NBME Pediatrics Form 1 - Answers & Explanations

Updated: Mar 6, 2020

1) Impaired humoral immunity

Common variable immunodeficiency (CVID) → defect in B-cell differentiation → ↓ plasma cells and immunoglobulins → ↑ sinopulmonary infections

• Combine immunodeficiency (eg, SCID) would have evidence of recurrent/severe viral and fungal infections (not just bacterial infections)

2) Posterior urethral valves

• Most common cause of urinary tract obstruction in newborn boys

• Vesicoureteral reflux is a common cause of recurrent UTI in kids

3) Nasal polyps

• Chronic URIs and steatorrhea are consistent with cystic fibrosis (CF)

• ~10-40% of CF patients have nasal polyps (due to chronic inflammation)

4) Hypothermia

• J wave = positive deflection occurring at the junction between the QRS complex and the ST segment (J wave = Osborn wave)

• J wave are suggestive of hypothermia (but are not pathognomonic)

• Height of J wave is proportional to the degree of hypothermia

5) Pyloric stenosis

• Forceful, projectile, non-bilious vomiting

• Dehydration & weight loss

• Dx: abdominal U/S

• Tx: Pyloromyotomy

6) Exocrine pancreatic insufficiency

• Failure to thrive, steatorrhea, meconium ileus, ↓ soft-tissue mass (< 5th percentile for weight) = Cystic fibrosis (CF)

• Pancreatic insufficiency → malabsorption with steatorrhea → fat-soluble vitamin deficiencies (A, D, E, K)

7) Calcium

• Seizures & prolonged QT = symptoms of hypocalcemia

• Infants of diabetic mothers often have decreased magnesium and calcium

• Infants have difficulty absorbing calcium due to surpassed PTH (ketonuria → ↓ magnesium → suppression of PTH → ↓ calcium)

8) Thick and thin blood smears • This patient went to a chloroquine resistant area → malaria

9) Hyperglycemia

• Pseudo-hyponatremia from hyperglycemia

• Hyperglycemia causes osmotic shifts of water from the ICF to the ECF → dilution hyponatremia

• Hyperglycemia → ↑ diuresis → osmotic diuresis → hyponatremia

10) Herpes simplex virus • Temporal lobe hyper/hypo-densities = HSV • Herpes encephalopathy = ↑ RBC, normal glucose, ↑/normal protein, ↑ lymphocytes

11) Osteoporosis

• Modifiable risk factors for osteoporosis: ↓ physical activity, low body weight, excessive EtoH or tobacco use, premature menopause, glucocorticoid use

• This patient is headed toward the female athlete triad: low BMI, irregular periods, and


12) Tuberous sclerosis • Skin hypopigmentation = ash-leaf spots • Periventricular masses = subependymal astrocytomas

13) Major depressive disorder • This patient has ≥ 5 of the 9 diagnostic symptoms of SIG-E-CAPS for ≥ 2 weeks

14) Shigellosis

• Fever, campy abdominal pain, dysentery = Shigella

• Seizures = common neurologic complication of shigella; associated with fever > 39 °C (102.2 °F)

• Ekiri syndrome = lethal toxic encephalopathy due to shigellosis

• Characterized by rapid development of seizures and coma in patients with high fever and dysentery

15) Shallow, poorly developed acetabulum • Barlow & Ortolani maneuver to screen for developmental dysplasia of the hip

• “click” = femoral head dislocating posteriorly with reduction of the femoral head into the acetabulum

• More common in firstborn girls born in breech position

16) Trimethoprim-Sulfamethoxazole

• TMP-SMX inhibits enzymes in the DNA synthesis pathway → megaloblastic anemia, leukopenia, granulocytopenia

• Avoided with co-administration of leucovorin (folic acid)

17) Lymphocytic infiltration • Hashimoto thyroiditis → lymphocytic infiltrate (autoimmune process)

• Lymphoid aggregates with germinal centers

• MCC of hypothyroidism in iodine-sufficient regions

18) Impetigo contagiosa • Honey-crusted lesions ≈ Impetigo • Unlikely to be herpes simplex since the lips are spared

19) Legg-Calvé-Perthes disease • Commonly presents between 5-7 years old with insidious onset of hip pain

• Slipped capital femoral epiphysis commonly presents in obese pre-teens

20) Aplastic anemia • Aplastic anemia = pancytopenia (↓ RBC, ↓ WBC, ↓ Platelets)

• Aplastic crisis = ↓ Erythrocytes

21) T lymphocytes • T-cell deficit → fungal/viral infections

22) Venous hum

• Innocent, benign murmur in children

• Turbulent flow of venous return in the jugular veins and SVC; occurs during systole

and diastole

• Accentuated or eliminated with head position; disappears when supine or with digital compression of the jugular vein

23) Serum lipid studies

• AAP recommends universal lipid studies for kids age 9-11 (pre-puberty), and again at age 17-21 (post-puberty)

• “heart disease” in father and grandfather ≈ hypercholesterolemia

24) Cruciate incision of the hymen

• Adolescent girl at usually age of menarche presenting with amenorrhea, cyclic

abdominal/pelvic pain and hematocolpos = Imperforate Hymen

• Hematocolpos (blood-filled vagina) → bulging, blue hymen membrane

25) Silver stain of bronchoalveolar fluid • Pneumocystis pneumonia (caused by the yeast-like fungus Pneumocystis jirovecii)

• Mother had history of IV drug use • Baby’s frequent thrush and failure to thrive (FTT) = immunocompromised

26) Mixed metabolic acidosis and respiratory alkalosis

• Salicylate toxicity (early) stimulates medulla respiratory centers → hyperventilation → respiratory alkalosis

• Salicylate toxicity (late) decreases cellular respiration via uncoupling oxidative phosphorylation → anaerobic metabolism → metabolic acidosis

• This child was brought to the ED 20 minutes after her mother found her, not 20 minutes after ingestion of the aspirin...

27) Pathologic fracture of the humerus • Clear pathological fracture of the humerus on x-ray

• Ewing sarcoma → ‘onion skinning’

28) Sinusitis • >10 day history of fever, headache, and nasal discharge

• Post-nasal drip → erythematous posterior pharyngeal wall

29) Bacterial pneumonia • Decreased breath sounds, right lower lobe density (consolidation), abdominal pain (referred pain 2/2 diaphragmatic irritation from basal pneumonia or from overuse of abdominal muscles 2/2 persistent cough)

30) Myotonic dystrophy • Usually presents with facial weakness, hand grip myotonia, dysphagia

• Arises from autosomal dominant expansion of CTG trinucleotide

31) Inguinal hernia • “milked” = reducible hernia

32) Hepatitis A Virus: immune, Hepatitis B Virus: not immune

• Hepatitis A antibody = immune

• Anti-HBc (HBV core antibody); IgM indicates acute/recent infection, IgG indicates

prior exposure or chronic infection

• HBsAg (HBV surface antigen) indicates hepatitis B infection

• Lack of Anti-HBs (HBV surface antibody) indicates no immunity

33) Measurement of serum β-hCG concentration

• Always rule out pregnancy first, even if she hasn’t begun menstruation yet (tanner

stage is highly indicative of impending menstruation)

• X-ray & CT = radiation exposure = dangerous for potential fetus

34) Serial blood cultures • Fever + new systolic murmur (mitral regurgitation) = Endocarditis

35) Elimination of lead from the child’s home • Lead impairs heme synthesis → microcytic anemia

36) Adams-Stokes attack • P waves, no QRS = AV block • High grade AV block (ie, complete or Mobitz type II) = Stokes-Adams attack

• Tx: Pacemaker

37) Bronchoscopy • Foreign body → air-trapping → hyperinflation → hyper-resonance & ↓ breath sounds

• Bronchoscopy for removal of foreign body

38) Pulmonary artery hypertension • Eisenmenger’s syndrome: chronic left-to-right shunting → pulmonary artery HTN → shunt reversal → cyanosis and polycythemia

39) Reduced-calorie diet • Lifestyle (diet and exercise) modification is first-line (exercise should be aerobic; weight training = anaerobic exercise)

40) Phototherapy • Unconjugated hyperbilirubinemia from birth trauma (cephalohematoma)

• This baby has been breast-feeding and has normal stool & urine output

• If the child had a positive Coombs test and signs of acute bilirubin encephalopathy (eg, high-pitched cry, lethargy, poor feeding, and hypotonia), they should be treated with exchange transfusion as this is a medical emergency

• Mild elevation (>10 mg/dL) tx: phototherapy • Severe elevation (>20-25 mg/dL) tx: exchange transfusions

41) Cooking meats completely • Humans and animals are reservoirs for Salmonella species (except Salmonella typhi)

• Humans are the only reservoir for S. tyhphi • Poultry (BBQ chicken), eggs, pets, and turtles are common sources

• Non-typhoidal Salmonella → gastroenteritis

42) Strict hand-washing techniques at the day-care center • Rotavirus is transmitted through the fecal/oral route via contact with contaminated hands, surfaces, and objects.

43) Cerebral edema • Decreasing plasma osmolarity too quickly → fluid shifts from ECF to ICF → ↑ ICP

• ↑ ICP → absence of venous pulsations

44) Physiologic pubertal development • Gynecomastia occurs in ~33% of pubescent boys; goes away with development

45) A 6-week course of oral AZT within 12 hours after delivery * guidelines on this are in flux - unlikely to be tested* • If mother is HIV ⊕ then baby gets 6 weeks of of AZT within 6 hours of birth

• Wether to add on other antiretrovirals after that is based on moms viral load and other risk factors

46) Intravenous cefotaxime • High leukocyte count (indicates infection) warrants antibiotics • She already takes penicillin prophylaxis (the bug she has is probably resistant)

• 3rd generation cephalosporins treats possible meningitis

47) Staphylococcus aureus • Fungal infection → dry skin that cracked and allowed bacteria from the skin to get in → cellulitis 2/2 staph infection → fever & pain

48) Delayed, normal, normal • Child should be sitting up by himself after 6 months (this patient is 9 months old and is still unable)

49) Closure of the ductus arteriosus

• Cyanotic newborn with no improvement on O2 therapy = cardiac cause

• This patient likely has Coarctation of the aorta that is dependent upon the patent

ductus arteriosus (PDA is distal to the coarctation)

• PDA closure → new onset CHF (severe hypotension, poor perfusion, tachypnea,

hepatomegaly, unexplained metabolic acidosis)

50) Voiding cystourethrography

Question is out of date - Should be 'Observation for recurrent symptoms'

• Does not meet indications for VCUG (voiding cystourethrography)

• Posterior urethral valves are the most common cause of UTI in a baby boy

• Voiding cystourethrography checks the posterior urethral valves

• However, cystourethrogram is generally not indicated in first time UTIs unless U/S

shows hydronephrosis, scarring or the patient is < 1 month old

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