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4. Pediatrics MCQs

Practice Set 197 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 3921

Topic: 4. Pediatrics

A 6-month-old infant with Spinal Muscular Atrophy Type I is admitted to the pediatric intensive care unit with acute respiratory distress. The patient exhibits a classic "bell-shaped" chest and paradoxical breathing. This respiratory pattern is primarily due to the severe weakness of which of the following structures, while another remains relatively spared?

. Weakness of the diaphragm with relative sparing of the intercostal muscles.
. Weakness of the intercostal muscles with relative sparing of the diaphragm.
. Weakness of the accessory neck muscles with relative sparing of the abdominal musculature.
. Global weakness of all respiratory muscles equally.
. Primary pulmonary hypoplasia independent of muscle function.

Correct Answer & Explanation

. Weakness of the intercostal muscles with relative sparing of the diaphragm.

Explanation

Correct Answer: B (Weakness of the intercostal muscles with relative sparing of the diaphragm.)Respiratory failure is the leading cause of morbidity and mortality in severe SMA (Type I). The classic respiratory presentation is a "bell-shaped" chest and paradoxical breathing. This occurs because the intercostal muscles (which normally stabilize and expand the rib cage) become profoundly weak early in the disease process, while the diaphragm (innervated by the phrenic nerve, C3-C5) is relatively spared until later stages. During inspiration, the strong diaphragm contracts and descends, pushing the abdominal contents outward. However, because the weak intercostals cannot stabilize the chest wall, the negative intrathoracic pressure causes the chest to collapse inward (paradoxical breathing). Over time, this leads to a bell-shaped deformity of the thorax.

Question 3922

Topic: 4. Pediatrics

A 28-year-old female with a history of recurrent childhood fractures and blue sclerae presents with progressive hearing loss. Audiometry reveals a mixed hearing loss pattern. What is the primary pathophysiologic mechanism responsible for the conductive component of her hearing loss?

. Chronic otitis media due to eustachian tube dysfunction.
. Otosclerosis and ossicular chain abnormalities.
. Degeneration of the cochlear hair cells.
. Compression of the vestibulocochlear nerve at the internal acoustic meatus.
. Abnormal endolymphatic fluid production.

Correct Answer & Explanation

. Otosclerosis and ossicular chain abnormalities.

Explanation

Correct Answer: BHearing loss is a common extra-skeletal manifestation of Osteogenesis Imperfecta, typically presenting as a mixed hearing loss. The conductive component, which frequently appears earlier in life, is primarily due to abnormalities in the ossicular chain and otosclerosis (abnormal bone remodeling in the middle ear). The sensorineural component, which often develops later, is due to cochlear dysfunction. While patients with OI can get otitis media, it is not the primary intrinsic cause of their characteristic hearing loss pattern.

Question 3923

Topic: 4. Pediatrics

A 3-year-old child with SMA Type II is prescribed risdiplam (Evrysdi) to improve motor function. This medication is a daily oral small molecule. What is the intended molecular outcome of this therapy?

. Delivery of a functional SMN1 gene via a viral vector.
. Inhibition of myostatin to promote muscle hypertrophy.
. Modification of SMN2 splicing to increase full-length SMN protein.
. Prevention of SMN protein degradation in the proteasome.
. Stimulation of anterior horn cell regeneration.

Correct Answer & Explanation

. Modification of SMN2 splicing to increase full-length SMN protein.

Explanation

Correct Answer: CRisdiplam is an orally administered small molecule that acts as an SMN2 splicing modifier. In patients with SMA, the SMN1 gene is deleted or mutated, and they rely on the backup SMN2 gene. However, SMN2 primarily produces a truncated, unstable protein due to alternative splicing (skipping of exon 7). Risdiplam modifies this splicing process, encouraging the inclusion of exon 7, thereby increasing the production of full-length, functional SMN protein. Onasemnogene abeparvovec (Zolgensma) is the viral vector gene therapy (AAV9) that delivers a functional SMN1 gene.

Question 3924

Topic: 4. Pediatrics

A 2-month-old infant is evaluated for profound hypotonia and absent deep tendon reflexes. Suspecting a neuromuscular disorder, the neurologist orders electrodiagnostic studies. If the infant has Spinal Muscular Atrophy, what is the expected pattern on electromyography (EMG) and nerve conduction studies (NCS)?

. Myopathic motor unit potentials on EMG with slowed nerve conduction velocities.
. Denervation potentials on EMG with normal nerve conduction velocities.
. Normal EMG with significantly slowed nerve conduction velocities.
. Decremental response on repetitive nerve stimulation.
. Fibrillation potentials on EMG with absent sensory nerve action potentials.

Correct Answer & Explanation

. Denervation potentials on EMG with normal nerve conduction velocities.

Explanation

Correct Answer: BSpinal Muscular Atrophy is a disease of the anterior horn cells (lower motor neurons). Therefore, EMG will show signs of active and chronic denervation (e.g., fibrillation potentials, positive sharp waves, and large amplitude motor unit potentials due to collateral sprouting). Because the peripheral nerves themselves (myelin and axons) are structurally intact initially, nerve conduction velocities (NCS) are typically normal. Myopathic potentials would be seen in muscular dystrophies. Slowed NCS would indicate a demyelinating peripheral neuropathy. A decremental response is classic for myasthenia gravis.

Question 3925

Topic: 4. Pediatrics
A 5-year-old girl with Osteogenesis Imperfecta Type III undergoes bilateral femoral rodding with Fassier-Duval (telescoping) rods. Two years later, she presents with a new mid-shaft femur fracture. Radiographs show that the male and female components of the rod have completely separated (disengaged) within the medullary canal. What is the most likely cause of this specific hardware failure?
. Deep infection of the intramedullary canal.
. Excessive bone growth exceeding the maximum expansion capacity of the rod.
. Failure to anchor the distal (male) component adequately in the distal epiphysis during the index procedure.
. Use of a rod diameter that was too large for the isthmus.
. Allergic reaction to the metal alloy of the rod.

Correct Answer & Explanation

. Failure to anchor the distal (male) component adequately in the distal epiphysis during the index procedure.

Explanation

Telescoping rods, such as the Fassier-Duval system, are designed to elongate with the child's growth. This mechanism relies on the secure fixation of the female component in the proximal epiphysis/metaphysis and the male component in the distal epiphysis. If the distal component is not adequately threaded and anchored into the distal epiphysis during the initial surgery, it will fail to pull out of the female component as the bone grows. Instead, the entire rod construct may migrate, or the bone will grow past it, eventually leading to the disengagement of the two components and loss of internal splinting, resulting in a fracture.

Question 3926

Topic: 4. Pediatrics
A 7-year-old child with Osteogenesis Imperfecta Type III has severe dentinogenesis imperfecta (DI). The dentist notes that the teeth are opalescent and the enamel is rapidly wearing away. Which of the following best describes the underlying pathophysiology of the enamel loss in this condition?
. A primary genetic defect in ameloblast function leading to hypoplastic enamel.
. Excessive osteoclast activity within the dental pulp cavity.
. Normal enamel that shears off easily due to the lack of support from the underlying defective, soft dentin.
. Chemical dissolution of the enamel due to abnormal salivary pH in OI patients.
. Failure of cementum to anchor the tooth, leading to excessive occlusal wear.

Correct Answer & Explanation

. Normal enamel that shears off easily due to the lack of support from the underlying defective, soft dentin.

Explanation

In dentinogenesis imperfecta associated with Osteogenesis Imperfecta, the primary genetic defect affects type I collagen, which is a major structural component of dentin. The enamel, which is of epithelial origin and does not rely on type I collagen, is structurally normal. However, because the underlying dentin is soft, abnormal, and poorly mineralized, it fails to provide a rigid, shock-absorbing foundation. Consequently, the otherwise normal enamel easily fractures and shears off under normal occlusal forces, leading to rapid tooth wear.

Question 3927

Topic: 4. Pediatrics

A 4-month-old infant with confirmed Spinal Muscular Atrophy (SMA) Type 1 is admitted to the pediatric intensive care unit with respiratory distress. Physical examination reveals a classic "bell-shaped" chest and paradoxical breathing. Which of the following best explains the specific pattern of respiratory muscle involvement leading to this clinical presentation?

. Primary degeneration of the phrenic nerve leading to early diaphragmatic paralysis.
. Severe weakness of the intercostal muscles with relative sparing of the diaphragm.
. Spasticity of the accessory muscles of respiration overpowering the diaphragm.
. Rapid degeneration of both diaphragmatic and intercostal motor neurons simultaneously.
. Primary myopathic degeneration of the diaphragm due to SMN protein deficiency.

Correct Answer & Explanation

. Severe weakness of the intercostal muscles with relative sparing of the diaphragm.

Explanation

Correct Answer: BIn severe forms of Spinal Muscular Atrophy (such as Type 1), there is a characteristic pattern of respiratory muscle weakness. The intercostal muscles are typically affected much earlier and more severely than the diaphragm, which is relatively spared until the later stages of the disease. This imbalance leads to a "belly breathing" or paradoxical breathing pattern: during inspiration, the relatively strong diaphragm contracts and descends, pushing the abdominal contents outward, while the weak intercostal muscles fail to stabilize the rib cage, causing the chest wall to collapse inward. This inefficient breathing pattern predisposes the infant to hypoventilation, atelectasis, and recurrent pneumonias.

Question 3928

Topic: 4. Pediatrics
A 6-year-old girl with Osteogenesis Imperfecta Type III underwent bilateral femoral rodding with Fassier-Duval telescoping rods two years ago. She now presents with a new angular deformity of the left femur. Radiographs reveal that the distal component of the rod has failed to migrate distally with the growing physis, and the bone has grown past the end of the rod, resulting in a fracture at the unprotected segment. This specific hardware complication is best described as:
. Rod migration
. Hyperplastic callus formation
. Failure to telescope
. Atypical femoral fracture
. Osteomyelitis

Correct Answer & Explanation

. Failure to telescope

Explanation

Fassier-Duval rods are designed to be anchored at the proximal and distal epiphyses/metaphyses and telescope (expand) as the child's bone grows. A common complication of these devices is the "failure to telescope" (sometimes referred to colloquially as "T-boning" or jamming). When the male and female components of the rod fail to slide past each other, the growing bone will eventually grow past the end of the rod. This leaves a segment of the diaphysis unprotected by the intramedullary device, creating a stress riser where the bone is highly susceptible to progressive bowing or fracture, as seen in this patient.

Question 3929

Topic: 4. Pediatrics

A 28-year-old female with a history of multiple childhood fractures and blue sclerae presents to her primary care physician complaining of progressive, bilateral hearing loss over the past three years. Audiometry reveals a mixed hearing loss pattern. Which of the following is the most likely primary etiology for the conductive component of her hearing deficit?

. Recurrent acute otitis media
. Otosclerosis and ossicular chain fixation
. Agenesis of the external auditory canal
. Cholesteatoma formation
. Sensorineural degeneration of the cochlea

Correct Answer & Explanation

. Otosclerosis and ossicular chain fixation

Explanation

Correct Answer: BHearing loss is a very common extra-skeletal manifestation of Osteogenesis Imperfecta, typically presenting in the second to fourth decade of life. It most frequently presents as a mixed hearing loss. The conductive component is primarily due to otosclerosis (abnormal bone remodeling in the middle ear) and fixation or structural abnormalities of the ossicular chain, particularly involving the stapes footplate. The sensorineural component, which often develops later, is related to cochlear dysfunction or microfractures within the otic capsule.

Question 3930

Topic: 4. Pediatrics

A neonate born at 36 weeks gestation presents with severe micromelia, a remarkably soft calvarium, and multiple rib and long bone fractures noted on a skeletal survey. The infant succumbs to respiratory failure shortly after birth. A post-mortem skin biopsy is performed for fibroblast culture and electron microscopy. Which of the following ultrastructural findings is most characteristic of this patient's condition?

. Accumulation of glycogen within lysosomes.
. Broad, ribbon-like type I collagen fibrils.
. Absence of dystrophin protein at the sarcolemma.
. Fragmented elastic fibers with cystic medial necrosis.
. Defective mineralization of the osteoid seam.

Correct Answer & Explanation

. Broad, ribbon-like type I collagen fibrils.

Explanation

Correct Answer: BThe clinical presentation of severe micromelia, a soft calvarium, multiple intrauterine fractures, and perinatal lethality is classic for Osteogenesis Imperfecta Type II. This severe phenotype is typically caused by a qualitative defect in type I collagen, often due to a dominant-negative mutation where the presence of abnormal collagen chains disrupts the assembly of the entire triple helix. On electron microscopy, this structurally abnormal collagen frequently appears as broad, disorganized, or "ribbon-like" fibrils, which contrasts sharply with the tightly packed, uniform, and striated fibrils of normal type I collagen.

Question 3931

Topic: 4. Pediatrics

A 6-year-old boy with Osteogenesis Imperfecta Type IV sustains a displaced midshaft femur fracture. The orthopedic surgeon is deciding between plate osteosynthesis and intramedullary rodding. Why is rigid plate fixation generally contraindicated for diaphyseal fractures in patients with severe Osteogenesis Imperfecta?

. It stimulates excessive hyperplastic callus formation leading to neurovascular compromise.
. It creates significant stress risers at the ends of the construct in osteopenic bone, leading to peri-implant fractures.
. It prevents the systemic distribution and efficacy of postoperative intravenous bisphosphonates.
. It requires a significantly longer period of strict cast immobilization compared to intramedullary rodding.
. It has an unacceptably high rate of deep infection due to the larger surgical exposure required.

Correct Answer & Explanation

. It creates significant stress risers at the ends of the construct in osteopenic bone, leading to peri-implant fractures.

Explanation

Correct Answer: BIn patients with Osteogenesis Imperfecta (OI), the bone is inherently osteopenic and brittle due to qualitative or quantitative defects in type I collagen. Rigid plate osteosynthesis creates a significant mechanical mismatch between the stiff metal plate and the fragile bone. This leads to profound stress shielding under the plate and massive stress risers at the proximal and distal ends of the construct. Consequently, patients are at an extremely high risk of sustaining peri-implant fractures (fractures occurring just past the end of the plate) once they resume weight-bearing. Therefore, load-sharing devices, specifically intramedullary rods (often telescoping, like Fassier-Duval rods, to accommodate growth), are the gold standard for diaphyseal fractures in OI as they protect the entire length of the bone.

Question 3932

Topic: 4. Pediatrics

In patients with Osteogenesis Imperfecta, the most common biochemical defect is a single base pair substitution that replaces glycine with a bulkier amino acid in the procollagen triple helix. Why is the substitution of glycine specifically so detrimental to the structural integrity of type I collagen?

. Glycine is required for the hydroxylation of proline and lysine residues.
. Glycine is the only amino acid with a side chain small enough to fit within the sterically restricted interior of the collagen triple helix.
. Glycine prevents the premature cleavage of procollagen extension peptides.
. Glycine forms vital disulfide bonds necessary for intermolecular cross-linking.
. Glycine is essential for the initial assembly of the three alpha chains at their C-terminal ends.

Correct Answer & Explanation

. Glycine is the only amino acid with a side chain small enough to fit within the sterically restricted interior of the collagen triple helix.

Explanation

Glycine must occur at every third position (Gly-X-Y) in the collagen alpha chain because its small hydrogen side chain is the only one that can fit into the crowded central core of the triple helix. Substitution with bulkier amino acids disrupts helical folding, leading to degradation or structural weakness.

Question 3933

Topic: 4. Pediatrics
A 6-year-old girl with Osteogenesis Imperfecta Type III undergoes bilateral femoral rodding with Fassier-Duval telescoping rods. Two years later, she presents with knee pain. Radiographs demonstrate proximal migration of the female component out of the distal epiphysis. What is the most common technical error leading to this specific failure mode?
. Failure to properly engage the threads of the distal epiphysis
. Failure to anchor the female component securely in the proximal epiphysis
. Over-reaming of the femoral diaphysis
. Asymmetric growth of the distal femoral physis
. Failure to cut the male rod to the correct length

Correct Answer & Explanation

. Failure to anchor the female component securely in the proximal epiphysis

Explanation

In the Fassier-Duval system, the female (hollow) rod must be securely anchored in the proximal epiphysis/metaphysis, and the male rod in the distal epiphysis. Failure to secure the female rod proximally allows it to migrate distally or fail to telescope properly.

Question 3934

Topic: 4. Pediatrics
An infant is diagnosed with Spinal Muscular Atrophy following newborn screening, which revealed a homozygous deletion of the SMN1 gene. Further genetic analysis demonstrates the presence of four copies of the SMN2 gene. How does this specific genetic profile most likely influence the child's clinical prognosis?
. It guarantees a Type 1 SMA phenotype with onset before 6 months of age.
. It predicts a milder clinical phenotype, likely SMA Type III or IV.
. It indicates a high likelihood of developing severe intellectual disability.
. It renders the patient unresponsive to survival motor neuron-enhancing therapies.
. It increases the risk of developing early-onset basilar invagination.

Correct Answer & Explanation

. It predicts a milder clinical phenotype, likely SMA Type III or IV.

Explanation

The clinical severity of SMA is inversely correlated with the number of SMN2 gene copies. A higher SMN2 copy number (e.g., 3 or 4) produces a greater amount of functional SMN protein, typically resulting in milder phenotypes such as SMA Type III or IV.

Question 3935

Topic: 4. Pediatrics

A 6-month-old male with a known FGFR3 mutation presents with failure to thrive and episodes of central sleep apnea. What is the most appropriate next step in management?

. Initiate continuous positive airway pressure (CPAP)
. MRI of the cervical spine and brainstem
. Flexion-extension radiographs of the cervical spine
. Tracheostomy
. Observation as this is transient in infancy

Correct Answer & Explanation

. MRI of the cervical spine and brainstem

Explanation

Central sleep apnea in an infant with achondroplasia is highly suggestive of cervicomedullary compression at the foramen magnum. An MRI is required to evaluate the severity of stenosis before considering urgent suboccipital decompression.

Question 3936

Topic: 4. Pediatrics

A 12-year-old boy presents with mild short stature, generalized joint pain, and an early waddling gait. Radiographs show delayed epiphyseal ossification in multiple joints and a double-layered appearance of the patella on the lateral view. Spine radiographs are notably normal. What is the most likely diagnosis?

. Achondroplasia
. Multiple epiphyseal dysplasia (MED)
. Spondyloepiphyseal dysplasia (SED)
. Mucopolysaccharidosis
. Osteogenesis imperfecta

Correct Answer & Explanation

. Multiple epiphyseal dysplasia (MED)

Explanation

Multiple epiphyseal dysplasia (MED) primarily affects the epiphyses with minimal spinal involvement, differentiating it from spondyloepiphyseal dysplasia (SED). The double-layered patella is a classic radiographic hallmark of the disease.

Question 3937

Topic: 4. Pediatrics

A newborn is evaluated for severe limb shortening, a 'hitchhiker thumb' deformity, cauliflower ears, and a rigid cervical kyphosis. A mutation in which of the following genes is responsible for this condition?

. FGFR3
. SLC26A2
. COMP
. COL2A1

Correct Answer & Explanation

. SLC26A2

Explanation

Diastrophic dysplasia is an autosomal recessive condition caused by a defect in the sulfate transporter gene, SLC26A2. Classic clinical features include the hitchhiker thumb, cauliflower ear deformity, and severe cervical kyphosis.

Question 3938

Topic: 4. Pediatrics

An infant with achondroplasia is being evaluated by a pediatric orthopedist. The parents report episodes of apnea and increased tone in the extremities. What is the most critical anatomical region to evaluate immediately?

. Atlantoaxial articulation
. Foramen magnum
. Thoracolumbar junction
. Lumbosacral junction

Correct Answer & Explanation

. Foramen magnum

Explanation

Foramen magnum stenosis in achondroplasia can cause lethal cervicomedullary compression, presenting as central sleep apnea, hypotonia, or hyperreflexia. Immediate evaluation with an MRI of the craniocervical junction is required.

Question 3939

Topic: 4. Pediatrics

A 5-year-old child presents with disproportionate short stature and waddling gait. Unlike typical achondroplasia, the child has completely normal facial features and head circumference. Genetic testing reveals a mutation in the COMP gene. What is the diagnosis?

. Hypochondroplasia
. Pseudoachondroplasia
. Multiple epiphyseal dysplasia
. Spondyloepiphyseal dysplasia congenita

Correct Answer & Explanation

. Pseudoachondroplasia

Explanation

Pseudoachondroplasia is caused by a mutation in the Cartilage Oligomeric Matrix Protein (COMP) gene. Unlike achondroplasia, patients have normal facial features and head size, but suffer from disproportionate short stature and early-onset osteoarthritis.

Question 3940

Topic: 4. Pediatrics

A 4-year-old child presents with a short trunk, severe coxa vara, and atlantoaxial instability. Radiographs demonstrate delayed ossification of the capital femoral epiphyses and a barrel-shaped chest. Genetic testing reveals a mutation in COL2A1. What is the diagnosis?

. Diastrophic dysplasia
. Cleidocranial dysplasia
. Spondyloepiphyseal dysplasia congenita
. Achondroplasia

Correct Answer & Explanation

. Spondyloepiphyseal dysplasia congenita

Explanation

Spondyloepiphyseal dysplasia congenita (SEDC) is a type II collagenopathy caused by mutations in the COL2A1 gene. It classically presents with a short trunk, coxa vara, and atlantoaxial instability.

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