Functional gastrointestinal disorders (FGID) include a set of 25 illnesses concentrated in one of five anatomic regions in the GI tract. They are called functional disorders because the locus of the problem is in how the gut functions, not the physical structure of the GI tract. Although benign (i.e., not medically dangerous), FGIDs are serious illnesses and account for approximately 17 million physician visits annually, making them some of the most common conditions encountered by gastroenterologists and general internists. FGIDs are associated with diminished quality of life, work absenteeism, and psychological distress. The functional GI disorder called irritable bowel syndrome (IBS) alone costs the U.S. health care system up to an estimated $30 billion annually in direct and indirect costs. Generally speaking, FGIDs strike women in larger numbers than men, usually first appear in the second and third decades of life, and decrease with age. The course of FGIDs is variable, with symptoms waxing and waning over time. Research evidence suggests that FGIDs might run in families, although it is unclear whether this finding reflects the influence of genetic, social learning, or combined factors.
The most common FGIDs include irritable bowel syndrome (IBS), functional or nonulcer dyspepsia (FD), functional constipation, and gastrointestinal reflux disease (GERD). IBS, the most common FGID, is characterized by lower abdominal pain/discomfort, bloating, and bowel dysfunction. Bowel dysfunction can alternate among diarrhea, constipation, and normal bowel function even though diagnostic testing shows no evidence of physical pathology. In patients with FD, on the other hand, pain is concentrated in the upper abdomen and is associated with abdominal fullness often after meals; bloating; and nausea. Patients with functional constipation pass small amounts of hard, dry bowel movements typically less than three times per week. There is substantial overlap among FGIDs. For example, approximately 40 percent of individuals with IBS have reflux symptoms and 45 percent have dyspepsia. Patients’ symptom pattern can transition between disorders such they that have symptoms of one disorder (e.g., IBS), which in turn are replaced by symptoms of another (e.g., dyspepsia). There is a higher prevalence of FGIDs in patients whose organic GI disorders (e.g., Crohn’s disease and ulcerative colitis) are in remission. Functional GI symptoms may also occur with medical disease (e.g., esophegitis, peptic ulcer) in a way that complicates medical diagnosis. In comparison to controls, FGID patients report more nongastrointestinal symptoms, including sexual dysfunction, insomnia, fibromyalgia, facial pain, chronic pelvic pain, and chronic fatigue. Diagnoses of FGIDs are based on characteristic bowel patterns, the nature, location, and quality of any accompanying symptoms (e.g., pain), and exclusion of other organic GI disease processes (e.g., infection or colon cancer) through physical examination and routine diagnostic tests.
Because of the benign nature of FGIDs, physical abnormalities cannot be detected or, if present (e.g., motility disturbance), correlate weakly or inconsistently with symptoms (e.g., pain). Because symptoms of FGIDs mimic other diseases whose symptoms correspond with physical abnormalities, patients with IBS often undergo extensive work-ups before obtaining a correct diagnosis. Although each of these diagnostic tests has utility in evaluating certain GI problems, their routine is not typically necessary to establish a diagnosis of a FGID. Because there is no “objective” marker of FGID symptoms, establishing a diagnosis, recognizing clinical features, and excluding other medical disorders that may have a similar clinical presentation can be problematic. The old view that FGID should be viewed as a “diagnoses of exclusion” has given way to an empirically validated symptom-based diagnostic system known as the “Rome” criteria.
The exact cause of FGIDs is not well established, but research suggests that they are best understood from the perspective of a biopsychosocial model. The biopsychosocial model holds that individual biology (e.g., genetic predisposition, GI physiology), behavior, and higher order cognitive processes (coping, illness beliefs, abnormal central processing of gut stimuli) influence FGIDs through their interaction with each other, with early life factors (e.g., trauma, modeling), and with the individual’s social and physical environments (e.g., reinforcement contingencies).
At the heart of the model is the belief that FGIDs involve a dysregulation in interactions among the central nervous system (CNS) and the enteric nervous system (ENS). This neural network is referred to as the brain-gut axis. The neural transmission lines of the brain-gut axis are bidirectional and reciprocal, with the CNS (brain-spinal cord) receiving information from the digestive tract and modulating the ENS (gut). Normal GI function involves a high degree of coordination between the brain and the gut. In FGID patients, however, there is a persistent disruption in the interaction of the brain-gut axis, which is manifested in enhanced sensitivity of the GI tract to common stimuli such as food, stress, and stool passage; disturbances in contractions of the GI tract (i.e., motility); and, at least among more severely affected patients, psychological dysfunction.
Research based on the biopsychosocial model has pointed to three main pathways through which psychological factors influence IBS. The first key pathway is directly through physiological systems. Psychological factors (e.g., stress, negative emotional states) can normatively induce changes in gut function, but their effect is particularly pronounced in IBS patients. Psychological factors (e.g., negative mood states, expectation, attention) can also contribute to FGIDs by influencing pain perception. The second pathway is through the adoption of illness behaviors that can exacerbate IBS symptoms, prolong recovery following diagnosis, obscure symptom profile, and compromise function. Health behaviors are strongly influenced by one’s psychological health. FGID patients, particularly the more severely affected, show higher levels of psychological distress and higher rates of psychiatric comorbidity than non-treatment-seeking patients and patients seen in primary care. Anxiety, mood, and somatization disorders are the most common cormorbid psychiatric disorders seen in FGID patients. A third pathway by which psychological factors (e.g., early abuse, interpersonal stressors, family reinforcement of illness behaviors) influence FGIDs is by mediating the risk for onset. This line of research has focused extensively on the high rates of abuse in treatment-seeking patients. For example, severely affected IBS patients with a positive history of abuse are more likely to have refractory symptoms and consume greater health care resources. Psychological factor (e.g., stress) may also increase the probability that a patient who develops an organic GI disorder will subsequently develop a FGID.
Because there is no biological marker for symptoms, the goals of medical treatment are normalization of bowel function, decreased pain/discomfort, and improvement in quality of life through a combination of pharmacologic agents, behavioral self-change interventions, and lifestyle modification. The exact constellation of treatment strategies is not prescriptive, but is based on the nature (e.g., predominant bowel habit) and severity of symptoms (mild, moderate, severe) of the individual patient. There is a general belief that patients whose symptoms are more severe have more complicated clinical profiles, which require a combination of pharmacologic agents, lifestyle change, and psychological treatments. By the same token, less severely affected patients typically respond to lifestyle modification (e.g., dietary change) and limited medication, if at all. The type of pharmacologic agent is based on the most predominant symptoms. For patients whose FGID involves diarrhea, a therapeutic trial of loperamide (trade name Imodium), diphenoxylate (Lomotil), psyllium (Metamucil), methylcellulose (Citrucel), or a low-dose tricyclic antidepressant may be pursued. Patients with constipation often undergo a trial of increased dietary fiber, supplemental fiber, an osmotic laxative (e.g., milk of magnesia, lactulose), or a stool softener if symptoms are not relieved by dietary fiber alone. Patients with pain/gas/bloating symptoms may benefit from a trial of an antispasmodic agent, such as dicyclomine (Bentyl) or hyoscyamine with Phenobarbital (Levsin), or a low-dose antidepressant.
With respect to psychological treatments, most research has focused on IBS. Four different classes of psychological treatments (brief psychodynamic psychotherapy with relaxation, hypnotherapy, cognitive-behavioral therapy, and cognitive therapy) have each been shown to be superior to symptom monitoring or routine medical care in reducing IBS symptoms. Treatments featuring cognitive therapy and hypnotherapy have been replicated and have been found to be superior to attention-placebo control conditions. Hypnotherapy has arguably the best empirical support in that its therapeutic benefits have been independently replicated by two different research groups and maintained over time. Hypnosis is a procedure that in the context of FGID patients uses suggestions for relaxation, calmness, and well-being and specific instructions called hypnotic inductions to alter patients’ gut sensations. The psychological treatment with the second-most-consistently positive track record is cognitive therapy. Cognitive therapy is a specific psychological treatment designed to reduce excessive emotional or physiological reactions associated with GI symptoms by modifying or eliminating negatively skewed thinking patterns (e.g., jumping to conclusions) and belief systems (perfectionism) that underlie these reactions. A related goal of cognitive therapy is to provide patients with a general set of problem-solving or coping skills to manage a wide range of situations associated with GI symptoms. Cognitive therapy techniques are often combined with behavioral interventions (e.g., structured muscle relaxation exercises, biofeedback training, social skills instruction), which are designed to alter maladaptive patterns of behaviors that influence illness experience. Data based on a series of smaller scale clinical trials with IBS patients indicate that psychological treatments are effective in reducing IBS symptoms in comparison to control conditions (waiting list control, symptom monitoring), although it is not know what type of treatments are most effective for what type of patients. Although IBS has been the target of most psychologically oriented clinical trials, there are a limited number of clinical trials showing that psychological treatment that features either psychodynamic psychotherapy or cognitive-behavioral therapy may be useful in reducing symptoms of nonulcer dyspepsia.
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