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					                             Board Review October 11th-October 15th
                                          “GI Week”
                                           Answers


Question 1 (2010:161): B

The concomitant findings of abdominal distention and an obstructive gas pattern on abdominal
radiography (Item C161A) reported for the boy in the vignette strongly suggest either a functional
or mechanical small bowel obstruction. In adults, postoperative adhesions are the leading cause of
small bowel obstruction, comprising nearly 75% of cases in one study. However, small bowel
obstruction due to postoperative adhesions is much less common in children. In one pediatric study,
the overall incidence of bowel obstruction was 1.1% during the 5 years after primary surgery. The
highest risk occurred after ileal surgery (9.2%), followed by exploratory laparotomy (6.5%) and
duodenal surgery (4.7%). For children undergoing appendectomy, readmission for obstruction
occurred in only 0.3% of cases.

Regardless of the specific cause, the initial goal of therapy for the child who has either functional or
mechanical bowel obstruction is to relieve the associated signs and symptoms, manifested in the
boy in the vignette by abdominal distention and bilious emesis, with the latter sign suggesting
complete bowel obstruction. Relief can be achieved for this boy by immediate institution of
nasogastric decompression. Although intravenous fluids and bowel rest eventually will be instituted,
the first goal of therapy is intestinal decompression. Computed tomography scan plays little primary
role in management but may be useful in identifying suspected obstructing lesions. Barium enema
may be considered in children whose age and mode of presentation suggest a diagnosis of
intussusception. Finally, emergency surgical intervention should be undertaken only after achieving
decompression and identifying the site of obstruction with an upper gastrointestinal tract contrast
radiographic series, at least to the ligament of Treitz (to detect intestinal malrotation) and with
small intestinal follow-through if needed.

The overall incidence of postappendectomy adhesive small bowel obstruction is low, but adhesions
develop with a much higher frequency when the surgical presentation is complicated by appendiceal
perforation. Lesions causing partial or complete luminal obstruction distal to the ligament of Treitz
often present with bilious vomiting. In the newborn period, this is an ominous sign that suggests a
surgical diagnosis, including intestinal stenosis, atresias, and malrotation with or without volvulus.
Beyond infancy, the significance of bile-stained vomiting is less clear. In one report of 230 children
presenting to an emergency department because of yellow or green emesis, only 20 were
determined to have a surgical disease. In another pediatric study of 44 patients who required a
Ladd procedure for malrotation and midgut volvulus, 80% presented with green bilious emesis.

The most common causes of bilious vomiting are shown in (Item C161B). Considering the clinical
history and age at presentation of the boy in the vignette, postoperative adhesive small intestinal
obstruction represents the most likely diagnosis. Once nasogastric decompression is achieved,
further management must include additional diagnostic studies and consideration of surgical
intervention. Prior data have shown that plain roentgenograms alone often are sufficient for
identifying intestinal malrotation by demonstrating a characteristic gas pattern. In the newborn
period, bilious vomiting should be considered a consequence of mechanical bowel obstruction until
proven otherwise. Once initial bowel decompression has been achieved, a small intestinal contrast
study can identify the nature and location of the obstructing lesion prior to surgery. In older
patients, for whom malrotation with volvulus is much less prevalent, the timing of additional
diagnostic studies depends on the response to nonoperative management. Prior investigations in
patients who had adhesive small intestine obstructions have demonstrated that a significant
percentage may respond to nasogastric decompression alone, obviating the need for emergency
surgery. Under these conditions, intestinal contrast studies using water-soluble contrast material
may be used to confirm luminal integrity and guide further therapy.

American Board of Pediatrics Content Specification:
       Formulate a management plan for a patient with postoperative intestinal obstruction


Question 2 (2010: 145): D

The severe abdominal pain, vomiting, and antalgic knee-chest positioning (assumed to relieve
pressure on the pancreas, a retroperitoneal structure lying between the duodenum and the spine),
coupled with marked pancreatic enzyme elevations described for the girl in the vignette suggests
pancreatitis. The 2-year history of apparently similar, yet less severe episodes indicates the
recurrent nature of the problem. Recurrent pancreatitis is the second most common pancreatic
disorder, after cystic fibrosis, in the pediatric age group. The early presentation of the condition in
this child, coupled with her father's history of premature atherosclerotic coronary artery disease,
indicate that a familial dyslipidemia is an important potential cause for her illness. Accordingly, the
clinician should obtain a serum lipid profile. Abdominal ultrasonography is not required to establish
a diagnosis of pancreatitis. Magnetic resonance cholangiopancreatography or the currently preferred
technique of endoscopic ultrasonography is useful in the diagnosis of gallstone pancreatitis, but the
absence of other signs of cholestasis (eg, jaundice) makes this diagnosis unlikely. Hypercalcemia,
particularly in the setting of hyperparathyroidism, is a known cause of acute and recurrent
pancreatitis, but the family history and presentation strongly suggest a lipid metabolic disorder.

Acute, sporadic pancreatitis is more common than recurrent, chronic pancreatitis during childhood
and adolescence. Most cases of acute, sporadic pancreatitis are due to blunt abdominal trauma or
are classified as "idiopathic." Causes of chronic, relapsing pancreatitis include infections,
autoimmune disorders, genetic conditions, and drugs.

Pancreatitis is a common complication of a lipoprotein metabolic disorders that are associated with
hypertriglyceridemia. Of the heritable hyperlipidemias, familial lipoprotein lipase (LPL) deficiency
and type V hyperlipidemia are the disorders most frequently associated with chronic, relapsing
pancreatitis. The LPL enzyme is responsible for intravascular hydrolysis of dietary triglycerides
carried in chylomicrons. Affected patients have functionally absent LPL and manifest grossly lipemic
plasma in the fasting state, with plasma triglyceride measurements in excess of 1,500 mg/dL (17.0
mmol/L) (and as high as 25,000 mg/dL [282.5 mmol/L]). Hypercholesterolemia is another
characteristic finding, with total plasma cholesterol concentrations approximating 10% to 20% of
the triglyceride value. Familial type V hyperlipidemia also is characterized by extremely high
triglyceride concentrations, typically ranging from 500 to 10,000 mg/dL (5.7 to 113.0 mmol/L), and
presents with elevations in both chylomicron and low-density lipoprotein concentrations.

The most common cause of recurrent pancreatitis in the United States is hereditary pancreatitis, of
which two types have been described. The molecular defects for both types I and II involve
mutations in the gene on chromosome 7q35 that codes for cationic trypsinogen, and both types are
transmitted as autosomal dominant disorders with 80% penetrance. Gene mutations allow for
autoactivation of trypsinogen in the pancreas instead of in the duodenum, leading to intrapancreatic
activation of other enzymes and subsequent pancreatic autodigestion and inflammation.

A sweat chloride test may be helpful in the diagnosis of cystic fibrosis (CF). In CF, mutation in the
cystic fibrosis transmembrane conductance regulator (CFTR), which serves as a chloride channel,
results in reduced chloride and water secretion. The consequence is production of abnormally thick,
viscid mucus by all exocrine organs, including the pancreas, where the CFTR is located on the apical
membrane of pancreatic ductular epithelium. In addition to causing exocrine pancreatic fibrosis and
insufficiency, ductular plugging leads to one or more episodes of pancreatitis in a small percentage
(<5%) of those who have CF.

American Board of Pediatrics Content Specification:


       Formulate a differential diagnosis for chronic or recurrent pancreatitis in children
Question 3 (2009:240): C

Appendicitis is the most common abdominal surgical condition in children. Obstruction of the
appendix with fecal matter or other debris leads to edema, bacterial overgrowth, mucosal
breakdown, and appendiceal inflammation. Early diagnosis and surgical treatment are the keys to
favorable outcomes.

Diagnosing appendicitis in children can be challenging. When present, the highly sensitive signs and
symptoms of abdominal pain that migrates to the right lower quadrant, fever, and abdominal
rebound or guarding often are enough to prompt surgical exploration. However, the presentation in
children frequently is not classic. The difficulties encountered in evaluating preverbal patients, the
overlap of appendicitis with many other causes of childhood abdominal pain, and the often atypical
presentations contribute to the 28% to 57% appendicitis misdiagnosis rate in children.

Laboratory and radiologic studies often are used as diagnostic adjuncts when appendicitis is
considered in a patient who has an atypical presentation, such as the child described in the
vignette. Abdominal computed tomography scan (Item C240) is the most useful for confirming the
diagnosis because its sensitivities and specificities approach 100%. There is debate in the literature
regarding the optimal use of oral or rectal contrast for such studies. Abdominal radiographs are not
helpful.

No laboratory tests are independently predictive of the presence or absence of appendicitis.
Although procalcitonin has not been studied in this setting, neither the total white blood count,
absolute neutrophil count, nor C-reactive protein measurement has been found to be adequately
sensitive or specific. However, with growing concern about the long-term effects of ionizing
radiation exposure in children, laboratory tests combined with clinical findings may prove useful in
identifying low-risk individuals for whom imaging can be avoided.




American Board of Pediatrics Content Specification:


       Know the laboratory evaluation of appendicitis




Question 4 (2009:255): E

Blunt abdominal trauma in children is second only to head injury as a cause of injury-related
mortality. The most commonly injured intra-abdominal organs are the liver and spleen, comprising
60% of childhood blunt abdominal injuries, with renal, pancreatic, and bowel injuries occurring
much less frequently. Most pediatric solid organ injuries are diagnosed by computed tomography
(CT) scan, although ultrasonography is being used increasingly as an initial screening test. Most
solid organ injuries are managed nonoperatively.
The patient described in the vignette demonstrates classic signs and symptoms of a splenic injury,
with left upper quadrant tenderness and left shoulder pain due to diaphragmatic irritation. Blunt
force from the fall onto the curb is the likely mechanism. The CT scan is the diagnostic modality of
choice because it can demonstrate the injury and extent of splenic damage (Item C255). With the
exception of patients who have massive splenic disruption and hemodynamic instability, spleen
preservation is preferred to splenectomy, with 90% to 98% of patients recovering fully without
surgery.

Although thoracic aortic dissection may be seen following blunt chest trauma (steering wheel versus
chest) or a high-velocity deceleration mechanism, abdominal aortic dissection is an uncommon
injury, especially in children, following blunt trauma.

Duodenal hematomas typically are seen after a focal blow to the upper abdomen (the so-called
"handlebar injury") or after a deceleration mechanism in a restrained passenger following a high-
speed motor vehicle crash. Accounting for only 2% of blunt abdominal injuries in one study, these
injuries are notoriously difficult to diagnose. They often are missed on initial, noncontrast abdominal
CTs, and affected patients may present days after the initial trauma with vomiting and diffuse
abdominal pain. A high index of suspicion related to the mechanism of injury is the key to timely
diagnosis.

Pancreatic injuries are uncommon and occur from similar mechanisms as intestinal injuries. These
injuries also may be missed on initial CT scans. Elevated pancreatic enzyme values and persistent
upper abdominal pain should prompt evaluation for a pancreatic injury. Conservative treatment in
patients without pancreatic duct injury usually leads to full recovery.

Retroperitoneal hemorrhage may result from significant renal trauma. Physical examination findings
include flank ecchymoses and back pain. A CT scan should demonstrate both the presence of
retroperitoneal blood as well as its source in the trauma victim.

American Board of Pediatrics Content Specification:


       Recognize the likely sites of injury following blunt abdominal trauma


Question 5 (2009:129): B

Lactose intolerance (lactose maldigestion) is a common cause of pediatric recurrent abdominal pain.
Lactase is a digestive enzyme located on the intestinal villi that converts the disaccharide lactose to
the monosaccharides glucose and galactose. The monosaccharides can be absorbed across the
intestinal epithelial cells. In an individual who has low intestinal lactase (lactose intolerance), the
lactose cannot be broken down and passes into the lower intestine and colon. The malabsorbed
lactose can cause osmotic diarrhea or be fermented by bacteria, resulting in pain, gas, and bloating.
Lactose intolerance can either be primary (lactase activity that gradually declines with aging) or
secondary (an infection or enteropathy damages the villi, resulting in lactose intolerance). Primary
lactose intolerance (adult-type hypolactasia) is extremely common, occurring in approximately 20%
of white adults, 80% of African American adults, and 90% of Asian adults. It is uncommon in
children younger 5 years of age, but as children grow, those who are genetically predisposed to
lactose intolerance may develop the condition gradually during their school age years.

Lactose intolerance may be diagnosed clinically by elimination diet and rechallenge or through
lactose breath hydrogen testing. Breath testing offers the advantage of providing a more definitive
diagnosis, so milk is not withdrawn from the diet unnecessarily. In a breath hydrogen test, an adult
is given approximately 50 g of lactose (the equivalent of 4 cups of milk) as a single dose. Patients
who cannot digest and absorb this amount of lactose have the lactose fermented to hydrogen by
intestinal bacteria, which can be measured in the breath. Because intestinal bacterial fermentation
is essential for an accurate test, patients should not receive antibiotics for at least 2 weeks prior to
the test.
Many patients who have lactose intolerance diagnosed on breath test can tolerate small amounts of
lactose in their diet. Specifically, hard cheeses, such as cheddar, which often have very little lactose
(<0.5 g/serving), can be eaten by many patients who have lactose intolerance. Other products,
such as whole or skim milk, ice cream, or buttermilk, have more lactose (approximately 10
g/serving) and are less likely to be tolerated (Item C129).

American Board of Pediatrics Content Specification:


       Recognize the role of lactose intolerance in recurrent abdominal pain



Question 6 (2008:83): C

The patient described in the vignette presents with bilious emesis in the first postnatal week. Bilious
emesis always is a surgical emergency in the newborn. The differential diagnosis includes any form
of anatomic or functional gastrointestinal obstruction, such as an ileus, that may be associated with
sepsis. This infant is not systemically ill, febrile, dehydrated, or hemodynamically unstable. Although
her abdomen is not distended, the absence of bowel sounds on auscultation and the paucity of
bowel gas on abdominal radiograph (Item C83A) are concerning for malrotation of the bowel with a
midgut volvulus. Early in this condition, findings on the physical examination may be as described,
but they can change rapidly, depending on how much the mesenteric perfusion has been
compromised. Later signs include rectal bleeding, hematemesis, palpable bowel loops, and an
uncomfortably distended abdomen with respiratory embarrassment and hypovolemic shock. If not
diagnosed and expeditiously addressed surgically, most of the small intestine may be lost.

Surgical exploration may need to precede any contrast gastrointestinal imaging (upper
gastrointestinal radiographic series (Item C83B) if the patient is unstable. Plain radiographs may
demonstrate a normal, nonspecific bowel gas pattern; duodenal obstruction with the appearance of
a "double bubble"(Item C83C); gastric distention with a paucity of distal intraluminal gas; or a
generalized pattern of dilated small bowel loops. Half of all cases of midgut volvulus occurring in the
first postnatal year appear in the first week, another 25% appear in weeks 1 through 4, and the
final 25% appear from 1 month to 1 year of age. These account for 90% of all cases of acute
volvulus in pediatric patients.

Anorectal atresia is associated with delayed or absent passage of stool. Abdominal distention
classically develops over the first 48 hours of postnatal life regardless of whether the infant is fed.
This condition and tracheoesophageal fistula (TEF) may be part of a broader spectrum of associated
malformations known as the VATER or VACTERL association (V=vertebral anomalies, A=anorectal
atresia, C=cardiac malformations, TE=TEF, R=renal anomalies, L=limb anomalies). TEF typically
presents with respiratory distress or poor handling of oropharyngeal secretions and may present
with gastrointestinal obstruction in utero or postnatally. The clinician should evaluate the patient
who has anorectal atresia or TEF carefully for other findings in the VACTERL spectrum.

Cystic fibrosis may be associated with meconium ileus and delayed passage of stool beyond 24
hours. Affected infants may have bilious emesis if fed, and plain abdominal radiography
demonstrates dilated loops of bowel of varying caliber. If associated with meconium peritonitis or a
pseudocyst, intraperitoneal calcification may be seen. A septic ileus is associated with systemic
illness, abdominal distention, and a paucity of bowel gas or dilated loops of bowel on radiographs.



Question 7 (2008: 48): B

Each year, more than 90,000 cases of ingested foreign bodies are reported to poison control centers
in the United States. Most of the foreign bodies are coins, and most pass into the lower
gastrointestinal tract without incident. Approximately 30% of ingested foreign bodies remain in the
esophagus for hours to days, and many of these require removal. Although less than 1% of
esophageal foreign bodies cause significant morbidity, complications have been reported, including
esophageal erosion and perforation, esophageal stenosis, aortoesophageal or tracheoesophageal
fistula, and death (Item C48A). Because most of the complications have been noted when foreign
bodies are retained for more than 24 hours, current guidelines recommend removal of most foreign
bodies within this time frame. Button batteries or sharp objects should be removed immediately, as
should any foreign body in a significantly symptomatic patient (eg, respiratory distress, persistent
retching, pain). Extra caution should be used in identifying and removing button batteries because
of the potential for erosion due to corrosive electrolytic effects. In some cases, button batteries may
be difficult to distinguish from coins.

Most children who have retained esophageal foreign bodies are symptomatic, although the
symptoms often are nonspecific, and in 40% of cases, there is no history of ingestion. Common
symptoms include drooling, chest pain, gagging, dysphagia, and refusal to eat as well as cough,
stridor, or wheezing. A high clinical index of suspicion should prompt appropriate evaluation of such
patients that includes anteroposterior and lateral radiographs (Item C48B) of the neck and chest
and an upright abdominal film. The use of metal detectors for localizing metallic ingested foreign
bodies has been reported and can be of use in identifying those that are below the diaphragm and,
therefore, require no further intervention. Esophageal foreign bodies most commonly are retained at
the thoracic inlet, at the level of the aortic arch, and at the lower esophageal junction. Of these
three locations, the thoracic inlet is the site in more than 60% of cases.

Spontaneous passage has been reported in about one third of esophageal foreign bodies. Objects
retained at the lower esophageal sphincter are most likely to pass within 24 hours of ingestion.



Question 8 (2009:161): A

The history described for the girl in the vignette is most consistent with cyclic vomiting syndrome
(CVS), a symptom complex usually considered a migraine variant. The hallmarks of this syndrome
are intense periods of vomiting that usually last between 8 and 48 hours. The typically affected
patient has an aura of intense nausea or malaise that is followed by vomiting of undigested food,
gastric fluid, and ultimately bile. During the peak of the attack, patients may vomit as frequently as
three to six times per hour. Physical examination findings usually are benign, but patients
characteristically are listless and in a state characterized as "conscious coma." Abdominal pain,
dehydration, headache, and electrolyte abnormalities can accompany the episode. Most episodes
are self-limited and resolve spontaneously. In between episodes, the patient usually feels
completely well and has no significant symptoms of nausea or vomiting. Precipitating factors for
episodes include infection, psychological stress, and menstrual periods (catamenial migraine), but
stressors cannot be identified in most episodes.

Although most patients who have CVS have a migraine variant, other conditions can present with
recurrent episodic vomiting, including pancreatitis, ureteropelvic junction obstruction, malrotation,
eosinophilic gastroenteritis, and even intracranial lesions. Most notably, certain metabolic defects
(urea cycle defects, fatty acid oxidation defects) can present with recurrent vomiting. Therefore, a
thorough evaluation should exclude other causes. Helpful diagnostic tests include upper
gastrointestinal radiographic series (to exclude malrotation), abdominal ultrasonography (to exclude
ureteropelvic junction obstruction), and magnetic resonance imaging of the head (to exclude
intracranial lesions). In addition, in the middle of a CVS episode, electrolytes should be measured
and metabolic studies (ammonia, urinary organic acids and acylcarnitine, plasma amino acids,
pyruvate, and lactate) obtained.

Supportive care during a vomiting episode of CVS includes intravenous fluids, antiemetics
(ondansetron), and antianxiety medications (lorazepam). If the episodes are frequent, prophylactic
antimigraine therapy is effective in reducing their frequency and severity. This therapy should be
instituted in consultation with a specialist (pediatric neurologist or gastroenterologist). Daily
amitriptyline is used commonly as first-line prophylactic therapy for children older than age 5 years;
cyproheptadine often is used in younger children. Lubiprostone is used in the treatment of
refractory constipation. Omeprazole, ranitidine, and sucralfate are used to treat reflux or gastritis
and have not been shown to be useful in treating CVS.

American Board of Pediatrics Content Specification:
       Plan the evaluation of a child with cyclic vomiting



Question 9 (2009:177): B

The chronic heartburn and dysphagia to solid foods, primarily meats, described for the boy in the
vignette strongly suggest either reflux esophagitis (possibly with an esophageal stricture) or
eosinophilic esophagitis (EE) (Item C177A). The most appropriate next test to evaluate the
dysphagia is esophagogastroduodenoscopy with biopsies. The endoscopy can characterize the
severity of inflammation, exclude Barrett esophagus (a premalignant complication of
gastroesophageal reflux [GER]), and potentially differentiate between GER and EE. Esophageal
manometry, radionuclide gastric emptying scan, measurement of serum immunoglobulin E, and 24-
hour esophageal pH probe study are potentially useful in the evaluation of GER or allergy, but they
are not the appropriate initial tests in evaluating solid food dysphagia.

GER is defined as excessive regurgitation of gastric contents (both acid and nonacid) into the
esophagus. The most common gastrointestinal symptoms are heartburn (pyrosis), dysphagia
(difficulty swallowing), and odynophagia (painful swallowing). GER also may result in extraintestinal
symptoms, including hoarseness, chronic cough, exacerbation of asthma, apnea, and aspiration
pneumonia. GER is extremely common in childhood. According to one cross-sectional study, 3% to
5% of healthy children report reflux symptoms at any given time. Because GER frequently is mild
and self-limited, empiric therapy with an antacid, histamine receptor blocker, or proton pump
inhibitor is appropriate and can alleviate symptoms. Prolonged, persistent reflux (ie, more than 3
months) or complicated reflux (ie, associated with hematemesis or respiratory symptoms) warrants
further evaluation. Among the useful tests to evaluate GER are upper gastrointestinal radiographic
series (which excludes malrotation and hiatal hernia), pH probe study or esophageal impedance
(which determine the extent and duration of reflux over a 24-hour period), gastric emptying scan
(which rules out gastroparesis), and esophageal motility evaluation (which assesses peristalsis and
esophageal sphincter pressure). Upper endoscopy with biopsy generally is the most valuable test
because it can determine if chronic GER has caused any esophageal injury (Item C177B).

In the past 10 years, researchers have recognized that not all heartburn or dysphagia is caused by
GER. EE presents similarly to reflux, but is believed to be an atopic condition. Affected patients tend
to have more dysphagia symptoms than heartburn. Often, there is a history of meat impaction in
the esophagus. As noted previously, upper endoscopy with biopsies frequently can differentiate
between the two conditions. GER usually is characterized by ulceration and injury limited to the
distal 5 cm of the esophagus. In contrast, EE is characterized by inflammation of the proximal,
middle, and distal esophagus, with large numbers of eosinophils seen on biopsy. Differentiating
between these two conditions is important because treatment of GER involves acid blockade. In
contrast, the therapies for EE include anti-inflammatory therapy (eg, fluticasone, budesonide), acid
blockade, or elimination diets.

American Board of Pediatrics Content Specification:


       Know the methods for evaluation of gastroesophageal reflux



Question 10 (2009: 193): C

Based on the documented history of giardiasis and ongoing diarrhea for the patient described in the
vignette, the most likely cause of his symptoms is persistent giardiasis, most likely from reinfection
from one of his siblings or a family pet. Many Giardia infections are asymptomatic, and siblings,
other children in child care, or family pets frequently can be reservoirs for the organism. Therefore,
a patient treated with a course of metronidazole is susceptible to reinfection if he or she is exposed
to asymptomatic carriers. Metronidazole resistance is extremely rare in Giardia parasites, and based
on the history provided, there is no reason to suspect Clostridium difficile infection, celiac disease,
or food allergy at this time.
Giardia is a flagellated enteric-coated protozoan that is the most common cause of intestinal
parasitic infections in the United States. The parasite exists in two forms, cysts and trophozoites.
Cysts (Item C193A) are extremely hardy and can survive in cold water for weeks to months. The
cysts also are resistant to chlorination. Once animals (eg, dogs, cats, beavers) or humans ingest
contaminated water, the cysts mature into trophozoites (Item C193B)in the intestine, where they
cause small intestinal inflammation, villous atrophy, and malabsorption. Asymptomatic carriage is
more common than symptomatic disease. However, in patients who do develop symptoms, the
most common features are diarrhea, nausea, distention, cramping, and anorexia. Because Giardia is
a small bowel pathogen, it does not cause rectal bleeding.

The most important aspect to diagnosing Giardia infection is having a strong clinical suspicion. A
number of good diagnostic tests of the stool are available, including microscopic examination for
ova and parasites (stool O and P), enzyme-linked immunofluorescence assays, and direct
fluorescence antibody tests. The microscopic examination ("O and P" test) has poorer sensitivity
(50%) from a single sample and ideally requires microscopic examination of three separate
samples. In contrast, the Giardia antigen-based tests have a sensitivity of approximately 90% from
a single stool sample. However, the O and P examination can identify other potential pathogens
(Blastocystis, ameba) that are not identified with the antigen tests. In some cases, endoscopy with
biopsy may be useful to exclude Giardia or other pathogens and to characterize the extent of villous
atrophy.

Suspected or established giardiasis can be treated with either metronidazole (5 mg/kg per dose
administered three times a day for 7 days) or nitazoxanide for 3 days (100 mg bid for children
younger than 3 years, 200 mg bid for children ages 4 through 11 years, 500 mg bid for patients
older than 12 years of age). If asymptomatic carriers are suspected in the family, it may be prudent
to evaluate and treat the entire family.

American Board of Pediatrics Content Specification:


       Plan the evaluation of a patient with suspected giardiasis



Question 11 (2009:141): B

The profuse watery, nonbloody diarrhea and history of vacationing in Mexico described for the child
in the vignette are consistent with traveler's diarrhea. By far, the most common cause of traveler's
diarrhea is enterotoxigenic Escherichia coli (ETEC), accounting for up to 75% of cases.

There are at least five types of diarrhea-producing E coli strains, which differ in epidemiologic
features and diarrhea type (Item C141).

The primary treatment of all diarrheal disease is to provide adequate fluid replacement by the oral
or parenteral routes. The use of additional antibiotic therapy depends on the type of E coli that is
suspected of causing the illness. Treatment of EHEC infections is entirely supportive. Antibiotics are
contraindicated because they can induce the expression and release of Shiga toxins, and their use
has been associated with a higher risk of hemolytic-uremic syndrome in children.

If a patient who has E coli diarrhea does not improve after several days of supportive care and
assays for Shiga toxin are negative, antimicrobial therapy can be considered. Antimicrobial agents
that may be used in the treatment of severe watery ETEC diarrhea in a traveler or for dysentery
caused by EIEC strains include trimethoprim-sulfamethoxazole, azithromycin, or ciprofloxacin.
Selection of the agent is based on patient age and antimicrobial susceptibility of the organism. Data
regarding the treatment of EAEC infections with antibiotics are sparse, and optimal therapy is
unknown.

Shigella, Salmonella, and Campylobacter sp are much less common causes of traveler's diarrhea,
but may be responsible for up to 30% of cases, 15% of cases, and 15% of cases,
respectively. Giardia lamblia is not recognized as a cause of acute traveler's diarrhea.

American Board of Pediatrics Content Specification:


       Plan treatment for a patient with Escherichia coli diarrhea



Question 12 (2009: 209): B

The infant described in the vignette has clinical features of Down syndrome (Item C209A). Infants
who have Down syndrome are at risk for a number of gastrointestinal malformations, most notably
duodenal atresia and Hirschsprung disease. The air in the distal small bowel apparent in the
radiograph obtained for the infant in the vignette excludes duodenal atresia and annular pancreas.
The lack of pneumatosis on the radiograph for this term infant makes necrotizing enterocolitis
unlikely. Neonatal intussusception is extremely rare, and meconium ileus is associated with cystic
fibrosis, not Down syndrome.

Hirschsprung disease is characterized by congenital absence of a portion of the enteric nervous
system (aganglionosis). The aganglionic segment of bowel typically begins at the anal verge and
extends proximally. Disease limited to the rectosigmoid colon ("short segment" Hirschsprung)
accounts for 80% to 90% of cases. The remainder of cases can involve a larger portion of the distal
colon ("long segment Hirschsprung"), the entire colon ("total colonic Hirschsprung"), or the colon
and small bowel. The aganglionic segment of bowel is unable to contract, leading to either severe
constipation or a functional bowel obstruction.

It can be difficult to distinguish between functional constipation and Hirschsprung disease in
childhood. Some distinguishing features are shown in (Item C209B). In general, patients who have
Hirschsprung disease have a history of delayed passage of meconium; 95% of affected infants fail
to pass meconium in the first day after birth. Stools of infants and toddlers who have Hirschsprung
disease often are very thin. Because of the hypertensive anal sphincter and aperistaltic distal colon,
affected children almost never have encopresis. On rectal examination, an infant or child who has
short segment Hirschsprung may have an "explosion of stool" after the examiner's finger is
removed.

If Hirschsprung disease is suspected strongly, the patient should undergo further diagnostic testing.
Anorectal manometry demonstrates a hypertensive anal sphincter that fails to relax. Barium enema
may demonstrate a narrowed rectosigmoid (aganglionic segment) (Item C209C) and a dilated
proximal colon, with a "transition zone" (area of caliber change between the normal and aganglionic
segment). The definitive test for Hirschsprung disease is rectal biopsy, which demonstrates absent
ganglion cells in the submucosa and muscularis propria of the rectum. If Hirschsprung disease is
identified, surgical resection of the aganglionic colon and anastomosis of the normal colon to the
anorectal canal is the treatment of choice.


American Board of Pediatrics Content Specification:


       Know how to distinguish between simple constipation and Hirschsprung disease in the newborn period

				
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