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Episode 676
DIP Ep 676-USMLE Step 2/3 Rapid Review Series 141 (Peds)
Pediatrics
Medium
5 - Very High
High Yield
Step 2Step 3COMLEX
PEDIATRICSNBME TRAPSSTRIDORINTUSSUSCEPTIONPYLORIC STENOSISHSPKAWASAKI
Topic
Pediatrics Rapid Review Series 141; Pediatric Upper Airway Obstruction (Croup vs Epiglottitis vs Bacterial Tracheitis vs Foreign Body Aspiration); Pediatric Abdominal Emergencies (Intussusception, Hypertrophic Pyloric Stenosis, Malrotation with Midgut Volvulus, Meckel Diverticulum, Necrotizing Enterocolitis); Pediatric Vasculitides & Exanthems (Henoch-Schönlein Purpura / IgA Vasculitis, Kawasaki Disease, Poststreptococcal Glomerulonephritis, Hemolytic Uremic Syndrome); NBME Distractor Design Principles.
Key Takeaway
Pediatric board items frequently present overlapping clinical signs that must be disambiguated by age, acuity, and anatomic location. Upper airway stridor in an unvaccinated toxic child leaning forward with drooling is Epiglottitis (intubate in OR), whereas barky cough with steeple sign is Croup (dexamethasone +/- racemic epinephrine). Non-bilious projectile vomiting with hypochloremic metabolic alkalosis is Pyloric Stenosis (ultrasound; rehydrate before pyloromyotomy), while bilious vomiting with corkscrew sign is Volvulus (upper GI series; emergent laparotomy).
Runtime: 26.4 min
Published: 2026-10-16
System: Pediatrics
Section: PEDIATRICS, EMERGENCY MEDICINE, RAPID REVIEW
Episode Notes
Source / episode info
- Episode: 676
- Title: DIP Ep 676-USMLE Step 2/3 Rapid Review Series 141 (Peds)
- Published: 2026-10-16
- Source: DIP Ep 676-USMLE Step 2/3 Rapid Review Series 141 (Peds)
One-liner
Rapid Review Series 141 delivers high-yield pediatric board topics: stridor and pediatric airway emergencies, surgical abdominal crises (pyloric stenosis, intussusception, malrotation), vasculitides (HSP vs Kawasaki), and NBME distractor analysis.
High-yield summary
- Pediatric Upper Airway Emergencies: Croup (Laryngotracheobronchitis: Parainfluenza virus, age 6 mo – 3 yr, subglottic narrowing with "steeple sign"; treat with oral dexamethasone; add racemic epinephrine for stridor at rest). Epiglottitis (Haemophilus influenzae type b, toxic, high fever, tripod position, drooling, "thumbprint sign" on lateral neck X-ray; do NOT agitate child or examine throat; secure airway immediately in OR with ENT/anesthesia; treat with IV Ceftriaxone + Vancomycin). Bacterial Tracheitis (Staphylococcus aureus superinfection after viral URI; high fever, toxic, copious purulent secretions, fails croup treatment). Foreign body aspiration (sudden unilateral wheezing/stridor in toddler; rigid bronchoscopy is diagnostic and therapeutic).
- Pediatric Abdominal Emergencies & Vomiting: Hypertrophic Pyloric Stenosis (age 3–6 weeks, firstborn male, non-bilious projectile vomiting, palpable "olive" mass in RUQ; hypochloremic, hypokalemic metabolic alkalosis; ultrasound shows pyloric muscle thickness > 3 mm; FIRST normalize electrolytes and hydration with IV fluids, THEN perform laparoscopic pyloromyotomy). Malrotation with Midgut Volvulus (neonates < 1 month, acute bilious vomiting, Ladd bands obstructing duodenum; Upper GI series shows "corkscrew" duodenal twisting and right-sided ligament of Treitz; emergent Ladd procedure to prevent total bowel infarction).
- Intussusception & Meckel Diverticulum: Intussusception (age 6 mo – 3 yr, episodic severe colicky abdominal pain with legs drawn to chest, currant jelly stools containing blood and mucus, target/doughnut sign on ultrasound; pneumatic [air] or hydrostatic contrast enema is diagnostic and therapeutic; in children > 2 yr look for pathologic lead points like Meckel diverticulum, polyps, or lymphoma). Meckel Diverticulum (failure of vitelline / omphalomesenteric duct to obliterate; Rule of 2s: 2% of population, 2 inches long, 2 feet from ileocecal valve, 2 ectopic tissues: gastric [most common, causes painless lower GI bleeding/melena] and pancreatic; 99mTc-pertechnetate scan identifies ectopic gastric mucosa).
- Pediatric Vasculitides (HSP vs Kawasaki): Henoch-Schönlein Purpura (IgA Vasculitis: palpable purpura on buttocks/lower extremities, arthralgias, colicky abdominal pain [risk of intussusception!], and IgA nephropathy with microscopic hematuria; platelet count and coagulation studies are NORMAL, differentiating it from ITP/TTP; supportive care). Kawasaki Disease (fever >= 5 days plus CRASH criteria: Conjunctivitis [bilateral, non-purulent], Rash [polymorphous], Adenopathy [cervical > 1.5 cm], Strawberry tongue / oral erythema, Hand/foot erythema and desquamation; primary complication is Coronary Artery Aneurysms; treat immediately with IVIG + High-Dose Aspirin).
- Pediatric Nephrology (PSGN vs HUS vs Minimal Change): Poststreptococcal Glomerulonephritis (PSGN: occurs 1–4 weeks after impetigo or pharyngitis; nephritic syndrome with gross hematuria [cola-colored urine], edema, hypertension, low C3 complement, subepithelial "humps" on EM). Hemolytic Uremic Syndrome (HUS: Shiga-toxin-producing E. coli O157:H7 following bloody diarrheal illness; classic triad: microangiopathic hemolytic anemia with schistocytes, thrombocytopenia, and acute kidney injury; supportive care, NO antibiotics or antimotility agents!). Minimal Change Disease (most common nephrotic syndrome in children, effacement of foot processes, selective proteinuria; dramatic response to corticosteroids).
Learning objectives
- Differentiate Croup, Epiglottitis, Bacterial Tracheitis, and Retropharyngeal Abscess by clinical exam and radiographic signs.
- Distinguish non-bilious vomiting (pyloric stenosis) from bilious vomiting (midgut volvulus) and formulate acute management.
- Interpret diagnostic tests for Intussusception (air enema) and Meckel Diverticulum (pertechnetate scan).
- Recognize diagnostic criteria and coronary complications of Kawasaki disease and explain aspirin indications.
- Analyze NBME question stems to avoid falling for distractor traps in pediatric emergency scenarios.
Board exam buzzwords
| Pediatric Condition | Pathophysiology / Etiology | Characteristic Diagnostic Sign | High-Yield Clinical Action |
|---|---|---|---|
| Croup (Laryngotracheobronchitis) | Parainfluenza virus subglottic edema | Barking seal-like cough, inspiratory stridor, "Steeple sign" on AP neck X-ray | Dexamethasone (single dose); nebulized racemic epinephrine for stridor at rest. |
| Acute Epiglottitis | Haemophilus influenzae type b supraglottic cellulitis | "Thumbprint sign" on lateral neck X-ray, toxic appearance, tripod position, drooling | Do NOT examine pharynx; immediate endotracheal intubation in operating room. |
| Hypertrophic Pyloric Stenosis | Hypertrophy of pyloric circular smooth muscle | Non-bilious projectile vomiting, palpable "olive" mass, target sign on ultrasound | Correct hypochloremic hypokalemic metabolic alkalosis with IV fluids before surgery. |
| Midgut Volvulus | Intestinal malrotation with narrow mesenteric pedicle twist | Sudden bilious emesis in neonate, "corkscrew" sign on upper GI series | Emergent surgical detorsion and Ladd procedure to prevent whole-gut necrosis. |
| Intussusception | Telescoping of proximal bowel into distal segment (ileocolic) | Currant jelly stools, episodic colicky pain, "target" sign on ultrasound | Air contrast enema (diagnostic and therapeutic; surgery if peritonitis present). |
| Kawasaki Disease | Medium-vessel necrotizing vasculitis with coronary tropism | Fever >= 5 days, strawberry tongue, bilateral nonexudative conjunctivitis, desquamation | IVIG (2 g/kg) + High-dose Aspirin within 10 days of fever onset to prevent coronary aneurysms. |
Rapid review table
| Clinical Presentation | Most Likely Pediatric Diagnosis | Key Diagnostic Distinction | Board Exam Trap |
|---|---|---|---|
| 4-week-old male with forceful non-bilious emesis after feeds; avid feeder. | Hypertrophic Pyloric Stenosis | Hypochloremic, hypokalemic metabolic alkalosis; thickened pylorus on US. | Operating before correcting dehydration and alkalosis causes fatal post-op apnea. |
| 2-week-old neonate with sudden green bilious emesis and abdominal distension. | Malrotation with Volvulus | Upper GI contrast series shows misplaced ligament of Treitz. | Never delay surgery for CT imaging; volvulus causes irreversible bowel ischemia in hours. |
| 10-month-old infant with episodic screaming, legs flexed to chest, and bloody mucus in diaper. | Ileocolic Intussusception | Ultrasound target sign; air enema is first-line therapeutic reduction. | Look for pathologic lead point (Meckel, Henoch-Schönlein Purpura) if child is > 2 years old. |
| 6-year-old with palpable purpura on buttocks, knee pain, and abdominal pain following a URI. | Henoch-Schönlein Purpura (IgA Vasculitis) | Platelet count is normal; IgA immune complex deposition. | Do not confuse with ITP; platelets are completely normal in HSP. |
| 3-year-old with bloody diarrhea 5 days ago now presents with pallor, petechiae, oliguria. | Hemolytic Uremic Syndrome (HUS) | Schistocytes on peripheral blood smear, thrombocytopenia, elevated BUN/Cr. | Do NOT administer antibiotics; antibiotic lysis of EHEC increases Shiga toxin release. |
Board-speak -> diagnosis
| Vignette Clue | Target Concept / Diagnosis | Why It Fits |
|---|---|---|
| Vignette Clue | Target Concept / Diagnosis | Why It Fits |
| 3-week-old firstborn boy has nonbilious vomiting after every feed. Exam shows mild dehydration and a firm, mobile mass in the right epigastrium. BMP: Na 132, K 3.1, Cl 88, HCO3 34. | Hypertrophic Pyloric Stenosis | Loss of gastric hydrochloric acid leads to hypochloremic, hypokalemic metabolic alkalosis requiring fluid resuscitation before surgery. |
| 14-month-old boy has bouts of inconsolable crying where he pulls his knees to his abdomen, followed by periods of lethargy. Stool contains dark red mucus. | Ileocolic Intussusception | Episodic colicky pain and currant jelly stools from venous congestion; air enema is diagnostic and therapeutic. |
| 4-year-old girl has high fever for 6 days, cracked lips, strawberry tongue, bilateral conjunctival injection without exudate, and swollen tender cervical lymph node. | Kawasaki Disease | Meets diagnostic criteria for Kawasaki disease; prompt treatment with IVIG and high-dose aspirin prevents coronary artery aneurysms. |
Management pearls
- Aspirin is usually contraindicated in pediatrics due to Reye syndrome (encephalopathy and microvesicular hepatic steatosis), but Kawasaki disease and systemic juvenile idiopathic arthritis (sJIA) are the two major exceptions where aspirin is mandatory.
- In croup, mild stridor only during agitation is treated with a single dose of oral dexamethasone (0.6 mg/kg); stridor at rest or sternal retractions requires both dexamethasone AND nebulized racemic epinephrine, followed by 3–4 hours of observation for rebound bronchospasm.
- In Henoch-Schönlein Purpura, the risk of ileoileal intussusception is elevated due to focal submucosal bowel wall hematomas serving as mechanical lead points.
Don't miss
🚨 Pyloric Stenosis Surgery Timing: The surgeon should NEVER take a pyloric stenosis patient straight to the OR! Anesthetizing an alkalotic, hypokalemic child carries an extreme risk of life-threatening cardiac dysrhythmias and post-anesthetic central apnea. Electrolytes MUST be normalized first.
🚨 HUS Antibiotic Contraindication: Never administer antibiotics to children with bloody diarrhea suspected of enterohemorrhagic E. coli (EHEC O157:H7). Antibiotics induce bacterial stress and bacteriophage lysis, triggering massive release of Shiga toxins and precipitating full-blown HUS!
OMM / COMLEX integration
🦴
High-Yield Viscerosomatics & Biomechanics for COMLEX candidates:
- Viscerosomatic autonomic reflexes for pediatric GI pathology: Stomach and pylorus reflex to T5–T9 on the right. In pyloric stenosis, acute palpatory hypertonicity, warmth, and paraspinal boggy fullness are present at T5–T9 on the right.
- Autonomics of the small bowel and cecum: T9–T11 sympathetics via the superior mesenteric ganglion; parasympathetics via the Vagus nerve (CN X). In intussusception and colic, occipitoatlantal (OA) and condylar decompression release vagal compression at the jugular foramen, helping normalize visceral peristalsis.