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4. Pediatrics MCQs

Practice Set 304 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 6061

Topic: 4. Pediatrics

A 9-month-old infant with achondroplasia presents with central sleep apnea, failure to thrive, and hyperreflexia. MRI reveals severe cervicomedullary compression at the foramen magnum. What is the most appropriate definitive management?

. Continuous positive airway pressure (CPAP)
. Ventriculoperitoneal shunt
. Suboccipital craniectomy and C1 laminectomy
. Observation as this often resolves spontaneously
. Halo gravity traction

Correct Answer & Explanation

. Suboccipital craniectomy and C1 laminectomy

Explanation

Central sleep apnea and hyperreflexia in an infant with achondroplasia strongly suggest cervicomedullary compression due to foramen magnum stenosis. The definitive treatment is prompt surgical decompression via suboccipital craniectomy and C1 laminectomy to prevent sudden death.

Question 6062

Topic: 4. Pediatrics

A neonate presents with a prominent forehead, short trunk, and large joints. Radiographs show dumbbell-shaped femora and distinct coronal clefts in the vertebral bodies. Which skeletal dysplasia is the most likely diagnosis?

. Achondroplasia
. Metatropic dysplasia
. Kniest dysplasia
. Morquio syndrome
. Campomelic dysplasia

Correct Answer & Explanation

. Kniest dysplasia

Explanation

Kniest dysplasia is a type II collagenopathy that classically presents with dumbbell-shaped long bones, prominent joints, and coronal clefts in the vertebral bodies on lateral radiographs. Affected individuals also frequently develop progressive kyphoscoliosis.

Question 6063

Topic: 4. Pediatrics

A 3-year-old child with achondroplasia presents with a persistent 40-degree thoracolumbar kyphosis. The child has been walking independently for over a year. Radiographs demonstrate significant anterior wedging of the L1 vertebral body. What is the most appropriate management?

. Observation and reassurance
. Thoracolumbosacral orthosis (TLSO) bracing
. Anterior spinal fusion
. Posterior spinal fusion
. Combined anterior and posterior spinal fusion

Correct Answer & Explanation

. Thoracolumbosacral orthosis (TLSO) bracing

Explanation

Thoracolumbar kyphosis in achondroplasia typically resolves once the child begins walking. However, if the curve persists beyond age 3 or features significant apical vertebral wedging, TLSO bracing is indicated to prevent rigid, progressive deformity.

Question 6064

Topic: 4. Pediatrics

A newborn is evaluated for short-trunk dwarfism, prominent joints, and a cleft palate. Spine radiographs demonstrate severe platyspondyly with classic coronal clefts in the vertebral bodies. A mutation in which gene is most likely responsible?

. FGFR3
. COMP
. COL2A1
. SLC26A2
. SOX9

Correct Answer & Explanation

. COL2A1

Explanation

Kniest dysplasia is a type II collagenopathy caused by a mutation in the COL2A1 gene. Classic spinal radiographic findings in infants include severe platyspondyly and characteristic coronal clefts in the vertebral bodies.

Question 6065

Topic: 4. Pediatrics

A 1-year-old child with achondroplasia is evaluated for sleep apnea, hypotonia, and newly developed hyperreflexia in the lower extremities. What is the most appropriate next step in management?

. Thoracolumbar bracing
. Cervical fusion
. MRI of the craniovertebral junction
. Sleep study and reassurance
. Lumbar decompression

Correct Answer & Explanation

. MRI of the craniovertebral junction

Explanation

Toddlers with achondroplasia presenting with sleep apnea, hyperreflexia, or hypotonia must be urgently evaluated for foramen magnum stenosis. MRI of the craniovertebral junction is the gold standard imaging choice to assess for cervicomedullary compression.

Question 6066

Topic: 4. Pediatrics

A 3-year-old with achondroplasia has a fixed thoracolumbar kyphosis of 45 degrees that has failed to resolve despite a year of independent ambulation. What is the recommended management?

. Observation only
. TLSO bracing
. Anterior spinal fusion
. Posterior instrumented fusion
. Extension casting under anesthesia

Correct Answer & Explanation

. TLSO bracing

Explanation

Most infant thoracolumbar kyphosis in achondroplasia resolves with walking. If a rigid kyphosis >30 degrees persists despite ambulation, an extension TLSO orthosis is the recommended first-line treatment to prevent structural deformity.

Question 6067

Topic: 4. Pediatrics

A newborn is diagnosed with diastrophic dysplasia. What is the underlying genetic mutation, and what is the typical natural history of scoliosis associated with this syndrome?

. DTDST (SLC26A2) mutation / progressive, rigid curves
. COMP mutation / benign, non-progressive curves
. FGFR3 / mild, flexible curves
. COL2A1 / early onset but spontaneously resolving
. COL1A1 / severe kyphoscoliosis requiring early fusion

Correct Answer & Explanation

. DTDST (SLC26A2) mutation / progressive, rigid curves

Explanation

Diastrophic dysplasia is caused by a defect in the sulfate transporter gene DTDST (SLC26A2). The associated scoliosis tends to be early-onset, rapidly progressive, and highly rigid, often requiring complex surgical intervention.

Question 6068

Topic: 4. Pediatrics

A 6-year-old child presents with prominent joints, short-trunk dwarfism, and severe kyphoscoliosis. Radiographs characteristically show coronal clefts in the vertebral bodies and dumbbell-shaped long bones. What is the most likely diagnosis?

. Achondroplasia
. Kniest dysplasia
. Diastrophic dysplasia
. Pseudoachondroplasia
. Cleidocranial dysplasia

Correct Answer & Explanation

. Kniest dysplasia

Explanation

Kniest dysplasia (a Type II collagenopathy) classically presents with short-trunk dwarfism, prominent joints, and severe kyphoscoliosis. Coronal clefts in the vertebrae and dumbbell-shaped long bones are pathognomonic radiographic findings.

Question 6069

Topic: 4. Pediatrics

A newborn presents with rhizomelic shortening of the limbs, frontal bossing, and midface hypoplasia. Radiographs show narrowing of the interpedicular distances in the lower lumbar spine. What is the genetic basis of this condition?

. Defect in type I collagen (COL1A1)
. Mutation in the FGFR3 gene resulting in gain of function
. Mutation in the COMP gene
. Deletion of the RUNX2 gene
. Mutation in the EXT1 gene

Correct Answer & Explanation

. Mutation in the FGFR3 gene resulting in gain of function

Explanation

This presentation is classic for achondroplasia, the most common form of short-limbed dwarfism. It is caused by a gain-of-function mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene, which inappropriately inhibits chondrocyte proliferation in the growth plate.

Question 6070

Topic: 4. Pediatrics

A 9-year-old child presents with waddling gait, knee pain, and restricted joint motion. Radiographs reveal delayed, irregular ossification of the capital femoral epiphyses and a "double-layer" appearance of the patella on the lateral view. Mutations in which of the following genes are most commonly associated with this condition?

. COMP (Cartilage Oligomeric Matrix Protein)
. SOX9
. FGFR3
. Type II collagen (COL2A1)
. CBFA1

Correct Answer & Explanation

. COMP (Cartilage Oligomeric Matrix Protein)

Explanation

Multiple Epiphyseal Dysplasia (MED) commonly presents with delayed, irregular ossification of epiphyses and a double-layer patella. The most common genetic mutation in MED involves the COMP gene, leading to abnormal chondrocyte extracellular matrix.

Question 6071

Topic: 4. Pediatrics

A 4-year-old boy is brought to the clinic for short stature and a waddling gait. His parents note he appeared completely normal at birth and grew normally for the first two years. Examination reveals disproportionate short stature with relatively normal facial features and head circumference. Radiographs show small, irregular epiphyses and metaphyseal flaring. This condition is caused by a mutation in the gene encoding which protein?

. Type X collagen
. FGFR3
. Cartilage Oligomeric Matrix Protein (COMP)
. Type I collagen
. Runx2

Correct Answer & Explanation

. Cartilage Oligomeric Matrix Protein (COMP)

Explanation

Pseudoachondroplasia presents with normal birth length and normal facial features, unlike true achondroplasia. It becomes apparent in early childhood and is caused by mutations in the COMP gene, similarly to Multiple Epiphyseal Dysplasia.

Question 6072

Topic: 4. Pediatrics

A 4-year-old child with frontal bossing, rhizomelic dwarfism, and trident hands is being evaluated. This condition is inherited in an autosomal dominant fashion, though most cases are sporadic. What is the underlying pathophysiology?

. Defect in type 1 collagen synthesis
. Gain-of-function mutation in the FGFR3 gene causing inhibition of chondrocyte proliferation
. Loss-of-function mutation in the RUNX2 gene
. Defect in cartilage oligomeric matrix protein (COMP)
. Mutation in the diastrophic dysplasia sulfate transporter (DTDST) gene

Correct Answer & Explanation

. Gain-of-function mutation in the FGFR3 gene causing inhibition of chondrocyte proliferation

Explanation

Achondroplasia is caused by a gain-of-function mutation in FGFR3, which leads to decreased chondrocyte proliferation in the proliferative zone of the physis. This results in the characteristic rhizomelic dwarfism.

Question 6073

Topic: 4. Pediatrics

A 7-year-old boy presents with short stature, waddling gait, and joint pain. Radiographs demonstrate delayed ossification of multiple epiphyses and a "double-layer" appearance of the patella. What gene is most commonly mutated in the autosomal dominant form of this condition?

. FGFR3
. COL2A1
. COMP
. SLC26A2
. RUNX2

Correct Answer & Explanation

. COMP

Explanation

Multiple Epiphyseal Dysplasia (MED) is most commonly caused by a mutation in the COMP (Cartilage Oligomeric Matrix Protein) gene. The "double-layer" patella is a classic radiographic hallmark of this condition.

Question 6074

Topic: 4. Pediatrics

A 4-year-old child with a known FGFR3 mutation presents for evaluation. Which of the following orthopedic complications is most associated with this condition?

. Atlantoaxial instability
. Thoracolumbar kyphosis
. Slipped capital femoral epiphysis
. Multiple osteochondromas
. Pathologic fractures from minor trauma

Correct Answer & Explanation

. Thoracolumbar kyphosis

Explanation

Achondroplasia (FGFR3 mutation) frequently presents with thoracolumbar kyphosis in infancy, which often resolves with ambulation but can persist. Foramen magnum stenosis is the key cervical issue, unlike the C1-C2 instability seen in Morquio syndrome or Down syndrome.

Question 6075

Topic: Pediatric Hip

A 7-year-old boy presents with waddling gait, knee pain, and short stature. Radiographs demonstrate delayed ossification of the capital femoral epiphyses bilaterally, mimicking Legg-Calve-Perthes disease, with a double-layered patella. What is the inheritance pattern and typical gene involved?

. Autosomal dominant, COMP gene
. Autosomal recessive, DTDST gene
. X-linked recessive, DMD gene
. Autosomal dominant, FBN1 gene
. Autosomal recessive, CBFA1 gene

Correct Answer & Explanation

. Autosomal dominant, COMP gene

Explanation

Multiple epiphyseal dysplasia (MED) is typically autosomal dominant and frequently caused by a mutation in the COMP (Cartilage Oligomeric Matrix Protein) gene. A double-layered patella is a classic radiographic sign of this dysplasia.

Question 6076

Topic: 4. Pediatrics

A 4-year-old child presents with recurrent fractures following minimal trauma. Clinical examination reveals blue sclerae, normal intelligence, and mild bowing of the long bones. The underlying genetic defect primarily impairs which of the following?

. Endochondral ossification
. Osteoclast-mediated bone resorption
. Quantity or quality of type I collagen
. Mineralization of osteoid matrix
. Cartilage oligomeric matrix protein

Correct Answer & Explanation

. Quantity or quality of type I collagen

Explanation

Osteogenesis Imperfecta (OI) is caused by mutations in the COL1A1 or COL1A2 genes. This leads to defective synthesis of type I collagen, resulting in brittle bones, blue sclerae, and dentinogenesis imperfecta.

Question 6077

Topic: 4. Pediatrics

A newborn is diagnosed with short-limbed dwarfism, characteristic "hitchhiker" thumbs, clubfeet, and cauliflower ears. What is the underlying genetic mechanism of this condition?

. Defect in the sulfate transporter gene (SLC26A2)
. Gain-of-function mutation in FGFR3
. Mutation in type II collagen (COL2A1)
. Defect in Runx2/Cbfa1 transcription factor
. Defect in diastrophic-associated homeobox genes

Correct Answer & Explanation

. Defect in the sulfate transporter gene (SLC26A2)

Explanation

Diastrophic dysplasia is an autosomal recessive disorder caused by a mutation in the SLC26A2 gene. This impairs sulfate transport, leading to undersulfated proteoglycans in cartilage matrix.

Question 6078

Topic: 4. Pediatrics

A patient with characteristic rhizomelic shortening and frontal bossing is diagnosed with achondroplasia. The underlying genetic mutation in FGFR3 exerts its effect on the growth plate by which of the following mechanisms?

. Loss of receptor function increasing chondrocyte proliferation
. Constitutive activation inhibiting chondrocyte proliferation
. Apoptosis of hypertrophic chondrocytes
. Failure of primary spongiosa mineralization
. Excessive production of type X collagen

Correct Answer & Explanation

. Constitutive activation inhibiting chondrocyte proliferation

Explanation

Achondroplasia is caused by an autosomal dominant gain-of-function mutation in FGFR3. This constitutive activation abnormally inhibits chondrocyte proliferation in the proliferative zone of the physis.

Question 6079

Topic: 4. Pediatrics

A 6-year-old boy presents with short stature, severe clubfeet, and bilateral swelling of his external ears. Radiographs reveal progressive cervical kyphosis. Which of the following genes is mutated in this patient's condition?

. FGFR3
. COL2A1
. SLC26A2
. COMP
. RUNX2

Correct Answer & Explanation

. SLC26A2

Explanation

Diastrophic dysplasia is characterized by short-limb dwarfism, 'hitchhiker' thumbs, clubfeet, and cauliflower ears. It is caused by an autosomal recessive mutation in the SLC26A2 (DTDST) sulfate transporter gene.

Question 6080

Topic: 4. Pediatrics

An 18-month-old child with a disproportionately large head, frontal bossing, and rhizomelic shortening of the limbs is diagnosed with a condition caused by a gain-of-function mutation in the FGFR3 gene. Which zone of the physis is directly inhibited by this mutation?

. Reserve zone
. Proliferative zone
. Hypertrophic zone
. Zone of provisional calcification
. Primary spongiosa

Correct Answer & Explanation

. Proliferative zone

Explanation

Achondroplasia is caused by a gain-of-function mutation in FGFR3. This directly inhibits chondrocyte proliferation within the proliferative zone of the growth plate.

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