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4. Pediatrics MCQs

Practice Set 192 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 3821

Topic: 4. Pediatrics

A neonate sustains multiple fractures during birth. Examination reveals blue sclerae and bowing of the upper and lower extremities. The underlying genetic defect typically involves the substitution of which crucial amino acid in the collagen triple helix?

. Proline
. Lysine
. Glycine
. Hydroxyproline
. Alanine

Correct Answer & Explanation

. Glycine

Explanation

Osteogenesis imperfecta (OI) is primarily caused by mutations in the COL1A1 or COL1A2 genes. These mutations typically lead to the substitution of glycine, the smallest amino acid essential for the tight coiling of the type I collagen triple helix.

Question 3822

Topic: 4. Pediatrics

A 4-year-old child presents with anterior and lateral bowing of the tibia. Radiographs show a pseudarthrosis. Examination reveals axillary freckling and multiple hyperpigmented macules.

What is the genetic mutation associated with this condition?

. Fibrillin-1
. FGFR3
. Neurofibromin
. Merlin
. COMP

Correct Answer & Explanation

. Neurofibromin

Explanation

The patient has Neurofibromatosis type 1 (NF1), characterized by anterolateral tibial bowing and congenital pseudarthrosis. NF1 is caused by a mutation in the NF1 gene on chromosome 17, which encodes the tumor suppressor protein neurofibromin.

Question 3823

Topic: 4. Pediatrics

A 3-year-old boy presents with marked anterolateral bowing of the tibia and an established pseudoarthrosis.

What is the most appropriate surgical treatment principle for managing this specific tibial pathology?

. Observation with serial bracing until skeletal maturity
. Resection of the pseudarthrosis, bone grafting, and rigid intramedullary fixation
. Early amputation at the level of the proximal tibia
. Open reduction and internal fixation with a dynamic compression plate
. Ilizarov bone transport without resection of the fibrous tissue

Correct Answer & Explanation

. Resection of the pseudarthrosis, bone grafting, and rigid intramedullary fixation

Explanation

Congenital pseudarthrosis of the tibia in NF1 is notoriously difficult to heal due to surrounding fibrous hamartoma. The gold standard surgical treatment involves aggressive resection of the hamartomatous tissue, autogenous bone grafting, and rigid intramedullary stabilization.

Question 3824

Topic: 4. Pediatrics

Achondroplasia is the most common form of short-limb dwarfism. At the cellular level, the underlying genetic mutation results in which of the following mechanisms?

. Constitutive activation of FGFR3 inhibiting chondrocyte proliferation
. Loss-of-function mutation in FGFR3 accelerating chondrocyte hypertrophy
. Defective synthesis of Type I collagen leading to brittle osteoid
. Impaired osteoclast function leading to failed bone remodeling
. Defective mineralization of the organic osteoid matrix

Correct Answer & Explanation

. Constitutive activation of FGFR3 inhibiting chondrocyte proliferation

Explanation

Achondroplasia is caused by a gain-of-function mutation in the FGFR3 gene. This results in constitutive activation of the receptor, which paradoxically inhibits chondrocyte proliferation in the proliferative zone of the physis.

Question 3825

Topic: 4. Pediatrics

A 12-year-old boy with a family history of multiple palpable bone bumps presents with a new, rapidly enlarging, painful mass on his distal femur. Radiographs reveal multiple sessile and pedunculated osteocartilaginous lesions pointing away from the joint spaces. What gene mutation is most likely responsible for his underlying baseline condition?

. GNAS
. EXT1 or EXT2
. NF1
. PTPN11
. FGFR3

Correct Answer & Explanation

. EXT1 or EXT2

Explanation

Multiple Hereditary Exostoses (MHE) is an autosomal dominant disorder caused by loss-of-function mutations in the EXT1 or EXT2 genes. These genes synthesize heparan sulfate, and their impairment disrupts normal physeal signaling, leading to multiple osteochondromas.

Question 3826

Topic: 4. Pediatrics

Which of the following skeletal dysplasias is most strongly associated with severe cervical kyphosis in infancy that may spontaneously resolve?

. A. Achondroplasia
. B. Pseudoachondroplasia
. C. Diastrophic Dysplasia
. D. Kniest Dysplasia
. E. Cleidocranial Dysplasia

Correct Answer & Explanation

. C. Diastrophic Dysplasia

Explanation

Correct Answer: CDiastrophic dysplasia is characterized by severe cervical kyphosis in early childhood. While many cases resolve spontaneously as the child grows, some require bracing or surgery if neurological deficits develop.

Question 3827

Topic: 4. Pediatrics

Pseudoachondroplasia is distinguished from Achondroplasia by which of the following clinical features?

. A. Presence of a normal craniofacial appearance
. B. Presence of rhizomelic shortening at birth
. C. Mutation in the FGFR3 gene
. D. Absence of ligamentous laxity
. E. Increased interpedicular distance

Correct Answer & Explanation

. A. Presence of a normal craniofacial appearance

Explanation

Correct Answer: AUnlike Achondroplasia, patients with Pseudoachondroplasia have a normal facial appearance (no frontal bossing or midface hypoplasia). It is caused by a mutation in COMP (Cartilage Oligomeric Matrix Protein) and is not usually evident at birth.

Question 3828

Topic: 4. Pediatrics

In Spondyloepiphyseal Dysplasia Tarda (SED Tarda), what is the typical inheritance pattern and timing of presentation?

. A. Autosomal Dominant; at birth
. B. X-linked Recessive; late childhood/adolescence
. C. Autosomal Recessive; infancy
. D. X-linked Dominant; at birth
. E. Autosomal Dominant; middle age

Correct Answer & Explanation

. B. X-linked Recessive; late childhood/adolescence

Explanation

Correct Answer: BSED Tarda is typically an X-linked recessive condition (mutations in TRAPPC2). It presents later than the congenital form, usually between ages 5 and 10, with trunk shortening and back pain due to platyspondyly.

Question 3829

Topic: 4. Pediatrics

An infant with Achondroplasia presents with central apnea and hypertonia. What is the most likely anatomical cause?

. A. Thoracolumbar gibbus
. B. Foramen magnum stenosis
. C. Atlantoaxial subluxation
. D. L5-S1 spondylolisthesis
. E. Syringomyelia

Correct Answer & Explanation

. B. Foramen magnum stenosis

Explanation

Correct Answer: BForamen magnum stenosis is a serious complication in infants with achondroplasia, potentially leading to compression of the cervicomedullary junction, resulting in apnea, quadriparesis, or sudden infant death syndrome (SIDS).

Question 3830

Topic: 4. Pediatrics

Pseudoachondroplasia is often confused with Achondroplasia. Which of the following features is most helpful in differentiating Pseudoachondroplasia from Achondroplasia?

. Presence of rhizomelic shortening
. Normal craniofacial features and head size
. Presence of ligamentous laxity
. Mutation in the FGFR3 gene
. Severity of the dwarfism

Correct Answer & Explanation

. Normal craniofacial features and head size

Explanation

Correct Answer: BPseudoachondroplasia (caused by a COMP mutation) is distinguished from Achondroplasia by the fact that patients have normal facial features and a normal-sized head. Achondroplasia patients typically have frontal bossing and midface hypoplasia. Additionally, Pseudoachondroplasia is not apparent at birth, whereas Achondroplasia is.

Question 3831

Topic: 4. Pediatrics

A 2-year-old child with Achondroplasia presents with a significant thoracolumbar kyphosis. What is the most appropriate initial management for this spinal deformity?

. Immediate posterior spinal fusion
. Anterior and posterior spinal fusion
. Observation and avoidance of unsupported sitting
. Thoracolumbosacral orthosis (TLSO) in all cases
. Halo-gravity traction

Correct Answer & Explanation

. Observation and avoidance of unsupported sitting

Explanation

Correct Answer: CThoracolumbar kyphosis in Achondroplasia often improves spontaneously once the child begins to walk and develops lumbar lordosis. Initial management focuses on observation and 'back protection,' which includes avoiding 'slumped' unsupported sitting in strollers or carriers. Bracing is reserved for persistent or progressive curves, and surgery is a last resort.

Question 3832

Topic: 4. Pediatrics

An 8-month-old infant with confirmed achondroplasia presents with a flexible thoracolumbar kyphosis of 35 degrees. Neurological examination is normal. What is the most appropriate management?

. Immediate posterior spinal fusion
. Bracing with a TLSO for 23 hours a day
. Observation and avoidance of unsupported sitting
. Anterior and posterior spinal fusion
. Extension casting

Correct Answer & Explanation

. Observation and avoidance of unsupported sitting

Explanation

Thoracolumbar kyphosis is common in infants with achondroplasia and typically resolves spontaneously as the child begins walking and developing lumbar lordosis. Management consists of observation and counseling parents to avoid unsupported sitting.

Question 3833

Topic: 4. Pediatrics

A 7-month-old infant with achondroplasia is noted to have a 40-degree thoracolumbar kyphosis on lateral sitting radiographs. There are no neurological deficits. What is the most appropriate initial management for this spinal deformity?

. Immediate custom thoracolumbosacral orthosis (TLSO) bracing
. Avoidance of early unsupported sitting and implementation of prone positioning
. Posterior spinal fusion from T10 to L3
. Anterior release and posterior spinal fusion
. Suboccipital decompression to address the root cause of the hypotonia

Correct Answer & Explanation

. Avoidance of early unsupported sitting and implementation of prone positioning

Explanation

Thoracolumbar kyphosis in infants with achondroplasia is primarily positional, exacerbated by hypotonia and a large head. It resolves in most cases by delaying unsupported sitting and encouraging prone positioning to build extensor trunk strength.

Question 3834

Topic: 4. Pediatrics
A 15-year-old female with osteogenesis imperfecta type IV presents with hyperreflexia, an abnormal gait, upgoing plantar reflexes, and lower cranial nerve dysfunction. What is the most likely structural diagnosis responsible for her neurological decline?
. Atlantoaxial rotatory fixation
. Syrinx formation within the cervical cord
. Dural ectasia in the lumbosacral spine
. Basilar invagination
. Thoracic disk herniation

Correct Answer & Explanation

. Basilar invagination

Explanation

Basilar invagination occurs in up to 25% of patients with osteogenesis imperfecta, particularly types III and IV. It results from cranial settling over a softened upper cervical spine, leading to brainstem compression and cranial nerve palsies.

Question 3835

Topic: 4. Pediatrics

A 6-month-old infant with achondroplasia is brought to the clinic due to episodes of central sleep apnea, progressive hyperreflexia, and delayed motor milestones. An urgent MRI reveals severe cervicomedullary compression. What is the most appropriate definitive management?

. Observation as the foramen magnum remodels during growth
. Application of a halo vest to stabilize the craniocervical junction
. Suboccipital decompression and C1 laminectomy
. Anterior odontoidectomy via a transoral approach
. Continuous positive airway pressure (CPAP) at night only

Correct Answer & Explanation

. Suboccipital decompression and C1 laminectomy

Explanation

Symptomatic foramen magnum stenosis in infantile achondroplasia is a life-threatening emergency that presents with apnea, cyanosis, and myelopathy. Urgent suboccipital decompression with C1 laminectomy is the definitive treatment to prevent sudden infant death.

Question 3836

Topic: 4. Pediatrics

A key clinical and radiographic feature that helps differentiate an infant with Spondyloepiphyseal Dysplasia Congenita (SEDC) from one with Achondroplasia at birth is:

. The presence of rhizomelic limb shortening in SEDC
. Delayed ossification of the pubic bone and distal femoral epiphyses in SEDC
. The presence of a narrowed interpedicular distance in the lumbar spine in SEDC
. Macrocephaly with frontal bossing in SEDC
. A trident hand appearance in SEDC

Correct Answer & Explanation

. Delayed ossification of the pubic bone and distal femoral epiphyses in SEDC

Explanation

SEDC involves significant delays in the ossification of epiphyses, most notably the absence of ossification in the pubic bones, distal femur, and proximal tibia at birth. Achondroplasia typically presents with normal timing of epiphyseal ossification.

Question 3837

Topic: 4. Pediatrics

An 8-month-old infant with achondroplasia presents with a flexible thoracolumbar kyphosis of 35 degrees. Neurological examination is completely normal. What is the most appropriate initial management?

. Observation and avoidance of unsupported sitting
. Thoracolumbosacral orthosis (TLSO)
. Posterior spinal fusion
. Anterior and posterior spinal fusion
. Laminectomy and decompression

Correct Answer & Explanation

. Observation and avoidance of unsupported sitting

Explanation

Flexible thoracolumbar kyphosis in infants with achondroplasia typically resolves spontaneously when they begin weight-bearing and walking. Management involves observation and avoiding unsupported sitting that exacerbates the deformity.

Question 3838

Topic: 4. Pediatrics

A 2-year-old child with achondroplasia presents with hypotonia, sleep apnea, and delayed motor milestones. MRI reveals severe cervicomedullary compression. Which of the following is the most appropriate treatment?

. Observation with serial MRI
. Continuous positive airway pressure (CPAP)
. Suboccipital decompression with or without C1 laminectomy
. Occipitocervical fusion
. Cervical bracing

Correct Answer & Explanation

. Suboccipital decompression with or without C1 laminectomy

Explanation

Symptomatic foramen magnum stenosis with cervicomedullary compression in achondroplasia requires urgent suboccipital decompression to prevent sudden death or permanent neurological injury. Fusion is rarely required unless gross instability exists.

Question 3839

Topic: 4. Pediatrics

Spondyloepiphyseal Dysplasia Congenita (SEDC) commonly involves atlantoaxial instability due to os odontoideum. Which underlying genetic mutation is responsible for this condition?

. FGFR3
. COL1A1
. COL2A1
. COMP
. DTDST

Correct Answer & Explanation

. COL2A1

Explanation

SEDC is caused by mutations in the COL2A1 gene, which affects type II collagen. This leads to defective endochondral ossification, significantly affecting the spine (platyspondyly) and epiphyses.

Question 3840

Topic: 4. Pediatrics

A 3-year-old child presents with a short trunk, prominent joints, and a cleft palate. Spinal radiographs demonstrate platyspondyly with unique vertical radiolucencies in the vertebral bodies. What is the most likely diagnosis?

. Diastrophic dysplasia
. Kniest dysplasia
. Achondroplasia
. Metatropic dysplasia
. Chondrodysplasia punctata

Correct Answer & Explanation

. Kniest dysplasia

Explanation

Coronal clefts, seen as vertical radiolucencies within the vertebral bodies, are a hallmark radiographic finding in infants and young children with Kniest dysplasia. They are often accompanied by dumbbell-shaped femora.

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