DIGESTIVE SYSTEM DISORDERS

Soon after the Gulf War, veterans reported gastrointestinal (GI) symptoms more frequently than most other symptoms (Kang et al. 2000b). That is understandable because there is a common and scientifically recognized association between acute and chronic stress and GI dysfunction (Creed et al. 2006; Drossman and Chang 2003). This dysfunction can lead to changes in intestinal movements (motility) that affect gastric emptying rates and intestinal transit time which in turn cause nausea, vomiting, bloating, diarrhea, and constipation. Psychological distress can also affect sensitivity of the visceral nerves, thus producing abdominal discomfort and pain (Drossman 2002, 2006a,b; Kellow et al. 2006a,b) (see Chapter 4 for more discussion on GI dysfunction in response to stress).

The functional GI disorders or syndromes, such as irritable bowel syndrome (IBS) and functional dyspepsia, are characterized by recurrent or prolonged clusters of symptoms that range in severity from occasional mild episodes to more persistent and disabling episodes with impaired health-related quality of life. So named because they are disturbances of GI functioning rather than diseases, these disorders are understood in a biopsychosocial construct (Drossman 1998); that is, genetic or early environmental predisposing factors, including family enablement of illness behaviors (Levy et al. 2000) and a history of early trauma or abuse (Drossman et al. 1995), coupled with acute or chronic exposure to stress or acute GI infection (Spiller and Campbell 2006) can precipitate or exacerbate the disorders. The disorders are then sustained or perpetuated in the presence of psychologic comorbidities, including PTSD, anxiety, depression, maladaptive coping style, and impaired social networks (Creed et al. 2006; Drossman et al. 2002; Levy et al. 2006).

Of particular relevance here is the growing evidence of development of postinfectious IBS. In some cases, functional GI disorders are triggered by pathogens, which usually cause acute gastroenteritis, and the symptoms are then sustained by stressful conditions (Drossman 1999; Dunlop et al. 2003; McKeown et al. 2006; Spiller and Campbell 2006). From a biologic perspective, the functional GI syndromes are characterized by dysregulation of neural pathways between the brain and gut (that is, the brain-gut axis) that produces persistent motility and sensory disturbances (visceral hypersensitivity), dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis (see Chapter 4), alteration in corticolimbic pain modulation, and inflammation of the bowel mucosa associated with altered bacterial flora (Drossman 2006a,b; Drossman et al. 2002). Diagnosis of a functional GI disorder is based on identification of specific bowel symptoms that fulfill the Rome Criteria1 and a minimal period of symptoms, usually 6 months (Drossman 2006a,b). The diagnostic criteria have rarely been included in the assessment of Gulf War veterans, so the veterans’ diagnoses have been presumptive, that is, based on sufficient clusters of symptoms that are consistent with the Rome criteria for diagnosis. However, diagnostic criteria were used in a few supportive studies of selected cohorts of Gulf War veterans that yielded relevant physiologic data (Dunphy et al. 2003).

1

The Rome Criteria, developed by the Rome Foundation, are symptom-based diagnostic criteria for functional GI disorders, including functional gastroduodenal disorders, functional bowel disorders, and the group of disorders formerly referred to as functional biliary disorders. IBS is defined by Rome III criteria as abdominal discomfort or pain of at least 3 months’ duration in which two of the following three are present: pain that is improved by defecation, association of the onset of pain with a change in the frequency of the stool, and association of the onset of pain with a change in the consistency (looser or harder) of the stool (http://www.romecriteria.org).



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