# Approach to Chronic Abdominal Pain

## Overview
Functional abdominal pain disorders and irritable bowel syndrome are among the most common reasons for gastroenterology consultation in both children and adults. The Rome IV criteria provide a unified framework for diagnosis across ages, emphasizing the brain-gut axis and biopsychosocial model. The Med-Peds physician must develop a rational, evidence-based approach that avoids both excessive investigation and missed organic disease.

## Definitions and Rome IV Criteria

### Pediatric Functional Abdominal Pain Disorders (Rome IV)
**Functional dyspepsia**: epigastric pain or burning, early satiety, or postprandial fullness not explained by organic disease; at least 4 days/month for >=2 months. **Irritable bowel syndrome (IBS)**: abdominal pain associated with defecation or change in stool frequency/form; at least 4 days/month for >=2 months. **Abdominal migraine**: paroxysmal episodes of intense periumbilical pain lasting >=1 hour, with intervals of usual health; incapacitating, associated with nausea/vomiting/anorexia/headache/photophobia/pallor; at least 2 episodes in 6 months. **Functional abdominal pain -- not otherwise specified**: abdominal pain not fitting the above categories; at least 4 days/month for >=2 months.

### Adult Functional GI Disorders (Rome IV)
**Functional dyspepsia**: epigastric pain syndrome (EPS) and/or postprandial distress syndrome (PDS); symptoms for >=3 months with onset >=6 months prior. **IBS**: recurrent abdominal pain >=1 day/week in the last 3 months, associated with defecation, change in stool frequency, or change in stool form; onset >=6 months prior. Subtypes: IBS-C (constipation-predominant), IBS-D (diarrhea-predominant), IBS-M (mixed), IBS-U (unclassified) **Centrally mediated abdominal pain syndrome (CAPS)**: continuous or near-continuous abdominal pain; not related to gut function; rarely or never associated with food intake or defecation.

## Epidemiology
Pediatric functional abdominal pain: 10-20% of school-age children; peak at 4-6 years and early adolescence. Adult IBS: 10-15% prevalence; female > male (2:1); onset most common in young adults. Both conditions cause significant functional impairment, school/work absenteeism, and healthcare utilization. Functional abdominal pain in childhood predicts IBS in adulthood.

## Pathophysiology: The Brain-Gut Axis

### Visceral Hypersensitivity
Altered pain processing in the enteric nervous system and central nervous system. Lower pain thresholds to visceral distension (rectal barostat studies) Central sensitization: amplified pain signaling in dorsal horn and cortical processing areas.

### Gut Dysmotility
Altered intestinal transit (accelerated in IBS-D, delayed in IBS-C) Abnormal colonic motility patterns. Small intestinal dysmotility contributing to bloating.

### Gut Microbiome
Dysbiosis with reduced microbial diversity in IBS. Post-infectious IBS: 10-15% of individuals develop IBS after acute gastroenteritis. Probiotics: modest evidence for specific strains (Lactobacillus rhamnosus GG in children with functional abdominal pain)

### Psychosocial Factors
Anxiety and depression are highly comorbid (50-70% in both children and adults with functional abdominal pain) Adverse childhood experiences (ACEs) increase risk. Parental anxiety and illness behavior modeling in children. Catastrophizing and pain-related fear amplify symptoms. Stress activates the HPA axis and CRF pathways, increasing visceral sensitivity and motility.

### Immune Activation and Mucosal Inflammation
Low-grade mucosal inflammation with increased mast cells in some IBS patients. Post-infectious IBS: persistent immune activation after resolved infection. Food antigens may trigger localized immune responses (distinct from IgE-mediated food allergy)

## Clinical Evaluation

### History
Pain characteristics: location, timing, duration, frequency, association with meals/defecation/activity. Associated GI symptoms: nausea, vomiting, diarrhea, constipation, bloating, mucus in stool. Red flags (alarm features) warranting further investigation. Psychosocial assessment: school functioning, family stressors, anxiety, depression, ACEs. Dietary history: fiber intake, FODMAPs, lactose, fructose. Medication history: NSAIDs, antibiotics. Family history: IBD, celiac disease, peptic ulcer disease, GI cancers.

### Red Flags (Alarm Features)

| Red Flag | Pediatric | Adult |
|----------|-----------|-------|
| Weight loss | Involuntary weight loss or growth failure | >5% unintentional weight loss in 6 months |
| GI bleeding | Hematemesis, hematochezia, occult blood | Rectal bleeding or iron deficiency anemia |
| Age of onset | N/A (always consider organic in infants) | Onset after age 50 |
| Nocturnal symptoms | Pain waking child from sleep | Nocturnal diarrhea or pain |
| Family history | IBD, celiac disease, peptic ulcer disease | GI cancer, IBD, celiac disease |
| Systemic features | Fever, arthritis, delayed puberty | Fever, palpable mass, progressive dysphagia |

#### Pediatric
Involuntary weight loss or growth failure; Persistent vomiting (especially bilious); GI blood loss (hematemesis, hematochezia, occult blood); Unexplained fever; Chronic severe diarrhea; Right upper quadrant or right lower quadrant pain; Family history of IBD, celiac disease, or peptic ulcer disease; Pain waking the child from sleep (though this can occur in functional pain too); Perianal disease; Arthritis, rash, delayed puberty.

#### Adult
Unintentional weight loss (>5% in 6 months); Rectal bleeding or iron deficiency anemia; Onset after age 50; Nocturnal symptoms; Family history of GI cancer, IBD, celiac disease; Palpable abdominal mass; Fever; Progressive dysphagia.

### Physical Examination
Growth assessment in children (height, weight, BMI, growth velocity); Abdominal exam: tenderness pattern, masses, hepatosplenomegaly, surgical scars; Perianal exam: fissures, tags, fistulae (Crohn disease); Joint exam: arthritis (IBD, celiac); Skin: rashes (dermatomyositis, celiac, Henoch-Schonlein purpura); Pubertal staging in adolescents.

## Diagnostic Workup

### Baseline Testing (If Alarm Features Absent)
CBC, CRP, ESR (to screen for inflammation) Celiac serologies (tTG-IgA + total IgA): celiac disease is a common mimic. Fecal calprotectin: excellent for distinguishing functional from inflammatory disease; <50 mcg/g makes IBD very unlikely. Urinalysis: exclude urinary causes. Consider: stool ova and parasites (if travel or exposure history), H. pylori testing (if dyspepsia)

### When to Pursue Further Investigation
Any alarm features present; Fecal calprotectin elevated (>250 mcg/g); Abnormal baseline labs (anemia, elevated inflammatory markers, hypoalbuminemia); Failure to respond to empiric treatment; Progressive or changing symptom pattern.

### Additional Investigations (Selective)
Abdominal ultrasound: biliary, renal, ovarian pathology. Upper endoscopy/colonoscopy: if IBD, celiac, or eosinophilic esophagitis suspected. MR enterography: small bowel Crohn disease. Breath testing: lactose or fructose malabsorption, SIBO (small intestinal bacterial overgrowth) Gastric emptying study: gastroparesis.

## Management

### Therapeutic Relationship and Education
Acknowledge that pain is real (not "in their head") Explain the biopsychosocial model in age-appropriate terms. Set expectations: goal is functional improvement, not pain elimination. Reassurance based on negative workup; avoid repeated unnecessary testing. Avoid reinforcing sick role (limiting school, excessive restrictions)

### Dietary Interventions
**Low-FODMAP diet**: strongest dietary evidence for IBS in adults; fermentable oligosaccharides, disaccharides, monosaccharides, and polyols; 4-6 week elimination then systematic reintroduction; requires dietitian guidance; emerging pediatric data. **Lactose reduction**: trial if lactose intolerance suspected. **Fiber supplementation**: soluble fiber (psyllium) beneficial for IBS-C; insoluble fiber may worsen symptoms. **Avoidance of trigger foods**: individualized.

### Psychological Therapies (Strongest Evidence Base)
**Cognitive behavioral therapy (CBT)**: most evidence in both children and adults; addresses catastrophizing, fear avoidance, and maladaptive coping. **Gut-directed hypnotherapy**: strong evidence in children (Vlieger et al.) and adults; induces deep relaxation and reduces visceral hypersensitivity; effects last >=5 years. **Mindfulness-based stress reduction**: adults; reduces symptom severity and improves quality of life. **Parent-focused interventions**: teaching parents to reinforce well behavior rather than pain behavior (social learning theory)

### Pharmacotherapy

#### Pediatric
**Probiotics**: Lactobacillus rhamnosus GG has modest evidence for functional abdominal pain in children. **Peppermint oil**: enteric-coated; some evidence for IBS in children and adults. **Cyproheptadine**: antihistamine/antiserotonergic; used for functional dyspepsia and abdominal migraine in children; also stimulates appetite. **Amitriptyline**: low-dose (0.1-0.5 mg/kg/day); neuromodulator for visceral pain; limited pediatric trial data but widely used. **Hyoscyamine**: antispasmodic; may reduce cramping. **Flunarizine/pizotifen**: for abdominal migraine prophylaxis.

#### Adult
**Antispasmodics**: hyoscyamine, dicyclomine, peppermint oil; for abdominal cramping. **Neuromodulators (gut-brain modulators)**: TCAs (amitriptyline 10-50 mg): first-line for IBS pain; particularly useful in IBS-D (anticholinergic slowing effect) SNRIs (duloxetine, venlafaxine): second-line. SSRIs (sertraline, fluoxetine): less evidence for pain but useful if comorbid anxiety/depression. **IBS-D specific**: loperamide (symptom relief), rifaximin (IBS-D without constipation; Xifaxan), eluxadoline (mu-opioid agonist/delta-opioid antagonist), bile acid sequestrants (cholestyramine if bile acid malabsorption suspected) **IBS-C specific**: linaclotide, plecanatide (guanylate cyclase-C agonists), lubiprostone (chloride channel activator), tegaserod (5-HT4 agonist, women <65 with IBS-C) **Anti-anxiety**: as indicated for comorbid anxiety disorders.

## Prognosis
Pediatric functional abdominal pain: 30-50% continue to have symptoms into adulthood. Adult IBS: chronic relapsing course; quality of life significantly impaired but no increase in mortality. Predictors of persistence: multiple somatic complaints, anxiety/depression, family reinforcement of illness behavior, early onset.

<image>A comprehensive brain-gut axis diagram showing the bidirectional communication between the central nervous system and the enteric nervous system in functional abdominal pain. The brain (showing cortical pain processing areas, amygdala for anxiety, hypothalamus for HPA axis activation) connects via the vagus nerve and spinal afferents to the gut (showing enteric nervous system, mast cells, microbiome, and visceral nociceptors). Arrows show how psychological stress amplifies visceral signals and how gut inflammation and dysbiosis send amplified signals centrally. Treatment intervention points are marked at each level: CBT and hypnotherapy at the brain, neuromodulators at the nerve pathways, probiotics and diet at the gut level.</image>

<image>A diagnostic approach flowchart for chronic abdominal pain in children and adults. Starting with a thorough history and physical exam, the chart branches based on presence or absence of alarm features. Without alarm features, baseline labs (CBC, CRP, celiac serology, fecal calprotectin) guide the next step: if all normal, diagnose functional abdominal pain per Rome IV criteria and initiate management. With alarm features or abnormal labs, further investigation is directed (endoscopy, imaging, specialized testing). A sidebar shows the Rome IV subcategories for both pediatric and adult functional abdominal pain disorders with their defining criteria.</image>

<image>A treatment pyramid for functional abdominal pain and IBS across ages. The base shows education, reassurance, and therapeutic relationship. The second tier shows dietary interventions (low-FODMAP, fiber, lactose reduction). The third tier shows psychological therapies (CBT, gut-directed hypnotherapy, mindfulness). The fourth tier shows pharmacotherapy stratified by age: pediatric options (probiotics, cyproheptadine, low-dose amitriptyline, peppermint oil) on the left and adult options (antispasmodics, neuromodulators, IBS-D and IBS-C specific agents) on the right. An annotation emphasizes that psychological therapies have the strongest long-term evidence base.</image>

## Clinical Pearls
Fecal calprotectin is the single best test to differentiate functional abdominal pain from IBD -- a normal level (<50 mcg/g) essentially excludes IBD and saves unnecessary endoscopy. Always screen for celiac disease in children and adults with chronic abdominal pain -- it is a common treatable mimic. The goal of treatment is functional improvement (return to school/work, normal activities), NOT pain elimination -- set this expectation early. Gut-directed hypnotherapy has the strongest long-term evidence in pediatric functional abdominal pain, with effects persisting >=5 years. Pain that wakes a child from sleep is traditionally considered an alarm feature, but studies show it can occur in functional pain -- use clinical judgment in context. Low-dose TCAs (amitriptyline) are effective neuromodulators for visceral pain in both children and adults -- the analgesic dose is much lower than the antidepressant dose. The low-FODMAP diet has strong evidence for adult IBS but requires dietitian guidance to ensure nutritional adequacy, especially in children. Avoid the cycle of repeated unnecessary testing -- it reinforces illness behavior and parental anxiety without improving outcomes.

## References
- Hyams JS, Di Lorenzo C, Saps M, et al. Childhood functional gastrointestinal disorders: child/adolescent. Gastroenterology. 2016;150(6):1456-1468.
- Lacy BE, Mearin F, Chang L, et al. Bowel disorders (Rome IV). Gastroenterology. 2016;150(6):1393-1407.
- Vlieger AM, Menko-Frankenhuis C, Wolfkamp SC, et al. Hypnotherapy for children with functional abdominal pain or irritable bowel syndrome: a randomized controlled trial. Gastroenterology. 2007;133(5):1430-1436.
- Ford AC, Moayyedi P, Chey WD, et al. ACG Monograph: Management of Irritable Bowel Syndrome. Am J Gastroenterol. 2018;113(Suppl 2):1-18.
- Abbott RA, Martin AE, Newlove-Delgado TV, et al. Psychosocial interventions for recurrent abdominal pain in childhood. Cochrane Database Syst Rev. 2017;1(1):CD010971.