Worsening Abdominal Pain and Bloating in a 30-Year-Old Woman

Mohammad Elbatta, MD; Jason Schairer, MD


August 12, 2019

The key to diagnosing irritable bowel syndrome is to exclude other conditions that would require further workup. Alarm symptoms or atypical symptoms that are not compatible with irritable bowel syndrome include rectal bleeding, nocturnal bowel movements, progressive abdominal pain, and weight loss.

Nocturnal symptoms are an important sign of pathology, because the motility of the gastrointestinal tract is depressed during sleep.[4] As a result, adults should not experience bowel movements during sleep. In addition, osmotic diarrhea usually occurs after the ingestion of a substrate that a person cannot digest or absorb. These patients should have symptoms after meals but be able to sleep through the night. If a person is waking up to have bowel movements, then an inflammatory, infectious, or secretory cause of diarrhea must be investigated.

Weight loss is not a feature of irritable bowel syndrome and should always prompt a workup for another etiology. The differential diagnosis includes cancer, inflammatory bowel disease, exocrine pancreatic insufficiency, chronic infections, hyperthyroidism, and severe malabsorption conditions.

SIBO is a condition in which native or nonnative bacteria are present in increased numbers, resulting in excessive fermentation, inflammation, or malabsorption. It typically occurs in association with anatomical abnormalities, motility disorders, or multifactorial causes (eg, cirrhosis, chronic pancreatitis). Most patients with SIBO present with nonspecific symptoms of bloating, flatulence, or abdominal discomfort, or they may be asymptomatic. Many patients diagnosed with severe SIBO have diarrhea. Although classic descriptions of SIBO include steatorrhea with greasy or bulky stools, this is uncommon and occurs principally if SIBO is caused by altered anatomy, such as blind loop syndrome. Rarely, patients have weight loss due to severe diarrhea, malabsorption, or poor oral intake. These symptoms do not match irritable bowel syndrome criteria.

Chronic idiopathic constipation, or functional constipation, is a common condition that affects the gastrointestinal tract, with an estimated prevalence of 4%-20% of the general population. This functional disorder is defined as the infrequent, persistently difficult passage of stools or seemingly incomplete defecation, which does not meet the criteria for irritable bowel syndrome. These patients usually do not have any physiologic abnormality.

In patients with symptoms compatible with irritable bowel syndrome on the basis of the Rome IV criteria, a limited number of diagnostic studies guided by the clinical setting are used to rule out other likely conditions. Appropriate tests for the workup of irritable bowel syndrome include a complete blood count, basic metabolic profile, C-reactive protein, and thyroid-stimulating hormone. If anemia is present, it could be microcytic, due to a chronic illness such as inflammatory bowel disease or iron deficiency associated with celiac disease (for which it is a primary presenting symptom). On the other hand, SIBO can prevent dietary vitamin B12 absorption at the terminal ileum, creating a macrocytic anemia.

The initial workup for irritable bowel syndrome does not routinely include colonoscopy, imaging tests (eg, ultrasonography, CT), or breath tests for SIBO. These have been found to be low yield for finding pathology.

The pathophysiology of irritable bowel syndrome remains uncertain. However, gastrointestinal motility, intestinal inflammation and food sensitivity, gastrointestinal infections with subsequent bacterial overgrowth and changes in the colonic microflora, genetics, and psychosocial alterations have all been implicated in the pathogenesis of the disease. Although motor abnormalities of the gastrointestinal tract (increased frequency and irregularity of luminal contractions, abnormal transit time) are detectable in some patients with irritable bowel syndrome, no predominant pattern of motor activity has emerged as a marker.

Hypersensitization of visceral afferent nerves in the gut has also been observed in these patients. Mucosal immune system activation has been revealed. On the basis of the history of acute diarrheal illness (infectious gastroenteritis) preceding the development of irritable bowel syndrome, malabsorption, increased enteroendocrine cells/lymphocytes, and antibiotic use have been proposed as plausible theories for the development of the entity. Food-specific antibodies, carbohydrate malabsorption, and gluten sensitivity may also play a role in developing the disease.

A genetic susceptibility to irritable bowel syndrome has been suggested, although familial patterns may also reflect underlying social factors. Associations between specific genes and irritable bowel syndrome are under investigation. Polymorphisms in the serotonin transporter gene result in altered serotonin reuptake efficacy, affecting intestinal peristalsis.


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