Functional abdominal pain is a common disorder in children. It is an abdominal pain that is distinct from that suggested by any underlying organic pathology. Subtypes of functional abdominal pain include irritable bowel syndrome, functional dyspepsia, and abdominal migraine. Functional abdominal pain is one of several categories of gastrointestinal (GI) disorders classified by the Rome IV criteria, with the other categories including functional nausea and vomiting or functional defecation disorders. 
The Rome IV criteria, published in 2016, allow for clinical diagnosis of functional abdominal pain and related functional conditions (irritable bowel syndrome, functional dyspepsia, abdominal migraine). As a change from the prior Rome III criteria, functional abdominal pain can be diagnosed based on symptoms “after appropriate medical evaluation the symptoms cannot be attributed to another medical condition” rather than the previous criteria’s requirement that there “is no evidence for organic disease.”
The diagnostic Rome IV criteria for functional abdominal pain must be fulfilled for at least 2 months before diagnosis, must be met at least 4 times per month, and include all of the following:
The development of functional abdominal pain is likely multifactorial. There appears to be sensitization to the range of normal physiological sensations, resulting in visceral hyperalgesia. For example, sensations such as bloating or indigestion may produce pain beyond what is typically experienced by non-affected individuals. In some cases, an initial sensitizing event, such as an infection, allergy, altered gut microbiome, or motility disorder occurs first and later progresses to hypersensitivity. Psychosocial factors such as stress or comorbid anxiety and depression are also associated with the development of hypersensitivity.
Some research suggests that functional abdominal pain may develop in children with other painful disorders, such as Crohn disease. In these cases, visceral hypersensitivity may develop, especially when anxiety is present.
Functional abdominal pain is common in children, with an estimated worldwide prevalence of 13.5%, and more commonly found in females and those with comorbid mental health conditions.
Research suggests the development of hypersensitivity plays a central role in functional abdominal pain. Efforts to quantify this include measurement of pain threshold with rectal distention with barostat, showing that children with functional abdominal pain report pain by rectal distention at a lower threshold than those with organic etiologies for their abdominal pain.
Some studies have found differences in the gastric or intestinal mucosa in children diagnosed with functional abdominal pain when compared with those without pain. For example, some small studies have identified inflammation or eosinophilia in children with functional abdominal pain.
It is unclear whether or how these findings are associated, or whether a subset of functional abdominal pain may have an underlying disease, or if hypersensitivity produces discomfort more than what would typically be produced by the underlying process.
The history and physical can provide a basis for the diagnosis of functional abdominal pain, but should also thoroughly explore features and risk factors of alternate potential etiologies.
Historical features should explore the chronicity and pattern of pain, relation to bowel patterns, other GI symptoms such as reflux and nausea. Goals include identifying potential etiologies for abdominal pain besides functional pain and ascertaining features that help classify subtypes of abdominal pain.
Functional abdominal pain has a chronic course. Some subtypes, such as irritable bowel syndrome, will have a daily or near daily occurrence. Others, such as abdominal migraine, will have severe episodes separated by weeks-to-months without pain. Acute onset severe pain increases concern for alternative etiologies.
Relationship to food provides crucial clues to potential etiologies. This includes temporal relationship to eating along with relationship to types of foods. Considerations may include lactose intolerance or another carbohydrate malabsorption, celiac disease, or sensitivity to symptoms evoked by digestion of certain foods, for example, fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs) that are found in many foods and result in bloating.
Difficulty with bowel movements, whether constipation, diarrhea, or both suggests irritable bowel syndrome. If resolution of constipation provides resolution of pain, a functional constipation rather than irritable bowel syndrome may be more likely. Other historical features in children can include time spent trying to defecate (some will spend an inappropriately short or long amount of time), hesitance to defecate at school, or history of encopresis (especially in young children) or "streaking" on underwear. For young children, relationship of symptoms to toilet training, and whether they have ever been continent or reverted to incontinence can be important.
Review of systems should include potential "red flag" symptoms such as blood in the stool, persistent vomiting, dysphagia, odynophagia, nocturnal diarrhea, unintentional weight loss, growth delay, unexplained fever, signs of abuse, referred pain, jaundice or other skin changes, and joint pain. A family history of inflammatory bowel disease can also increase suspicion for an underlying inflammatory disorder, and a past surgical history may also increase suspicion for pathology related to adhesions.
The location of pain can be informative. Young children often have difficulty localizing and describing pain, and may report either peri-umbilical pain or whole abdomen pain. Older children and adolescents can often localize pain, though may describe generalized or pain with changing locations. They may also describe the pain as cramping or bloating. Consistent description of severe pain, sharp pain, and in a specific quadrant should increase suspicion of pathology related to the quadrant.
On physical exam, diffuse abdominal tenderness may be encountered, but in functional disorders, patients often tolerate deep palpation despite tenderness. If constipation is a feature, a mass consistent with increased stool burden may be present. Other aspects of the physical exam should focus on identifying the presence of features that may suggest other etiology. Often, a lack of findings is present and reassuring to both patient and practitioner.
No specific diagnostic studies are required for the identification of functional abdominal pain. Diagnostic workup is focused on identifying potential alternate etiology, providing appropriate workup indicated by presenting symptoms and exam findings.
Management of functional abdominal pain has several strategies.
As visceral hypersensitivity is thought to play a central role in the symptoms of functional abdominal pain, reducing the pain-generating sensations may reduce the frequency and severity of pain. This approach includes identifying contributing conditions, such as lactose or fructose intolerance, and managing these appropriately. In patients who report bloating, dietary measures may be effective such as utilizing a low-FODMAP diet to exclude foods with certain classes of carbohydrates including wheat, various fruits, lactose, fructose, and some artificial sweeteners. If constipation is a feature, incorporating non-stimulant laxatives such as PEG-3350 or increased fiber diets can be helpful.
When pharmacological methods are considered, selective serotonin reuptake inhibitors (SSRIs) or tricyclic antidepressants (TCAs) are often used to treat functional abdominal pain. The mechanism by which these treatments alleviate functional abdominal pain is not understood. One proposed mechanism is serotonin-mediated effects on the GI tract, such as increased motility, another, for TCAs, is a norepinephrine-mediated decrease in pain sensitivity as is hypothesized for their use in other pain disorders, and a third potential mechanism is through their anticholinergic effects on the GI system. In cases where comorbid psychopathology is present, antidepressants can alleviate depression or anxiety contributing to symptoms, providing additional benefit. Despite the theoretical benefits, studies are inconclusive on the efficacy of antidepressant therapy for functional abdominal pain in children.
Some patients report relief with antispasmodic medication, such as hyoscyamine or dicyclomine, used as either a suppressive maintenance medication or to abort acute attacks, depending on the presentation of symptoms. Peppermint oil or menthol has been thought to be helpful in functional abdominal pain by an anti-spasmodic mechanism.
Other non-dietary and non-pharmacologic approaches include cognitive-behavioral therapy, hypnotherapy, biofeedback therapy, lifestyle change, and stress reduction, osteopathic manipulation, yoga, and meditation, among others.
Functional abdominal pain is not a diagnosis of exclusion. Discussion of functional abdominal pain as a legitimate and common explanation of pain should be initiated early, and not after other diagnostics have failed to demonstrate a cause.
Though it is not a diagnosis of exclusion, any patient presenting with abdominal pain requires an adequate workup for potential etiologies of the pain. The differential diagnosis varies based on the chronicity of pain, the location, the age of the patient, and aggravating factors. Consideration should be given to the presence of "red flag" symptoms such as a fever, sudden worsening, young age, pain causing wakening from sleep, bloody stools, anemia, and weight loss or failure to thrive. Signs of an acute or surgical abdomen should prompt immediate workup; these may be a sudden onset of pain, absent bowel sounds, guarding, rebound tenderness, and a motionless patient in obvious distress.
Depending on the signs and symptoms present, consideration could be given to inflammatory bowel diseases such as Crohn's disease or ulcerative colitis. Common organic disease entities causing abdominal pain may include lactose intolerance or celiac disease.
Classifying functional abdominal pain into subtypes can be helpful in directing treatment. Subtypes include irritable bowel syndrome, abdominal migraine, or functional dyspepsia. If the pain is episodic and associated with headache or other migraine-like features (photophobia/phonophobia, nausea), abdominal migraine may be considered. When symptoms are associated temporally with the consumption of food and present in the upper abdomen, it may be consistent with functional dyspepsia. Irritable bowel syndrome is associated with difficulties with stool, either constipation, diarrhea, or mixed. In some cases, functional abdominal pain fits none of these categories and remains unspecified.
Functional abdominal pain has a chronic course. Though there is a lack of underlying organic pathology, continued pain can impact school performance and social relationships, causing distress and disability. Longitudinal studies suggest many children have persistent pain years after original diagnosis. Historical studies indicate that adults with irritable bowel syndrome are more likely to have had symptoms consistent with a functional GI disorder as a child. Research suggests that comorbid features such as anxiety or depression or extraintestinal features such as headaches are a more significant determinant of long-term prognosis than the diagnosis alone.
As functional abdominal pain does not have an underlying organic pathology, complications based on the disease process itself are not expected. Complications may arise due to the impact of chronic pain on social functioning and school performance or may be related to comorbid depression and anxiety compounded by the persistence of symptoms.
Discussion of functional abdominal pain with the patient should begin at the first clinical encounter for abdominal pain. With proper attention paid to the physical exam and historical findings and appropriate workup only as indicated by findings, reassurance can be provided that further workup is unnecessary. Normalization of symptoms can be helpful though it is important that the patient and family understands each symptom must be taken seriously. Care must be taken to not overemphasize symptoms, as this may provoke further anxiety over symptoms, reinforcing them. Parents should also be educated to provide a consistent response to symptoms. The effect of stress and comorbid anxiety or depression, if present, should be explained. It is important that the child continues to attend school.
Given the interrelatedness of factors leading to the development of functional abdominal pain, an interprofessional approach is recommended.
A team of healthcare professionals should take into account underlying disease and childhood health events, frequent association with depression and anxiety (psychologist), and the potential for initiation of an intensive diagnostic workup if non-organic etiologies are suspected. There is also the risk of inappropriate treatment with opioids or other measures resulting in adverse patient outcomes. The need for an interdisciplinary approach is clear.
The use of a patient-centered, primary care home to coordinate care and diagnostics can ensure healthcare professional use a focused approach.
Appropriate diagnostic workup includes subspecialists to exclude organic disease to the extent suggested by symptoms and allows longitudinal care that incorporates past disease and psychosocial factors. Communicating with and involving other providers delivers improved outcomes.
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