CHAPTER 125

Abdominal Pain

George Gershman, MD

Abdominal pain, which may be acute or chronic, is among the most common symptoms of childhood and accounts for 2% to 4% of pediatric visits. Most children with acute abdominal pain have self-limiting conditions such as viral or bacterial gastroenteritis. However, a sudden onset of abdominal pain can be caused by serious, life-threatening conditions (eg, acute appendicitis, intussusception, hemolytic uremic syndrome). Chronic abdominal pain is among the most common chronic pain entities in children and adolescents, affecting an estimated 0.3% to 19% of children worldwide. Furthermore, chronic abdominal pain can have significant psychosocial and financial costs, which often persist into adulthood, making this a global health problem with an effect well beyond the individual child and family. In clinical practice, it is generally believed that pain that exceeds 2 months’ duration can be considered chronic. Most children with chronic abdominal pain experience so-called functional abdominal pain (FAP). Over the last 20 years several functional gastrointestinal (GI) disorders associated with FAP have been established on a symptoms-based Rome classification system. In the latest version (Rome IV), a new category of FAP disorders has been included: FAP not otherwise specified (FAP-NOS), for children and adolescents whose symptoms do not match a specific FAP-associated disorder, such as functional dyspepsia, irritable bowel syndrome (IBS), or abdominal migraine. The diagnostic criteria for FAP-NOS must be fulfilled at least 4 times per month for a minimum of 2 months prior to diagnosis and include all of the following: episodic or continuous abdominal pain that does not occur solely during physiological events (eg, eating, menses); insufficient criteria for IBS, functional dyspepsia, or abdominal migraine; and after appropriate evaluation, abdominal pain that cannot be fully explained by any other medical condition.

An organic etiology is found in fewer than 10% of school-age children with chronic abdominal pain. However, failure to recognize the cause and/or delaying therapy can have devastating effects.

Epidemiology

Chronic abdominal pain is one of the most common symptoms in children, with a reported prevalence approaching 19%. Available data indicate an even higher prevalence of FAP disorders in school-age children in low-income countries. According to community- and school-based studies, up to 38% of children and adolescents experience abdominal pain weekly, with up to 24% of children reporting symptoms persisting longer than 8 weeks.

There is evidence to suggest a steady rise of abdominal pain symptoms in children approaching age 5 years and between ages 8 and 10 years.

There is no sex-related difference in the prevalence of abdominal pain until adolescence, when girls become more vulnerable to abdominal pain (the female to male ratio approaches 1.4:1).

Additional factors associated with a high prevalence of chronic abdominal pain are a positive family history and low socioeconomic status. Abdominal pain is an essential part of several functional GI disorders, such as IBS, functional dyspepsia, and abdominal migraine.

Pathophysiology

The 3 main causes of acute or chronic organic abdominal pain are inflammation, distention of the viscera, and ischemia.

Abdominal pain can originate from abdominal viscera (visceral pain), parietal peritoneum, abdominal wall, retroperitoneal skeletal muscles (somatic pain), and extra-abdominal sites (so-called referred pain). Impulses of visceral pain are carried out primarily by small, unmyelinated, slow-conducting afferent C fibers incorporated into the autonomic sensory pathways. Each visceral organ receives dual sympathetic and parasympathetic innervations. Sensory fibers associated with the sympathetic nervous system traverse prevertebral (ie, celiac, superior, and inferior mesenteric ganglion) and paravertebral ganglion and terminate in the spinal cord. Sensory fibers contained in the vagus and pelvic nerves (ie, parasympathetic branch of the autonomic nervous system) terminate in the brain stem and lumbosacral spinal cord, respectively. Sensory fibers from visceral organs that connect with the spinal column terminate across 4 to 5 spinal segments, explaining why visceral pain is poorly localized and often perceived along the midline as a dull or aching sensation. For example, the onset of acute appendicitis is usually manifested by pain in the periumbilical or epigastric areas before the pain migrates to the right lower quadrant. It is frequently accompanied by symptoms of autonomic disturbance (eg, nausea, pallor).

Somatic pain is induced by irritation of parietal peritoneum and supportive tissue. The signals from the pain receptors (ie, nociceptors) are transmitted for the most part by rapid conducting myelinated A delta fibers responsible for tactile, thermal, and chemical stimulation and discrimination of location and intensity of stimuli. As a result, somatic pain is well localized, intense, and sharp. The important characteristic of somatic pain is aggravation by movement. Therefore, the child with somatic abdominal pain is likely to lie still, in contrast with the restless patient with visceral pain.

The classic example of referred pain is abdominal pain induced by inflammation of parietal pleura at the onset of pneumonia as the result of shared central projections of the parietal pleura and abdominal wall.

The location of abdominal pain is determined by the level of spinal cord connection with the corresponding visceral organs through the afferent sensory fibers. The structures of foregut origin, such as distal esophagus, stomach, duodenum, liver, and pancreas, are innervated by the nerves that enter the spinal cord at the level T5-9 segments. Pain from these organs is perceived between the xiphoid and umbilicus. The structures related to the primitive midgut (ie, small intestine, appendix, and right colon) project the afferent fibers to the T8-9 segments of the spinal cord. As a result, the associated pain affects the periumbilical area. The structures related to the embryonic hindgut, including the left colon and the rectum, share the innervations, which involve the spinal segments T10-L1 and allocate the pain between the umbilicus and symphysis pubis.

Radiation of the pain may help in diagnosis (eg, pain related to acute cholecystitis or biliary colic is often referred to the area just under the inferior angle of the right scapula or above the right clavi-cle). Another example of referred pain is pain between the scapulae and middle back region in patients with pancreatitis.

The pathophysiology of FAP is different from acute or chronic organic abdominal pain. The genesis of FAP is related to abnormalities in the enteric nervous system and dysregulation of the brain-gut interaction. Currently, it is believed that children with FAP may have abnormal responses to the normal physiological functions related to eating, such as intestinal distention during peristalsis, and hormonal changes during digestion. Functional abdominal pain may also be related to psychological conditions such as anxiety and parental separation.

Research data suggest that visceral hyperalgesia is the key element in the pathophysiology of FAP. This theory implies sensitization of the various receptors associated with afferent innervation of the GI tract by an infectious or allergic process or abnormal processing of afferent signals by the central nervous system.

Clinical Presentation

Children who experience abdominal pain may present with pain that may be characterized as persistent or intermittent, waxing and waning or steady and unrelenting, sharp or dull, and worsened or unaffected by movement. They may have associated symptoms, including vomiting, diarrhea, constipation, fever, weight loss, headache, and anorexia (Box 125.1).

Pain from distention of smooth muscle also waxes and wanes, is poorly localized, and is unaffected by motion. Distention of any hollow viscus, including the stomach, intestines, biliary tree, fallopian tubes, or ureters, can result in such symptomatology. A classic example of such pain is renal colic, from which the patient is writhing because of the discomfort.

Differential Diagnosis

In assessing the possible disease entities that may account for abdominal pain, patient age and duration of symptoms are the key differential components. The location of the pain may provide a clue to the etiology. Disease affecting the stomach is usually appreciated in the epigastrium. Duodenal problems are noted between the xiphoid and the umbilicus, small intestinal pathology is appreciated in the periumbilical area, and cecal inflammation may be felt from the epigastrium to McBurney point. Disease in the colon is less specifically noted but is usually felt in the hypogastrium. Pain related to the urinary bladder and rectum may project to suprapubic or sacral areas. Pain may also be referred to the back. Renal colic is also noted in the back but more in a lateral or costovertebral angle site.

Acute and Chronic Abdominal Pain

Infants

Medical Conditions

A unique disorder of infants, infant colic has been referred to as paroxysmal fussiness of infancy and defined as prolonged, hard-to-soothe, and unexplained crying behavior (see Chapter 49). The onset of colic is usually between 2 and 4 weeks of age, with resolution by 3 to 4 months of age. Although colic has been attributed to recurrent abdominal pain, such pain has never been established as the cause of colic. Colic is characterized by fussiness and crying. Symptoms usually appear after feeding, particularly late in the day around family dinnertime. Infants cry, clench their fists, and flex their legs. A gas-cry-air-swallowing cycle seems to occur. The symptoms may respond to a number of measures, including rhythmic motion and anti-gas medications. Infants with colic usually appear well otherwise and often have accelerated weight gain secondary to repeated feeding made in efforts to soothe them.

Abdominal pain may also occur with food allergy, particularly cow’s milk protein allergy. Generally, symptoms such as vomiting, diarrhea, stools positive for occult blood, failure to thrive, rhinitis, eczema, pallor, irritability, and a positive family history of allergies are associated findings. Disaccharidase deficiency (eg, lactose intolerance) may result in abdominal pain, but diarrhea is also usually present.

Surgical Conditions

Intussusception occurs most often in infants 6 months and older. The infant or toddler may have been previously well or have experienced a recent bout of diarrhea. Vomiting is reported in about 50% of patients, and pallor is frequently present. Lethargy is a not-uncommon associated symptom. An etiology is noted in fewer than 2.5% of affected infants, although a lead point (lymphoma or Meckel diverticulum) may be found in 5% to 10% of older children. The intussusception most often involves the area around the ileocecal valve. Compression of the vessels within the bowel wall may lead to necrosis and gangrene. The presence of blood and mucus in the stools gives a currant jelly appearance, although the initial stool is often normal, having been the stool that was present in the rectum prior to the intussusception.

The abdominal examination of affected children may be benign except for pain over the area of the intussusception or the presence of a mass. Bowel sounds may be increased secondary to the obstruction. A rectal examination may reveal blood and the presence of a mass. Fever and leukocytosis may also be noted. A flat radiograph of the abdomen is usually nonspecific. Intussusception is diagnosed by abdominal ultrasonography or barium enema. Hydrostatic reduction is the treatment of choice of intussusception; it is successful in almost 90% to 95% of children. Failure of hydrostatic reduction or associated complications is related to delayed diagnosis and severe edema and necrosis of the affected bowel. Surgical intervention is then required.

School-age Children

Medical Conditions

As noted previously, most children with chronic abdominal pain suffer from FAP disorders. By definition, abdominal pain in children with FAP-NOS is not affected by eating, defecation, menses, or other physiological functions. It may be triggered by a new environment, difficulties at school, or domestic problems. The pain is usually periumbilical and quite severe. It can be recurrent or continuous and may affect daily activity.

Abdominal pain in children with IBS is associated with changes in stool frequency and appearance, and pain that improves with defecation. Additional symptoms associated with IBS are increased frequency of stools (ie, ≥4 stools per day) or decreased stooling (ie, ≤2 stools per week), lumpy/hard or loose/watery stool, straining, urgency or feeling of incomplete evacuation, passage of mucus, and bloating or feeling of abdominal distention. Children with IBS are often anxious and experience multiple somatic symptoms.

Although many children seem to outgrow FAP and IBS, long-term follow-up studies suggest that a significant number remain symptomatic into adulthood.

Children with functional dyspepsia experience postprandial fullness, early satiety, nausea, vomiting, and epigastric pain.

Epigastric pain syndrome (1 of 2 subtypes of functional dyspepsia in the Rome IV classification) includes bothersome (severe enough to interfere with normal activities) pain or burning localized to the epigastrium. The pain is not generalized or localized to other abdominal or chest regions and is not relieved by defecation or passage of flatus. Supportive criteria can include burning quality of the pain but without a retrosternal component, and pain commonly induced or relieved by ingestion of a meal but that may also occur while fasting. Acid blockade with H₂-receptor antagonists and proton pump inhibitors can be offered for predominant symptoms of pain.

Abdominal migraine is characterized by recurrent paroxysmal episodes of intense, acute periumbilical, midline, or diffuse abdominal pain that lasts from 1 to several hours. Pain is often incapacitating. Children return to their usual state of health for weeks or months between the paroxysms of pain. The pain interferes with normal activities and is often accompanied by pallor, anorexia, photophobia, headache, nausea, and vomiting. There is an increased incidence of maternal migraine in children with abdominal migraine.

As mentioned previously, an organic etiology is found in fewer than 10% of school-age children with chronic abdominal pain. The symptoms and signs of organic diseases are persistent right upper and right lower quadrant pain, pain that awakens the child from sleep, dysphagia, persistent vomiting, arthritis, perirectal disease, GI blood loss, nocturnal diarrhea, involuntary weight loss, deceleration of linear growth, delayed puberty, unexplained fever, and a family history of inflammatory bowel disease, celiac disease, or peptic ulcer disease.

Peptic ulcers may develop in children in 3 circumstances. Acute infantile ulcers may occur in newborns secondary to stress and hypoxia. Stress ulcers may also occur in children who experience trauma, including burns and hypoxia (eg, after submersion). The routine uses of H₂-receptor antagonists or proton pump inhibitors has reduced the incidence of ulcers in hospitalized children who were critically ill.

The most common type of ulcer in children is acute, druginduced ulcerations of the stomach and the duodenum caused by nonsteroidal anti-inflammatory drugs. Chronic peptic ulcers may develop in prepubertal children and teenagers with no apparent precipitating factors. A positive family history of peptic ulcer disease is reported in 25% to 50% of children. Unlike the classic ulcer symptoms of adults, in which pain occurs on an empty stomach and is relieved by eating, children may find that ulcer-related pain does not follow a specific clinical pattern. Positive family history, microcytic anemia, and stools positive for occult blood should raise clinical suspicion and prompt referral of the child to the pediatric gastroenterologist. There is clear evidence linking ulcer disease and infection with Helicobacter pylori in adults. The relationship between H pylori and peptic ulcer disease in children is less strong, although two-thirds of pediatric patients with endoscopic evidence of peptic ulcer disease have H pylori infection.

Mesenteric adenitis may produce symptoms indistinguishable from appendicitis, although affected children may not appear as ill as patients with acute appendicitis. Nausea and vomiting and a history of an antecedent upper respiratory infection are often present.

Infections such as tonsillitis or pneumonia may present with fever and abdominal pain. In addition, acute viral hepatitis could result in pain and tenderness localized to the right upper quadrant in association with anorexia. Young children with hepatitis A may be anicteric (see Chapter 127).

Pancreatitis produces abdominal pain that is often felt in the back. Historically, mumps was the most common cause of pancreatitis. Other infections, such as hepatitis B, Epstein-Barr virus, coxsackievirus B, and Mycoplasma pneumoniae, are the common infectious etiologies of acute pancreatitis.

Acute pancreatitis can be induced by some medications (eg, steroids, chemotherapeutic agents). Familial and recurrent forms of pancreatitis are also reported. Trauma, particularly from injuries sustained as a result of an impact against handlebars of bicycles, is a common cause. In children with pancreatitis and no apparent etiology, trauma related to child abuse should be considered.

Parasitic infestations, particularly with Giardia intestinalis, may produce abdominal pain, often with bloating and diarrhea.

Genitourinary problems may result in abdominal pain. An abnormal urinalysis provides clues to the etiology. Renal stones occur infrequently in children, and boys are more often affected than girls. In two-thirds of affected children, stones are detected incidentally or in association with a urinary tract infection. Stones may be composed of calcium phosphate or oxalate, magnesium, uric acid, cystine, or xanthine. In addition to flank or abdominal pain, patients may also experience hematuria, fever, recurrent urinary tract infection, and persistent pyuria.

Hematologic and vascular disorders, such as sickle cell disease, rheumatic fever, and Henoch-Schönlein purpura, may also present with abdominal pain. Sickle cell anemia should be considered in black children with abdominal pain. Pain may be related to vasoocclusive events, including bowel ischemia and splenic infarction or cholecystitis. Henoch-Schönlein purpura, which is also referred to as anaphylactoid purpura, is characterized by a hemorrhagic skin rash, joint pain, and renal abnormalities in addition to abdominal pain. This pain may result from a number of processes, including vasculitis, inflammation and ischemia of the bowel wall, and intussusception of the small intestine.

Diabetes mellitus may precipitate to abdominal pain secondary to cramping of accessory muscles of respiration during a bout of ketoacidosis.

Acute intermittent porphyria is an uncommon cause of abdominal pain in children. The pain is often colicky and may be associated with constipation, nausea, and vomiting. Neurologic symptoms such as pain or paresthesia in the extremities may be present. Often, symptoms are precipitated by the ingestion of medications (eg, barbiturates, sulfa drugs). Some antispasmodic medications, such as Donnatal elixir, contain phenobarbital and can precipitate an attack. The diagnosis is made by evaluating the urine for the presence of protoporphyrin.

Primary peritonitis is secondary to infection with Streptococcus pneumoniae and is seen in children with nephrotic syndrome, cirrhosis, and sickle cell disease and in young girls with fever, abdominal pain, and vaginal discharge and no predisposing condition.

Surgical Conditions

Appendicitis is the most common surgical condition that produces abdominal pain in school-age children. Appendicitis may even occur in newborns, in whom it is seen in association with conditions that lead to diminished passage of stool, such as cystic fibrosis and Hirschsprung disease. The condition is frequently difficult to diagnose in children younger than 3 or 4 years for 2 reasons: examination of such young children for pain is difficult, and symptoms are similar to those of acute gastroenteritis (eg, fever, abdominal pain, anorexia). Classically, patients report periumbilical pain that localizes to the right lower quadrant in 1 to 5 hours. They often have a low-grade fever, with a temperature of 38°C (100.4°F). Vomiting and increased urinary frequency may occur. Stool consistency and pattern are variable (see Chapter 77).

The physical examination may reveal guarding and localized pain as well as rebound tenderness. A positive psoas or obturator sign may be present, indicating inflammation of these muscles. Tenderness may also be noted on rectal examination. Leukocytosis greater than 10,000/mL is also usually present. A radiograph of the abdomen may reveal 1 of 4 signs: a fecalith in the appendix (appendicolith), air in the cecum (sentinel loop), blurring of the shadow of the psoas muscle, or edema of the abdominal wall on the right side. A chest radiograph is also useful to rule out the presence of pneumonia, which may produce symptoms that mimic appendicitis.

Meckel diverticulum may be responsible for abdominal pain in a number of ways. It may serve as the lead point for an intussusception, cause symptoms of ulcer disease (pain or hemorrhage) secondary to the presence of ectopic gastric mucosa, or become acutely inflamed as in appendicitis. Meckel diverticulum follows the rule of 2s: it affects 2% of the population, is 2 feet from the ileocecal valve, is 2 inches in length, and is 2 times more common in males than in females.

Adolescents

In female adolescents, gynecologic problems such as torsion of the ovary, mittelschmerz, dysmenorrhea, and pelvic inflammatory disease must be considered as causes of abdominal pain (see Chapter 61). In addition, pain may result from gall bladder disease secondary to cholelithiasis or cholecystitis. Cholelithiasis is also a consideration in adolescent patients with abdominal pain and fatty food intolerance who were previously pregnant.

Evaluation

History

A thorough history should be obtained (Box 125.2). A detailed description of pain may suggest a specific etiology. For example, pain worsened by eating can occur in children with gastroesophageal reflux disease, gastritis, cholecystitis, or pancreatitis. Nocturnal pain or pain relieved by a meal is more common in children with peptic ulcer disease. Pain relieved by defecation is suggestive of IBS. Pain aggravated by defecation raises suspicion of chronic inflammatory bowel disease. Localization of abdominal pain is an important additional diagnostic clue; FAP is usually localized along the midline or periumbilical area. Associated symptoms, such as fever, weight loss, anorexia, vomiting, diarrhea, leukocytosis, and an elevated sedimentation rate, also suggest an organic etiology.

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