Deployment-associated functional gastrointestinal disorders: do we know the etiology?

Functional gastrointestinal disorders (FGD) are a collection of symptoms with no known anatomical or biochemical abnormality [1]. Irritable bowel syndrome (IBS) and dyspepsia are two of the most common types of FGD. The etiology of these disorders is unknown, but speculated mechanisms include altered gastrointestinal motility, visceral hypersensitivity, aberrant brain–gut interaction, food intake, and psychological factors, perhaps with a genetic predisposition [2]. Acute gastrointestinal infection can precipitate or exacerbate the clinical expression of IBS and dyspepsia [3, 4]. Various studies in non-military populations have demonstrated the onset of IBS after gastroenteritis. This type of IBS is known as post-infectious IBS (PI-IBS). The current study makes an association between infective gastroenteritis and subsequent development of FGD in military personnel. Porter and colleagues conducted a retrospective case– control study to determine whether self-reported diarrhea and/or vomiting and psychological stress during deployment were associated with increased risk of FGD in active-duty military personnel during their first deployment to Iraq and Afghanistan from 2008 to 2009 [5]. Using active-duty military medical encounter data from the Defense Medical Surveillance System, they identified 129 cases (constipation = 67, dyspepsia = 15, IBS = 22, overlapping syndrome = 25) and 396 controls of FGD using ICD-9 codes. Reports of diarrhea and vomiting during deployment were obtained from the Post-deployment Health Assessment Survey completed by all military personnel after deployment. Diarrhea during deployment was significantly associated with higher odds of all FGD except dyspepsia. Vomiting during deployment was associated with higher odds of all FGD. Combat and non-combat-related stress was recorded in detail; no association between stress and increased risk of FGD was noted. The importance of gastrointestinal infection in pathogenesis of IBS is now well recognized. More than 60% of travelers report the onset of diarrhea during travel abroad [6]. Therefore, prevalence of FGD should be high in returned travelers. Development of IBS and dyspepsia after travel abroad has been reported [7–9]. The high prevalence of diarrhea during deployment abroad has also been noticed among military personnel [10]. More than 50% of military personnel developed acute gastroenteritis while on duty in the Gulf during the first Gulf War [11]. Therefore, the positive association between diarrhea and vomiting, a surrogate marker for gastroenteritis, during deployment and subsequent development of FGD is an expected finding. Certain limitations of the study should be highlighted. The International Classification of Diseases, Ninth Revision (ICD-9) was used to collect cases of FGD in the present study. The potential advantages of using ICD-9 codes in research are that a large number of cases and controls can be collected inexpensively for comparison. The disadvantage is that misdiagnosis of FGD, with no known definite diagnostic marker, is likely to be very high. In one study, only 45% of patients with an ICD-9 diagnosis of IBS met any of the three diagnostic criteria of IBS (Manning, Rome I, or Rome II criteria) [12]. Gastroenteritis was defined as the presence of diarrhea and/or The views expressed in this article are those of the author and do not necessarily represent the views of the Department of Veterans Affairs or the Department of Defense.