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4. Pediatrics MCQs

Practice Set 205 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 4081

Topic: 4. Pediatrics

A 10-year-old boy with achondroplasia presents to the clinic complaining of progressive knee pain. Physical examination demonstrates marked bilateral genu varum with a lateral thrust during gait. What is the primary anatomical driver of this progressive knee deformity in achondroplasia?

. Premature closure of the medial proximal tibial physis
. Ligamentous laxity of the lateral collateral ligament
. Asymmetric ossification of the lateral femoral condyle
. Relative overgrowth of the fibula
. Posteromedial bowing of the tibial diaphysis

Correct Answer & Explanation

. Relative overgrowth of the fibula

Explanation

In achondroplasia, disproportionate overgrowth of the fibula relative to the tibia leads to varus alignment at the knee, knee pain, and lateral thrust. This is a common indication for 8-plates or osteotomies in older children.

Question 4082

Topic: 4. Pediatrics

A 4-year-old boy with rhizomelic short stature and frontal bossing presents with new-onset hyperreflexia, clonus, and central sleep apnea. Radiographs show decreasing interpedicular distances from L1 to L5. What is the primary mechanism of the underlying genetic defect, and what is the most appropriate next step in management?

. FGFR3 loss of function; immediate suboccipital decompression
. FGFR3 gain of function; MRI of the cervical spine
. COMP mutation; polysomnography and continuous positive airway pressure
. COL1A1 mutation; bisphosphonate therapy
. FGFR3 gain of function; posterior spinal fusion for kyphosis

Correct Answer & Explanation

. FGFR3 gain of function; MRI of the cervical spine

Explanation

Achondroplasia is caused by an autosomal dominant, gain-of-function mutation in FGFR3, which inhibits chondrocyte proliferation in the growth plate. The new-onset upper motor neuron signs and sleep apnea strongly suggest cervicomedullary compression at the foramen magnum, requiring urgent MRI of the cervical spine.

Question 4083

Topic: 4. Pediatrics

A 9-year-old boy presents with a waddling gait and joint pain. His facial features and intelligence are normal. Radiographs reveal delayed, irregular ossification of multiple epiphyses. A lateral knee radiograph demonstrates a double-layer patella. A mutation in which of the following genes is highly characteristic of this radiographic finding?

. COMP
. MATN3
. SLC26A2
. COL9A2
. FGFR3

Correct Answer & Explanation

. SLC26A2

Explanation

A double-layer patella is a pathognomonic radiographic sign for the autosomal recessive form of Multiple Epiphyseal Dysplasia (rMED). This condition is caused by a mutation in the SLC26A2 gene, which encodes an intracellular sulfate transporter.

Question 4084

Topic: 4. Pediatrics

A 7-year-old girl is evaluated for short-limb dwarfism, joint laxity, and a waddling gait. Unlike classic achondroplasia, her facial features and head circumference are completely normal. Spinal radiographs reveal tongue-like anterior projections of the vertebral bodies. A mutation in which of the following genes is the most likely cause of her condition?

. FGFR3
. COMP
. COL2A1
. SLC26A2
. SOX9

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 distinguished from achondroplasia by normal craniofacial features and intelligence, accompanied by severe joint laxity and epiphyseal/metaphyseal changes.

Question 4085

Topic: 4. Pediatrics

A 16-year-old male with an open proximal femur physis presents with a symptomatic chondroblastoma crossing the physis into the metaphysis. How does this transphyseal involvement affect the surgical approach and prognosis?

. It requires primary wide resection to prevent systemic metastasis
. It necessitates prophylactic systemic chemotherapy
. It increases the risk of growth arrest but is still managed with extended curettage
. It mandates immediate epiphysiodesis of the contralateral limb
. It makes the lesion radioresistant

Correct Answer & Explanation

. It increases the risk of growth arrest but is still managed with extended curettage

Explanation

Chondroblastomas can cross the open physis. The treatment remains extended curettage; however, careful technique is required, and parents must be counseled on the high risk of iatrogenic physeal damage and subsequent growth arrest.

Question 4086

Topic: 4. Pediatrics

While performing an intralesional curettage of a chondroblastoma in the proximal humerus of a 14-year-old patient, the surgeon must be particularly careful to avoid iatrogenic damage to which of the following structures?

. The articular cartilage leading to rapid chondrolysis
. The axillary nerve leading to deltoid paralysis
. The physis leading to premature growth arrest and angular deformity
. The circumflex humeral arteries leading to avascular necrosis
. The rotator cuff insertion leading to functional deficit

Correct Answer & Explanation

. The physis leading to premature growth arrest and angular deformity

Explanation

Because chondroblastomas are epiphyseal lesions that typically occur in patients with open growth plates, surgical curettage risks damaging the adjacent physis, which can result in premature growth arrest or limb deformity.

Question 4087

Topic: 4. Pediatrics

A 4-year-old boy is evaluated for short stature. Examination reveals rhizomelic shortening of the limbs, frontal bossing, and a trident hand. Radiographs show narrowing of the interpedicular distances in the lumbar spine. Which zone of the physis is primarily affected by the genetic mutation responsible for this condition?

. Reserve zone
. Proliferative zone
. Hypertrophic zone
. Primary spongiosa
. Secondary spongiosa

Correct Answer & Explanation

. Proliferative zone

Explanation

Correct Answer: Proliferative zoneThe patient has achondroplasia, the most common form of short-limbed dwarfism. It is caused by an autosomal dominant gain-of-function mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. This mutation leads to constitutive activation of the receptor, which paradoxically inhibits chondrocyte proliferation in the proliferative zone of the physis, leading to decreased endochondral ossification and shortened long bones.

Question 4088

Topic: 4. Pediatrics

A 5-year-old girl presents with a waddling gait, short stature, and bowing of the lower extremities. Radiographs demonstrate coxa vara and flaring of the metaphyses with normal epiphyses. Laboratory studies, including calcium, phosphorus, and alkaline phosphatase, are normal. A mutation in which of the following genes is most likely responsible?

. FGFR3
. COL10A1
. PTH1R
. COMP
. RMRP

Correct Answer & Explanation

. COL10A1

Explanation

Correct Answer: COL10A1The clinical and radiographic presentation is classic for Schmid type metaphyseal chondrodysplasia. It is characterized by short stature, coxa vara, bowed legs, and a waddling gait. The epiphyses are normal, but the metaphyses are flared and irregular. It is caused by mutations in the COL10A1 gene, which encodes type X collagen, a protein exclusively expressed by hypertrophic chondrocytes in the growth plate.

Question 4089

Topic: 4. Pediatrics

An infant is diagnosed with a rare skeletal dysplasia characterized by severe shortening of the limbs and prominent, irregular, 'cupped' metaphyses. Laboratory evaluation reveals significant hypercalcemia and hypophosphatemia despite normal parathyroid hormone levels. What is the underlying genetic defect?

. Activating mutation of the PTH/PTHrP receptor (PTH1R)
. Inactivating mutation of the PHEX gene
. Mutation in the tissue-nonspecific alkaline phosphatase (ALPL) gene
. Defect in the type X collagen gene (COL10A1)
. Gain-of-function mutation in FGFR3

Correct Answer & Explanation

. Activating mutation of the PTH/PTHrP receptor (PTH1R)

Explanation

Correct Answer: Activating mutation of the PTH/PTHrP receptor (PTH1R)Jansen type metaphyseal chondrodysplasia is a rare autosomal dominant disorder caused by an activating mutation in the PTH1R gene (parathyroid hormone/parathyroid hormone-related peptide receptor). This leads to ligand-independent activation of the receptor, resulting in severe hypercalcemia and hypophosphatemia, mimicking hyperparathyroidism, along with severe metaphyseal changes and short stature.

Question 4090

Topic: 4. Pediatrics

A 3-year-old boy with short-limbed dwarfism is noted to have fine, sparse, light-colored hair. Radiographs show metaphyseal flaring and irregularity. He has a history of recurrent severe respiratory infections. Which of the following is the most critical systemic association to screen for in this patient?

. Cellular immunodeficiency
. Congenital heart defects
. Renal tubular acidosis
. Sensorineural hearing loss
. Craniosynostosis

Correct Answer & Explanation

. Cellular immunodeficiency

Explanation

Correct Answer: Cellular immunodeficiencyThe presentation is highly suggestive of Cartilage-Hair Hypoplasia (McKusick type metaphyseal chondrodysplasia). It is an autosomal recessive disorder caused by mutations in the RMRP gene. Patients present with short-limbed dwarfism, fine sparse hair, and notably, a cellular immunodeficiency (T-cell defect) that makes them highly susceptible to severe, recurrent infections. They also have an increased risk of malignancies such as lymphomas.

Question 4091

Topic: 4. Pediatrics

A 7-year-old child with achondroplasia presents with progressive bowing of the lower extremities. Clinical examination and standing radiographs confirm severe genu varum. What is the primary biomechanical and anatomical driver of this specific deformity in achondroplasia?

. Premature closure of the medial proximal tibial physis
. Relative overgrowth of the fibula compared to the tibia
. Ligamentous laxity of the lateral collateral ligament
. Defective mineralization of the primary spongiosa
. Avascular necrosis of the medial femoral condyle

Correct Answer & Explanation

. Relative overgrowth of the fibula compared to the tibia

Explanation

Correct Answer: Relative overgrowth of the fibula compared to the tibiaGenu varum is a common orthopedic manifestation in achondroplasia. It is primarily driven by the disproportionate growth between the tibia and the fibula. The fibula is relatively less affected by the FGFR3 mutation than the tibia, leading to fibular overgrowth. This overgrowth exerts a tethering effect and biomechanical force that drives the tibia into a varus deformity.

Question 4092

Topic: 4. Pediatrics

In a patient with Schmid type metaphyseal chondrodysplasia, the genetic defect primarily affects a specific collagen type. Which zone of the growth plate is predominantly abnormal as a direct result of this specific collagen deficiency?

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

Correct Answer & Explanation

. Hypertrophic zone

Explanation

Correct Answer: Hypertrophic zoneSchmid type metaphyseal chondrodysplasia is caused by a mutation in the COL10A1 gene, which encodes type X collagen. Type X collagen is a short-chain collagen that is synthesized exclusively by hypertrophic chondrocytes. Therefore, the hypertrophic zone of the physis is the primary site of pathology, leading to the characteristic metaphyseal flaring and irregularity seen on radiographs.

Question 4093

Topic: 4. Pediatrics

A 6-month-old infant with achondroplasia is brought to the clinic. The parents report episodes of apnea and profound hypotonia. Which of the following is the most appropriate next step in management?

. Reassurance as this is normal development for achondroplasia
. MRI of the cervicomedullary junction to evaluate for foramen magnum stenosis
. Immediate bracing for thoracolumbar kyphosis
. Genetic testing for a secondary skeletal dysplasia
. Initiation of growth hormone therapy

Correct Answer & Explanation

. MRI of the cervicomedullary junction to evaluate for foramen magnum stenosis

Explanation

Correct Answer: MRI of the cervicomedullary junction to evaluate for foramen magnum stenosisInfants with achondroplasia are at high risk for foramen magnum stenosis due to abnormal endochondral ossification of the skull base. This can lead to cervicomedullary compression, presenting as central apnea, profound hypotonia, hyperreflexia, or even sudden death. An MRI of the craniocervical junction is urgently indicated to assess the degree of stenosis and determine if surgical decompression is required.

Question 4094

Topic: 4. Pediatrics

A 10-year-old boy presents with short stature and mild disproportionate shortening of the limbs. Unlike classic achondroplasia, his facial features are normal without frontal bossing or midface hypoplasia. Radiographs show mild narrowing of the lumbar interpedicular distances. Which of the following statements regarding his condition is most accurate?

. It is caused by a mutation in the COMP gene
. It is inherited in an autosomal recessive pattern
. It is caused by a different mutation in the same gene responsible for achondroplasia
. It typically presents with severe hypercalcemia in infancy
. It is associated with severe cellular immunodeficiency

Correct Answer & Explanation

. It is caused by a different mutation in the same gene responsible for achondroplasia

Explanation

Correct Answer: It is caused by a different mutation in the same gene responsible for achondroplasiaThe patient's presentation is consistent with hypochondroplasia, which is clinically similar to but milder than achondroplasia. Patients typically lack the characteristic facial features (frontal bossing, midface hypoplasia) seen in achondroplasia. Like achondroplasia, hypochondroplasia is caused by mutations in the FGFR3 gene, but it involves different specific point mutations (most commonly N540K) that result in a less severe phenotype.

Question 4095

Topic: 4. Pediatrics

When evaluating a child for a suspected skeletal dysplasia with predominantly metaphyseal involvement, which of the following radiographic patterns is the hallmark of this specific group of disorders?

. Delayed ossification of the epiphyses with normal metaphyses
. Flared and irregular metaphyses with normal epiphyseal ossification centers
. Severe platyspondyly with anterior beaking of the vertebrae
. Diffuse osteosclerosis with obliteration of the medullary canal
. Multiple cartilaginous exostoses arising from the metaphyses

Correct Answer & Explanation

. Flared and irregular metaphyses with normal epiphyseal ossification centers

Explanation

Correct Answer: Flared and irregular metaphyses with normal epiphyseal ossification centersSkeletal dysplasias are often categorized by the region of the bone most affected. In predominantly metaphyseal dysplasias (such as Schmid, Jansen, and McKusick types), the hallmark radiographic finding is flaring, widening, and irregularity (cupping or fraying) of the metaphyses, while the epiphyseal ossification centers remain relatively normal in size, shape, and time of appearance.

Question 4096

Topic: 4. Pediatrics

A 4-year-old boy presents with short stature, a waddling gait, and progressive bowing of the lower extremities. Radiographs reveal flaring and irregularity of the metaphyses, particularly at the proximal femur, with coxa vara. The epiphyses are normal, and laboratory values for calcium, phosphorus, and alkaline phosphatase are within normal limits. Which of the following gene mutations is most likely responsible for this condition?

. FGFR3
. COL10A1
. PTH1R
. RMRP
. COMP

Correct Answer & Explanation

. COL10A1

Explanation

Correct Answer: COL10A1Schmid type metaphyseal chondrodysplasia is the most common of the metaphyseal chondrodysplasias. It is an autosomal dominant condition caused by mutations in the COL10A1 gene, which encodes type X collagen (found primarily in the hypertrophic zone of the physis). It presents with coxa vara, genu varum, and metaphyseal flaring. Normal laboratory values help differentiate it from rickets.

Question 4097

Topic: 4. Pediatrics

A neonate is evaluated for severe short stature and prominent eyes. Radiographs demonstrate widely separated, irregular, and 'cupped' metaphyses. Laboratory studies reveal asymptomatic hypercalcemia and hypophosphatemia with normal parathyroid hormone (PTH) levels. What is the underlying pathophysiology of this skeletal dysplasia?

. Activating mutation of the PTH/PTHrP receptor
. Defect in type X collagen synthesis
. Mutation in the tissue-nonspecific alkaline phosphatase gene
. Defect in the RMRP RNA gene
. Gain-of-function mutation in FGFR3

Correct Answer & Explanation

. Activating mutation of the PTH/PTHrP receptor

Explanation

Correct Answer: Activating mutation of the PTH/PTHrP receptorJansen type metaphyseal chondrodysplasia is a rare autosomal dominant disorder caused by an activating mutation in the PTH1R gene (PTH/PTHrP receptor). This leads to ligand-independent activation of the receptor, causing severe hypercalcemia, hypophosphatemia, and profound metaphyseal changes (cupping and irregularity) despite normal or low PTH levels.

Question 4098

Topic: 4. Pediatrics

A 10-year-old boy is evaluated for short stature. He has mild disproportionate short limbs but lacks the characteristic facial features of achondroplasia (no frontal bossing or midface hypoplasia). Radiographs show mild narrowing of the lumbar interpedicular distances and mild metaphyseal flaring. Which of the following mutations is most likely responsible?

. FGFR3
. COL1A1
. COMP
. SOX9
. RUNX2

Correct Answer & Explanation

. FGFR3

Explanation

Correct Answer: FGFR3Hypochondroplasia is caused by mutations in the FGFR3 gene, similar to achondroplasia, but typically at a different locus (e.g., Asn540Lys instead of Gly380Arg). It presents as a milder form of achondroplasia without the classic craniofacial features, but still exhibits mild rhizomelia, metaphyseal flaring, and narrowing of the interpedicular distances.

Question 4099

Topic: 4. Pediatrics

A 7-year-old child with Schmid metaphyseal chondrodysplasia presents with progressive bilateral coxa vara. The neck-shaft angle is 90 degrees bilaterally, and the Hilgenreiner-epiphyseal angle (HEA) is 65 degrees. What is the most appropriate surgical intervention?

. Bilateral epiphysiodesis of the greater trochanters
. Proximal femoral valgus osteotomies
. In situ pinning of the capital femoral epiphyses
. Observation until skeletal maturity
. Varus derotational osteotomies

Correct Answer & Explanation

. Proximal femoral valgus osteotomies

Explanation

Correct Answer: Proximal femoral valgus osteotomiesIn Schmid metaphyseal chondrodysplasia, progressive coxa vara is a common complication. Indications for surgical intervention include a neck-shaft angle less than 90-100 degrees or a Hilgenreiner-epiphyseal angle (HEA) greater than 60 degrees (which indicates high shear forces across the physis). Proximal femoral valgus osteotomy is the treatment of choice to correct the deformity and convert shear forces to compressive forces.

Question 4100

Topic: 4. Pediatrics

An infant with achondroplasia is noted to have a flexible thoracolumbar kyphosis during a routine orthopedic evaluation. What is the most appropriate initial management for this spinal deformity?

. Immediate posterior spinal fusion
. Extension bracing for 23 hours a day
. Avoidance of unsupported sitting and use of a firm stroller
. Anterior and posterior spinal fusion
. Observation with no restrictions on sitting posture

Correct Answer & Explanation

. Avoidance of unsupported sitting and use of a firm stroller

Explanation

Correct Answer: Avoidance of unsupported sitting and use of a firm strollerThoracolumbar kyphosis is extremely common in infants with achondroplasia, primarily due to generalized hypotonia and a disproportionately large head. The deformity is typically flexible initially. The standard of care is to prevent the flexible deformity from becoming a rigid, structural wedging of the vertebrae. This is achieved by avoiding unsupported sitting and using firm backing in strollers and car seats. The kyphosis usually resolves spontaneously once the child develops adequate truncal tone and begins to walk. Surgical intervention or rigid bracing is reserved for severe, progressive, or rigid deformities that do not resolve with walking.

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