Pathophysiology

The symptoms of FGIDs may be the result of dysfunctions of the intestinal sensory and motor systems. The pathophysiology of functional abdominal pain is complex and not fully understood. Visceral hypersensitivity and motility disturbances are thought to be involved in functional abdominal pain. The traditional concept that motility disorders alone have an important role in functional pain has not been confirmed. It is believed that visceral hypersensitivity leading to abnormal bowel sensitivity to stimuli (physiologic, psychologic, noxious) might have a more dominant role in functional abdominal pain. Visceral hypersensitivity could be due to abnormal interpretation of normal signals by the brain or aberrant signals sent to the brain or a combination. Intestinal pain receptors respond to mechanical and/or chemical stimuli. The visceral receptors can respond to both mechanical and chemical stimuli, but the mucosal receptors are primarily stimulated by chemical stimuli.

The viscera are innervated by dual set of nerves (vagal and splanchnic spinal nerves or pelvic and splanchnic spinal nerves). The spinal afferents carry impulses to the spinal cord. The dorsal horn of the spinal cord regulates conduction of impulses from peripheral nociceptive receptors to the spinal cord and brain, and the pain experience is further influenced by cognitive and emotional centers. Chronic peripheral nervous system pain can produce increased neural activity in higher central nervous system centers, leading to perpetuation of pain. Psychosocial stress can affect pain intensity and quality through these mechanisms. The child’s response to pain can be influenced by stress, personality type, and the reinforcement of illness behavior within the family. The autonomic and enteric nervous systems can overlie the initiation, perception, and perpetuation of pain.

A normal functioning enteric nervous system (ENS) is important for coordination of intestinal motility, secretion and blood flow. Abnormalities of the enteric nervous system may be an underlying factor for functional abdominal pain. Inflammation of the intestine and its role in the pathogenesis of functional abdominal pain could be due to the effects of the inflammatory mediators and cytokines (released by the various inflammatory cells) on the ENS. The dysregulation in the brain-gut interactions can also lead to functional abdominal pain. The role of certain triggers for pain, such as lactose, sorbitol, fructose, bile acids, or fatty acids, could be due to the altered sensitivity or motor function, because some patients have relief when eliminating these from their diet. Altered intestinal permeability enabling passage of food antigens into the mucosa leading to prolonged stimulation of the intestinal mucosal immune system and the ENS is also a possible cause for functional abdominal pain.

Evaluation and Diagnosis

While evaluating a patient with chronic abdominal pain, distinguishing organic pain and functional pain can be challenging. A wide range of potential organic causes of chronic abdominal pain (see Table 298-13) must be considered before establishing a diagnosis of functional pain (nonorganic). Frequently cited causes of chronic abdominal pain include constipation, esophagitis, gastritis, inflammatory bowel disease, and possibly giardiasis. There is little evidence that the frequency, severity, or location of the pain helps to distinguish between organic and nonorganic pain. It is controversial whether nighttime awakening due to pain is concerning for organic disorders or if it can be seen with functional pain syndromes.

Children with chronic abdominal pain might have associated headaches, anorexia, nausea, vomiting, excessive gas, diarrhea or constipation, and joint pain, but this does not help distinguish between functional and organic disorder. Negative lifestyle events and high life stress levels also do not help to distinguish organic and nonorganic pain, despite several reports of higher levels of life stress in children with chronic abdominal pain. Daily stressors may increase the likelihood for pain episodes, but there is no evidence that psychological issues distinguishes between organic and nonorganic abdominal pain. Nonetheless, it is important to investigate and manage the psychologic factors because there is evidence suggesting that children with chronic abdominal pain have more anxiety and depression symptoms. Whether this causes pain or is the result of pain is not known.

Children with functional pain do not have higher levels of conduct disorder or oppositional behavior compared to the controls but they can be more prone to emotional symptoms or psychiatric disorders later in life. Parents of patients with functional abdominal pain have more symptoms of somatization, anxiety, and depression. Both the family and the affected child when an adult have a higher incidence of irritable bowel syndrome (IBS).

A through history and physical examination would identify the alarm symptoms and signs (Tables 334-4 and 334-5). The presence of alarm symptoms and signs warrants further investigation. The absence of alarm symptoms and signs, a normal physical examination, and a normal stool hemoccult test is sufficient for an initial diagnosis of functional abdominal pain. The laboratory, radiologic, or endoscopic approach to children with chronic abdominal pain should be individualized, depending on the findings suggested by a detailed history and physical examination.

Laboratory studies may be unnecessary if the history and physical examination lead to a diagnosis of functional abdominal pain. Nonetheless, medical tests can reassure the patient and family, and at times the physician, if there is significant functional disability and poor quality of life. A complete blood cell count, sedimentation rate, C-reactive protein, basic chemistry panel, celiac panel, stool culture, stool test for ova and parasites, and urinalysis are reasonable screening studies. The risk of celiac disease may be 4 times higher in these patients compared with the general population. Elevated stool calprotectin levels usually suggest an inflammatory etiology.

If indicated, an ultrasound examination of the abdomen can give information about kidneys, gallbladder, and pancreas; with lower abdominal pain, a pelvic ultrasonogram may be indicated. An upper GI x-ray series is indicated if one suspects a disorder of the stomach or small intestine.

Helicobacter pylori infection does not seem to be associated with chronic abdominal pain, but in patients with symptoms suggesting gastritis or ulcer, an H. pylori test (fecal H. pylori antigen) may be performed. Breath hydrogen testing is done for ruling out lactose or sucrose malabsorption. Lactose intolerance is so common that the finding may be coincidental, and the clinician must be cautious in attributing chronic abdominal pain to this condition.

Esophagogastroduodenoscopy is indicated with symptoms suggesting persistent upper GI pathology. In the absence of this suspicion, esophagogastroduodenoscopy is unlikely to identify an abnormality and is usually not necessary.

Treatment

Making a positive diagnosis of functional abdominal pain is important and can be done by the primary care pediatrician in most 4-18 yr old children with chronic abdominal pain if there are no alarm symptoms or signs, a normal physical examination, and a negative stool occult blood testing. In practice, on many occasions children do not get a conclusive diagnosis of functional abdominal pain. This can lead to unwarranted referrals and increased anxiety to the patient and the family. Even if a diagnostic evaluation is initiated during the initial office visit, a discussion about functional abdominal pain as the most likely diagnosis during that visit will help the patient and family to understand the diagnosis better. Close following and counseling by one consistent health care provider is essential.

The most important component of the treatment is reassurance and education of the child and family. The child and family need to be reassured that no evidence of a serious underlying disorder is present. The family and the child with functional pain might worry about the inability to identify an organic cause and may be resistant to a diagnosis of nonorganic disease. Explanation in simple language that although the pain is real, there is no underlying serious disorder usually alleviates the anxiety in the patient and family. Children of families that do not accept a functional cause of the symptoms are more likely to have persistent somatic complaints and school absences. The parents should be instructed to avoid reinforcing the symptoms with secondary gain. If children have missed school or have been removed from routine activities because of the pain, it is important that they return to regular activities.

Treatment goals should be set for return to function and minimizing pain. Complete disappearance of pain would be an unreasonable goal to set. Cognitive-behavioral therapy is helpful in the short term for managing pain and functional disability (Table 334-6). Biofeedback, guided imagery, and relaxation techniques have been useful in some children with functional pain. Even though studies have not shown consistent benefits from medications, time-limited use of medications is usually part of the multidisciplinary approach. The commonly used medications include acid suppressants for dyspepsia symptoms, antispasmodics, and low-dose amitriptyline. For chronic abdominal pain with IBS symptoms, antidiarrheals and nonstimulating laxatives are used. Peppermint oil for 2 wk improves IBS symptoms in children. There is no evidence that lactose-restricted diet and fiber supplements decrease the frequency of attacks in chronic abdominal pain in children. Proton pump inhibitors or visceral muscle relaxants (anticholinergics) have been used empirically but are often unhelpful in the absence of specific indication.

Table 334-6 EFFECTIVENESS OF TREATMENTS FOR ABDOMINAL PAIN IN CHILDREN

The effectiveness of analgesics, antispasmodics, sedatives, and antidepressants is currently unknown.

GI, gastrointestinal.

From Berger MY, Gieteling MJ, Benninga MA: Chronic abdominal pain in children, BMJ 334:997–1002, 2007.