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4. Pediatrics MCQs

Practice Set 206 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 4101

Topic: 4. Pediatrics

Schmid metaphyseal chondrodysplasia is characterized by short stature, coxa vara, and a waddling gait. Which of the following gene mutations is responsible for the pathogenesis of this specific condition?

. FGFR3
. COL10A1
. PTH1R
. RMRP
. COMP

Correct Answer & Explanation

. COL10A1

Explanation

Correct Answer: COL10A1Schmid metaphyseal chondrodysplasia is an autosomal dominant disorder caused by mutations in the COL10A1 gene, which encodes type X collagen. Type X collagen is uniquely expressed by hypertrophic chondrocytes in the growth plate. A defect in this collagen leads to abnormal endochondral ossification, resulting in metaphyseal flaring, coxa vara, and short stature. FGFR3 mutations cause achondroplasia and hypochondroplasia. PTH1R mutations cause Jansen metaphyseal chondrodysplasia. RMRP mutations cause Cartilage-Hair Hypoplasia (McKusick type). COMP mutations are associated with pseudoachondroplasia and multiple epiphyseal dysplasia.

Question 4102

Topic: 4. Pediatrics

A 3-year-old child presents with severe short stature, micrognathia, and prominent eyes. Radiographs demonstrate severe, irregular metaphyseal flaring with a 'ragged' appearance. Laboratory testing reveals hypercalcemia and hypophosphatemia. Which of the following is the most likely diagnosis?

. Schmid metaphyseal chondrodysplasia
. Jansen metaphyseal chondrodysplasia
. McKusick metaphyseal chondrodysplasia
. Achondroplasia
. Hypophosphatasia

Correct Answer & Explanation

. Jansen metaphyseal chondrodysplasia

Explanation

Correct Answer: Jansen metaphyseal chondrodysplasiaJansen metaphyseal chondrodysplasia is a rare, severe autosomal dominant disorder caused by an activating mutation in the PTH1R gene (the receptor for parathyroid hormone and parathyroid hormone-related peptide). This ligand-independent activation leads to severe hypercalcemia, hypophosphatemia, and undetectable or very low PTH levels. Clinically, patients have severe short stature, characteristic facial features (micrognathia, prominent eyes), and profound metaphyseal irregularities. Schmid type does not have these severe lab abnormalities. Hypophosphatasia presents with low alkaline phosphatase, not hypercalcemia driven by PTH receptor overactivity.

Question 4103

Topic: 4. Pediatrics

In an infant with achondroplasia, which of the following clinical presentations should prompt immediate investigation for cervicomedullary compression at the foramen magnum?

. Delayed independent walking until 18 months of age
. Central sleep apnea and profound hypotonia
. A waddling gait with hyperlordosis
. Flexible thoracolumbar kyphosis
. Progressive genu varum

Correct Answer & Explanation

. Central sleep apnea and profound hypotonia

Explanation

Correct Answer: Central sleep apnea and profound hypotoniaForamen magnum stenosis is the most critical and potentially life-threatening neurological complication in infants with achondroplasia. The abnormal endochondral ossification affects the base of the skull, leading to a narrowed foramen magnum. Symptoms of cervicomedullary compression include central sleep apnea, profound hypotonia, hyperreflexia, clonus, and in severe cases, sudden infant death. Any infant with achondroplasia exhibiting these signs requires urgent MRI evaluation and potential neurosurgical decompression. Delayed walking, waddling gait, flexible kyphosis, and genu varum are expected, non-emergent findings in achondroplasia.

Question 4104

Topic: 4. Pediatrics

A 6-year-old child with achondroplasia presents with progressive genu varum. What is the primary biomechanical and anatomical cause of this specific lower extremity deformity in this patient population?

. Premature closure of the medial proximal tibial physis
. Overgrowth of the fibula relative to the tibia
. Medial collateral ligament laxity
. Avascular necrosis of the medial femoral condyle
. Vitamin D deficiency rickets

Correct Answer & Explanation

. Overgrowth of the fibula relative to the tibia

Explanation

Correct Answer: Overgrowth of the fibula relative to the tibiaGenu varum is a very common deformity in patients with achondroplasia. The primary anatomical driver for this is the disproportionate growth between the tibia and the fibula. The fibula experiences relative overgrowth compared to the tibia, which acts as a tether, forcing the tibia into a varus bow. This is often accompanied by internal tibial torsion. While ligamentous laxity is present in achondroplasia, the structural bony disproportion is the primary cause of the varus deformity. Premature closure of the medial physis describes Blount disease, which is a different pathology.

Question 4105

Topic: 4. Pediatrics

Which of the following clinical features most reliably distinguishes hypochondroplasia from achondroplasia during a physical examination?

. Presence of lumbar spinal stenosis in adulthood
. Autosomal dominant inheritance pattern
. Absence of frontal bossing and midface hypoplasia
. Mutation in the FGFR3 gene
. Disproportionate short stature with rhizomelic shortening

Correct Answer & Explanation

. Absence of frontal bossing and midface hypoplasia

Explanation

Correct Answer: Absence of frontal bossing and midface hypoplasiaHypochondroplasia is clinically considered a milder variant of achondroplasia. Both are caused by mutations in the FGFR3 gene (though typically different specific mutations), both are autosomal dominant, and both present with disproportionate short stature. However, a key distinguishing clinical feature is the craniofacial appearance. Patients with achondroplasia classically have macrocephaly, frontal bossing, and midface hypoplasia. In contrast, patients with hypochondroplasia typically have a normal facial appearance and a normal or only slightly enlarged head circumference.

Question 4106

Topic: Pediatric Hip

A 5-year-old child with Schmid metaphyseal chondrodysplasia is evaluated for a waddling gait. Radiographs of the pelvis and lower extremities are most likely to demonstrate which of the following characteristic findings?

. Coxa valga and genu valgum with narrow physes
. Coxa vara and genu varum with widened, irregular physes
. Slipped capital femoral epiphysis with normal metaphyseal bone
. Fragmented, stippled epiphyses of the proximal femur
. Dense, sclerotic metaphyseal bands

Correct Answer & Explanation

. Coxa vara and genu varum with widened, irregular physes

Explanation

Correct Answer: Coxa vara and genu varum with widened, irregular physesSchmid metaphyseal chondrodysplasia is characterized radiographically by abnormalities confined primarily to the metaphyses, while the epiphyses remain normal (distinguishing it from epiphyseal dysplasias). The classic radiographic findings include coxa vara (decreased neck-shaft angle), genu varum, and widened, irregular, and cupped physes (metaphyseal flaring). The waddling gait is a direct clinical consequence of the coxa vara and resulting abductor mechanical disadvantage. Stippled epiphyses are seen in chondrodysplasia punctata, and dense sclerotic bands are seen in heavy metal poisoning or bisphosphonate use.

Question 4107

Topic: 4. Pediatrics

A 3-year-old child presents with severe short stature, prominent eyes, and micrognathia. Laboratory investigations reveal marked hypercalcemia, hypophosphatemia, and undetectable intact parathyroid hormone (PTH) levels. Radiographs show severe metaphyseal irregularities and wide growth plates. Which of the following gene mutations is most likely responsible for this condition?

. FGFR3
. COL10A1
. PTH1R
. RMRP
. COMP

Correct Answer & Explanation

. PTH1R

Explanation

Correct Answer: PTH1RThis clinical picture is classic for Jansen type metaphyseal chondrodysplasia. It is caused by an activating mutation in the PTH1R (parathyroid hormone 1 receptor) gene. This leads to ligand-independent activation of the receptor, resulting in severe hypercalcemia and hypophosphatemia despite suppressed or undetectable levels of PTH. Radiographically, it presents with severe metaphyseal changes.COL10A1is associated with Schmid type,FGFR3with achondroplasia/hypochondroplasia,RMRPwith McKusick type (cartilage-hair hypoplasia), andCOMPwith pseudoachondroplasia.

Question 4108

Topic: Pediatric Hip

A 5-year-old boy presents with short stature, a waddling gait, and progressive bowing of the lower extremities. Radiographs reveal coxa vara, genu varum, and flaring of the metaphyses, but the spine and epiphyses are entirely normal. Genetic testing is most likely to reveal a mutation in the gene encoding for which of the following proteins?

. Type II collagen
. Type IX collagen
. Type X collagen
. Fibroblast growth factor receptor 3
. Cartilage oligomeric matrix protein

Correct Answer & Explanation

. Type X collagen

Explanation

Correct Answer: Type X collagenThe patient's presentation of metaphyseal flaring, coxa vara, and genu varum with normal epiphyses and spine is characteristic of Schmid type metaphyseal chondrodysplasia. This condition is inherited in an autosomal dominant pattern and is caused by mutations in theCOL10A1gene, which encodes for Type X collagen. Type X collagen is primarily expressed by hypertrophic chondrocytes in the growth plate.

Question 4109

Topic: 4. Pediatrics

A 7-year-old child presents with disproportionate short stature. Radiographs show narrowing of the interpedicular distance in the lower lumbar spine and mild metaphyseal flaring. However, the child has a normal facial appearance without frontal bossing or midface hypoplasia. Which of the following is the most likely diagnosis?

. Achondroplasia
. Hypochondroplasia
. Pseudoachondroplasia
. Multiple epiphyseal dysplasia
. Cleidocranial dysplasia

Correct Answer & Explanation

. Hypochondroplasia

Explanation

Correct Answer: HypochondroplasiaHypochondroplasia is caused by a different, typically milder, mutation in theFGFR3gene compared to achondroplasia. Patients exhibit similar but less severe skeletal features, such as narrowing of the interpedicular distance and short limbs. Crucially, they lack the characteristic craniofacial features of achondroplasia, such as frontal bossing and midface hypoplasia. Pseudoachondroplasia involves both epiphyses and metaphyses and is caused by aCOMPmutation.

Question 4110

Topic: 4. Pediatrics

In a 10-year-old patient with achondroplasia and severe symptomatic genu varum, radiographic analysis typically shows varus deformity primarily associated with which of the following anatomical patterns?

. Proximal femoral varus with normal knee alignment
. Distal femoral varus with relative tibial overgrowth
. Proximal and distal tibial varus with relative fibular overgrowth
. Distal tibial valgus compensating for proximal varus
. Isolated diaphyseal bowing of the femur

Correct Answer & Explanation

. Proximal and distal tibial varus with relative fibular overgrowth

Explanation

Correct Answer: Proximal and distal tibial varus with relative fibular overgrowthGenu varum is a very common orthopedic manifestation in achondroplasia. It is typically driven by relative overgrowth of the fibula compared to the tibia, leading to varus bowing at both the proximal and distal tibia. Surgical correction often requires tibial osteotomies combined with fibular shortening or epiphysiodesis to address the length discrepancy between the two bones.

Question 4111

Topic: 4. Pediatrics

A couple, both of whom have achondroplasia, are expecting a child. They seek genetic counseling regarding the risk to their offspring. What is the probability that their child will be born with homozygous achondroplasia, a condition that is typically lethal in the perinatal period?

. 0%
. 25%
. 50%
. 75%
. 100%

Correct Answer & Explanation

. 25%

Explanation

Correct Answer: 25%Achondroplasia is an autosomal dominant disorder. When both parents are heterozygous for theFGFR3mutation (which is the case for viable adults with achondroplasia), there is a 25% chance of the offspring inheriting two mutant alleles (homozygous achondroplasia). This condition causes severe rib cage deformity and pulmonary hypoplasia, and is almost universally lethal shortly after birth. There is a 50% chance of heterozygous achondroplasia and a 25% chance of average stature.

Question 4112

Topic: 4. Pediatrics

A 4-year-old boy is diagnosed with the most common form of short-limbed dwarfism, characterized by rhizomelic shortening and frontal bossing. Which of the following best describes the pathophysiology of his condition?

. Defect in type I collagen synthesis
. Loss-of-function mutation in the FGFR3 gene leading to increased chondrocyte hypertrophy
. Gain-of-function mutation in the FGFR3 gene leading to decreased chondrocyte proliferation
. Mutation in the COMP gene affecting the cartilage extracellular matrix
. Defect in the PTHrP receptor leading to delayed ossification

Correct Answer & Explanation

. Gain-of-function mutation in the FGFR3 gene leading to decreased chondrocyte proliferation

Explanation

Correct Answer: Gain-of-function mutation in the FGFR3 gene leading to decreased chondrocyte proliferationAchondroplasia is the most common skeletal dysplasia and is characterized by predominantly metaphyseal involvement with rhizomelic short stature. It is caused by a gain-of-function mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. Normally, FGFR3 acts as a negative regulator of bone growth. The mutation causes the receptor to be constitutively active, leading to profound inhibition of chondrocyte proliferation and hypertrophy in the proliferative zone of the physis.

Question 4113

Topic: 4. Pediatrics

A 5-year-old child presents with short stature, a waddling gait, coxa vara, and genu varum. Radiographs show flaring and irregularity of the metaphyses, but the epiphyses and spine are completely normal. Genetic testing reveals a mutation in the COL10A1 gene. What is the most likely diagnosis?

. Achondroplasia
. Jansen metaphyseal chondrodysplasia
. Schmid metaphyseal chondrodysplasia
. Cartilage-hair hypoplasia
. Multiple epiphyseal dysplasia

Correct Answer & Explanation

. Schmid metaphyseal chondrodysplasia

Explanation

Correct Answer: Schmid metaphyseal chondrodysplasiaSchmid metaphyseal chondrodysplasia is an autosomal dominant condition caused by mutations in the COL10A1 gene, which encodes type X collagen (found in the hypertrophic zone of the physis). It presents with short stature, coxa vara, and genu varum. Radiographically, it affects the metaphyses (flaring, cupping) while sparing the epiphyses and the spine. Jansen type is caused by a PTH1R mutation, and Cartilage-hair hypoplasia (McKusick type) is associated with the RMRP gene.

Question 4114

Topic: 4. Pediatrics

An infant presents with severe short stature, prominent eyes, and a highly arched palate. Radiographs demonstrate severe metaphyseal irregularities described as a 'chopped wood' appearance. Laboratory studies are most likely to show which of the following abnormalities?

. Hypercalcemia and hypophosphatemia
. Hypocalcemia and hyperphosphatemia
. Normal calcium and elevated alkaline phosphatase
. Elevated parathyroid hormone (PTH) levels
. Decreased 1,25-dihydroxyvitamin D levels

Correct Answer & Explanation

. Hypercalcemia and hypophosphatemia

Explanation

Correct Answer: Hypercalcemia and hypophosphatemiaThe clinical and radiographic presentation ('chopped wood' metaphyses) is classic for Jansen metaphyseal chondrodysplasia. This rare autosomal dominant disorder is caused by an activating mutation in the PTH/PTHrP receptor (PTH1R). This ligand-independent activation leads to biochemical findings identical to primary hyperparathyroidism: severe hypercalcemia and hypophosphatemia, but with undetectable or very low levels of actual circulating PTH.

Question 4115

Topic: 4. Pediatrics

A 3-year-old Amish child presents with disproportionate short stature, fine sparse hair, and flaring of the rib costochondral junctions. Radiographs show metaphyseal widening and irregularity. This patient is at the highest risk for which of the following systemic complications?

. Severe hypercalcemia
. Sensorineural hearing loss
. Restrictive cardiomyopathy
. Cellular immunodeficiency
. Renal tubular acidosis

Correct Answer & Explanation

. Cellular immunodeficiency

Explanation

Correct Answer: Cellular immunodeficiencyThe patient has Cartilage-Hair Hypoplasia (McKusick type metaphyseal chondrodysplasia), an autosomal recessive disorder common in the Amish and Finnish populations, caused by mutations in the RMRP gene. It is characterized by short-limbed dwarfism, fine sparse hair, and metaphyseal dysplasia. A critical systemic association is cellular immunodeficiency (T-cell defect), making these patients highly susceptible to severe infections, particularly varicella. They also have an increased risk of malignancies like lymphomas.

Question 4116

Topic: 4. Pediatrics

A 7-year-old boy with achondroplasia presents with progressive, symptomatic genu varum. Radiographs confirm severe bowing centered at the proximal tibia with relative fibular overgrowth. What is the most appropriate surgical management?

. Observation until skeletal maturity
. Distal femoral varus-producing osteotomies
. Proximal tibial and fibular valgus-producing osteotomies
. Guided growth using tension band plates on the lateral proximal tibia
. Epiphysiodesis of the proximal fibula alone

Correct Answer & Explanation

. Proximal tibial and fibular valgus-producing osteotomies

Explanation

Correct Answer: Proximal tibial and fibular valgus-producing osteotomiesGenu varum is common in achondroplasia and is typically driven by relative overgrowth of the fibula compared to the tibia, leading to a varus thrust and lateral ligamentous laxity. When symptomatic and severe, surgical correction is indicated. The standard of care is valgus-producing osteotomies of the proximal tibia and fibula. Guided growth on the lateral side would worsen the varus. While medial guided growth is sometimes attempted, the fibular overgrowth often necessitates concurrent fibular management or definitive osteotomy.

Question 4117

Topic: 4. Pediatrics

Parents of a newborn diagnosed with achondroplasia are counseled regarding potential complications. Which of the following represents the most significant cause of mortality in the first year of life for patients with this condition?

. Thoracolumbar kyphosis leading to spinal cord compression
. Recurrent respiratory infections secondary to immunodeficiency
. Cor pulmonale from severe restrictive lung disease
. Atlantoaxial rotatory subluxation
. Cervicomedullary compression due to foramen magnum stenosis

Correct Answer & Explanation

. Cervicomedullary compression due to foramen magnum stenosis

Explanation

Correct Answer: Cervicomedullary compression due to foramen magnum stenosisThe most critical and potentially lethal complication in infants with achondroplasia is stenosis of the foramen magnum. This can lead to cervicomedullary compression, resulting in central apnea, profound hypotonia, quadriparesis, and sudden death. All infants with achondroplasia require careful neurological evaluation and often neuroimaging (MRI) or polysomnography to screen for this condition. If severe compression is identified, suboccipital decompression is urgently indicated.

Question 4118

Topic: 4. Pediatrics

Which of the following clinical or radiographic features best differentiates hypochondroplasia from achondroplasia?

. Absence of frontal bossing and midface hypoplasia
. Presence of rhizomelic shortening
. Narrowing of the interpedicular distance in the lumbar spine
. Mutation in the FGFR3 gene
. Severe genu valgum

Correct Answer & Explanation

. Absence of frontal bossing and midface hypoplasia

Explanation

Correct Answer: Absence of frontal bossing and midface hypoplasiaHypochondroplasia is a milder skeletal dysplasia that is also caused by mutations in the FGFR3 gene (though typically different specific mutations than achondroplasia). While patients with hypochondroplasia have short stature and may have narrowing of the lumbar interpedicular distances, they characteristically lack the distinct craniofacial features of achondroplasia, such as frontal bossing and midface hypoplasia. Their facial appearance is typically normal.

Question 4119

Topic: 4. Pediatrics

A 9-month-old infant with achondroplasia is noted to have a flexible thoracolumbar kyphosis. Neurological examination is normal. What is the most appropriate initial management?

. Immediate posterior spinal fusion
. Anterior and posterior spinal fusion
. Avoidance of unsupported sitting and use of a firm mattress
. Extension bracing (e.g., TLSO) for 23 hours a day
. Observation with no restrictions, as it always resolves spontaneously

Correct Answer & Explanation

. Avoidance of unsupported sitting and use of a firm mattress

Explanation

Correct Answer: Avoidance of unsupported sitting and use of a firm mattressThoracolumbar kyphosis is present in over 90% of infants with achondroplasia. It is primarily postural, exacerbated by hypotonia and a large head size. The vast majority of these curves are flexible and will resolve spontaneously once the child begins to walk and develops lumbar lordosis. The standard initial management is to avoid unsupported sitting (which exacerbates the kyphosis) and to carry the child in a supportive device. Bracing is reserved for curves that persist after walking age or become rigid.

Question 4120

Topic: 4. Pediatrics

A 4-year-old child presents with bowed legs, coxa vara, and a waddling gait. Radiographs show widened, irregular metaphyses but completely normal epiphyses. Genetic testing confirms a mutation in the COL10A1 gene. Which zone of the physis is primarily targeted by this genetic mutation?

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

Correct Answer & Explanation

. Hypertrophic zone

Explanation

Schmid metaphyseal chondrodysplasia is caused by a mutation in COL10A1, which encodes type X collagen. Type X collagen is uniquely expressed by chondrocytes in the hypertrophic zone of the physis.

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