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1. General Principles & Basic Science MCQs

Practice Set 23 of 789

This practice set contains high-yield board review questions covering key concepts in 1. General Principles & Basic Science. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 441

Topic: Infection, Pharmacology & VTE

A 2-week-old neonate presents with irritability, poor feeding, and pseudoparalysis of the right lower extremity. Ultrasound shows a right hip effusion. Aspiration reveals purulent fluid. Empiric antibiotic coverage must include agents effective against Staphylococcus aureus and which of the following organisms?

. Streptococcus pneumoniae
. Group B Streptococcus and Gram-negative bacilli
. Neisseria gonorrhoeae
. Haemophilus influenzae type B
. Kingella kingae

Correct Answer & Explanation

. Group B Streptococcus and Gram-negative bacilli

Explanation

Neonatal (under 1 month) septic arthritis is most commonly caused by S. aureus, Group B Streptococcus, and Gram-negative bacilli. Empiric treatment typically includes an antistaphylococcal agent combined with a third-generation cephalosporin or gentamicin.

Question 442

Topic: 1. General Principles & Basic Science
Which of the following laboratory parameters is a component of the Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score?
. Serum potassium
. Serum sodium
. Serum calcium
. Lactate dehydrogenase (LDH)
. Erythrocyte sedimentation rate (ESR)

Correct Answer & Explanation

. Serum sodium

Explanation

The LRINEC score helps distinguish necrotizing fasciitis from severe cellulitis. It incorporates C-reactive protein, total WBC count, hemoglobin, serum sodium, creatinine, and glucose.

Question 443

Topic: Infection, Pharmacology & VTE

A 14-year-old boy is recovering from an uncomplicated CA-MRSA skin and soft tissue infection that was surgically drained. He is to be discharged on oral antibiotics. The isolate is sensitive to trimethoprim-sulfamethoxazole, clindamycin, and tetracyclines. Which of the following antibiotics is known to also inhibit bacterial toxin production?

. Trimethoprim-sulfamethoxazole
. Doxycycline
. Clindamycin
. Amoxicillin-clavulanate
. Ciprofloxacin

Correct Answer & Explanation

. Clindamycin

Explanation

Clindamycin is a lincosamide antibiotic that binds to the 50S ribosomal subunit. In addition to its bacteriostatic effect, it powerfully inhibits the synthesis of bacterial toxins, such as PVL, making it highly effective for toxin-mediated infections.

Question 444

Topic: Infection, Pharmacology & VTE

A 7-year-old boy presents with a 3-day history of fever, limp, and severe right thigh pain. Blood cultures are drawn.

Based on the likely diagnosis of deep infection, what is the most appropriate next step in management after initiating empiric antibiotics?

. Immediate hip aspiration
. Surgical debridement and drainage of the focal lesion
. Immobilization in a spica cast
. Observation and repeat MRI in 2 weeks
. Switch to oral antibiotics after 48 hours

Correct Answer & Explanation

. Surgical debridement and drainage of the focal lesion

Explanation

The clinical presentation suggests acute osteomyelitis or a deep subperiosteal abscess. Once a focal fluid collection or abscess is identified, prompt surgical drainage and debridement are required for adequate source control.

Question 445

Topic: Infection, Pharmacology & VTE

In chronic orthopedic implant infections, Staphylococcus epidermidis evades host defenses primarily through the production of a glycocalyx biofilm. Which of the following phases of biofilm formation involves "quorum sensing"?

. Initial reversible attachment
. Irreversible attachment via adhesins
. Maturation and production of the extracellular polymeric substance
. Dispersion and detachment of planktonic bacteria
. Immediate lysis of competing host flora

Correct Answer & Explanation

. Maturation and production of the extracellular polymeric substance

Explanation

Quorum sensing is a cell-to-cell communication mechanism that coordinates gene expression based on bacterial density. It is crucial during the maturation phase of the biofilm, regulating the production of the protective extracellular polymeric substance (EPS).

Question 446

Topic: 1. General Principles & Basic Science

A 6-year-old child with sickle cell disease presents with bilateral tibial pain and fever. Ultrasound shows no subperiosteal fluid collections. Blood cultures are pending. Which of the following imaging modalities is most specific for differentiating acute osteomyelitis from bone infarction in this patient?

. Technetium-99m bone scan alone
. Magnetic Resonance Imaging with gadolinium
. Indium-111 labeled white blood cell scan combined with Technetium-99m marrow scan
. Plain radiography
. Non-contrast computed tomography

Correct Answer & Explanation

. Indium-111 labeled white blood cell scan combined with Technetium-99m marrow scan

Explanation

Distinguishing osteomyelitis from bone infarction in sickle cell patients is challenging. A combination of a radiolabeled WBC scan and a bone marrow scan provides the highest specificity; osteomyelitis shows increased WBC uptake with discordant marrow uptake, whereas infarction shows decreased uptake on both.

Question 447

Topic: Infection, Pharmacology & VTE

A 25-year-old construction worker stepped on a rusty nail that penetrated deeply through the rubber sole of his work boot into his foot. Seven days later, he develops signs of osteomyelitis of the calcaneus. In addition to S. aureus, which organism must be covered by empiric antibiotics?

. Streptococcus pyogenes
. Clostridium perfringens
. Pseudomonas aeruginosa
. Pasteurella multocida
. Eikenella corrodens

Correct Answer & Explanation

. Pseudomonas aeruginosa

Explanation

Deep puncture wounds through rubber-soled footwear are classically associated with Pseudomonas aeruginosa osteomyelitis. The rubber sole provides a warm, moist environment where the bacteria thrive.

Question 448

Topic: Infection, Pharmacology & VTE

Which of the following complications is significantly more common in pediatric osteomyelitis caused by community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) compared to methicillin-sensitive Staphylococcus aureus (MSSA)?

. Pathologic fracture
. Deep venous thrombosis (DVT)
. Growth arrest
. Chronic recurrent multifocal osteomyelitis
. Malignant transformation

Correct Answer & Explanation

. Deep venous thrombosis (DVT)

Explanation

CA-MRSA osteomyelitis in children has a known strong association with adjacent deep venous thrombosis (DVT) and septic emboli compared to MSSA. This hypercoagulability requires clinical vigilance and often necessitates anticoagulation.

Question 449

Topic: Infection, Pharmacology & VTE

In acute hematogenous osteomyelitis in a young child, what anatomical feature of the metaphyseal blood vessels strongly predisposes the metaphysis to bacterial seeding?

. High-velocity arterial flow
. Sluggish flow in venous capillary loops
. Abundant local macrophages
. Direct connection to the joint space in all joints
. Lack of a continuous endothelial lining

Correct Answer & Explanation

. Sluggish flow in venous capillary loops

Explanation

The metaphyseal venous sinusoids feature sluggish, turbulent blood flow and a local deficiency in phagocytic cells. This creates an ideal microenvironment for bloodborne bacteria to deposit and proliferate.

Question 450

Topic: Infection, Pharmacology & VTE

A 4-year-old boy presents with a limp and right hip pain. He is afebrile (37.2°C) but refuses to bear weight on the right leg. Laboratory tests show a WBC of 10,500/mm3 and an ESR of 22 mm/hr. What is the approximate probability of septic arthritis according to the Kocher criteria?

. 3%
. 40%
. 71%
. 93%
. 99%

Correct Answer & Explanation

. 3%

Explanation

The Kocher criteria for septic arthritis of the pediatric hip include fever > 38.5C, inability to bear weight, ESR > 40, and WBC > 12,000. Having only one positive criterion (non-weight bearing) correlates with a roughly 3% probability.

Question 451

Topic: Infection, Pharmacology & VTE

An 8-year-old girl with homozygous sickle cell disease presents with fever and severe tibial pain. Blood cultures are drawn. Empiric antibiotic therapy should ideally include robust coverage for which two most common organisms in this specific population?

. S. aureus and S. pneumoniae
. S. aureus and Salmonella species
. Group A Streptococcus and E. coli
. P. aeruginosa and S. aureus
. Kingella kingae and S. aureus

Correct Answer & Explanation

. S. aureus and Salmonella species

Explanation

While Staphylococcus aureus remains the most common overall cause of osteomyelitis in sickle cell disease, Salmonella species are disproportionately elevated in this population. Empiric therapy with a third-generation cephalosporin and an anti-staphylococcal agent is standard.

Question 452

Topic: Infection, Pharmacology & VTE
A 14-month-old child presents with acute onset of a limp and a swollen left knee. Arthrocentesis yields purulent fluid with 65,000 WBCs, but routine Gram stain and standard cultures are negative at 48 hours. Which of the following fastidious organisms is the most likely culprit?
. Neisseria gonorrhoeae
. Borrelia burgdorferi
. Kingella kingae
. Haemophilus influenzae
. Mycoplasma pneumoniae

Correct Answer & Explanation

. Kingella kingae

Explanation

Kingella kingae is a fastidious Gram-negative organism that is now a leading cause of septic arthritis and osteomyelitis in children aged 6 months to 4 years. It is notoriously difficult to culture and often requires inoculation into BACTEC blood culture bottles.

Question 453

Topic: Infection, Pharmacology & VTE

A 10-year-old girl presents with recurrent episodes of multifocal bone pain. Radiographs reveal lytic lesions with sclerotic borders in the clavicle and distal tibia. Biopsy shows sterile, non-specific inflammation. Which of the following is the most appropriate initial treatment?

. Prolonged IV antibiotics
. Surgical curettage and bone grafting
. Nonsteroidal anti-inflammatory drugs (NSAIDs)
. Intra-articular corticosteroid injections
. Radiation therapy

Correct Answer & Explanation

. Nonsteroidal anti-inflammatory drugs (NSAIDs)

Explanation

Chronic recurrent multifocal osteomyelitis (CRMO) is an autoinflammatory, non-infectious bone disease. The first-line treatment is NSAIDs, which provide significant symptomatic relief and can induce remission in most patients.

Question 454

Topic: Infection, Pharmacology & VTE

A 2-week-old neonate in the NICU is noted to have a swollen, immobile right shoulder. Ultrasound confirms an effusion, and aspiration is planned. In addition to Staphylococcus aureus, which organism is a highly prominent cause of septic arthritis specifically in this age group?

. Kingella kingae
. Streptococcus pneumoniae
. Group B Streptococcus
. Haemophilus influenzae type B
. Salmonella enteritidis

Correct Answer & Explanation

. Group B Streptococcus

Explanation

Group B Streptococcus (Streptococcus agalactiae) and Gram-negative bacilli (such as E. coli) are major causes of neonatal septic arthritis and osteomyelitis, heavily influencing the choice of empiric antibiotics in neonates.

Question 455

Topic: 1. General Principles & Basic Science

What is the primary pathophysiological mechanism leading to the development of avascular necrosis (AVN) of the femoral head following neglected septic arthritis of the infant hip?

. Direct bacterial invasion and lysis of the chondrocytes
. Bacterial endotoxin-mediated osteoclast activation
. Increased intra-articular pressure compressing extraosseous retinacular vessels
. Septic emboli occluding the artery of the ligamentum teres
. Reactive hyperemia leading to rapid, massive bone resorption

Correct Answer & Explanation

. Increased intra-articular pressure compressing extraosseous retinacular vessels

Explanation

The infant hip capsule is thick and strong; as purulent fluid rapidly accumulates, intra-articular pressure rises drastically. This pressure tamponades the extraosseous retinacular blood vessels, leading to ischemia and subsequent AVN.

Question 456

Topic: Infection, Pharmacology & VTE

In a 7-year-old child being treated for acute hematogenous osteomyelitis, which inflammatory marker is most useful for evaluating the response to antibiotic therapy and guiding the transition from intravenous to oral medications?

. White blood cell count (WBC)
. Erythrocyte sedimentation rate (ESR)
. C-reactive protein (CRP)
. Procalcitonin
. Serum ferritin

Correct Answer & Explanation

. C-reactive protein (CRP)

Explanation

CRP peaks within 48 hours of infection onset and drops rapidly with effective treatment, making it the most reliable dynamic marker for monitoring therapeutic response. ESR can remain elevated for weeks despite adequate treatment.

Question 457

Topic: Infection, Pharmacology & VTE

A 7-year-old boy presents with a massive knee effusion and a slight limp, but he retains full range of motion with only minimal pain. He is afebrile. Which of the following findings most strongly differentiates Lyme arthritis from pyogenic septic arthritis?

. Refusal to bear weight on the affected limb
. Peripheral WBC count > 15,000
. Knee synovial fluid WBC count > 50,000
. The disproportionate lack of severe pain with range of motion
. A markedly elevated ESR > 80 mm/hr

Correct Answer & Explanation

. The disproportionate lack of severe pain with range of motion

Explanation

Lyme arthritis classically presents with a large joint effusion but remarkably little pain on active or passive range of motion compared to the extreme pain seen in acute pyogenic septic arthritis.

Question 458

Topic: Infection, Pharmacology & VTE

A 12-year-old steps on a rusty nail that pierces his rubber-soled sneaker, subsequently developing osteomyelitis in the foot. Following surgical debridement, what is the most appropriate empiric oral antibiotic choice for the most likely organism?

. Amoxicillin-clavulanate
. Clindamycin
. Ciprofloxacin
. Linezolid
. Doxycycline

Correct Answer & Explanation

. Ciprofloxacin

Explanation

Puncture wounds occurring through rubber-soled shoes are strongly associated with Pseudomonas aeruginosa osteomyelitis. Ciprofloxacin provides excellent oral anti-pseudomonal coverage and bone penetration.

Question 459

Topic: 1. General Principles & Basic Science

When performing an ultrasound-guided anterior aspiration of the hip joint in a child for suspected septic arthritis, which important neurovascular structure lies immediately medial to the optimal needle trajectory?

. Lateral femoral cutaneous nerve
. Femoral artery
. Sciatic nerve
. Superior gluteal nerve
. Obturator nerve

Correct Answer & Explanation

. Femoral artery

Explanation

The standard anterior approach to the hip joint aims lateral to the femoral neurovascular bundle. The femoral artery lies directly medial to the correct needle tract and should be protected during insertion.

Question 460

Topic: 1. General Principles & Basic Science

The lung attains half of its adult volume at what age:

. 2 years
. 4 years
. 6 years
. 8 years
. 10 years

Correct Answer & Explanation

. 8 years

Explanation

The lung attains 30% of its adult volume at 4 years and 50% at 8 years.

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