Falcon Reviews

A USMLE/COMLEX Overview by Michael Lloyd, MD

Any half-decent pediatrician could generate a list a mile long for the causes of pediatric abdominal pain. Having so many possible etiologies can be daunting, and the writers of USMLE Step 1 and Step 2 exams and COMLEX Level 1 and Level 2 exams are banking on your anxiety over this endless list, making you feel like every question will be similar to the one below:

1-  A child has abdominal pain. Your most likely treatment is:

A)  Open laparotomy

B)  A popsicle for rehydration

C)  A pat on the back

D)  Convince the parents that a transfusion is necessary, despite their religious beliefs.

In fact, such questions wouldn’t be very productive on the USMLE/COMLEX; and in reality, the test writers will give you a few characteristics in each question, which will point you in the right direction. A close look at the age, gender, quality, location, associated symptoms and timing of the pain should assist you in making the diagnosis with confidence. For example, look at this USMLE question:

2-  A 5-week-old male infant develops nonbilious projectile vomiting, and you palpate an olive-shaped, nontender mass in the upper middle abdominal quadrant. There is an associated hypokalemic hypochloremic metabolic alkalosis, and dehydration. What is the likely diagnosis and appropriate initial management?

A)  Gastroenteritis, intravenous antibiotics

B)  Hirschprung’s disease, obtain radiographs and surgical consultation

C)  Choanal atresia, pass a nasogastric tube

D)  Pyloric stenosis, intravenous fluids and electrolytes followed by surgical consultation

As you see in the question above, you need to know some of the distinguishing features of each disease so you can tell them apart. There are few causes of projectile nonbilious vomiting, and only one of them is associated with an olive-shaped mass in the epigastrum. At this point in the question, the writers have already given you all you need to make the diagnosis — now it’s up to you to start fluid resuscitation, and call the surgeon.

A systematic approach to abdominal pain in the pediatric patient will help you in your quest to make the correct diagnosis. It will also help you avoid missing less common — and possibly fatal — disorders.

On the USMLE Step 1 and Step 2, or the COMLEX Level 1 and Level 2, when you are presented with a question describing a pediatric patient with abdominal pain, look for the distinguishing features, and see which ones fit best with the various categories of disease listed below. Each category is followed by a short list of disorders, with a brief description of some characteristic features. The purpose of this list is to provide a framework for you to think about abdominal pain. Use it to guide further studies into each of the listed disorders below.


  • Gastroenteritis – one of the most common causes of abdominal pain, nausea, vomiting, and sometimes diarrhea. Rotavirus and Norwalk          virus are the most common viral etiologies, and are commonly passed via daycare facilities.
  • Food poisoning – with toxins from clostridium, bacillus, salmonella species, and staph aureus, is likely if others who ate the same food are                    similarly affected.
  • Viral hepatitis, pancreatitis


  • Inflammatory bowel disease – children can present with Crohn’s disease and Ulcerative Colitis (UC). Look for erythema nodosum, iridocyclitis, and sclerosing cholangitis. X-rays may show skip lesions (indicating Crohn’s) or toxic megacolon (indicating UC).
  • Necrotizing enterocolitis – common in preterm infants, presents with bilious vomiting, fevers, and rectal bleeding. CT scans show air in the gut wall. Treat with IV antibiotics, IV fluid resuscitation, and surgical intervention, as needed.
  • Henoch-Schonlein Purpura – GI bleeding, hematuria, palpable purpural rash on lower extremities and buttocks. Look for a history of recent URTI.
  • Mesenteric lymphadenitis – enlarged lymph nodes following a viral infection.
  • Vasculitides (PAN, Kawasaki disease, SLE, JRA) – most have many systemic manifestations. Look for coronary artery aneurysms in Kawasaki disease, and treat with aspirin. Still’s disease is the systemic form of juvenile rheumatoid arthritis, and presents with high fevers and a salmon-colored, evanescent rash. SLE should present with joint disease, a malar rash, serositis, and psychiatric complaints, as well.


  • Tumors of solid organs – such as neuroblastoma, Wilm’s tumor (associated with Von Willibrands’ disease, aniridia and hemihypertophy), and      retroperitoneal rhabdomyoscarcoma.
  • Leukemia – may also have bone pain, malaise, petechial rash, and hepatosplenomegaly.
  • Lymphoma – especially Burkitt’s lymphoma, Hodgkin lymphoma, and anaplastic large cell lymphoma.


  • Pyloric stenosis – as described above, within the first two months, commonly in males. Nonbilious vomiting, olive-shaped epigastric mass, sucussion splash on abdominal exam, hypokalemic, hypochloremic metabolic alkalosis and deyhdration. Surgical treatment.
  • Intestinal atresia – presents within the first week of life with bilious vomiting and a double bubble sign on KUB.
  • TE fistula – early presentation of choking during feedings and food regurgitation. You can’t pass an NG tube – surgical intervention.
  • Hirschprung’s disease – can present any time within the first year, with feculent vomiting. There is a lack of ganglia seen on colonic biopsy.
  • Gastroschisis – anterior abdominal defect present at birth. Off the midline, with small bowel exposed; low incidence of associated abnormalities.
  • Omphalocele – anterior abdominal defect present at birth that is midline through a defective umbilical ring. Other abdominal organs may be contained within the hernia sac; many associated anomalies.
  • Intussuseption – telescoping of the colon onto itself; presents in young childhood with bilious vomiting, colicky abdominal pain, and currant-jelly stools. Palpable mass on abdominal exam. Barium enema is diagnostic and therapeutic.
  • Meckel’s diverticulum – presence of ectopic gastric tissue; usually within two feet of the ileocolic junction, has two layers of tissue, presents within two years of life, 2% of the population affected. Technetium “Meckel’s” scan to diagnose; surgical removal is curative.
  • Midgut volvulus – sudden onset of pain and bilious vomiting, due to malrotation of abdominal organs around the ligament of Trietz. Upper GI series helpful in diagnosis, and surgery can be curative.


  • Inborn errors of metabolism – check urine and serum amino acids, and look for syndromic features; there may be a history of seizures or mental retardation; can present at any time during childhood.
  • Diabetic ketoacidosis – history of polyuria, polydipsia, vomiting. Ketones in the urine and an anion-gap acidosis. Treat with volume replacement and insulin.
  • Lactase deficiency – bloating, cramping, diarrhea, and vomiting after ingestion of meals containing lactose – can run in families. Treat with avoidance of dairy products.


  • Depression – can be common in adolescent range. Look for anhedonia, poor concentration, and changed behaviors. Treat with therapy or medications as needed.
  • Somatoform disorders – various presentations involving the transfer of anxiety, anger, or other feeling to a physical symptom. Treat with counseling and family therapy.
  • Functional abdominal pain – a wastebasket diagnosis. You should rule out common and dangerous etiologies of abdominal pain first.


  • The most common surgical cause of abdominal pain. RLQ pain, nausea, vomiting, rebound tenderness at McBurney’s point. Negative “hamburger sign” (offer the patient a hamburger – if they want to eat it, they don’t have appendicitis). Surgical treatment.


  • Treat according to Pediatric acute life support guidelines. Use imaging (Focused Abdominal Ultrasound for Trauma, CT abdomen, neck and pelvis), and physical exam findings to diagnose. Surgery is often indicated.


  • Pelvic inflammatory disease – find in sexually active young women; positive chandelier’s sign, look for cervicitis and tests to show Chlamydia or gonococcal infection. Treat with antibiotics (ceftriaxone, doxycycline). Admit if systemically ill.
  • Testicular torsion – sudden abdominal/groin pain and vomiting in a young man. Swollen, erythematous scrotum on exam. Ultrasound to distinguish from epididymitis. Prompt surgical intervention is crucial. Fixation of the other testis is often performed during surgical intervention.
  • Ectopic pregnancy – positive β-HCG, ultrasound to reveal tubal or mesenteric gestational sac. Watch for rupture with associated hemorrhage and shock. Surgical treatment is often required.
  • Ovarian cysts – intermittent pain, with cysts seen on pelvic ultrasound. Conservative management is usually adequate.


  • Nephrolithiasis – presents with flank pain that radiates to the groin. Diagnosis can be made with urinalysis or various imaging studies. Treat with pain management or lithotripsy.
  • Polycystic kidney disease – usually asymptomatic, but ultrasound reveals multiple large cystic spaces in each kidney. Can be autosomal dominant or autosomal recessive. Conservative management is most common.


1.  Brochert, A. Crush Step 2, The Ultimate Step 2 Review. 2003. Hanley & Belfus, Philadelphia, PA.

2.  Marino, B. Blueprints Pediatrics: Fourth edition. 2007. Lippincott Williams & Wilkins. Philadelphia, PA.


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