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

USMLE Step 2 CK Lecture Notes 2021: Pediatrics (2020) provides step-by-step explanations to real exam questions, making complex topics easier to understand.

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    USMLE ® Step 2 CK Lecture Notes 2021 Pediatrics medbookvn.com

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    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. This publication is designed to provide accurate information in regard to the subject matter covered as of its publication date, with the understanding that knowledge and best practice constantly evolve. The publisher is not engaged in rendering medical, legal, accounting, or other professional service. If medical or legal advice or other expert assistance is required, the services of a competent profes- sional should be sought. This publication is not intended for use in clinical practice or the delivery of medical care. To the fullest extent of the law, neither the publisher nor the editors assume any liability for any injury and/or damage to persons or property arising out of or related to any use of the material contained in this book. © 2020 by Kaplan, Inc. Published by Kaplan Medical, a division of Kaplan, Inc. 750 Third Avenue New York, NY 10017 All rights reserved. The text of this publication, or any part thereof, may not be reproduced in any manner whatsoever without written permission from the publisher. 10 9 8 7 6 5 4 3 2 1 Course ISBN: 978-1-5062-6147-8 Course Kit ISBN: 978-1-5062-6135-5 Retail ISBN: 978-1-5062-6145-4 Retail Kit ISBN: 978-1-5062-6137-9 Kit item s come as a set and should not be broken out and sold separately. Kaplan Publishing print books are available at special quantity discounts to use for sales promotions, employee premiums, or educational purposes. For more information or to purchase books, please call the Simon & Schuster special sales department at 866-506-1949.

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    Editors William G. Cvetnic, MD, MBA Fellow of the American Academy of Pediatrics Board Certified in Pediatrics and Neonatal-Perinatal Medicine Jacksonville, Florida Eduardo Pino, MD Associate Professor, Department of Pediatrics Marshall University School of Medicine Medical Director, Hoops Family Children’s Hospital Cabell Huntington Hospital Huntington, West Virginia

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    We want to hear what you think. What do you like or not like about the Notes? Please email us at medfeedback@kaplan.com .

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    Chapter Title 00 v 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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    vi USMLE Step 2 CK l Pediatrics Chapter 18: Rheumatic and Vasculitic Disorders 187 Chapter 19: Hematology 197 Chapter 20: Oncology 213 Chapter 21: Neurology 219 Chapter 22: Infectious Disease 237 Chapter 23: Adolescence 261 Index 267 Additional resources available at kaptest.com/usmlebookresources

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    Chapter Title 00 1 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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    2 USMLE 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 Newborn 3 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 S kin 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 H ead 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 e xtremitie S 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 age medbookvn.com

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    4 USMLE 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 Newborn 5 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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    6 USMLE 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 Newborn 7 – 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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    8 USMLE 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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