USMLE Step 2 CK Lecture Notes 2021: Pediatrics (2020)

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USMLE
®
Step 2 CK
Lecture Notes
2021
Pediatricsmedbookvn.com

USMLE® is a joint program of the Federation of State Medical Boards (FSMB) and the National
Board of Medical Examiners (NBME), which neither sponsor nor endorse this product.
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Chapter Title 00v
Table of Contents
Chapter 1: The Newborn 1
Chapter 2: Genetics/Dysmorphology 21
Chapter 3: Growth and Nutrition 31
Chapter 4: Development 43
Chapter 5: Behavioral/Psychological Disorders 49
Chapter 6: Immunizations 53
Chapter 7: Child Abuse and Neglect 61
Chapter 8: Respiratory Disease 67
Chapter 9: Allergy and Asthma 81
Chapter 10: Immune-Mediated Disease 91
Chapter 11: Disorders of the Eye 99
Chapter 12: Disorders of the Ear, Nose, and Throat 105
Chapter 13: Cardiology 113
Chapter 14: Gastrointestinal Disease 139
Chapter 15: Renal and Urologic Disorders 155
Chapter 16: Endocrine Disorders 167
Chapter 17: Orthopedic Disorders 179

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Chapter Title 001
Learning Objectives
❏ Calculate an Apgar score
❏ Use knowledge of birth injuries to predict symptomology
❏ Demonstrate understanding of newborn screening, fetal growth/maturity, and
neonatal infections
APGAR SCORE
A newborn infant at birth is noted to have acrocyanosis, heart rate 140/min, and
grimaces to stimulation. She is active and has a lusty cry. What is her Apgar score?
Table 1-1. Apgar Scoring System
Evaluation 0 Points 1 Point 2 Points
Heart rate 0 <100/min >100/min
Respiration None Irregular, shallow, gasps Crying
Color Blue Pale, blue extremities Pink
Tone None Weak, passive Active
Reflex irritability None Facial grimace Active withdrawal
Apgar scores are routinely assessed at 1 and 5 minutes, and every 5 minutes thereafter as long
as resuscitation is continuing.
• The 1-minute score gives an idea of what was going on during labor and delivery.
• The 5-minute score gives an idea of response to therapy (resuscitation).
In general, the Apgar score is not predictive of outcome; however, infants with score 0−3 at
≥5 minutes compared to infants with score 7−10 have a worse neurologic outcome.
The Newborn 1

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2USMLE Step 2 CK l Pediatrics
Newborn Care
• Vitamin K IM
• Prophylactic eye erythromycin
• Umbilical cord care
• Hearing test
• Newborn screening tests
BIRTH INJURIES
On physical exam, a 12-hour-old newborn is noted to have nontender swelling
of the head that does not cross the suture line. What is the most likely diagnosis?
Table 1-2. Common Injuries During Deliveries
Injury Specifics Outcome
Skull fractures In utero from pressure against bones or
forceps; linear: most common
• Linear: no symptoms and no treatment needed
• Depressed: elevate to prevent cortical injury
Brachial palsy Erb-Duchenne: C5–C6; cannot abduct
shoulder; externally rotate and supinate
forearm; Klumpke: C7–C8 ± T1; paralyzed
hand ± Horner syndrome
Most with full recovery (months); depends on
whether nerve was injured or lacerated; Rx: proper
positioning and partial immobilization; massage
and range of motion exercises; if no recovery in
3–6 mo, then neuroplasty
Clavicular fracture Especially with shoulder dystocia in vertex
position and arm extension in breech
Palpable callus within a week; Rx: with
immobilization of arm and shoulder
Facial nerve palsy Entire side of face with forehead; forceps
delivery or in utero pressure over facial nerve
Improvement over weeks (as long as fibers were
not torn); need eye care; neuroplasty if no
improvement (torn fibers)
Caput succedaneum Diffuse edematous swelling of soft tissues of
scalp; crosses suture lines
Disappears in first few days; may lead to molding
for weeks
Cephalohematoma Subperiosteal hemorrhage: does not cross
suture lines
May have underlying linear fracture; resolve in 2 wk
to 3 mo; may calcify; jaundice

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Chapter 1 l The Newborn3
PHYSICAL EXAMINATION
A newborn infant has a blue-gray pigmented lesion on the sacral area. It is clearly
demarcated and does not fade into the surrounding skin. What is the most likely diagnosis?
A newborn has a flat, salmon-colored lesion on the glabella, which becomes darker red
when he cries. What is the best course of management?
Table 1-3. Physical Examination—Common Findings
Finding/Diagnosis Description/Comments
Skin
Cutis marmorata Lacy, reticulated vascular pattern over most of body when baby is cooled; improves over first
month; abnormal if persists
Salmon patch
(nevus simplex)
Pale, pink vascular macules; found in nuchal area, glabella, eyelids; usually disappears
Mongolian spots Blue to slate-gray macules; seen on presacral, back, posterior thighs; > in nonwhite infants;
arrested melanocytes; usually fade over first few years; differential: child abuse
Erythema toxicum,
neonatorum
Firm, yellow-white papules/pustules with erythematous base; peaks on second day of life; contain
eosinophils; benign
Hemangioma Superficial: bright red, protuberant, sharply demarcated; most often appear in first 2 months;
most on face, scalp, back, anterior chest; rapid expansion, then stationary, then involution (most
by 5–9 years of age); Rx: beta blockers, embolization; deeper: bluish hue, firm, cystic, less likely
to regress; Rx: (steroids, pulsed laser) only if large and interfering with function
Head
Preauricular
tags/pits
Look for hearing loss and genitourinary anomalies.
Coloboma of iris Cleft of lid, iris, lens, retina, or choroid. In iris, manifests as keyhole appearance at the 6 o’clock
position. May be autosomal-dominant or part of CHARGE syndrome.
Leukocoria—white
reflex
Retinoblastoma; cataract; retinopathy of prematurity; retinal detachment; larval granulomatosis
Aniridia Hypoplasia of iris; defect may go through to retina; association with Wilms tumor
extremitieS
Polydactyly Extra digit, partial digit, or cleft digit after the 4th finger (ulnar side); world’s most common minor
malformation; usually surgically removed at 1–2 years of agemedbookvn.com

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4USMLE Step 2 CK l Pediatrics
NEWBORN SCREENING
A 1-month-old fair-haired, fair-skinned baby presents with projectile vomiting of
4 days’ duration. Physical exam reveals a baby with eczema and a musty odor.
Which screening test would most likely be abnormal?
As per the American College of Medical Genetics, every newborn is screened for a core
panel of 29 disorders, with an additional 25 recommended (Expanded Newborn Screening
Program; varies per state).
• All states now use tandem mass spectrometry; typically done after 24–48 hrs of
feedings prior to baby leaving the birth hospital
• With early discharge, may be performed at first postnatal visit (3–5 days) for
improved accuracy
• In addition to a heel stick blood sample, current program also includes a hearing
test and pulse oximetry for critical congenital heart disease.
Examples of the more common disorders in the expanded program include:
• Phenylketonuria, tyrosinemia type I, 21-hydroxylase deficiency, classic
galactosemia
• HbS/β-thal, Hb SS, HbS/HbC
• Congenital hypothyroidism
• Cystic fibrosis
Table 1-4. Two Newborn Screening Diseases*
Phenylketonuria (PKU) Classic Galactosemia
Defect Phenylalanine hydroxylase;
accumulation of PHE in body
fluids and central nervous system
Gal-1-P uridylyltransferase deficiency;
accumulation of gal-1-P with injury to
kidney, liver, and brain
Presentation Intellectual disability vomiting,
growth retardation, purposeless
movements, athetosis, seizures
Jaundice (often direct), hepatomegaly,
vomiting, hypoglycemia, cataracts,
seizures, poor feeding, poor weight
gain, intellectual disability
Associations Fair hair, fair skin, blue eyes,
tooth abnormalities,
microcephaly
Predisposition to E. coli sepsis;
developmental delay, speech
disorders, learning disabilities
Other
comments
Normal at birth; gradual MR over
first few months
May begin prenatally—transplacental
galactose from mother
Treatment Low PHE diet for life No lactose—reverses growth failure,
kidney and liver abnormalities and
cataracts, but not
neurodevelopmental problems
G-1-P, galactose-1-phosphate; PHE, phenylalanine
*Items in bold have a greater likelihood of appearing on the exam.

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Chapter 1 l The Newborn5
Hearing Loss
Pediatric hearing loss is more prevalent than diabetes mellitus and all childhood cancers. A
universal newborn hearing screening is recommended prior to newborn discharge, with the
goal of evaluating all hearing loss by age 3 months. Usually the otoacoustic emissions test (OAE)
is used, where a small earphone/microphone is placed in the ear and sounds are played.
• If hearing is normal, an echo is reflected back into the ear canal and is measured
by the microphone.
• If hearing is not normal (patient does not pass), newborns are given the audi-
tory brainstem response test (ABR) (most accurate hearing measure through age
6 months). Sounds are presented through a small earphone, measured with head
electrodes, and analyzed by a computer.
• Normal OAE: intact hearing through the cochlea
• Normal ABR: also establishes the integrity of the auditory nerve
As for the causes of hearing loss, up to 60% prelingual is genetic (>60 gene loci, >500 syndromes
with hearing loss); 70-80% is autosomal recessive, with 50% having a defect in connexin 26
(a gap junction protein). Examples include Waardenburg syndrome (most common autosomal
dominant condition with hearing loss), neurofibromatosis-2 (AD), Alport syndrome (AR).
Up to 25% are nongenetic and up to 25% are idiopathic. Examples include CMV (most com-
mon congenital cause; then other congenital infections); otitis media with effusion (OME)
(most common childhood cause); bacterial meningitis, especially pneumococcus (occurs
early and in >30%); trauma, especially to temporal bone; medication (aminoglycosides, loop
diuretics, cisplatin); acoustic (loud music, especially with earbuds/phones; audiograms show
high-frequency loss at 4,000 Hz).
FETAL GROWTH AND MATURITY
Table 1-5. Intrauterine Growth Restriction (IUGR)
Type Reason Main Etiologies Complications
Symmetric Early, in utero
insult that
affects growth
of most organs
Genetic syndromes,
chromosomal
abnormalities, congenital
infections, teratogens,
toxins
Etiology dependent;
delivery of oxygen and
nutrients to vital organs
usually normal
Asymmetric
(head sparing)
Relatively late
onset after fetal
organ
development;
abnormal
delivery of
nutritional
substances and
oxygen to the
fetus
Uteroplacental
insufficiency secondary to
maternal diseases
(malnutrition, cardiac,
renal, anemia) and/or
placental dysfunction
(hypertension,
autoimmune disease,
abruption)
Neurologic (asphyxia) if
significant decreased
delivery of oxygen to
brain

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6USMLE Step 2 CK l Pediatrics
Gestational Age and Size at Birth
Preterm Large for Gestational Age
(LGA)—Fetal Macrosomia
Post-term
• Premature—liveborn
infants delivered prior to
37 weeks as measured
from the first day of the
last menstrual period
• Low birth weight (<2,500
grams), possibly due to
prematurity, IUGR, or
both
• Birth weight >4,500
grams at term
• Predisposing factors:
obesity, diabetes
• Higher incidence of birth
injuries and congenital
anomalies
• Infants born after 42
weeks’ gestation from last
menstrual period
• When delivery is delayed
≥3 weeks past term,
significant increase in
mortality
• Characteristics
– Increased birth weight
– Absence of lanugo
– Decreased/absent
vernix
– Desquamating, pale,
loose skin
– Abundant hair, long
nails
– If placental insufficiency,
may be meconium
staining
ENDOCRINE DISORDERS
Infants of Diabetic Mothers
You are called to see a 9.5-pound newborn infant who is jittery. Physical exam reveals
a large plethoric infant who is tremulous. A murmur is heard. Blood sugar is low.
• Maternal hyperglycemia (types I and II DM) → fetal hyperinsulinemia
• Insulin is the major fetal growth hormone → increase in size of all organs except
the brain
• Major metabolic effect is at birth with sudden placental separation → hypoglycemia
• Infants may be large for gestational age and plethoric (ruddy).
• Other metabolic findings: hypocalcemia and hypomagnesemia (felt to be a result
of delayed action of parathyroid hormone)
• Common findings
– Birth trauma (macrosomia)
– Tachypnea (transient tachypnea, respiratory distress syndrome, cardiac failure,
hypoglycemia)
– Cardiomegaly—asymmetric septal hypertrophy (insulin effect, reversible)
– Polycythemia (and hyperviscosity) → hyperbilirubinemia → jaundice

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Chapter 1 l The Newborn7
– Renal vein thrombosis (flank mass, hematuria, thrombocytopenia) from polycythemia
– Increased incidence of congenital anomalies
° Cardiac—especially VSD, ASD, transposition
° Small left colon syndrome (transient delay in development of left side of
colon; presents with abdominal distention)
° Caudal regression syndrome: spectrum of structural neurologic defects of
the caudal region of spinal cord which may result in neurologic impairment
(hypo, aplasia of pelvis & LE)
• Prognosis—Infants of diabetic mothers are more predisposed to diabetes and LGA
infants are at increased risk of childhood obesity.
• Treatment—careful monitoring and glucose control during pregnancy + close
monitoring of infant after delivery; early frequent feeds (oral, NG if hypoglycemia
continues) followed by IV dextrose if euglycemia has not resulted
Clinical Recall
Which of the following is commonly seen in infants of diabetic mothers?
A. Microsomia
B. Small heart size
C. Polycythemia
D. Renal artery thrombosis
E. Slow respiratory rate
Answer: C
RESPIRATORY DISORDERS
Pneumonia
Choanal atresia
Respiratory Distress
Respiratory Nonrespiratory
Respiratory
distress
syndrome
Transient
tachypnea
of the
newborn
Meconium
aspiration
syndrome
Diaphragmatic hernia
Cardiac: cyanotic CHD
Heme: anemia, polycythemia
Other: infectious, metabolic, neurologic
Figure 1-1. Respiratory Distress

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8USMLE Step 2 CK l Pediatrics
Respiratory Distress Syndrome (RDS)
Shortly after birth, a 33-week gestation infant develops tachypnea, nasal flaring,
and grunting and requires intubation. Chest radiograph shows a hazy, ground-glass
appearance of the lungs.
• Deficiency of mature surfactant (surfactant matures over gestation with the addition
of phosphatidyl groups; therefore, the incidence of surfactant deficiency diminishes
toward term.)
• Inability to maintain alveolar volume at end expiration → decreased functional
residual capacity and atelectasis
• Primary initial pulmonary hallmark is hypoxemia. Then, hypercarbia and respiratory
acidosis ensue.
• Diagnosis
– Best initial diagnostic test—chest radiograph
° Findings: ground-glass appearance, low lung volume, air bronchograms
– Most accurate diagnostic test—L/S ratio (part of complete lung profile; lecithin-to-
sphingomyelin ratio)
° Done on amniotic fluid prior to birth
• Best initial treatment—oxygen
• Most effective treatment—intubation and exogenous surfactant administration
• Primary prevention
– Avoid prematurity (tocolytics)
– Antenatal betamethasone
Transient Tachypnea of the Newborn (TTN)
• Slow absorption of fetal lung fluid → decreased pulmonary compliance and tidal
volume with increased dead space
• Tachypnea after birth
• Generally minimal oxygen requirement
• Common in term infant delivered by Cesarean section or rapid second stage
of labor
• Chest x-ray (best test)—air-trapping, fluid in fissures, perihilar streaking
• Rapid improvement generally within hours to a few days
Meconium Aspiration
• Meconium passed as a result of hypoxia and fetal distress; may be aspirated in utero or
with the first postnatal breath → airway obstruction and pneumonitis → failure and
pulmonary hypertension
• Chest x-ray (best test)—patchy infiltrates, increased AP diameter, flattening of
diaphragm
• Other complications—air leak (pneumothorax, pneumomediastinum)

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