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What are FGIDs?

Functional gastrointestinal disorders (FGIDs) are the most common maladies treated by gastroenterologists and overlap with many similar disorders identified and treated by other subspecialists. 

FGIDs are characterized by symptomatic complaints for which no structural abnormalities can be identified. The pathophysiology of these disorders is based on a bio-psychosocial concept whereby alterations in normal physiology coincide with genetic and environmental cues to result in specific gastrointestinal symptoms.  Treatment is based on the specific type and severity of the disorder and the predominant symptom(s). 


The term “functional” is applied to disorders which have no structural basis. These physiologic derangements cannot be identified through routine serologic, endoscopic or radiologic testing. The diagnosis of these disorders is based on a strict set of subjective criteria and many of these disorders are considered by the general medical population to be diagnoses of exclusion.  Thus, in many instances it is difficult for doctors to make these diagnoses and for patients to comprehend the diagnosis they are given. These disorders are, however, very real with their pathogenesis rooted in a complex interplay of biological, psychological and social aberrations.  

To better define these disorders, a committee of academic experts in the field of functional GI syndromes initially convened for the purpose of establishing a diagnostic, therapeutic and research based classification system for these disorders. This group known as the “Rome” committee first met 15-20 years ago and has since reconvened every few years to update the criteria used to define FGIDs based on new research. The most recent update, known as “Rome III” was completed in 2006 and now categorizes the adult FGIDs into 6 major domains inclusive of 28 symptom specific disorders. Each is represented by its own diagnostic criteria.


FGIDs are the most common disorders treated by gastroenterologists. While the exact prevalence of each specific disorder is unknown, the most common FGIDs such as irritable bowel syndrome (IBS) are identified in approximately 10% of the world’s population. It is important to be aware of these disorders not only because of their prevalence, but also because they overlap with many functional disorders in subspecialties other than gastroenterology. An example of this concept would be fibromyalgia—a disorder commonly seen by rheumatologists which is also diagnosed via symptom-based criteria. Furthermore, a patient with a functional complaint may be seen by physicians specializing in different sub-specialties. A patient with functional chest pain may be seen by a gastroenterologist, pulmonologist, cardiologist, and thoracic and/or vascular surgeon before a functional diagnosis is made. Therefore, it is important that all physicians are aware of these disorders to avoid unnecessary testing and referrals. 


IBS is the single most common disorder seen in GI practice. Its prevalence has been estimated between 10-20% in the US and 7-10% worldwide. It is characterized by abdominal discomfort associated with altered bowel habits. The diagnostic criteria have undergone multiple revisions with the Rome III criteria being the current standard (Table 1). Updated diagnostic critieria (Rome IV) are expected in 2014-2015. While many FGIDs are diagnosed by exclusion of other possible causes of patients’ symptoms, the diagnosis of IBS can be made with confidence and without significant diagnostic testing if the patient meets the Rome III criteria.  


What are the Rome III diagnostic criteria for IBS?


Recurrent abdominal pain or discomfort occurring at least 3 days per month in the last 3 months associated with 2 or more of the following criteria:

 -Improvement in pain/discomfort with defecation

 -Onset of pain / discomfort associated with a change in stool frequency

 -Onset of pain / discomfort associated with a change in stool consistency

***These criteria fulfilled for the last 3 months with symptom onset at least 6 months prior to diagnosis. 


Familial studies on patients with IBS have shown that both genetic and environmental signals can predispose individuals to develop IBS. These cues may then be modulated by psychosocial factors such as daily stressors and poor coping skills. While not necessary for the development of IBS, these do alter the perception and severity of symptoms. For example, IBS patients with severe symptoms and increased health care seeking have significantly increased psychiatric co-morbidity when compared to the general population, whereas patients with milder symptoms and less health care seeking behaviors have no increase in psychological disturbances compared to the same population. 

Furthermore, IBS develops from a heterogeneous group of disturbances in many different aspects of normal physiology including changes in gut motility, visceral sensitivity, intestinal inflammation, changes in the gut microbiome, dietary triggers, and neurotransmitter imbalance and signaling which also affect the development and severity of IBS symptoms. While the exact alterations and the relative weight each of these changes carries in the development of IBS differs between individuals, it is the interplay and imbalance of these factors which is presumed to underlie the development of IBS and many other FGIDs. It is also these differences that also make the “perfect treatment” such an elusive entity. 


The treatment of FGIDs is difficult because each disorder has its own set of prevailing symptoms which can wax and wane in severity. Furthermore, FGIDs can present as isolated disorders, overlap concurrently, and change over time into completely different FGIDs. Therapeutic generalizations can, however, be made. Like many other medical conditions, FGID symptoms can be categorized as mild, moderate, or severe and the type of treatment(s) to be implemented can be based on these classifications. The most important intervention in the treatment of FGIDs is the establishment of an appropriate physician-patient working relationship . This results in reductions in health care seeking behavior and symptom improvement across this entire spectrum of illnesses. 


Once this relationship has been established, the next goal is to establish the severity of disease. The following Table provides generalizations used to assist in this decision analysis and the treatments available based on disorder severity


Tricyclic antidepressants (e.g. desipramine) should be avoided in IBS-C patients (since they may cause or worsen constipation) but can help both pain and diarrhea in IBS-D patients.

Selective serotonin reuptake inhibitors (e.g. paroxetine) should be avoided in IBS-D patients since they may cause or worsen diarrhea.