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4. Pediatrics MCQs

Practice Set 286 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 5701

Topic: 4. Pediatrics

A pediatrician refers a 9-month-old infant with achondroplasia to the orthopedic clinic due to concerns about delayed walking and poor head control. What is the typical developmental and cognitive profile for a child with this condition?

. Hypertonia with severe intellectual disability
. Hypotonia and delayed motor milestones with normal intelligence
. Normal muscle tone with delayed speech and cognitive milestones
. Progressive loss of motor milestones due to neurodegeneration

Correct Answer & Explanation

. Hypotonia and delayed motor milestones with normal intelligence

Explanation

Correct Answer: Hypotonia and delayed motor milestones with normal intelligenceIn infancy, hypotonia is typical in achondroplasia, and the acquisition of developmental motor milestones is often delayed. However, intelligence and life span are usually normal.

Question 5702

Topic: 4. Pediatrics

A 14-year-old male with achondroplasia asks about his expected final adult height. According to established growth data for this condition, what is the mean adult height for males?

. 112 +/- 5.0 cm
. 124 +/- 5.9 cm
. 131 +/- 5.6 cm
. 145 +/- 6.2 cm

Correct Answer & Explanation

. 131 +/- 5.6 cm

Explanation

Correct Answer: 131 +/- 5.6 cmThe mean adult height in males with achondroplasia is 131 +/- 5.6 cm, whereas in females it is 124 +/- 5.9 cm.

Question 5703

Topic: 4. Pediatrics

Two individuals are shown in the clinical photograph below. The patient on the right has achondroplasia. When comparing the trunk and shoulder dimensions of a patient with achondroplasia to an individual of normal stature, which of the following statements is most accurate?


. The trunk is significantly shorter, and the shoulders are wider
. There is no difference in trunk height, but the chest and shoulders are narrower
. The trunk is disproportionately long, and the chest is barrel-shaped
. Both the trunk height and shoulder width are proportionally reduced

Correct Answer & Explanation

. There is no difference in trunk height, but the chest and shoulders are narrower

Explanation

Correct Answer: There is no difference in trunk height, but the chest and shoulders are narrowerAchondroplasia is a disproportionate short-limb dwarfism. As demonstrated in the clinical comparison image, there is no difference between the patients in the height of the trunk; however, the chest and shoulders are narrower in achondroplasia.

Question 5704

Topic: 4. Pediatrics

Achondroplasia is caused by a mutation in the FGFR3 gene. What is the specific effect of this mutation on the physeal growth plate?

. Loss-of-function leading to hypertrophic zone expansion
. Gain-of-function resulting in inhibition of chondrocyte proliferation
. Loss-of-function resulting in premature physeal closure
. Gain-of-function leading to increased osteoclast activity
. Defective type II collagen synthesis in the resting zone

Correct Answer & Explanation

. Gain-of-function resulting in inhibition of chondrocyte proliferation

Explanation

Achondroplasia is caused by an autosomal dominant gain-of-function mutation in FGFR3. This results in the suppression of chondrocyte proliferation and hypertrophy, primarily affecting the proliferative zone of the physis.

Question 5705

Topic: 4. Pediatrics

An 8-month-old infant with achondroplasia presents with hypotonia, central sleep apnea, and hyperreflexia. What is the most critical next step in evaluation?

. Polysomnography
. MRI of the cervicomedullary junction
. CT of the cervical spine
. Electroencephalogram (EEG)
. Genetic testing for a secondary mutation

Correct Answer & Explanation

. MRI of the cervicomedullary junction

Explanation

These symptoms strongly suggest foramen magnum stenosis causing cervicomedullary compression, a life-threatening complication in infants with achondroplasia. MRI of the cervicomedullary junction is the modality of choice to assess the degree of compression.

Question 5706

Topic: 4. Pediatrics

A 7-year-old child with achondroplasia presents with symptomatic genu varum. Which of the following is the primary pathophysiological driver of this lower extremity deformity?

. Premature closure of the medial distal femoral physis
. Ligamentous laxity of the lateral collateral ligament
. Relative overgrowth of the fibula compared to the tibia
. Avascular necrosis of the medial tibial plateau
. Malunion of occult tibial fractures

Correct Answer & Explanation

. Relative overgrowth of the fibula compared to the tibia

Explanation

Genu varum in achondroplasia is predominantly caused by the relative overgrowth of the fibula compared to the tibia. This leads to lateral bowing and a varus thrust at the knee, which may require surgical realignment if progressive.

Question 5707

Topic: 4. Pediatrics

Two individuals with achondroplasia are expecting a child and request genetic counseling regarding the risk of homozygous achondroplasia. What is the probability that their child will inherit this fatal form of the condition?

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

Correct Answer & Explanation

. 25%

Explanation

Achondroplasia is an autosomal dominant condition. Therefore, two affected parents (who are heterozygotes) have a 25% chance of having a child with homozygous achondroplasia, which is typically lethal in the perinatal period.

Question 5708

Topic: 4. Pediatrics

Which of the following best describes the classic radiographic appearance of the pelvis in a patient with achondroplasia?

. Protrusio acetabuli with coxa vara
. Squared iliac wings with a 'champagne glass' pelvic cavity
. Dysplastic acetabula with an 'hour-glass' pelvic inlet
. Small iliac wings with severe coxa valga
. Fragmented capital femoral epiphyses with wide teardrop distances

Correct Answer & Explanation

. Squared iliac wings with a 'champagne glass' pelvic cavity

Explanation

The classic pelvic radiographic findings in achondroplasia include squared, shortened iliac wings and horizontal acetabular roofs. This creates a wide, flat pelvic inlet commonly described as resembling a 'champagne glass'.

Question 5709

Topic: 4. Pediatrics

A 4-year-old child presents with short-limbed dwarfism. Which of the following clinical findings best differentiates pseudoachondroplasia from achondroplasia?

. The presence of rhizomelic shortening
. The presence of normal craniofacial features
. The presence of a trident hand
. The presence of lumbar lordosis
. The presence of ligamentous laxity

Correct Answer & Explanation

. The presence of normal craniofacial features

Explanation

Pseudoachondroplasia is characterized by normal craniofacial features and head circumference. This distinguishes it from achondroplasia, which classically features frontal bossing and midface hypoplasia.

Question 5710

Topic: 4. Pediatrics

A 5-year-old child with achondroplasia develops signs of cor pulmonale. What is the most likely underlying etiology of this condition?

. Congenital heart defect (VSD)
. Restrictive lung disease from severe scoliosis
. Chronic hypoxemia due to upper airway obstruction and sleep apnea
. Pulmonary hypoplasia secondary to a narrow thorax
. Left ventricular hypertrophy from essential hypertension

Correct Answer & Explanation

. Chronic hypoxemia due to upper airway obstruction and sleep apnea

Explanation

Cor pulmonale in achondroplasia is most commonly a complication of chronic hypoxemia secondary to severe obstructive sleep apnea. This condition is exacerbated by midface hypoplasia, a small pharynx, and relatively enlarged tonsils and adenoids.

Question 5711

Topic: 4. Pediatrics

Parents of a 6-month-old infant with achondroplasia are concerned about a prominent bump on the child's back when sitting. Clinical exam reveals a flexible thoracolumbar kyphosis. What is the most appropriate advice for the parents?

. Avoid unsupported sitting and use a firm mattress to allow spontaneous resolution
. Immediate application of a Milwaukee brace
. Surgical anterior release and posterior fusion
. Begin aggressive physical therapy for paraspinal muscle strengthening
. Limit prone positioning to prevent worsening of the deformity

Correct Answer & Explanation

. Avoid unsupported sitting and use a firm mattress to allow spontaneous resolution

Explanation

Thoracolumbar kyphosis is present in over 90% of infants with achondroplasia due to hypotonia and a heavy head. Avoiding unsupported sitting and using a firm mattress typically allows the kyphosis to spontaneously resolve once the child develops lumbar lordosis and begins walking.

Question 5712

Topic: 4. Pediatrics

A couple of normal stature has a child diagnosed with achondroplasia. Which of the following factors is most strongly associated with the de novo mutation seen in this patient?

. Advanced maternal age
. Advanced paternal age
. Maternal folate deficiency
. In utero exposure to teratogens
. Consanguinity

Correct Answer & Explanation

. Advanced paternal age

Explanation

Over 80% of achondroplasia cases are the result of a de novo mutation in the FGFR3 gene. This sporadic genetic event is strongly correlated with advanced paternal age.

Question 5713

Topic: 4. Pediatrics

Achondroplasia is caused by a mutation in the fibroblast growth factor receptor 3 (FGFR3) gene. This mutation directly affects which zone of the growth plate?

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

Correct Answer & Explanation

. Proliferative zone

Explanation

Achondroplasia results from an activating mutation in FGFR3, which inhibits chondrocyte proliferation. This primarily affects the proliferative zone of the physis, leading to defective endochondral ossification.

Question 5714

Topic: 4. Pediatrics

Approximately 80% of achondroplasia cases arise from de novo mutations. Which of the following is the most significant risk factor for these sporadic occurrences?

. Advanced maternal age
. Advanced paternal age
. Maternal folate deficiency
. In utero teratogen exposure
. History of recurrent miscarriages

Correct Answer & Explanation

. Advanced paternal age

Explanation

De novo mutations in the FGFR3 gene accounting for achondroplasia are strongly associated with advanced paternal age. The mutations occur almost exclusively in the father's germline.

Question 5715

Topic: 4. Pediatrics

The parents of an 8-month-old infant with achondroplasia are concerned about a prominent curve in the child's lower back when sitting unsupported. Radiographs confirm a flexible thoracolumbar kyphosis. What is the recommended initial management?

. Immediate posterior spinal fusion
. Thoracolumbosacral orthosis (TLSO) 23 hours a day
. Prohibit unsupported sitting and encourage prone positioning
. Physical therapy for core strengthening
. Anterior tethering of the spine

Correct Answer & Explanation

. Prohibit unsupported sitting and encourage prone positioning

Explanation

Infantile thoracolumbar kyphosis in achondroplasia is largely postural due to hypotonia and macrocephaly. Initial management involves preventing unsupported sitting; the deformity usually resolves once the child begins to stand and walk.

Question 5716

Topic: 4. Pediatrics

A 4-year-old child presents for evaluation of short stature. Pelvic radiographs display classic findings associated with achondroplasia. Which of the following accurately describes these expected radiographic features?

. Deep, dysplastic acetabula with coxa valga
. Squared iliac wings, narrow sciatic notches, and horizontal acetabula
. Coxa vara with a fragmentation of the capital femoral epiphysis
. Small, irregular capital femoral epiphyses with a normal pelvis
. Complete agenesis of the sacrum

Correct Answer & Explanation

. Squared iliac wings, narrow sciatic notches, and horizontal acetabula

Explanation

Classic pelvic radiographic findings in achondroplasia include a 'champagne glass' pelvis. This is characterized by squared iliac wings, narrow sacrosciatic notches, and flat, horizontal acetabular roofs.

Question 5717

Topic: 4. Pediatrics

Patients with achondroplasia frequently develop symptomatic genu varum. What is the primary anatomic cause of this deformity?

. Premature closure of the medial distal femoral physis
. Traction apophysitis of the tibial tubercle
. Overgrowth of the fibula relative to the tibia
. Vitamin D deficiency causing metabolic rickets
. Congenital absence of the anterior cruciate ligament

Correct Answer & Explanation

. Overgrowth of the fibula relative to the tibia

Explanation

Genu varum in achondroplasia is typically caused by disproportionate growth between the tibia and fibula. The fibula outgrows the tibia, exerting a varus bowing force on the lower extremity.

Question 5718

Topic: 4. Pediatrics

A 6-year-old boy presents with disproportionate short stature. The orthopedic surgeon suspects pseudoachondroplasia rather than achondroplasia. Which of the following physical examination findings most strongly supports pseudoachondroplasia?

. Rhizomelic shortening of the limbs
. Frontal bossing and midface hypoplasia
. Normal facial appearance and normal head circumference
. Trident hands with brachydactyly
. Severe lumbar lordosis

Correct Answer & Explanation

. Normal facial appearance and normal head circumference

Explanation

Unlike achondroplasia, patients with pseudoachondroplasia have a normal facial appearance and head circumference. They also typically present later in childhood (ages 2-3) when growth delay becomes apparent.

Question 5719

Topic: 4. Pediatrics

Achondroplasia is characterized by a failure of normal endochondral ossification. Consequently, which of the following skeletal structures typically attains a normal size in these patients?

. Humerus
. Femur
. Clavicle
. Tibia
. Radius

Correct Answer & Explanation

. Clavicle

Explanation

The clavicle and cranial vault develop primarily via intramembranous ossification, which is unaffected in achondroplasia. Long bones (like the humerus and femur) rely on endochondral ossification and are therefore shortened.

Question 5720

Topic: 4. Pediatrics

A major cause of sudden death in the first year of life for infants with achondroplasia is respiratory arrest. This is primarily attributed to which of the following?

. Tracheomalacia
. Severe restriction of the thoracic cage
. Brainstem compression at the foramen magnum
. Primary pulmonary hypoplasia
. Severe gastroesophageal reflux

Correct Answer & Explanation

. Brainstem compression at the foramen magnum

Explanation

Foramen magnum stenosis can lead to severe brainstem and upper cervical cord compression. This can result in central sleep apnea, respiratory arrest, and sudden infant death if not decompressed surgically.

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