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Infection, Pharmacology & VTE MCQs

Practice Set 6 of 68

This practice set contains high-yield board review questions covering key concepts in Infection, Pharmacology & VTE. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 101

Topic: Infection, Pharmacology & VTE

A 3-year-old boy refuses to bear weight on his right leg. His temperature is 38.8°C (101.8°F), ESR is 55 mm/hr, WBC is 14,000/mm3, and plain radiographs of the right hip are normal. Joint aspiration yields purulent fluid. What is the most critical immediate intervention?

. Intravenous antibiotics and observation
. Urgent surgical irrigation and debridement of the hip joint
. Serial aspirations of the hip joint
. MRI of the pelvis with contrast
. Application of a spica cast

Correct Answer & Explanation

. Urgent surgical irrigation and debridement of the hip joint

Explanation

Septic arthritis of the hip in a pediatric patient is a surgical emergency. Urgent open or arthroscopic irrigation and debridement is required to decompress the joint, remove purulent material, and prevent avascular necrosis and cartilage destruction.

Question 102

Topic: Infection, Pharmacology & VTE

A 4-year-old boy presents with a 2-day history of right hip pain and a limp. He is afebrile (37.2 degrees C), WBC is 10,500/mm3, ESR is 15 mm/hr, and he can bear weight with a limp. He refuses internal rotation of the hip. What is the most appropriate next step in management?

. Immediate surgical irrigation and debridement
. Ultrasound-guided hip aspiration
. Observation and administration of NSAIDs
. Intravenous antibiotics
. MRI of the pelvis with contrast

Correct Answer & Explanation

. Observation and administration of NSAIDs

Explanation

The patient has 0 out of 4 Kocher criteria (fever >38.5 C, non-weight bearing, ESR >40, WBC >12,000), making septic arthritis highly unlikely. The most likely diagnosis is transient synovitis, which is treated supportively with NSAIDs and observation.

Question 103

Topic: Infection, Pharmacology & VTE

A 4-year-old boy refuses to bear weight on his right leg. He has a temperature of 38.5 degrees C, ESR of 45 mm/hr, WBC of 13,000/mm3, and refuses to move his hip. According to the Kocher criteria, what is the approximate probability he has septic arthritis rather than transient synovitis?

. 5%
. 40%
. 71%
. 99%
. 100%

Correct Answer & Explanation

. 99%

Explanation

This patient has 4 Kocher criteria: non-weight-bearing, temperature >38.5 C, ESR >40, and WBC >12,000. The presence of 4 criteria predicts a 99% probability of septic arthritis, distinguishing it from transient synovitis.

Question 104

Topic: Infection, Pharmacology & VTE

A 4-year-old boy presents with a 2-day history of right hip pain, a temperature of 38.8°C (101.8°F), an inability to bear weight, a WBC count of 14,000/mm3, and an ESR of 50 mm/hr. What is the most appropriate next step in management?

. Intravenous antibiotics and observation
. MRI of the right hip
. Ultrasound-guided aspiration of the right hip
. Bone scintigraphy
. Surgical drainage without aspiration

Correct Answer & Explanation

. Ultrasound-guided aspiration of the right hip

Explanation

The patient has 4 out of 4 Kocher criteria, yielding a 99% probability of septic arthritis. Immediate joint aspiration is the gold standard for definitive diagnosis before initiating antibiotic therapy.

Question 105

Topic: Infection, Pharmacology & VTE

A 45-year-old farmer sustains an open tibia fracture with gross soil and manure contamination. Which of the following antibiotic regimens is most appropriate for initial management in the emergency department?

. Cefazolin alone
. Cefazolin and an aminoglycoside
. Cefazolin, an aminoglycoside, and high-dose penicillin
. Vancomycin alone
. Ciprofloxacin alone

Correct Answer & Explanation

. Cefazolin, an aminoglycoside, and high-dose penicillin

Explanation

Farm injuries with gross soil or manure contamination are at high risk for clostridial infection. The addition of high-dose penicillin to a first-generation cephalosporin and an aminoglycoside provides the necessary anaerobic coverage.

Question 106

Topic: Infection, Pharmacology & VTE
Which of the following best describes the mechanism of action of rivaroxaban, an oral anticoagulant commonly used for venous thromboembolism prophylaxis after total joint arthroplasty?
. Direct thrombin inhibitor
. Vitamin K antagonist
. Direct Factor Xa inhibitor
. Indirect Factor Xa inhibitor via antithrombin III
. Platelet ADP receptor antagonist

Correct Answer & Explanation

. Direct Factor Xa inhibitor

Explanation

Rivaroxaban and apixaban are direct oral anticoagulants that work by directly inhibiting Factor Xa. Dabigatran is a direct thrombin (Factor IIa) inhibitor, while low-molecular-weight heparins act indirectly via antithrombin III.

Question 107

Topic: Infection, Pharmacology & VTE

In the pathophysiology of chronic osteomyelitis, what is the term used to describe the segment of necrotic bone that has become separated from the surrounding viable bone?

. Involucrum
. Cloaca
. Sequestrum
. Brodie's abscess
. Physeal scar

Correct Answer & Explanation

. Sequestrum

Explanation

A sequestrum is a piece of dead, devascularized bone that separates from normal bone in chronic osteomyelitis. The involucrum is the new bone formation that surrounds the sequestrum.

Question 108

Topic: Infection, Pharmacology & VTE

According to the Kocher criteria, which combination strongly differentiates septic arthritis of the hip from transient synovitis in a pediatric patient?

. ESR > 40 mm/hr, WBC > 12,000, inability to bear weight, fever > 38.5 C
. CRP > 2.0 mg/dL, WBC > 10,000, morning stiffness, rash
. Radiographic joint space widening, ESR > 20, positive Barlow test
. History of recent URI, low-grade fever, limp
. Ultrasound showing effusion, afebrile, normal inflammatory markers

Correct Answer & Explanation

. ESR > 40 mm/hr, WBC > 12,000, inability to bear weight, fever > 38.5 C

Explanation

The Kocher criteria include non-weight-bearing status, ESR > 40 mm/hr, fever > 38.5 C, and a WBC count > 12,000 cells/mm3. The presence of all four criteria yields a 99% predictive probability for septic arthritis.

Question 109

Topic: Infection, Pharmacology & VTE
A patient is prescribed fondaparinux for DVT prophylaxis following total hip arthroplasty. What is the specific mechanism of action of this medication?
. Direct thrombin inhibitor
. Vitamin K antagonist
. Indirect selective inhibitor of Factor Xa via antithrombin III
. Direct selective inhibitor of Factor Xa
. Inhibitor of ADP-induced platelet aggregation

Correct Answer & Explanation

. Indirect selective inhibitor of Factor Xa via antithrombin III

Explanation

Fondaparinux is a synthetic pentasaccharide that binds to antithrombin III, causing a conformational change that indirectly and selectively inhibits Factor Xa. Unlike Rivaroxaban, it is not a direct Factor Xa inhibitor.

Question 110

Topic: Infection, Pharmacology & VTE

Which of the following is the most common site for primary epiphyseal osteomyelitis:

. Proximal femur
. Distal femur
. Proximal tibia
. Distal tibia
. Proximal humerus

Correct Answer & Explanation

. Distal femur

Explanation

Osteomyelitis of the epiphysis is less common than osteomyelitis of the metaphysis. Osteomyelitis of the epiphysis may occur from spread across transphyseal vessels or primary hematogenous seeding. The most common location is the distal femoral epiphysis, and it most commonly affects infants and young children.

Question 111

Topic: Infection, Pharmacology & VTE

A normal (negative) result is used to rule out septic arthritis of the hip on which of the following tests:

. Plain radiographs
. Ultrasound
. C ulture of joint fluid
. C-reactive protein
. None of the above

Correct Answer & Explanation

. None of the above

Explanation

False-negative results may occur with each of the tests. C ulture results may be negative in up to a quarter of patients. Ultrasound may be false-negative in up to 20% of patients with septic arthritis of the hip. C-reactive protein may be normal early in the course of disease. The diagnosis is based upon a constellation of findings, including clinical examination.Correct Answer: None of the above

Question 112

Topic: Infection, Pharmacology & VTE

A 4-year-old presents with fever, inability to bear weight on the right leg, a white blood cell count of 14,000/mm3, and an erythrocyte sedimentation rate (ESR) of 50 mm/hr. According to the Kocher criteria, what is the probability of septic arthritis?

. Less than 10%
. Approximately 40%
. Approximately 70%
. Greater than 90%
. 100%

Correct Answer & Explanation

. Greater than 90%

Explanation

The patient meets all 4 Kocher criteria (fever, non-weight-bearing, WBC >12,000, ESR >40). The probability of septic arthritis with 4 positive predictors is 93-99%.

Question 113

Topic: Infection, Pharmacology & VTE

A 2-year-old girl is brought to the emergency department with a limp, refusal to bear weight on the right leg, and a fever of 38.2 C. Aspiration of the hip yields purulent fluid. Given the patient's age and contemporary vaccination protocols, which of the following organisms is increasingly recognized as a leading cause of pediatric septic arthritis?

. Staphylococcus aureus
. Streptococcus pneumoniae
. Neisseria gonorrhoeae
. Kingella kingae
. Haemophilus influenzae type b

Correct Answer & Explanation

. Kingella kingae

Explanation

Kingella kingae is a fastidious Gram-negative organism that is now considered the most common bacterial cause of septic arthritis in children aged 6 to 36 months in areas with routine Hib and pneumococcal vaccination.

Question 114

Topic: Infection, Pharmacology & VTE

When evaluating a pediatric patient with a painful hip, the classic Kocher criteria are used to differentiate septic arthritis from transient synovitis. Which of the following is NOT one of the original four parameters described by Kocher?

. History of fever greater than 38.5 C
. Inability to bear weight
. Erythrocyte sedimentation rate (ESR) greater than 40 mm/hr
. White blood cell count greater than 12,000 cells/mm3
. Joint space widening greater than 2mm on plain radiograph

Correct Answer & Explanation

. Joint space widening greater than 2mm on plain radiograph

Explanation

The four classic Kocher criteria are fever >38.5 C, non-weight-bearing status, ESR >40 mm/hr, and WBC >12,000 cells/mm3. Joint space widening on plain films is not part of this specific predictive model.

Question 115

Topic: Infection, Pharmacology & VTE

C hronic recurrent multifocal osteomyelitis is caused by which of the following:

. Staphylococcus epidermidis
. Corynebacterium
. Spirochetal infection
. Viral infection
. No organism has been isolated

Correct Answer & Explanation

. No organism has been isolated

Explanation

Chronic recurrent multifocal osteomyelitis presents as chronic joint pain at multiple locations and at different times. No organism has been isolated from patients presenting with chronic recurrent multifocal osteomyelitis. There is no role for surgery or antibiotics because symptoms generally resolve over a period of time.

Question 116

Topic: Infection, Pharmacology & VTE

Which of the following organisms is the most common cause of obturator internus muscle abscess in children:

. Streptococcus A
. Staphylococcus aureus
. Salmonella
. Escherichia coli
. Pseudomonas aeruginosa

Correct Answer & Explanation

. Staphylococcus aureus

Explanation

Abscess of the obturator internus muscle may mimic septic arthritis. It is best diagnosed by magnetic resonance image. <1>Staphylococcus aureus is the most common causative organism, accounting for 75% of cases of obturator internus muscle abscess. Antibiotic treatment should be tried first and is successful in most cases.

Question 117

Topic: Infection, Pharmacology & VTE

Which of the following studies is likely to help in distinguishing osteomyelitis from infarct in a patient with sickle cell anemia:

. Magnetic resonance imaging
. C omputed tomography
. Bone and bone marrow scans
. Ultrasound
. Plain radiographs

Correct Answer & Explanation

. Bone and bone marrow scans

Explanation

The combination of bone and bone marrow scan is the only imaging method that is useful in distinguishing osteomyelitis from infarct in patients with sickle cell anemia. The bone marrow scan is normal, but the bone scan shows increased uptake in a patient with osteomyelitis.

Question 118

Topic: Infection, Pharmacology & VTE

A 5-year-old boy presents with acute atraumatic right hip pain and a limp. He refuses to bear weight. His temperature is 38.8 C (101.8 F), ESR is 45 mm/hr, and WBC count is 13,500/mm3. According to the Kocher criteria, what is the approximate probability that this patient has septic arthritis rather than transient synovitis?

. 15%
. 40%
. 73%
. 93%
. 99%

Correct Answer & Explanation

. 99%

Explanation

The Kocher criteria include non-weight-bearing status, temperature >38.5 C, ESR >40 mm/hr, and WBC >12,000/mm3. The presence of all four criteria indicates an approximate 99% probability of septic arthritis.

Question 119

Topic: Infection, Pharmacology & VTE

A 5-year-old boy presents with right hip pain and a limp. According to the Kocher criteria, which set of findings yields the highest probability of septic arthritis?

. Non-weight-bearing, ESR > 40 mm/hr, fever > 38.5 C, and WBC > 12,000/mm3
. Weight-bearing with a limp, normal ESR, fever > 39.0 C, normal WBC
. Non-weight-bearing, normal ESR, no fever, WBC > 15,000/mm3
. Knee pain, ESR > 20 mm/hr, fever > 38.0 C, WBC > 10,000/mm3
. Groin pain, ESR > 10 mm/hr, afebrile, CRP > 1.0 mg/dL

Correct Answer & Explanation

. Non-weight-bearing, ESR > 40 mm/hr, fever > 38.5 C, and WBC > 12,000/mm3

Explanation

The Kocher criteria for septic arthritis of the hip include non-weight-bearing, ESR > 40 mm/hr, fever > 38.5 C, and WBC > 12,000/mm3. Having all four criteria gives a 99% probability of septic arthritis.

Question 120

Topic: Infection, Pharmacology & VTE
A 50-year-old retired boilermaker with shortness of breath comes to the Respiratory Clinic. He has smoked ten cigarettes per day for the past 30 years. The GP wonders if he has obstructive lung disease and the man arrives with his spirometry results, which show: forced expiratory volume in 1 s (FEV1) 1.74 l (predicted 3.0 l), forced vital capacity (FVC) 2.5 l (predicted 2.8 l); post-salbutamol FEV1 1.81 l, post-salbutamol FVC 2.7 l; transfer factor 55%. Which of the following is the most likely diagnosis?
. Asbestos-related pleural plaque disease
. Asthma
. Emphysema
. Pulmonary embolism
. Pulmonary fibrosis

Correct Answer & Explanation

. Emphysema

Explanation

Correct Answer: C. The FVC is only slightly reduced, but the ratio of FEV1 to FVC is significantly reduced. Transfer factor is also reduced at 55%. With reversibility of less than 10% post-salbutamol, the most likely diagnosis is chronic obstructive pulmonary disease (COPD), specifically emphysema.

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