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4. Pediatrics MCQs

Practice Set 296 of 334

This practice set contains high-yield board review questions covering key concepts in 4. Pediatrics. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 5901

Topic: 4. Pediatrics

Parents of a 6-month-old infant with achondroplasia report that the child has episodes of sleep apnea, snoring, and difficulty feeding. Neurological exam reveals hyperreflexia in the lower extremities. What is the most critical next step in management?

. Thoracolumbar bracing for infantile kyphosis
. Observation, as this is a typical self-limiting phase of achondroplasia
. Urgent MRI of the cervical spine and craniocervical junction
. Initiation of growth hormone therapy
. Electromyography of the lower extremities

Correct Answer & Explanation

. Urgent MRI of the cervical spine and craniocervical junction

Explanation

Infants with achondroplasia are at high risk for foramen magnum stenosis, which can present with sleep apnea, hyperreflexia, and hypotonia. Urgent evaluation with an MRI of the craniocervical junction is required to assess for cord compression, which may necessitate surgical decompression to prevent sudden death.

Question 5902

Topic: 4. Pediatrics

A skeletal survey of a child with achondroplasia will typically demonstrate which of the following pathognomonic pelvic radiographic findings?

. Coxa valga with a remarkably deep acetabulum
. Champagne glass pelvic cavity with squared iliac wings
. Protrusio acetabuli with an hourglass appearance
. A widened pubic symphysis and completely hypoplastic ilia
. Vertical acetabular roofs with narrowed greater sciatic notches

Correct Answer & Explanation

. Champagne glass pelvic cavity with squared iliac wings

Explanation

Achondroplasia classically presents with a 'champagne glass' pelvic cavity, which is wider than it is deep. Additional defining radiographic findings include squared, abbreviated iliac wings, horizontal acetabular roofs, and narrow greater sciatic notches.

Question 5903

Topic: 4. Pediatrics

A 4-year-old child with disproportionate short stature is diagnosed with achondroplasia. What is the underlying genetic mutation and its typical inheritance pattern?

. FGFR3, Autosomal Dominant
. FGFR3, Autosomal Recessive
. COL1A1, Autosomal Dominant
. COMP, Autosomal Dominant
. CBFA1, Autosomal Dominant

Correct Answer & Explanation

. FGFR3, Autosomal Dominant

Explanation

Achondroplasia is caused by a gain-of-function mutation in the FGFR3 gene, inherited in an autosomal dominant pattern. Approximately 80% of cases are due to de novo mutations associated with advanced paternal age.

Question 5904

Topic: 4. Pediatrics

A 5-year-old child presents with disproportionate short stature, normal facies, and marked joint laxity. Radiographs demonstrate delayed epiphyseal ossification and irregular metaphyses. Genetic testing reveals a mutation in the COMP (Cartilage Oligomeric Matrix Protein) gene. What is the most likely diagnosis?

. Achondroplasia
. Hypochondroplasia
. Multiple Epiphyseal Dysplasia
. Pseudoachondroplasia
. Spondyloepiphyseal Dysplasia Congenita

Correct Answer & Explanation

. Pseudoachondroplasia

Explanation

Pseudoachondroplasia is an autosomal dominant disorder caused by mutations in the COMP gene. Unlike true achondroplasia, patients have normal facial features and head circumference at birth, with growth failure and joint laxity becoming apparent in early childhood.

Question 5905

Topic: 4. Pediatrics

Parents bring their 6-month-old infant with short-limbed dwarfism for evaluation. The child has hypotonia and hyperreflexia. An MRI of the cervicomedullary junction is ordered. What is the primary cause of the underlying pathology at this anatomical site in this condition?

. Defective endochondral ossification of the cranial base
. Premature closure of the sagittal suture
. Defective intramembranous ossification of the calvaria
. Atlantoaxial instability due to odontoid hypoplasia
. Hypertrophy of the ligamentum flavum

Correct Answer & Explanation

. Defective endochondral ossification of the cranial base

Explanation

Achondroplasia results in defective endochondral ossification, which affects the long bones and the cranial base. This leads to a narrowed foramen magnum, which can cause cervicomedullary compression in infants.

Question 5906

Topic: 4. Pediatrics

A newborn is evaluated for skeletal dysplasia. Physical examination reveals short limbs, clubfeet, 'hitchhiker' thumbs, and cystic swelling of the external ears (cauliflower ears). Which of the following gene mutations is most likely responsible for this phenotype?

. FGFR3
. SLC26A2
. COMP
. COL2A1
. SOX9

Correct Answer & Explanation

. SLC26A2

Explanation

The clinical presentation is classic for diastrophic dysplasia. It is inherited in an autosomal recessive pattern due to a mutation in the SLC26A2 gene, which encodes a sulfate transporter.

Question 5907

Topic: 4. Pediatrics

A 6-year-old child presents with a history of frequent long bone fractures, blue sclerae, and early-onset hearing loss. A genetic defect in which of the following processes is primarily responsible for this clinical presentation?

. Defective formation of the ruffled border in osteoclasts
. Impaired synthesis of cartilage oligomeric matrix protein
. Defective triple helix formation of type I collagen
. Gain-of-function mutation in fibroblast growth factor receptor 3
. Deficient activity of carbonic anhydrase II

Correct Answer & Explanation

. Defective triple helix formation of type I collagen

Explanation

The patient has Osteogenesis Imperfecta, which is most commonly caused by mutations in the COL1A1 or COL1A2 genes. This leads to defective synthesis and triple helix formation of type I collagen, making bones brittle.

Question 5908

Topic: 4. Pediatrics

A newborn is noted to have severe short-limbed dwarfism, a "hitchhiker" thumb deformity, clubfeet, and cystic swelling of the external ear (cauliflower ear). Which of the following genes is mutated in this autosomal recessive skeletal dysplasia?

. FGFR3
. COMP
. SLC26A2
. COL2A1
. RUNX2

Correct Answer & Explanation

. SLC26A2

Explanation

The clinical picture describes diastrophic dysplasia, which is caused by a mutation in the SLC26A2 gene. This gene encodes a sulfate transporter essential for proper cartilage matrix sulfation.

Question 5909

Topic: 4. Pediatrics

A 6-year-old child presents with short-limbed dwarfism, a waddling gait, and prominent joint laxity. Unlike achondroplasia, the child has a completely normal facial appearance. Radiographs show delayed epiphyseal ossification and irregular metaphyses. A mutation in which of the following genes is responsible?

. FGFR3
. RUNX2
. COMP
. COL2A1
. SOX9

Correct Answer & Explanation

. COMP

Explanation

Pseudoachondroplasia is distinguished from achondroplasia by normal facies, normal intelligence, and marked joint laxity. It is caused by mutations in the Cartilage Oligomeric Matrix Protein (COMP) gene.

Question 5910

Topic: 4. Pediatrics
A 9-year-old boy sustains a pathologic fracture of the proximal humerus after a minor fall. Radiographs show a centrally located, cystic lesion in the metaphysis extending to the physis, featuring a "fallen leaf" sign. Which of the following statements is true regarding the classification of this lesion?
. It is 'latent' because it caused a pathologic fracture.
. It is 'active' if it remains adjacent to the physis.
. It requires immediate en bloc resection.
. It is primarily composed of spindle cells and multinucleated giant cells.
. The fluid within the cyst typically has high levels of factor VIII.

Correct Answer & Explanation

. It is 'active' if it remains adjacent to the physis.

Explanation

Unicameral bone cysts (UBCs) are classified as 'active' if they are adjacent to (within 1 cm of) the physis. They are 'latent' if they have migrated away from the physis into the diaphysis as the bone grows.

Question 5911

Topic: 4. Pediatrics

A 14-month-old male with achondroplasia presents with central sleep apnea, hyperreflexia, and hypotonia.

What is the most critical next step in his evaluation?

. Polysomnography alone
. Cervical spine flexion-extension radiographs
. MRI of the craniovertebral junction
. Genetic testing for FGFR3 mutation
. Observation as this is a normal developmental variant

Correct Answer & Explanation

. MRI of the craniovertebral junction

Explanation

Infants with achondroplasia are at high risk for foramen magnum stenosis, which can cause cervicomedullary compression leading to central sleep apnea, myelopathy, and sudden death. MRI of the craniovertebral junction is critical for evaluation and surgical planning for possible decompression.

Question 5912

Topic: 4. Pediatrics

An 8-month-old infant with achondroplasia presents with delayed motor milestones, hypotonia, and witnessed episodes of central sleep apnea.

What is the most appropriate next step in evaluation?

. Overnight polysomnography and CPAP titration
. Skeletal survey to assess for atlantoaxial instability
. MRI of the craniocervical junction
. Genetic testing for FGFR3 mutation
. Measurement of serum alkaline phosphatase

Correct Answer & Explanation

. MRI of the craniocervical junction

Explanation

Infants with achondroplasia are at high risk for foramen magnum stenosis, leading to cervicomedullary compression that presents with hypotonia, hyperreflexia, or central sleep apnea. MRI of the craniocervical junction is the gold standard for diagnosing this potentially lethal complication, which requires urgent surgical suboccipital decompression.

Question 5913

Topic: 4. Pediatrics
An infant born at 38 weeks gestation is noted to have profound osteopenia, severe limb deformities with multiple acute and healing fractures, and deep blue sclerae. The infant succumbs to respiratory failure secondary to a small, frail thorax shortly after birth. According to the Sillence classification, which type of osteogenesis imperfecta does this patient have?
. Type I
. Type II
. Type III
. Type IV
. Type V

Correct Answer & Explanation

. Type II

Explanation

Sillence Type II osteogenesis imperfecta is the perinatal lethal form. It is characterized by severe bone fragility, multiple in utero fractures, profound deformities, and death in the neonatal period, typically due to pulmonary hypoplasia and respiratory failure.

Question 5914

Topic: 4. Pediatrics

A 12-month-old infant with achondroplasia presents for a routine check-up. The parents note a prominent outward curve in the child's lower back when sitting upright. Radiographs confirm a moderate thoracolumbar kyphosis.

What is the most appropriate initial management for this spinal finding?

. Immediate posterior spinal fusion
. Rigid thoracolumbar orthosis (TLSO) bracing for 23 hours a day
. Avoidance of unsupported sitting and observation
. Anterior and posterior spinal fusion
. Growth-friendly spinal instrumentation (e.g., growing rods)

Correct Answer & Explanation

. Avoidance of unsupported sitting and observation

Explanation

Thoracolumbar kyphosis is common in infants with achondroplasia due to generalized hypotonia and relatively large head size. The vast majority (>90%) will spontaneously resolve once the child begins to walk and develop lumbar lordosis. Initial management consists of avoiding unsupported sitting and observation.

Question 5915

Topic: 4. Pediatrics

Hereditary Multiple Exostoses (HME) is an autosomal dominant condition linked to mutations in the EXT1 and EXT2 genes. Which of the following best describes the pathophysiologic consequence of these genetic mutations?

. Overexpression of fibroblast growth factor receptor 3 (FGFR3)
. Defective synthesis of heparan sulfate proteoglycans
. Abnormal cleavage of type II collagen
. Constitutive activation of the Wnt/beta-catenin pathway
. Inhibition of parathyroid hormone-related peptide (PTHrP)

Correct Answer & Explanation

. Defective synthesis of heparan sulfate proteoglycans

Explanation

EXT1 and EXT2 genes encode glycosyltransferases responsible for synthesizing heparan sulfate. Mutations lead to shortened heparan sulfate chains, disrupting normal chondrocyte proliferation and Indian hedgehog (Ihh) signaling at the growth plate.

Question 5916

Topic: 4. Pediatrics

A 12-year-old male with Hereditary Multiple Exostoses (HME) presents for routine evaluation.

Which of the following best describes the underlying molecular pathophysiology of his condition?

. Mutation in the FGFR3 gene
. Defective synthesis of heparan sulfate
. Overexpression of MDM2
. Mutation in the GNAS1 gene
. Defect in type I collagen synthesis

Correct Answer & Explanation

. Defective synthesis of heparan sulfate

Explanation

HME is caused by mutations in the EXT1 or EXT2 genes, which are tumor suppressor genes responsible for heparan sulfate synthesis. Reduced heparan sulfate leads to abnormal Indian hedgehog (Ihh) signaling and premature hypertrophic differentiation of chondrocytes. FGFR3 mutations are associated with achondroplasia.

Question 5917

Topic: 4. Pediatrics

Osteochondromas in patients with Hereditary Multiple Exostoses characteristically point away from the adjacent joint as they grow. Pathophysiologically, these lesions originate from aberrant endochondral ossification occurring in which specific region?

. Hypertrophic zone of the physis
. Groove of Ranvier
. Zone of provisional calcification
. Primary spongiosa
. Resting zone of the physis

Correct Answer & Explanation

. Groove of Ranvier

Explanation

Osteochondromas arise from a defect in the perichondrial ring (Groove of Ranvier). This allows physeal chondrocytes to herniate and grow perpendicular to the normal bone axis, eventually pointing away from the joint due to muscle pull.

Question 5918

Topic: 4. Pediatrics

A 10-year-old girl is evaluated for multiple painless, bony bumps around her knees and wrists. Radiographs reveal multiple osteochondromas pointing away from the joint line.

Which of the following accurately describes the molecular pathogenesis of her condition?

. Mutation in GNAS resulting in increased intracellular cAMP
. Loss-of-function mutation in EXT1 or EXT2 causing decreased heparan sulfate synthesis
. Gain-of-function mutation in FGFR3 causing premature physeal closure
. Overexpression of MDM2 and CDK4 leading to uncontrolled cell cycle progression
. Mutation in the RET proto-oncogene

Correct Answer & Explanation

. Loss-of-function mutation in EXT1 or EXT2 causing decreased heparan sulfate synthesis

Explanation

Hereditary Multiple Exostoses (HME) is an autosomal dominant condition caused by mutations in the EXT1 or EXT2 genes. This leads to a defect in heparan sulfate synthesis, disrupting normal chondrocyte regulation at the physis.

Question 5919

Topic: Pediatric Upper Extremity & Spine

A 6-year-old boy sustains a supracondylar humerus fracture. Which of the following physical examination findings is most characteristic of the most common nerve palsy associated with this injury?

. Inability to extend the wrist
. Inability to flex the interphalangeal joint of the thumb
. Decreased sensation over the dorsal first web space
. Inability to abduct the fingers
. Decreased sensation over the volar tip of the index finger

Correct Answer & Explanation

. Inability to flex the interphalangeal joint of the thumb

Explanation

Correct Answer: BThe most common nerve palsy seen with supracondylar humerus fractures is a neurapraxia of the anterior interosseous branch of the median nerve (AIN). The AIN innervates the flexor pollicis longus, the flexor digitorum profundus to the index and middle fingers, and the pronator quadratus. A palsy results in the inability to flex the interphalangeal joint of the thumb and the distal interphalangeal joint of the index finger. It is a purely motor nerve, so sensation remains intact. Nearly all cases resolve spontaneously without surgical intervention.

Question 5920

Topic: Pediatric Upper Extremity & Spine

A 6-year-old boy sustains a displaced supracondylar humerus fracture. Post-reduction, he is unable to flex the interphalangeal joint of his thumb. While this specific deficit represents the most common nerve palsy associated with this injury, which of the following nerve injuries is the second most common nerve palsy associated with this fracture pattern?

. Ulnar nerve
. Radial nerve
. Median nerve (main trunk)
. Anterior interosseous nerve
. Posterior interosseous nerve

Correct Answer & Explanation

. Radial nerve

Explanation

Correct Answer: BThe patient's inability to flex the interphalangeal joint of the thumb indicates a neurapraxia of the anterior interosseous branch of the median nerve (AIN). AIN palsy is the most common nerve palsy seen with supracondylar humerus fractures in children. This is followed closely by radial nerve palsy, making it the second most common. Nearly all cases of neurapraxia following supracondylar humerus fractures resolve spontaneously without the need for surgical exploration.

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