1.Overview and definition

Functional gastrointestinal disorders (FGIDs) are defined in the Rome classification, the international criteria for FGIDs, as abdominal symptoms of gastrointestinal origin, mainly abdominal pain, that (1) exist for at least 6 months before diagnosis, 2) meet the respective diagnostic criteria for the last 3 months, and 3) are not triggered by organic lesions. Since the establishment of the Rome III criteria in 2006, FGIDs have been broadly classified into neonatal/infantile (0–3 years) and pediatric/adolescent (4–18 years). For the first time, FGIDs have been classified according to developmental age. FGIDs include several disease groups, among which functional abdominal pain syndrome (FAPS) is the most common. FAPS is crucial in terms of psychosomatic correlation.

2.Epidemiology

Epidemiological data on FGIDs, particularly FAPS, in children are limited because the definitions of subtypes have changed over time and the disease has not been appropriately diagnosed and classified. In a prospective study of 171 patients aged 5–18 years referred to a tertiary care pediatric gastroenterology outpatient clinic for recurrent abdominal pain and ruled out organic disease, 68% met the Rome I criteria for irritable bowel syndrome (IBS) in adults. In a prospective study of 107 children referred to a tertiary care center for abdominal pain and denied organic disease, 45% of patients with IBS and 23% with functional dyspepsia (FD), functional abdominal pain (FAP), and abdominal migraine met the Rome II criteria.

3.Pathophysiology

FGIDs can be divided mainly into dysmotility of the gastrointestinal tract and abdominal nerve hypersensitivity. In FD, dysmotility is characterized by impaired adaptive relaxation, in which the gastric fundus stores and pumps gastric contents into the gastric body, and by reduced gastric emptying capacity from the vestibule through the pyloric ring to the duodenum. This hypomotility is a major factor in pericardial distention and early satiety. In IBS, the main symptoms are diarrhea and constipation due to dysmotility and abdominal pain due to hypersensitivity. The pathogenesis of abdominal migraine and FAP-not otherwise specified (FAP-NOS) remains unclear; however, motor dysfunction and hypersensitivity may be involved, probably via the central nervous system and enteric plexus system.

In the latest Rome classification (Rome IV), the most significant changes from the previous classification include the name change to functional abdominal pain disorder (FAPD; previously abdominal pain-related functional gastrointestinal disorders) and the removal of FAPS with headache, leg pain, and difficulty sleeping as a subclass of FAP.

4.Symptoms and diagnosis

Rome IV criteria define IBS as abdominal pain that meets one or more of the following: (1) related to defecation, (2) change in defecation frequency at onset, and (3) change in stool shape (appearance) at onset. As with adults, IBS in children is classified into four subtypes: IBS with diarrhea (IBS-D), IBS with constipation (IBS-C), IBS with mixed body habits, and IBS unclassified. The Japanese Society of Clinical Oncology classifies FD into diarrhea, constipation, gas, and recurrent abdominal pain (RAP) types according to its pathological conditions and treatment guidelines.

FD is characterized by persistent and recurrent pain and discomfort in the upper abdomen that occur independently of defecation. As for adults, FD in children is classified into two groups: postprandial stress syndrome, which presents with postprandial gastric distention and early satiety (feeling full after eating only a small amount), and epigastric pain syndrome, which presents with epigastric pain and burning sensation in the epigastric region, regardless of whether it occurs before or after eating.

Abdominal migraine is characterized by abdominal pain with headache and gastrointestinal symptoms and partially overlaps with cyclic vomiting syndrome and FAP-NOS.

5.Treatment and countermeasures

FGIDs are medically significant because they are highly symptomatic in the acute phase and are often associated with other functional disorders, such as migraine, tension-type headache, psychogenic fever, and OD. These affect learning and interpersonal interactions, such as difficulty attending school, and significantly reduce the patient’s activities of daily living at home and in extracurricular activities.

In general pediatric outpatient clinics, medical examination and treatment aim to differentiate between acute onset and recurrent chronic abdominal pain and rule out organic diseases, taking into consideration the age at onset. The occurrence of abdominal pain and abnormal bowel movements after the resolution of inflammatory (e.g., following acute enteritis or inflammatory bowel disease) may indicate post-infectious IBS or other FAPS-related complications, such as FD. If endoscopy or other specialized examination is required to rule out organic disease, the patient must be referred to a gastroenterologist. A child experiencing disruptions in daily life, mental instability, and physical symptoms must be referred to a pediatric psychosomatic or child psychiatric specialist for psychological evaluation and intervention. However, do not rely solely on the specialist, but continue outpatient follow-up.

Organize patient information with the goal of restoring normal defecation habits. Begin by assessing defecation status. This involves carefully reviewing the stool frequency, characteristics, aggravating and relieving factors, etc. Perform abdominal examination to check for the presence of gas and stool. Encourage the patient to maintain a daily bowel movement record to monitor changes in stool patterns.

Explain the condition to the patient and provide dietary guidance and lifestyle improvement. If constipation is the main complaint, prioritize a high-fiber diet and respond to the urge to defecate. In addition, attention should be paid to the posture of defecation, and if necessary, patients should be instructed to bend forward and ground their feet properly. If the main complaint is diarrhea, patients should avoid spicy foods and caffeine, which can aggravate the symptoms. A gluten-free diet or a low FODMAP diet that limits gas-producing polysaccharides can be also effective. Since a lack of sleep can aggravate symptoms, patients should maintain regular sleep habits (going to bed early and getting up early), engage in light exercise upon waking, and allow time for bowel movement before school.

In FD, prokinetics, Chinese herbal remedies Rokunshi-to, and proton pump inhibitors are the first choice; however, antispasmodics (such as anticholinergics) and Chinese herbal remedies (such as Anzhongzhan) are also used empirically. In IBS-C, osmotic laxatives, such as magnesium oxide, which can change stool properties, are used first. Dimethicone also has few side effects and is easy to prescribe. Although not covered by insurance, prokinetics may have a certain effect on intestinal peristalsis. Stimulant laxatives, such as sennosides, are recommended to improve peristalsis; however, they should be used only as needed, considering the exacerbation of abdominal symptoms when taken internally and the tolerance to treatment if taken for a long time. In IBS-D, polycarbophil calcium is also recommended. As bowel control agents, some Chinese herbal preparations, such as Xiao Jian Zhong Tang and Da Jian Zhong Tang, may be effective. Regarding antiflatulent agents, the following hypothesis was proposed: changes in the intestinal microflora improve microinflammation of the intestinal mucosa and suppress IBS symptoms. For gas type, RAP type, and FAP-NOS of IBS, there is no evidence, and only anticholinergic agents are used empirically. Depending on the symptoms, psychotropic drugs such as anxiolytics and sleep-inducing drugs should be considered; however, treatment should be left to specialists in consideration of dependency. In addition, a 5-HT3 antagonist (ramosetron) is approved for diarrhea in adults, and new drugs, such as a chloride channel agonist (lubiprostone) and a guanylate cyclase C receptor agonist (linaclotide), are approved for constipation in Japan.

6.Prognosis

The prognosis of FGIDs or the FAPD subcategory in pediatric and adolescent patients is currently not well-established. In adults, only a few rep orts of FD after administration of proton pump inhibitors or eradication of Helicobacter pylori are available. Reports on IBS in adults are limited.

OKUMI, Hirokuni

Ihoukai Medical Association, Okumi Clinic /

Osaka General Medical and Educational Research Institute Affiliated Clinic for Parents and Children