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4. Pediatrics MCQs

Practice Set 199 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 3961

Topic: 4. Pediatrics
A 14-month-old child presents with refusal to bear weight and a knee effusion. Fluid analysis shows a WBC count of 65,000 cells/microL with a negative Gram stain. The suspected organism is a fastidious Gram-negative rod that is part of the normal pediatric respiratory flora. Which method is most critical for isolating the likely causative organism?
. Inoculation onto standard MacConkey agar plates
. Polymerase chain reaction (PCR) for Borrelia burgdorferi
. Inoculation of synovial fluid directly into aerobic blood culture vials (BACTEC)
. Dark-field microscopy
. Culture on Thayer-Martin media at room temperature

Correct Answer & Explanation

. Inoculation of synovial fluid directly into aerobic blood culture vials (BACTEC)

Explanation

Kingella kingae is the most common cause of septic arthritis in children aged 6 months to 4 years. It is notoriously difficult to culture on standard solid media, and diagnostic yield significantly increases when joint fluid is inoculated into blood culture vials (BACTEC).

Question 3962

Topic: 4. Pediatrics

A 4-year-old boy presents with rhizomelic short stature, frontal bossing, and a depressed nasal bridge. The genetic mutation underlying his condition primarily disrupts normal bone growth through which of the following cellular mechanisms?

. Defective type I collagen synthesis leading to brittle bone
. Constitutive activation of FGFR3 inhibiting chondrocyte proliferation in the proliferative zone
. Impaired sulfate transport into the cartilage matrix
. Defective cleavage of type II collagen propeptides
. Accumulation of keratan sulfate within lysosomes

Correct Answer & Explanation

. Constitutive activation of FGFR3 inhibiting chondrocyte proliferation in the proliferative zone

Explanation

The patient has achondroplasia, caused by a gain-of-function mutation in the FGFR3 gene. This constitutive activation inhibits normal chondrocyte proliferation and hypertrophy in the physis, particularly affecting endochondral ossification.

Question 3963

Topic: 4. Pediatrics

A 9-year-old boy sustains a minimally displaced pathologic fracture through a central, entirely lytic lesion in the proximal humerus metaphysis. A "fallen leaf" sign is present. The lesion abuts the physis. What is the most appropriate management after the fracture has initially healed?

. En bloc resection with massive allograft
. Extensive curettage and bone grafting
. Aspiration and local methylprednisolone injection
. Observation only with no intervention
. Radiofrequency ablation

Correct Answer & Explanation

. Aspiration and local methylprednisolone injection

Explanation

The presentation and "fallen leaf" sign are classic for an active Unicameral Bone Cyst (UBC). Following fracture union, active UBCs near the physis are typically treated with less invasive methods such as aspiration and injection (steroids or bone marrow aspirate) to avoid physeal injury.

Question 3964

Topic: 4. Pediatrics

A 10-day-old neonate presents with fever, irritability, and decreased spontaneous movement of the right lower extremity. On examination, the infant cries with passive range of motion of the right hip. An ultrasound reveals a significant joint effusion. What is the most appropriate next step in management?

. Intravenous antibiotics and close observation
. Urgent hip aspiration and surgical drainage
. MRI of the pelvis with and without contrast
. Pavlik harness application
. Immediate closed reduction and spica casting

Correct Answer & Explanation

. Urgent hip aspiration and surgical drainage

Explanation

Neonatal septic arthritis of the hip (coxitis) is a surgical emergency requiring urgent joint aspiration and surgical drainage. Delaying surgical decompression can lead to rapid destruction of the cartilaginous femoral head and permanent joint damage.

Question 3965

Topic: 4. Pediatrics

A newborn is noted to have severe short limb dwarfism, rigid bilateral clubfeet, abducted "hitchhiker" thumbs, and cystic swelling of the pinnae. Mutations in which of the following genes or proteins are responsible for this condition?

. FGFR3
. COMP
. COL1A1
. SLC26A2 (Sulfate transporter)
. RUNX2

Correct Answer & Explanation

. SLC26A2 (Sulfate transporter)

Explanation

The clinical presentation is classic for diastrophic dysplasia, which is caused by a mutation in the SLC26A2 gene coding for a diastrophic dysplasia sulfate transporter (DTDST). It is inherited in an autosomal recessive pattern.

Question 3966

Topic: 4. Pediatrics

A 6-month-old infant with achondroplasia presents with poor feeding, hypotonia, and episodes of central apnea. Which of the following is the most critical screening study to perform?

. Echocardiogram
. MRI of the cervicomedullary junction
. Renal ultrasound
. Radiographs of the lower extremities
. Pulmonary function tests

Correct Answer & Explanation

. MRI of the cervicomedullary 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 infant death. MRI is the modality of choice for evaluation.

Question 3967

Topic: 4. Pediatrics

A 4-year-old child with disproportionate short-trunk dwarfism is evaluated. Radiographs show delayed ossification of the femoral heads, severe coxa vara, and platyspondyly. Ocular examination reveals high myopia. A mutation in which of the following genes is the most likely cause?

. FGFR3
. COL1A1
. COL2A1
. COMP
. CBFA1

Correct Answer & Explanation

. COL2A1

Explanation

Spondyloepiphyseal dysplasia congenita (SEDC) presents with short-trunk dwarfism, coxa vara, platyspondyly, and ocular issues like high myopia or retinal detachment. It is caused by a mutation in the COL2A1 gene.

Question 3968

Topic: 4. Pediatrics

A 3-year-old child presents with a waddling gait and joint hyperlaxity. The child appeared normal at birth but developed disproportionate short-limb dwarfism over the last year. Facial features and intelligence are normal. Radiographs show small, irregular epiphyses and metaphyseal flaring. A mutation in which gene is responsible?

. COMP
. FGFR3
. SLC26A2
. SOX9
. IHH

Correct Answer & Explanation

. COMP

Explanation

Pseudoachondroplasia is caused by a mutation in Cartilage Oligomeric Matrix Protein (COMP). Unlike true achondroplasia, children appear normal at birth, develop symptoms in early childhood, have normal facies, and exhibit significant joint laxity.

Question 3969

Topic: 4. Pediatrics

A 9-year-old girl from Connecticut presents with a massive, painless effusion of her right knee. She is afebrile and bears weight with a mild limp. Joint fluid aspiration yields 25,000 WBCs/mm3. Serology is positive for Borrelia burgdorferi. What is the most appropriate initial management?

. Urgent arthroscopic irrigation and debridement
. Intravenous ceftriaxone for 14 days
. Oral doxycycline for 28 days
. Intra-articular corticosteroid injection
. Serial aspirations until the effusion resolves

Correct Answer & Explanation

. Oral doxycycline for 28 days

Explanation

Lyme arthritis frequently presents as a massive, relatively painless knee effusion in an endemic area. The initial treatment for late Lyme arthritis in a child > 8 years old is a 28-day course of oral doxycycline.

Question 3970

Topic: Pediatric Hip
A 10-year-old boy presents with bilateral knee and hip pain, and a waddling gait. Radiographs show delayed, irregular, and fragmented ossification centers of the capital femoral epiphyses. Lateral knee radiographs demonstrate a "double-layer" patella. Spinal radiographs are entirely normal. What is the most likely diagnosis?
. Spondyloepiphyseal dysplasia congenita
. Multiple epiphyseal dysplasia
. Legg-Calvรฉ-Perthes disease
. Pseudoachondroplasia
. Mucopolysaccharidosis

Correct Answer & Explanation

. Multiple epiphyseal dysplasia

Explanation

Multiple epiphyseal dysplasia (MED) presents with delayed and irregular ossification of multiple epiphyses leading to early osteoarthritis, but uniquely leaves the spine relatively spared (differentiating it from SED). A "double-layer" patella is a classic radiographic sign.

Question 3971

Topic: 4. Pediatrics

A newborn presents with short-limbed dwarfism, rigid equinovarus foot deformities, "hitchhiker" thumbs, and cystic swelling of the pinnae (cauliflower ears). What is the underlying genetic mutation for this condition?

. DTDST (SLC26A2) gene
. FGFR3 gene
. COL1A1 gene
. COMP gene
. RUNX2 gene

Correct Answer & Explanation

. DTDST (SLC26A2) gene

Explanation

Diastrophic dysplasia is an autosomal recessive disorder caused by a mutation in the DTDST (SLC26A2) gene. This gene encodes a sulfate transporter, and its mutation leads to impaired sulfation of cartilage proteoglycans.

Question 3972

Topic: 4. Pediatrics

A 6-year-old girl with blue sclerae and a history of multiple low-impact fractures is diagnosed with Osteogenesis Imperfecta (OI). Which underlying genetic defect is most commonly responsible for her condition?

. Mutation in the FGFR3 gene
. Defect in the COMP gene
. Mutation in COL1A1 or COL1A2 genes
. Mutation in the RUNX2 gene
. Deficiency of tissue-nonspecific alkaline phosphatase

Correct Answer & Explanation

. Mutation in COL1A1 or COL1A2 genes

Explanation

Osteogenesis imperfecta is most commonly caused by autosomal dominant mutations in the COL1A1 or COL1A2 genes. These genes encode the alpha chains of type I collagen, leading to brittle bones and varying degrees of connective tissue abnormalities.

Question 3973

Topic: 4. Pediatrics
A 5-year-old child presents with a history of recurrent low-energy fractures, blue sclerae, and early-onset hearing loss. Genetic testing confirms Osteogenesis Imperfecta Type I. What is the underlying molecular defect?
. Mutation in the FGFR3 gene
. Defect in the COMP gene
. Quantitative defect in Type I collagen synthesis
. Qualitative defect in Type I collagen synthesis
. Mutation in the RUNX2 gene

Correct Answer & Explanation

. Quantitative defect in Type I collagen synthesis

Explanation

Osteogenesis Imperfecta Type I is characterized by a quantitative defect, meaning there is decreased production of structurally normal Type I collagen. Types II, III, and IV involve qualitative defects where abnormal collagen is produced.

Question 3974

Topic: 4. Pediatrics

A 6-year-old boy presents with disproportionate short trunk dwarfism, normal intelligence, a barrel chest, and severe coxa vara. Radiographs show significant delay in epiphyseal ossification and platyspondyly. What is the molecular basis of this child's skeletal dysplasia?

. Type I collagen defect
. Type II collagen defect
. Type X collagen defect
. FGFR3 mutation
. COMP mutation

Correct Answer & Explanation

. Type II collagen defect

Explanation

Spondyloepiphyseal dysplasia (SED) affects the spine and epiphyses, leading to a short trunk and coxa vara. It is caused by mutations in the COL2A1 gene, resulting in defective Type II collagen, the primary structural collagen in hyaline cartilage.

Question 3975

Topic: 4. Pediatrics

A 4-year-old child presents with a waddling gait, short stature, and significant joint laxity. Unlike classic achondroplasia, the child has normal facial features and head circumference. Radiographs show delayed epiphyseal ossification and irregular, fragmented epiphyses. A mutation in which gene is responsible for this condition?

. FGFR3
. COMP
. COL1A1
. CBFA1
. EXT1

Correct Answer & Explanation

. COMP

Explanation

Pseudoachondroplasia is clinically distinguished from achondroplasia by normal facial features and intelligence. It is caused by mutations in the Cartilage Oligomeric Matrix Protein (COMP) gene, leading to accumulation of abnormal protein in the chondrocyte rER.

Question 3976

Topic: 4. Pediatrics

A 6-year-old boy with oligoarticular JIA presents with an asymmetric gait. His right knee is swollen and warm but painless. On examination, his right leg is 2 cm longer than his left. What is the most likely mechanism for this leg length discrepancy?

. Premature physeal closure of the left leg
. Epiphyseal avascular necrosis of the right knee
. Hyperemia causing physeal overgrowth in the affected right leg
. Disuse atrophy and contracture of the left leg
. Unrecognized slipped capital femoral epiphysis on the right

Correct Answer & Explanation

. Hyperemia causing physeal overgrowth in the affected right leg

Explanation

Chronic inflammation and synovitis in JIA cause localized hyperemia around the affected joint. In young children, this increased blood flow stimulates the adjacent physes, leading to accelerated bone growth and limb overgrowth on the affected side.

Question 3977

Topic: 4. Pediatrics

A 7-year-old child with systemic JIA suddenly deteriorates in the hospital, developing an unremitting fever, hepatosplenomegaly, and encephalopathy. Laboratory studies reveal a paradoxical sharp drop in the erythrocyte sedimentation rate (ESR), profound thrombocytopenia, and a serum ferritin level of 15,000 ng/mL. What life-threatening complication has developed?

. Septic shock secondary to an opportunistic infection
. Macrophage activation syndrome
. Reye syndrome
. Acute lymphoblastic leukemia transformation
. Hemolytic uremic syndrome

Correct Answer & Explanation

. Macrophage activation syndrome

Explanation

Macrophage Activation Syndrome (MAS) is a severe, life-threatening complication of systemic JIA. It is characterized by unremitting fever, hepatosplenomegaly, massive hyperferritinemia, cytopenias, and a paradoxical drop in ESR due to hypofibrinogenemia.

Question 3978

Topic: 4. Pediatrics

Which of the following pediatric patients with Juvenile Idiopathic Arthritis (JIA) requires the most frequent slit-lamp examinations to screen for asymptomatic uveitis?

. A 4-year-old girl with oligoarticular JIA and positive antinuclear antibodies (ANA)
. A 10-year-old boy with enthesitis-related arthritis and positive HLA-B27
. A 14-year-old girl with polyarticular rheumatoid factor-positive JIA
. A 6-year-old boy with systemic JIA and negative ANA
. A 12-year-old girl with psoriatic JIA and negative ANA

Correct Answer & Explanation

. A 4-year-old girl with oligoarticular JIA and positive antinuclear antibodies (ANA)

Explanation

Young girls (onset <7 years) with oligoarticular JIA and a positive ANA are at the highest risk for developing chronic, asymptomatic anterior uveitis. They require screening slit-lamp exams every 3 to 4 months.

Question 3979

Topic: 4. Pediatrics

A 6-year-old girl with persistent oligoarticular JIA affecting her right knee presents with a noticeable leg length discrepancy. Which of the following best describes the expected discrepancy and its mechanism?

. Right leg is shorter due to premature physeal closure
. Right leg is shorter due to disuse osteopenia and growth arrest
. Right leg is longer due to chronic hyperemia stimulating physeal overgrowth
. Right leg is longer due to asymmetrical mechanical loading
. Both legs remain equal, but pelvic obliquity mimics a discrepancy

Correct Answer & Explanation

. Right leg is longer due to chronic hyperemia stimulating physeal overgrowth

Explanation

In the early, active stages of JIA involving a single large joint like the knee, chronic inflammation causes localized hyperemia. This increased blood flow stimulates the adjacent physes, resulting in overgrowth and a longer affected limb.

Question 3980

Topic: 4. Pediatrics

A 7-year-old child with oligoarticular JIA affecting the right knee is noted to have a leg length discrepancy, with the right leg being 1.5 cm longer than the left. What is the primary mechanism causing this overgrowth?

. Chronic disuse atrophy of the contralateral leg
. Inflammatory hyperemia stimulating physeal growth in the affected limb
. Premature physeal closure of the unaffected limb
. Recurrent hemarthroses mimicking hemophilic arthropathy
. Asymmetric pelvic tilt secondary to a hip contracture

Correct Answer & Explanation

. Inflammatory hyperemia stimulating physeal growth in the affected limb

Explanation

In children with active JIA, chronic inflammation in a large joint (like the knee) leads to local hyperemia. This increased blood flow stimulates the adjacent physes, leading to accelerated bone growth and a resultant ipsilateral leg length discrepancy.

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