Irritable Bowel Syndrome is Strongly Associated with Generalized Anxiety Disorder: A Community Study

S. Lee; J. Wu; Y. L. Ma; A. Tsang; W.-J. Guo; J. Sung

Disclosures

Aliment Pharmacol Ther. 2009;30(6):643-651. 

In This Article

Discussion

We set out to evaluate the prevalence and comorbidity of IBS and GAD in a general population-based study. We found that IBS was strongly comorbid with GAD and that comorbid IBS-GAD had more impairment and core depressive symptoms. The main strengths of our study included the use of a random general population sample, internationally standardized and updated measures of IBS and GAD, and the concurrent assessment of impairment and help-seeking.

Our prevalence estimate of IBS (5.4%) was somewhat lower than those previously reported in Western studies[1] but consistent with other Asian studies.[3,4] While the exact reasons for these cross-national variations in prevalence remain unclear, the lower prevalence observed in our study is probably attributable to the more stringent Rome III criteria of IBS used instead of older criteria such as Manning or Rome I criteria in previous studies. Despite a higher prevalence in females than males, the prevalence of IBS did not differ significantly between the genders. This contrasted with the finding of female predominance in Western countries.[10,26] However, it was congruent with previous studies of IBS in Singapore, Korea and Hong Kong where no gender difference in prevalence was found, suggesting possible cross-national variations in the distribution of IBS across the two genders.[2,4,27] IBS prevalence increased with age in our study though the relationship between age and IBS prevalence was not conclusive in the literature. Some studies found the prevalence to decrease with age,[4,28] whereas others found no clear relationship.[2,29] Although older respondents in our study could have GI symptoms as a result of concurrent medications or organic pathology, the prevalence of organic pathology should be low among people with IBS diagnosed by Rome criteria in community settings.

The 12-month prevalence (4%) of GAD in the present study was within the range reported in Western countries[30,31] and nearly identical with what was found in a previous study (4.1%) in Hong Kong.[32] That being female and older than 35 years carried a higher risk of developing GAD[11,33] were expected findings. This was also true of GAD being found to be more common among people with lower education level.[30]

Consistent with previous community studies[34,35] which suggested a possible association between IBS and certain mental disorders, we confirmed that IBS and GAD were associated at both symptom and disease levels. Furthermore, comorbid IBS and GAD added to the impairment of their sufferers. The higher level of impairment could result from a greater number of symptoms in comorbid respondents as well as a synergistic effect of the symptoms of the two illnesses.

The comorbidity of IBS and GAD was probably complex in origin and might involve both psychological and physiological processes that should be further studied. Hazlett-Stevens et al.[9] found that anxiety specific to visceral sensations was a strong predictor of IBS. As individuals with GAD were cognitively predisposed to catastrophize the potential consequences of their worries, such visceral anxiety in IBS could be greatly magnified and become even more impairing when the two illnesses co-occurred. Furthermore, given the hypochondriacal tendency of people with GAD, the physical symptoms of IBS could reinforce their anxious inability to tolerate and cope with these discomforts, thereby forming a vicious spiral between physical and psychological symptoms.[36] These interactive pathological processes might intensify avoidance and other maladaptive behaviours that in turn compromised comorbid individuals' functional capacity and quality of life. The comorbidity of IBS and GAD could also be explained by overlapping pathophysiology. The latter might include an excess of corticotropin releasing hormone associated with both anxiety and IBS-like symptoms in the 'emotional motor system' that regulated pain perception, arousal and vigilance.[6] The fact that both IBS and GAD might benefit from treatment with selective serotonin reuptake inhibitors might suggest the presence of shared central and/or peripheral serotoninergic dysfunction in the two illnesses.[37,38]

Although the full diagnosis of depression was not assessed in our study, core depressive symptoms, a proxy for depression, were consistently associated with GAD among IBS respondents. In contrast, it was not associated with IBS among GAD respondents. This suggested that depression might mediate the association between IBS and GAD in individuals with varying degrees of IBS or GAD differently. The exact relationships among depression, IBS and GAD would need to be clarified by prospective research. Nonetheless, there were several possible explanations for depression being a risk correlate associated with GAD among IBS respondents. First, both community and clinical studies showed that depression occurred in about half of the people who suffered from GAD, especially when GAD was more severe or chronic.[39] Second, the noncore symptoms of GAD and depression overlapped to some extent (e.g. difficulties in concentration, sleep disturbance, and fatigue). Third, IBS respondents with depressed mood could be prone to developing poor self-image in connection with their embarrassing bowel symptoms and increased anxiety about social situations, thereby triggering the onset of GAD.

The present study showed that about 1 in 6 people with IBS in the community might have comorbid GAD that added to the severity and impairment of IBS. The level of psychiatric comorbidity is likely to be higher in clinical settings where more severe IBS and a greater variety of mental disorders are encountered even though the latter may not be recognized. As GAD is highly treatable, it is worthwhile to screen for it among IBS patients using self-rating scales and/or trained nurses for brief mental status assessment. Psychiatric screening may also uncover GAD that masquerades as severe or treatment-resistant IBS and reduce costly investigations and/or harmful treatments. As GAD is impairing by itself as well as via its adverse interactions with IBS, successful treatment of psychiatric morbidity in comorbid individuals may accrue benefit beyond that of the treatment of either illness alone.

A number of limitations rendered our findings preliminary as well as suggested possibilities for further research. First, the telephone interview method was used because of its affordability and lesser tendency to bring about psychiatric stigma, which is still severe in Hong Kong. Although the epidemiological profiles of GAD and IBS we found were mostly consistent with previous studies, the participation rate, while higher than other telephone surveys of IBS,[4] could be increased so that the generalizability of our findings might be improved. Second, core depressive symptoms were a significant risk correlate in this study, but full assessment for depression was lacking. Consequently, we could make no more than preliminary conclusions about the relationship among IBS, GAD and depression. There is also the need to examine other kinds of mental disorders that may be comorbid with GAD and depression, such as panic disorder.[40] Third, this study was cross-sectional and could not establish the causal relationship between IBS and GAD. Future research should obtain temporal information such as age-of-onset of illness or be prospective in nature. Fourth, the differential association between various subtypes of IBS and GAD remains to be substantiated because of small sample size for each subtype and lack of stool form chart for assessing stool consistency in the telephone survey, which might lead to inaccurate subtyping of IBS. Finally, the diagnoses generated through phone interviews conducted by trained students were an epidemiological proxy for detailed assessments made by clinicians. Future study will be enhanced by having GI specialists reappraise a sub-sample of respondents to establish concordance between telephone and clinical assessments.

In conclusion, IBS is strongly associated with generalized anxiety disorder and comorbidity further adds morbidity to the patients. Our results suggest a genuine association between IBS and GAD in population settings without sampling bias associated with increased help-seeking behaviour at referral centres. Early detection and intervention of concomitant GAD should therefore be incorporated as an essential component of the management of IBS patients even in primary care settings.

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