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4. Pediatrics MCQs

Practice Set 198 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 3941

Topic: 4. Pediatrics

A 10-year-old patient with achondroplasia develops progressive symptomatic genu varum. What is the primary anatomical driver of this deformity?

. Medial tibial plateau collapse from avascular necrosis
. Premature closure of the medial distal femoral physis
. Relative overgrowth of the fibula compared to the tibia
. Severe lateral collateral ligament laxity

Correct Answer & Explanation

. Relative overgrowth of the fibula compared to the tibia

Explanation

Genu varum in achondroplasia is primarily caused by asymmetric growth, specifically the overgrowth of the fibula relative to the shorter tibia. This creates a deforming force that bows the tibia into varus.

Question 3942

Topic: 4. Pediatrics

A newborn is evaluated for multiple musculoskeletal anomalies. Examination reveals severe shortening of the limbs, bilateral clubfeet, "hitchhiker" thumbs, and swelling of the external ears (cauliflower ears). A mutation in which of the following genes is responsible for this condition?

. FGFR3
. COMP
. SLC26A2 (DTDST)
. COL2A1
. CBFA1 (RUNX2)

Correct Answer & Explanation

. SLC26A2 (DTDST)

Explanation

Diastrophic dysplasia is characterized by short stature, hitchhiker thumbs, cauliflower ears, and severe clubfeet. It is an autosomal recessive disorder caused by a mutation in the SLC26A2 sulfate transporter gene.

Question 3943

Topic: 4. Pediatrics
A 5-year-old child presents with disproportionate short stature characterized by a short trunk and barrel chest. Radiographs reveal platyspondyly, delayed ossification of the femoral heads, and severe coxa vara. Visual and hearing assessments show myopia and sensorineural hearing loss. The primary defect involves which of the following collagens?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type II collagen

Explanation

Spondyloepiphyseal dysplasia congenita (SEDC) affects the spine and epiphyses, causing a short-trunk dwarfism with visual and hearing impairments. It is caused by mutations in the COL2A1 gene, which encodes Type II collagen.

Question 3944

Topic: 4. Pediatrics

A 7-year-old child presents with short-limb dwarfism, joint laxity, and early-onset osteoarthritis. Unlike achondroplasia, the patient's facial features and head circumference are completely normal. Radiographs show delayed epiphyseal ossification and irregular metaphyses. A mutation in the COMP (Cartilage Oligomeric Matrix Protein) gene is identified. What is the diagnosis?

. Achondroplasia
. Pseudoachondroplasia
. Multiple epiphyseal dysplasia
. Diastrophic dysplasia
. Hypochondroplasia

Correct Answer & Explanation

. Pseudoachondroplasia

Explanation

Pseudoachondroplasia presents with severe short-limb dwarfism but normal facies and normal intelligence, caused by a COMP gene mutation. Multiple epiphyseal dysplasia (MED) can also have COMP mutations but typically lacks the severe short-limb dwarfism seen here.

Question 3945

Topic: Pediatric Hip
A 6-year-old boy presents with bilateral hip pain and a waddling gait. Radiographs reveal bilateral, symmetric fragmentation and flattening of the femoral capital epiphyses, with normal acetabuli and normal spine radiographs. His father had similar early-onset arthritis. Which of the following best differentiates this condition from Legg-Calvé-Perthes disease?
. Unilateral involvement is typical in MED
. Symmetric, bilateral involvement and autosomal dominant inheritance favor MED
. Presence of platyspondyly favors MED
. Elevated inflammatory markers favor MED
. Scoliosis is a hallmark of MED

Correct Answer & Explanation

. Symmetric, bilateral involvement and autosomal dominant inheritance favor MED

Explanation

Multiple Epiphyseal Dysplasia (MED) usually presents with symmetric, bilateral epiphyseal changes and has an autosomal dominant inheritance. Legg-Calvé-Perthes disease is predominantly unilateral and lacks a strong inherited pattern.

Question 3946

Topic: 4. Pediatrics

A 6-month-old infant with achondroplasia presents with hypotonia, central apnea during sleep, and hyperreflexia. What is the most appropriate next step in management?

. Observation as this is a normal variant in achondroplasia
. Prescribe continuous positive airway pressure (CPAP)
. MRI of the cervical spine and craniocervical junction
. Suboccipital decompression and C1 laminectomy
. Treatment with recombinant human growth hormone

Correct Answer & Explanation

. MRI of the cervical spine and craniocervical junction

Explanation

Infants with achondroplasia are at high risk for foramen magnum stenosis, which can cause cervicomedullary compression leading to central apnea, hypotonia, and sudden death. MRI of the craniocervical junction is the diagnostic test of choice to evaluate for critical stenosis prior to surgical decompression.

Question 3947

Topic: 4. Pediatrics

A newborn presents with short stature, severe rigid clubfeet, 'hitchhiker' thumbs, and cystic swelling of the pinnae (cauliflower ears). Which of the following gene mutations is most likely responsible for this condition?

. FGFR3
. COL2A1
. COMP
. SLC26A2 (DTDST)
. SOX9

Correct Answer & Explanation

. SLC26A2 (DTDST)

Explanation

Diastrophic dysplasia is an autosomal recessive disorder caused by a mutation in the SLC26A2 (DTDST) gene, which affects a sulfate transporter. It is characterized by hitchhiker thumbs, rigid equinovarus foot deformities, and auricular cysts.

Question 3948

Topic: 4. Pediatrics

Achondroplasia is characterized by a disproportionate short stature. Which of the following accurately describes the primary genetic and cellular etiology of this condition?

. A defect in type II collagen synthesis encoded by COL2A1
. A defect in the cartilage oligomeric matrix protein (COMP) gene
. An activating mutation in the fibroblast growth factor receptor 3 (FGFR3) gene inhibiting the proliferative zone
. A mutation in the diastrophic dysplasia sulfate transporter (DTDST) gene
. A mutation in the RUNX2 transcription factor gene

Correct Answer & Explanation

. An activating mutation in the fibroblast growth factor receptor 3 (FGFR3) gene inhibiting the proliferative zone

Explanation

Achondroplasia is caused by a gain-of-function mutation in the FGFR3 gene. This overactivity abnormally inhibits chondrocyte proliferation within the proliferative zone of the physis.

Question 3949

Topic: 4. Pediatrics

A newborn is evaluated for skeletal dysplasia. Examination reveals severe micromelia, "hitchhiker" thumbs, clubfeet, and cystic swelling of the pinnae (cauliflower ear). What is the underlying genetic defect?

. FGFR3
. COL2A1
. COMP
. SLC26A2 (DTDST)
. CBFA1

Correct Answer & Explanation

. SLC26A2 (DTDST)

Explanation

Diastrophic dysplasia presents with hitchhiker thumbs, severe clubfeet, and cauliflower ears. It is an autosomal recessive condition caused by a mutation in the sulfate transporter gene (SLC26A2/DTDST).

Question 3950

Topic: 4. Pediatrics

A 6-year-old child presents with disproportionate short stature, normal craniofacial features, significant ligamentous laxity, and early-onset osteoarthritis of the hips. Radiographs show delayed epiphyseal ossification and platyspondyly with anterior beaking. A defect in which of the following genes is the most likely cause?

. COMP
. FGFR3
. COL1A1
. SOX9
. PTPN11

Correct Answer & Explanation

. COMP

Explanation

Pseudoachondroplasia is caused by mutations in the Cartilage Oligomeric Matrix Protein (COMP) gene. It classically presents with normal facies (unlike achondroplasia), severe early osteoarthritis, and ligamentous laxity.

Question 3951

Topic: 4. Pediatrics

Which of the following describes the underlying pathophysiology of achondroplasia at the level of the physis?

. Failure of primary spongiosa formation in the metaphysis
. Accelerated apoptosis of hypertrophic chondrocytes
. Inhibition of chondrocyte proliferation in the proliferative zone
. Defective type I collagen synthesis in the osteoid seam
. Absence of secondary ossification centers

Correct Answer & Explanation

. Inhibition of chondrocyte proliferation in the proliferative zone

Explanation

Achondroplasia is caused by a gain-of-function mutation in FGFR3, which leads to the constitutional inhibition of chondrocyte proliferation in the proliferative zone of the physis.

Question 3952

Topic: 4. Pediatrics
An 18-month-old child presents with an acute monoarticular effusion of the knee, fever, and refusal to bear weight. Gram stain of the synovial aspirate is negative. Which of the following is the most sensitive method to isolate Kingella kingae from this patient's synovial fluid?
. Prolonged incubation on MacConkey agar
. Inoculation into aerobic blood culture vials
. Plating on Lowenstein-Jensen medium
. Sabouraud dextrose agar culture at room temperature
. Anaerobic culture on thioglycolate broth

Correct Answer & Explanation

. Inoculation into aerobic blood culture vials

Explanation

Kingella kingae is a fastidious organism responsible for many pediatric joint infections. Its isolation is significantly improved by inoculating synovial fluid directly into aerobic blood culture vials (BACTEC).

Question 3953

Topic: 4. Pediatrics

An 8-month-old male with achondroplasia presents for routine follow-up. Radiographs demonstrate a 30-degree thoracolumbar kyphosis. Neurologic exam is normal. What is the most appropriate management of the spinal deformity?

. Observation and reassurance
. Immediate custom TLSO bracing
. Serial casting
. Posterior spinal fusion
. Anterior and posterior spinal fusion

Correct Answer & Explanation

. Observation and reassurance

Explanation

Thoracolumbar kyphosis is common in infants with achondroplasia due to hypotonia. It typically resolves spontaneously once the child begins to walk independently, so observation is the initial standard of care.

Question 3954

Topic: 4. Pediatrics

A 3-year-old child presents with short stature, ligamentous laxity, and a waddling gait. He had a normal appearance at birth and has a normal facial appearance. Radiographs show fragmented epiphyses. A mutation in the COMP gene is confirmed. What is the diagnosis?

. Achondroplasia
. Hypochondroplasia
. Pseudoachondroplasia
. Multiple epiphyseal dysplasia
. Osteogenesis imperfecta

Correct Answer & Explanation

. Pseudoachondroplasia

Explanation

Pseudoachondroplasia is caused by a mutation in the COMP gene. Unlike achondroplasia, children are normal at birth, lack facial involvement, and exhibit marked joint laxity.

Question 3955

Topic: 4. Pediatrics

A 48-year-old female with a history of Roux-en-Y gastric bypass presents with diffuse bone pain, muscle weakness, and a waddling gait. Radiographs demonstrate the findings shown in the provided image.

Which of the following best describes the primary underlying histologic pathogenesis of this condition?

. Increased osteoclastic bone resorption outstripping osteoblastic activity
. Failure of osteoid mineralization with widened osteoid seams
. Defective synthesis of type I collagen
. Abnormal endochondral ossification at the physis
. Aseptic necrosis of the trabecular bone

Correct Answer & Explanation

. Failure of osteoid mineralization with widened osteoid seams

Explanation

Osteomalacia is characterized by impaired mineralization of the bone matrix, leading to wide, unmineralized osteoid seams. The radiographic presence of pseudofractures (Looser zones) is a pathognomonic finding in advanced cases.

Question 3956

Topic: 4. Pediatrics

A 12-month-old male with achondroplasia is brought to the clinic by his parents due to a noticeable "hump" in his lower back. Physical examination reveals a flexible thoracolumbar kyphosis that corrects when the child is suspended prone. Neurological examination is unremarkable. What is the most appropriate initial management?

. Immediate posterior spinal fusion
. Application of a custom Thoracolumbosacral Orthosis (TLSO)
. Observation and reassurance
. Anterior spinal tethering
. Cervicomedullary decompression

Correct Answer & Explanation

. Observation and reassurance

Explanation

Thoracolumbar kyphosis is common in infants with achondroplasia and typically resolves spontaneously as the child develops truncal muscle tone and begins to walk. Bracing or surgery is strictly reserved for progressive, rigid deformities or those associated with neurological compromise.

Question 3957

Topic: 4. Pediatrics

A 5-year-old child presents with disproportionate short stature, a waddling gait, and profound joint laxity. Unlike classic achondroplasia, the child has completely normal facial features and intelligence. Radiographs show delayed epiphyseal ossification and irregular, fragmented metaphyses. A mutation in which of the following genes is most likely responsible?

. FGFR3
. COMP
. SLC26A2
. COL1A1
. RUNX2

Correct Answer & Explanation

. COMP

Explanation

Pseudoachondroplasia is an autosomal dominant skeletal dysplasia caused by mutations in the Cartilage Oligomeric Matrix Protein (COMP) gene. It is clinically distinguished from achondroplasia by the presence of normal craniofacial features and the absence of clinical manifestations at birth.

Question 3958

Topic: 4. Pediatrics

A 2-year-old child presents with a low-grade fever, limp, and refusal to bear weight on the right leg. Inflammatory markers are only mildly elevated. A knee aspirate yields purulent synovial fluid, but standard Gram stain is negative. Which of the following fastidious pathogens is highly suspected and best identified using nucleic acid amplification testing (PCR)?

. Staphylococcus aureus
. Streptococcus pneumoniae
. Kingella kingae
. Neisseria gonorrhoeae
. Haemophilus influenzae type b

Correct Answer & Explanation

. Kingella kingae

Explanation

Kingella kingae is a leading cause of osteoarticular infections in children aged 6 months to 4 years. It is a fastidious organism that is notoriously difficult to culture on standard solid media, making PCR or inoculation into liquid blood culture vials the diagnostic methods of choice.

Question 3959

Topic: 4. Pediatrics

Which of the following gene mutations is responsible for Achondroplasia, resulting in a gain-of-function that inhibits chondrocyte proliferation at the physis?

. COL1A1
. COMP
. FGFR3
. RUNX2
. SOX9

Correct Answer & Explanation

. FGFR3

Explanation

Achondroplasia is caused by an activating (gain-of-function) mutation in the FGFR3 gene. This mutation over-inhibits chondrocyte proliferation in the proliferative zone of the growth plate, leading to rhizomelic dwarfism.

Question 3960

Topic: Pediatric Hip

A 2-week-old neonate presents with asymmetric hip creases, fever, and pseudoparalysis of the right lower extremity. Ultrasound confirms a large hip effusion, and emergent surgical drainage is performed. The clinical image below demonstrates severe sequelae of a missed diagnosis in a similar patient.

What is the most devastating long-term complication of delayed diagnosis of neonatal septic arthritis of the hip?

. Coxa magna with joint space widening
. Complete avascular destruction of the femoral head and neck with hip subluxation
. Slipped capital femoral epiphysis
. Legg-Calve-Perthes disease
. Isolated acetabular dysplasia without femoral head involvement

Correct Answer & Explanation

. Complete avascular destruction of the femoral head and neck with hip subluxation

Explanation

Delay in treating neonatal septic arthritis of the hip results in catastrophic destruction of the cartilaginous femoral head and neck due to infection and increased intra-articular pressure compromising the vascular supply. This results in the classic Choi type IV sequelae (destruction of head and neck).

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