Generalised Anxiety Disorder (GAD)
The concept of generalised anxiety disorder is subject to discussion. Although the disorder is regarded as prevalent in primary care as well as in specialised settings, because of the high comorbidity rates associated with GAD the controversy is about whether to consider GAD an independent disorder or as a residual or prodrome of other disorders (Wittchen et al., 1994). The diagnostic category of GAD has changed a lot in the past two decades (Brawman-Mintzer and Lydiard, 1996). The shifting diagnostic criteria, the relative low diagnostic reliability, and questions regarding the diagnostic validity probably contributed to the relative little attention that has been paid to the investigation of GAD compared with most other anxiety disorders.
Prevalence
The most recent epidemiological study using DSM-III-R criteria is the NCS in the United States. The prevalence rate for current GAD was 1.6%, 12-month prevalence was 3.1% and lifetime prevalence was 5.1% (Wittchen et al., 1994). These figures make GAD more common than panic disorder in the NCS. It is shown that GAD is more common in primary care, and one of the least common anxiety disorders in mental health centres (Brawman-Mintzer and Lydiard, 1996).
Demographics and Risk Factors
Generalised anxiety disorder is twice as common among women as among men. In the age group 25 - 35 years the prevalence is highest (Wittchen et al., 1994). Risk factors for GAD are being separated, widowed or divorced (the same risk factors as for panic disorder), and unemployment or being a homemaker is a significant correlate of GAD. However, another recent study (Bienvenu et al., 1998) suggests that being widowed is not a risk factor.
Natural Course
Generalised anxiety disorder appears to have a chronic course. Woodman et al. (1999) conducted a five-year follow-up study comparing primary GAD patients to panic disorder patients. At baseline the GAD subjects were significantly older, had a higher level of education and occupational class, earlier age of onset and longer illness duration. At follow-up, significantly more GAD patients continued to meet full criteria for the baseline disorder, and fewer were in partial or complete remission or had fluctuations. Although global severity, measured by clinical global impression (CGI), was less at baseline, at follow-up the improvement on the CGI was significantly less for the GAD patient compared with the panic disorder patients. Findings from this study support the validity of the GAD concept, in view of the diagnostic stability and different natural course (Woodman et al., 1999).
Comorbidity
Lifetime comorbidity for GAD is very high, 90.4% of cases (Wittchen et al., 1994).
The strongest comorbidities are with affective disorders (mania 10.5%, major depression 62.4%, dysthymia 39.5%). Comorbidity figures with other anxiety disorders are 23.5% for panic disorder, 25.7% for agoraphobia, 35.1% for simple phobia and 34.4% for social phobia. Alcohol abuse and dependence were seen in 37.6% of cases and drugs in 27.6%. Another study by Brawman-Mintzer et al. (1993) report comorbid social phobia in 23% and simple phobia in 21% of cases as the most frequent, after excluding lifetime depression from their study. The high comorbidity figures have led to disagreement concerning the existence of GAD as an independent diagnostic entity, and to assumptions that GAD is a prodrome or residual of other disorders (Brawman-Mintzer and Lydiard, 1996). Also, at least partly the same genetic factors contribute to major depression and GAD, as shown by Kendler (1996). However, in the NCS it is shown that at least 30% of current GAD patients had neither current nor recent (but only lifetime) comorbid disorders. This is put forward by the authors as supporting the validity of GAD as an independent diagnosis (Wittchen et al., 1994), although this does not preclude GAD from being a prodrome of any other disorder.
Generalised anxiety disorder is frequently seen in primary health care, and especially in patients with medically unexplained somatic complaints such as chest pain and irritable bowel symptoms (Roy-Byrne, 1996). As such, it is also associated with somatisation disorder and chronic fatigue syndrome (Fischler et al., 1997). Comorbidity with axis-II disorders is also high, reported up to 49% (Sanderson et al., 1994).
