Functional Abdominal Pain Syndrome

The Clinical Problem Functional abdominal pain syndrome (FAPS) is a state of chronic recurrent abdominal pain that is not due to structural, organic, or metabolic diseases, as far as can be detected by current routine clinical examinations [7]. Abdominal pain in FAPS is unrelated to provocation, exaggeration, or relief by everyday physiological stimuli such as eating, exercise, defecation, or menstruation [7]. FAPS is one of the functional gastrointestinal disorders (FGIDs) and is distinct from other categories of FGIDs such as irritable bowel syndrome (IBS), unspecified functional bowel disorder, epigastric pain syndrome in functional dyspepsia, functional chest pain of presumed esophageal origin, functional gallbladder and sphincter of Oddi disorders, and functional anorectal pain in adults [10]. Infant colic in neonates and toddlers, as well as IBS, abdominal migraine, functional dyspepsia, and FAPS in children and adolescents, can also be related to pain [10]. For instance, IBS is characterized by abdominal pain or discomfort that is perceived as a weak sensation of abdominal pain and is characterized by more than two of the following three conditions: relief by defecation, onset associated with changes in stool frequency, and onset associated with changes in stool form [19]. Epigastric pain syndrome in functional dyspepsia is defined by chronic pain or burning localized to the epigastrium of at least moderate severity, at least once per week, and by intermittent pain, not generalized or localized to other abdominal or chest regions, that is not relieved by defecation or passage of flatus and does not fulfill the criteria for gallbladder or sphincter of Oddi disorders [25]. The gastrointestinal symptoms of these pain-related FGIDs have different features. However, the basic mechanisms of pain may not be mutually exclusive among these disorders.