Functional Abdominal Pain in Children

Etiology

The development of functional abdominal pain is likely multifactorial. Some children appear to exhibit a heightened sensitivity to the range of normal physiological sensations, resulting in visceral hyperalgesia. For example, sensations such as bloating or indigestion may cause pain that exceeds what is typically experienced by unaffected 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, characterized by increased sensations of pain or other visceral sensations, including bloating or cramping. Psychosocial factors such as stress or comorbid anxiety and depression are also associated with the development of hypersensitivity.[2][4] Some research results suggest that functional abdominal pain may develop in children with other painful disorders, such as Crohn disease. In these cases, visceral hypersensitivity may develop, especially in patients with coexisting anxiety.[5]

Epidemiology

Functional abdominal pain is common in children, with recent study results showing an estimated worldwide prevalence of 11.7%, and is more commonly found in girls (14.5%) than boys (9.4%) and in those with comorbid affective disorders and psychosocial stressors. The prevalence is similar globally, with some variation observed in individual studies.[6] 

Pathophysiology

Research suggests that the development of visceral hypersensitivity plays a central role in functional abdominal pain, though the underlying mechanism is poorly understood. The association of functional abdominal pain with psychosocial factors supports the role of central pain sensitization.[7] Efforts to quantify this effect include measuring pain thresholds using a barostat, which inflates a balloon catheter to distend the rectum. Study results show that children with functional abdominal pain report discomfort at lower volumes of rectal distention than children with abdominal pain from organic causes.[8]

Histopathology

In general, researchers have not consistently identified histopathologic differences in children with functional abdominal pain. However, some small studies have reported gastric or intestinal mucosal abnormalities, such as mild inflammation or eosinophilia, in affected children compared with asymptomatic controls.[4] There is uncertainty whether these findings represent an underlying disease in a subset of patients or simply reflect visceral hypersensitivity that amplifies discomfort from otherwise minor physiologic processes. 

History and Physical

The history and physical examination support the diagnosis of functional abdominal pain and help rule out other etiologies. Clinicians should inquire about the chronicity and pattern of pain, its relationship to bowel patterns, and other gastrointestinal symptoms, such as reflux and nausea, to identify potential causes of abdominal pain beyond functional pain and identify features that aid in classifying subtypes of functional pain. Functional abdominal pain typically follows a chronic course. Some subtypes, such as irritable bowel syndrome, usually occur daily or nearly daily. Other subtypes, such as abdominal migraine, are notable for severe episodes separated by weeks to months without pain. Acute-onset severe pain increases the likelihood of alternative etiologies.

The relationship of pain to food can provide critical diagnostic clues, including the timing of pain after meals and its association with specific foods. Potential considerations include lactose intolerance, other forms of carbohydrate malabsorption, celiac disease, or sensitivity to fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs), which can trigger bloating and discomfort. Difficulty with bowel movements, whether constipation, diarrhea, or both, suggests irritable bowel syndrome. Resolution of pain with treatment of constipation favors a diagnosis of functional constipation over functional pain. Likewise, a history of spending excessive or minimal time on the toilet, a reluctance to defecate at school, and a history of encopresis or stool streaking on underwear support a diagnosis of functional constipation. The 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 also increases suspicion for an underlying inflammatory disorder, and a history of abdominal surgery increases the likelihood of pathology related to adhesions.

The location of pain can be a valuable indicator of underlying conditions. Young children often have difficulty localizing and describing pain, and may report either peri-umbilical pain or generalized abdominal pain. Older children and adolescents can usually localize pain, though they may describe generalized pain or changing locations. They may also describe the pain as cramping or bloating. A consistent description of severe pain, sharp pain, and localization in a specific quadrant suggests organic pathology related to a particular location. On physical examination, diffuse abdominal tenderness may be encountered; however, patients often tolerate deep palpation despite tenderness in functional disorders. With constipation, a palpable mass indicating retained stool may be noted. 

Aspects of the general physical examination that suggest nonfunctional etiologies include poor growth or weight loss, which may indicate malabsorption or chronic inflammation, as well as signs of malnutrition or delayed puberty. Physical findings can also include pallor due to anemia resulting from gastrointestinal blood loss, jaundice suggestive of liver disease, or rashes associated with systemic conditions, such as erythema nodosum in inflammatory bowel disease or dermatitis herpetiformis in celiac disease. Ocular and oral findings, such as icterus or aphthous ulcers, can provide additional diagnostic clues. Abdominal examination may reveal organomegaly, masses, localized tenderness, peritoneal signs, or distension with visible peristalsis. Perianal inspection can identify fissures, fistulas, tags, abscesses, or gross or occult blood, which are more typical of Crohn disease or other inflammatory conditions. Systemic manifestations, such as joint swelling or tenderness and digital clubbing, may also point toward chronic inflammatory or hepatic disease. In children with functional abdominal pain, the physical examination is typically unremarkable and does not reveal specific abnormal findings. However, abnormalities should prompt further evaluation for underlying organic causes of pain.

Evaluation

The American Academy of Pediatrics and the North American Society for Pediatric Gastroenterology, Hepatology and Nutrition state that in children aged 4 to 18 years with chronic abdominal pain, clinicians can diagnose functional abdominal pain when there are no alarming features, the physical examination is unremarkable, and stool occult blood is negative, without the need for further diagnostic evaluation.[9] If the presenting symptoms or physical examination suggest an alternative etiology, targeted laboratory or imaging studies should be performed based on the clinical context, with an emphasis on avoiding unnecessary invasive diagnostic procedures.[3] Alarming signs and symptoms include fever, vomiting, hematochezia, and involuntary weight loss or poor linear growth.

When indicated, initial laboratory investigation may include a complete blood count, sedimentation rate, C-reactive protein, urinalysis, stool ova and parasite studies, stool test for occult blood, celiac testing, and abdominal ultrasound. Clinicians may occasionally order these studies primarily to address family anxiety rather than to identify a specific alternative etiology for the child’s pain. However, research examining the utility of abdominal ultrasonography has concluded that it does not significantly contribute to the diagnosis of functional abdominal pain.[9]

Treatment / Management

The first treatment approach to functional abdominal pain focuses on patient and family education combined with a biopsychosocial management strategy. The biopsychosocial model acknowledges that functional abdominal pain stems from the interplay of biological factors, psychological influences, and social environment, guiding management that addresses all 3 domains to enhance outcomes. Clinicians should explain that the pain is real but not dangerous and encourage continuation of everyday activities. Families are counseled to avoid reinforcing pain-related behaviors. Cognitive behavioral therapy or other psychological interventions may be introduced if symptoms persist or functional impairment develops. Other nondietary and nonpharmacological approaches include cognitive-behavioral therapy, hypnotherapy, biofeedback therapy, lifestyle changes, stress reduction,[10] osteopathic manipulation,[11] yoga,[12] and meditation,[13] among others.[7] Open-label placebo has also been shown to significantly reduce pain scores and the need for other pain medications.[14] (A1)

Dietary modifications and pharmacologic treatment are not considered first-line therapies and are generally reserved for refractory cases or when clear symptom triggers are identified. 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 and treating contributing conditions like lactose or fructose intolerance. In patients who report bloating, dietary measures such as using a low-FODMAP diet to exclude foods with certain carbohydrates, including wheat, fruits, lactose, fructose, and some artificial sweeteners, may be helpful. Probiotics, such as Lactobacillus reuteri and Lactobacillus rhamnosus, have been shown to help alleviate pain in some children. They can be given for 6 to 8 weeks and resumed if symptoms recur.[15] Incorporating nonstimulant laxatives, such as polyethylene glycol-3350, or increasing fiber intake can be beneficial when constipation is present.[4](B3)

When pharmacological methods are considered, selective serotonin reuptake inhibitors or tricyclic antidepressants are sometimes prescribed. The mechanism by which these treatments alleviate functional abdominal pain is not well understood. One proposed mechanism is serotonin-mediated effects on the gastrointestinal tract, such as increased motility. Another potential mechanism for tricyclic antidepressants is a norepinephrine-mediated decrease in pain sensitivity, as hypothesized for their use in other pain disorders. A third proposed mode of action is through the anticholinergic effects of these medications on the gastrointestinal system.

In cases where comorbid psychopathology is present, antidepressants can alleviate depression or anxiety, exacerbating abdominal symptoms, providing additional benefit. However, study results are inconclusive on the efficacy of antidepressant therapy for functional abdominal pain in children.[16] No specific medication is universally recommended, but treatment can be individualized based on patient factors, as many antidepressants and antispasmodics have a generally favorable adverse effect profile.[17] Some patients report relief with antispasmodic medications, such as hyoscyamine or dicyclomine, used either to suppress ongoing symptoms or to stop acute attacks, depending on how symptoms present. Peppermint oil or menthol is believed to help with functional abdominal pain due to its antispasmodic properties.[4](A1)

Differential Diagnosis

Functional abdominal pain is not a diagnosis of exclusion. Clinicians should present it as a legitimate and common cause of symptoms and begin this discussion early, rather than waiting until diagnostic tests fail to reveal an organic condition. Although it is not a diagnosis of exclusion, any patient presenting with abdominal pain requires a thorough investigation for potential alternative diagnoses. The differential diagnosis varies based on the chronicity of the pain, its location, the patient's age, and any aggravating factors. Consideration should be given to "red flag" symptoms such as a fever, sudden worsening, young age, pain causing wakening from sleep, bloody stools, anemia, and weight loss or growth faltering. Signs of an acute or surgical abdomen should prompt immediate workup; these include a sudden onset of pain, absent bowel sounds, guarding, rebound tenderness, and a motionless patient in obvious distress. Depending on the signs and symptoms, the differential diagnosis includes inflammatory bowel diseases such as Crohn disease or ulcerative colitis, lactose intolerance, or celiac disease.

Classifying functional abdominal pain into subtypes helps direct treatment. Subtypes include irritable bowel syndrome, abdominal migraine, functional dyspepsia, and functional abdominal pain, NOS. If the pain is episodic and associated with headache or other migraine-like features (photophobia/phonophobia, nausea), abdominal migraine may be present. When symptoms are temporally associated with food consumption and upper abdominal pain, it suggests functional dyspepsia. Irritable bowel syndrome is related to difficulties with stool, either constipation, diarrhea, or both. In some cases, functional abdominal pain fits none of these categories and remains unspecified (eg, NOS).[2]

Prognosis

Functional abdominal pain typically follows a chronic course. Although no underlying organic pathology is present, ongoing pain can interfere with school performance and social interactions, leading to distress and functional disability. Results from longitudinal studies indicate that many children continue to experience symptoms for years after the initial diagnosis. Historical research also suggests that adults with irritable bowel syndrome are more likely to have experienced functional gastrointestinal symptoms during childhood. Long-term prognosis appears to be influenced more by comorbid features, such as anxiety, depression, or extraintestinal symptoms like headaches, than by the specific functional abdominal pain diagnosis itself.[4][18]

Complications

Because functional abdominal pain does not involve underlying organic disease, complications from the condition itself are unlikely. Instead, adverse events usually result from the impact of ongoing pain on school performance and social life, as well as from comorbid anxiety or depression worsened by persistent symptoms.