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
fractures
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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