” for the next editions of DSM. Confirming evidence of improved validity, spec- ificity, and predictive validity may justify these revisions.