Postinfectious IBS symptoms are facilitated by psychological distress via central nervous system (such as the hypothalamic-pituitary adrenal axis) effects on mucosal inflammation and enhanced pain via anterior cingulate cortex activation (Barbara et al., 2008; Drossman, 1999; Dunlop et al., 2003; Gwee et al., 1999).
Furthermore there is a large body of physiological data in IBS including among Gulf War veterans that demonstrate altered physiological functioning (such as diarrhea and constipation caused by altered migrating motor complexes and high-amplitude propagated contractions) that separates this condition from mere symptom reporting tendency (somatization). One study showed lowered visceral sensitivity, pain intensity, and anxiety in relation to rectal distention and cutaneous hand stimulation among Gulf War veterans compared to nondeployed veterans and civilians (Dunlop et al., 2003). Another study showed altered autonomic activity and lowered pain thresholds in response to acute physical and psychological stress (Murray et al., 2004) and an association of altered gastrointestinal motility and GI symptoms when IBS subjects are administered CRF, a stress hormone (Fukudo et al., 1998). A full review of this area can be found elsewhere (Kellow et al., 2006a,b).
The data on organic disorders are scanty and negative. See Table 4-9 for a summary of the primary studies reviewed above.
There are some limitations in the epidemiological body of evidence, mostly related to methods of effect assessment. One is that with the exception of two published abstracts, the self-reporting of GI symptoms did not fulfill the criteria for diagnosing a functional GI disorder, although in at least one published case series the diagnoses can be inferred (Sostek et al., 1996). In addition, existing studies in the deployed military population cannot yet determine the degree to which the gastrointestinal symptoms are specific to IBS and other FGIDs or are part of a larger spectrum of illness (that is, multisystem disease; see also the section on multisymptom illnesses in this chapter). Within civilian populations persons with these disorders exist on a spectrum where mild to moderate symptoms are limited to the GI tract, but more severe illness is associated with increased comorbidities. Therefore, the committee recommends that further studies in a deployed military population be undertaken to determine the presence of medical and psychosocial comorbidities in those with FGIDs. Finally, the committee concludes that there was also a lack of adequate medical diagnostic testing to identify a GI structural disease.
Nevertheless, taken together, the overall pattern of symptoms found in the few primary and numerous secondary studies confirms an association between deployment to the Gulf War and functional GI symptoms, including abdominal pain, diarrhea, nausea, and vomiting, and a few studies exist that provide presumptive data to allow standardized diagnosis of functional GI disorders. These studies are strengthened by physiological and mechanistic data in war veterans with IBS, and particular reference is made to the emerging evidence for preexisting acute gastroenteritis as a predictive factor in postinfectious IBS and dyspepsia. The committee recommends that further studies be conducted to determine the role of prior acute gastroenteritis among deployed soldiers in the development of FGIDs. Thus, the association of deployment-related stress with GI symptoms is accepted, the association with functional GI disorders is supported but not complete, and an association with structural GI diseases cannot be determined.
The committee concludes that there is sufficient evidence for an association between deployment to the Gulf War and gastrointestinal symptoms consistent with functional GI disorders such as irritable bowel syndrome and functional dyspepsia. The committee also concludes that there is inadequate/insufficient