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4. Pediatrics MCQs

Practice Set 208 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 4141

Topic: 4. Pediatrics

A 2-year-old boy from an Amish community presents with disproportionate short-limbed dwarfism, sparse, light-colored hair, and a history of recurrent severe viral infections. Radiographs reveal flaring and irregularity of the metaphyses. Which of the following genes is most likely mutated in this patient?

. COL10A1
. PTH1R
. RMRP
. SBDS
. FGFR3

Correct Answer & Explanation

. RMRP

Explanation

This patient has Cartilage-Hair Hypoplasia (McKusick type), an autosomal recessive metaphyseal chondrodysplasia. It is caused by mutations in the RMRP gene and is uniquely associated with cellular immunodeficiency and sparse hair.

Question 4142

Topic: 4. Pediatrics

In a patient with Schmid type metaphyseal chondrodysplasia, genetic testing reveals a mutation in the COL10A1 gene. The defective protein produced by this gene is primarily synthesized in which specific region of the growing physis?

. Reserve zone
. Proliferative zone
. Hypertrophic zone
. Primary spongiosa
. Zone of Ranvier

Correct Answer & Explanation

. Hypertrophic zone

Explanation

Schmid metaphyseal chondrodysplasia is caused by mutations in the COL10A1 gene, which encodes type X collagen. Type X collagen is exclusively synthesized by chondrocytes in the hypertrophic zone of the physis.

Question 4143

Topic: 4. Pediatrics

An infant presents with profound hypercalcemia, hypophosphatemia, and markedly irregular, cupped metaphyses on radiographs. Serum parathyroid hormone (PTH) levels are undetectable. What is the primary pathophysiologic mechanism of this condition?

. Ectopic secretion of parathyroid hormone-related peptide (PTHrP)
. Inactivating mutation of the calcium-sensing receptor
. Activating mutation of the PTH/PTHrP receptor
. Defective degradation of vitamin D
. Activating mutation in the FGFR3 receptor

Correct Answer & Explanation

. Activating mutation of the PTH/PTHrP receptor

Explanation

Jansen metaphyseal chondrodysplasia is caused by an activating (gain-of-function) mutation in the PTH1R gene. This leads to ligand-independent signaling of the PTH/PTHrP receptor, causing hypercalcemia and severe metaphyseal dysplasia despite suppressed PTH.

Question 4144

Topic: Pediatric Hip

A 7-year-old boy with known Schmid metaphyseal chondrodysplasia presents with a worsening waddling gait. Pelvic radiographs demonstrate bilateral coxa vara with a Hilgenreiner-epiphyseal (HE) angle of 75 degrees. What is the most appropriate management?

. Observation with annual radiographs
. Bilateral spica casting
. Bilateral valgus-producing proximal femoral osteotomies
. Epiphysiodesis of the greater trochanters
. Bisphosphonate infusions

Correct Answer & Explanation

. Bilateral valgus-producing proximal femoral osteotomies

Explanation

In Schmid metaphyseal chondrodysplasia, progressive coxa vara with a Hilgenreiner-epiphyseal (HE) angle greater than 60 degrees carries a high risk of pseudarthrosis and progressive deformity. Valgus-producing proximal femoral osteotomies are indicated to correct the mechanical axis and shear forces.

Question 4145

Topic: 4. Pediatrics

A 6-year-old boy presents with short stature. Examination shows mild rhizomelic limb shortening, but a normal facial appearance without frontal bossing or midface hypoplasia. Radiographs show narrowing of the interpedicular distances in the lower lumbar spine and mild metaphyseal flaring. Which genetic mutation is most likely?

. COMP
. FGFR3 (N540K mutation)
. COL10A1
. SLC26A2
. RMRP

Correct Answer & Explanation

. FGFR3 (N540K mutation)

Explanation

The patient's presentation is consistent with hypochondroplasia, a milder variant of achondroplasia. It is most commonly caused by the N540K mutation in the FGFR3 gene, and patients typically lack the severe craniofacial features seen in classic achondroplasia.

Question 4146

Topic: 4. Pediatrics

A 5-month-old infant with achondroplasia is brought to the clinic due to episodic apneic spells, brisk deep tendon reflexes, and sustained ankle clonus. What is the most critical next step in management?

. Reassurance and clinical observation
. Overnight polysomnography only
. Emergent MRI of the craniocervical junction
. Lumbar puncture to rule out meningitis
. Initiation of growth hormone therapy

Correct Answer & Explanation

. Emergent MRI of the craniocervical junction

Explanation

Infants with achondroplasia are at high risk for foramen magnum stenosis, leading to cervicomedullary compression. Signs of myelopathy (hyperreflexia, clonus) or central apnea require urgent MRI of the craniocervical junction to evaluate the need for surgical decompression.

Question 4147

Topic: 4. Pediatrics

A 9-year-old boy is evaluated for mild short stature. Historical radiographs from age 2 showed striking metaphyseal irregularities and fraying. Current radiographs, however, show that these metaphyseal changes have nearly completely resolved. Mutations in which gene are most classically associated with this spontaneously resolving dysplasia?

. MMP13
. FGFR3
. COL10A1
. PTH1R
. SBDS

Correct Answer & Explanation

. MMP13

Explanation

Metaphyseal anadysplasia is a rare skeletal dysplasia defined by severe metaphyseal changes in early childhood that spontaneously regress or resolve with age. It is typically caused by mutations in the MMP13 or MMP9 genes.

Question 4148

Topic: 4. Pediatrics
Which of the following variants of Langerhans cell histiocytosis predominantly affects infants under the age of 2, presents with diffuse hepatosplenomegaly, severe skin rash, and bone marrow infiltration, and frequently has a fatal clinical course?
. Hand-Schüller-Christian disease
. Letterer-Siwe disease
. Hashimoto-Pritzker disease
. Eosinophilic granuloma
. Erdheim-Chester disease

Correct Answer & Explanation

. Letterer-Siwe disease

Explanation

Letterer-Siwe disease is the acute, disseminated, multisystem form of Langerhans cell histiocytosis. It primarily strikes infants and is characterized by a rapid, frequently fatal course involving the skin, liver, spleen, and bone marrow.

Question 4149

Topic: 4. Pediatrics

A 7-year-old boy presents with a solitary lytic lesion in the proximal femur. Biopsy reveals mononuclear cells with grooved nuclei and abundant eosinophils. Which of the following genetic mutations is most frequently implicated in the pathogenesis of this disease?

. GNAS
. EXT1
. BRAF V600E
. RUNX2
. FGFR3

Correct Answer & Explanation

. BRAF V600E

Explanation

The described histology is classic for Langerhans Cell Histiocytosis (LCH). The BRAF V600E somatic mutation is identified in up to 60% of LCH cases, marking it as a clonal neoplastic process rather than a purely reactive one.

Question 4150

Topic: 4. Pediatrics

A 7-year-old child presents with asymmetrical overgrowth of the medial aspect of the distal femoral epiphysis, causing a progressive valgus deformity. The lesion is osteocartilaginous. What is the most likely diagnosis?

. Multiple Hereditary Exostoses
. Ollier's Disease
. Dysplasia Epiphysealis Hemimelica
. Meyer's Dysplasia
. Blount's Disease

Correct Answer & Explanation

. Dysplasia Epiphysealis Hemimelica

Explanation

Correct Answer: CDysplasia Epiphysealis Hemimelica (Trevor's disease) typically presents as an asymmetrical overgrowth of an epiphysis, most commonly in the lower limb (talus, knee, or hip). It leads to joint deformity, restricted motion, and mechanical symptoms.

Question 4151

Topic: 4. Pediatrics

A 4-year-old child with achondroplasia presents with new-onset sleep apnea, lower extremity hyperreflexia, and clumsiness. Which of the following is the most appropriate next step in management?

. Polysomnography alone to titrate CPAP therapy
. Immediate tracheostomy to secure the airway
. MRI of the craniocervical junction to evaluate for stenosis
. CT scan of the brain to rule out hydrocephalus
. Electromyography to assess peripheral nerve function

Correct Answer & Explanation

. MRI of the craniocervical junction to evaluate for stenosis

Explanation

Central sleep apnea and hyperreflexia in achondroplasia strongly suggest cervicomedullary compression at the foramen magnum. MRI of the craniocervical junction is critical to evaluate the need for suboccipital decompression.

Question 4152

Topic: 4. Pediatrics
A patient with Osteogenesis Imperfecta Type I typically exhibits blue sclerae, hearing loss, and recurrent fractures. Which of the following best describes the underlying collagen defect in this specific type?
. Production of structurally abnormal type II collagen
. Decreased quantity of structurally normal type I collagen
. Production of structurally abnormal type I collagen
. Defective cross-linking of collagen fibers
. Defective mineralization of the osteoid matrix

Correct Answer & Explanation

. Decreased quantity of structurally normal type I collagen

Explanation

Osteogenesis Imperfecta Type I is a quantitative defect resulting in a decreased amount of structurally normal type I collagen. Types II, III, and IV typically involve qualitative defects (structurally abnormal collagen).

Question 4153

Topic: 4. Pediatrics

A 5-year-old with short-trunk dwarfism presents with neck pain. Radiographs reveal delayed ossification of the pubic symphysis, coxa vara, and an absent odontoid process. What is the most likely underlying genetic defect?

. COMP
. COL1A1
. FGFR3
. COL2A1
. SLC26A2

Correct Answer & Explanation

. COL2A1

Explanation

Spondyloepiphyseal Dysplasia Congenita (SEDC) presents at birth with short-trunk dwarfism, coxa vara, and cervical instability due to odontoid hypoplasia. It is an autosomal dominant disorder caused by a mutation in the COL2A1 gene.

Question 4154

Topic: 4. Pediatrics

A 3-year-old child presents with disproportionate short-limb dwarfism and joint laxity. Unlike classic achondroplasia, the child's facial features and head circumference are completely normal. Radiographs show platyspondyly with anterior tongue-like projections. What best distinguishes this diagnosis from achondroplasia?

. Presence of severe craniofacial abnormalities
. Normal facial features and delayed clinical recognition until walking age
. X-linked recessive inheritance pattern
. Mutation in the FGFR3 gene
. Lethality in the immediate neonatal period

Correct Answer & Explanation

. Normal facial features and delayed clinical recognition until walking age

Explanation

Pseudoachondroplasia presents with normal craniofacial features and is typically not recognized until 2 to 3 years of age, unlike achondroplasia which is obvious at birth. It is caused by a COMP gene mutation.

Question 4155

Topic: 4. Pediatrics

A child with short-trunk dwarfism exhibits a flat midface, prominent joints, and a cleft palate. Radiographs show broad, shortened long bones described as "dumbbell-shaped" femora, and coronal clefts in the vertebral bodies. What is the most likely diagnosis?

. Metatropic dysplasia
. Kniest dysplasia
. Chondrodysplasia punctata
. Osteopetrosis
. Hypochondroplasia

Correct Answer & Explanation

. Kniest dysplasia

Explanation

Kniest dysplasia is a type II collagenopathy characterized by a flat midface, cleft palate, and prominent joints. The radiographic hallmarks include dumbbell-shaped femora and coronal clefts of the vertebrae.

Question 4156

Topic: 4. Pediatrics
A female infant is born with asymmetric limb shortening, ichthyosiform skin lesions, and early-onset cataracts. Radiographs demonstrate punctate calcifications in the epiphyses of the long bones. What is the most likely diagnosis?
. Multiple hereditary exostoses
. Chondrodysplasia punctata
. Campomelic dysplasia
. Metaphyseal chondrodysplasia
. Achondrogenesis

Correct Answer & Explanation

. Chondrodysplasia punctata

Explanation

Chondrodysplasia punctata (specifically Conradi-Hünermann syndrome) is an X-linked dominant condition characterized by "stippled" epiphyses, asymmetric limb shortening, cataracts, and scaly skin lesions.

Question 4157

Topic: 4. Pediatrics

A 4-year-old child presents with short stature, a waddling gait, and progressive coxa vara and bowlegs. Radiographs show widened, irregular metaphyseal growth plates at the knees, but the epiphyses and spine are completely normal. A mutation in which gene is responsible?

. COL2A1
. COL1A1
. COMP
. COL10A1
. SOX9

Correct Answer & Explanation

. COL10A1

Explanation

Metaphyseal chondrodysplasia, Schmid type, is caused by a mutation in the COL10A1 gene (encoding Type X collagen), which is restricted to the hypertrophic zone of the growth plate. It presents with metaphyseal flaring and normal epiphyses/spine.

Question 4158

Topic: 4. Pediatrics

An infant is born with a remarkably long, narrow trunk, exceptionally short extremities, and a prominent coccygeal tail-like appendage. Over the next few years, the child develops severe kyphoscoliosis, reversing the proportions to a short-trunk appearance. Which gene is most likely mutated?

. FGFR3
. RUNX2
. TRPV4
. Cathepsin K
. SLC26A2

Correct Answer & Explanation

. TRPV4

Explanation

Metatropic dysplasia is caused by mutations in the TRPV4 gene. It is uniquely characterized by a change in body proportions over time: starting with a long trunk and short limbs, then developing severe kyphoscoliosis resulting in a short trunk.

Question 4159

Topic: 4. Pediatrics

A 10-year-old boy presents with mild disproportionate short stature. Unlike patients with achondroplasia, his facial features are normal, but radiographs still show narrowing of the lower lumbar interpedicular distances. Which of the following best describes the pathogenesis of his condition?

. Mutation in the proximal tyrosine kinase domain of the FGFR3 gene
. Mutation in the transmembrane domain of the FGFR3 gene
. Defect in the production of type X collagen
. Autosomal recessive inheritance with defective sulfate transport
. Mutation in the COMP gene leading to delayed epiphyseal ossification

Correct Answer & Explanation

. Mutation in the proximal tyrosine kinase domain of the FGFR3 gene

Explanation

Hypochondroplasia is a milder form of dwarfism than achondroplasia and typically presents with normal facial features. It is caused by different mutations in the FGFR3 gene, most commonly in the proximal tyrosine kinase domain, whereas classic achondroplasia mutations occur in the transmembrane domain.

Question 4160

Topic: 4. Pediatrics

A 4-year-old child with rhizomelic short stature, frontal bossing, and a trident hand presents for evaluation. The underlying pathophysiology involves a mutation in the FGFR3 gene. How does this mutation affect the physeal growth plate?

. Decreased proliferation of chondrocytes in the reserve zone
. Gain of function leading to inhibition of chondrocyte proliferation in the proliferative zone
. Loss of function leading to accelerated chondrocyte hypertrophy
. Defective type 1 collagen synthesis causing matrix failure
. Impaired mineralization of the hypertrophic zone

Correct Answer & Explanation

. Gain of function leading to inhibition of chondrocyte proliferation in the proliferative zone

Explanation

Achondroplasia is caused by an autosomal dominant, gain-of-function mutation in FGFR3. This overactivity continuously inhibits chondrocyte proliferation and hypertrophy in the growth plate, leading to severely restricted endochondral ossification.

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