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’