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Infection, Pharmacology & VTE MCQs

Practice Set 19 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 361

Topic: Infection, Pharmacology & VTE
Biofilm is believed to play a major role in the pathogenesis of periprosthetic joint infection. Biofilm allows for the bacterial population to evade the effects of antimicrobial therapy primarily through
. adherence and colonization.
. formation of a protective scaffold.
. coating with host proteins.
. direct inhibition of antibiotics.

Correct Answer & Explanation

. formation of a protective scaffold.

Explanation

The intrinsic risk for colonization and subsequent infection associated with implants is exacerbated by implants’ tendency to become coated in host proteins such as fibrinogen and fibronectin shortly after implantation. Following initial adherence and colonization, bacteria are thought to form a complex matrix of an extracellular polymeric substance, serving as a protective scaffold in which they can survive despite the competence of the host’s immune system or the presence of antimicrobial agents. There is no evidence that biofilm directly inhibits antibiotics.

Question 362

Topic: Infection, Pharmacology & VTE
A 2-year-old child refused to walk 3 days prior to being seen because of pain in the left hip. The pain has gradually subsided and the child is now walking. He is afebrile and has full motion of the hips. Laboratory studies show a normal CBC with differential and C-reactive protein. An ultrasound shows a joint effusion in the right hip. What is the most likely diagnosis?
. Juvenile inflammatory arthritis
. Septic arthritis
. Osteomyelitis of the femur
. Leukemia
. Toxic synovitis

Correct Answer & Explanation

. Toxic synovitis

Explanation

The most likely diagnosis is toxic synovitis, and the normal C-reactive protein supports that diagnosis. Juvenile inflammatory arthritis is extremely rare to present with hip involvement. The child most likely does not have a bacterial infection because he has improved rapidly without treatment. A normal CBC with differential precludes the diagnosis of leukemia.

Question 363

Topic: Infection, Pharmacology & VTE
Figures 32a and 32b show the AP and lateral radiographs of an 11-year-old boy who has a severe limp, a fever, and swelling and tenderness of the thigh. Aspiration of the bone reveals purulent material. The patient has most likely been symptomatic for
. 24 hours.
. 2 days.
. 5 days.
. 7 to 14 days.
. 6 months.

Correct Answer & Explanation

. 7 to 14 days.

Explanation

DISCUSSION: In patients with an osteomyelitic infection, radiographic findings at 1 to 5 days usually show soft-tissue swelling only. Seven to 14 days after symptoms begin, radiographs will most likely show the classic signs of acute osteomyelitis. Reactive bone formation would be expected by 6 months.

Question 364

Topic: Infection, Pharmacology & VTE

A 25-year-old professional soccer player sustains a severe valgus injury to the right knee. MRI demonstrates a complete tear of the superficial medial collateral ligament (sMCL). The distal aspect of the torn sMCL is flipped superficial to the pes anserinus. This specific finding is associated with:

. High likelihood of nonoperative healing
. A Stener-like lesion of the knee, typically requiring surgical repair
. Isolated deep MCL injury
. Spontaneous reduction with knee extension
. Concomitant popliteal artery occlusion

Correct Answer & Explanation

. A Stener-like lesion of the knee, typically requiring surgical repair

Explanation

A Stener-like lesion of the knee occurs when the distal aspect of a torn superficial MCL is displaced superficial to the pes anserinus expansion. Because the pes anserinus blocks the torn ends from approximating, this lesion often fails nonoperative management and requires surgical repair or reconstruction.

Question 365

Topic: Infection, Pharmacology & VTE

A 25-year-old football player is diagnosed with a grade 3 medial collateral ligament (MCL) tear. MRI reveals the tear is located at the distal (tibial) insertion with the ligament flipped superficial to the pes anserinus. What is the most appropriate management?

. Hinged knee brace for 6 weeks
. Immediate surgical repair
. Immobilization in extension for 4 weeks
. Cortisone injection and early return to play
. Platelet-rich plasma injection and physical therapy

Correct Answer & Explanation

. Hinged knee brace for 6 weeks

Explanation

A Stener-like lesion of the MCL occurs when the distal MCL avulses and flips superficial to the pes anserinus, preventing anatomic reduction and healing. This specific distal tear pattern is an indication for acute surgical repair.

Question 366

Topic: Infection, Pharmacology & VTE
A 65-year-old woman with type II diabetes mellitus (most recent Hgb A1C was 8.2) has had 3 days of left knee pain. Physical examination of the left knee reveals erythema, warmth and a large effusion. Range of motion is painful and limited to 30 degrees of flexion. She is found to be hypotensive and not responding to volume resuscitation. She requires phenylephrine to maintain Mean Arterial Pressure (MAP) of 70. ESR and CRP are elevated and Lactate is 3.1 mmol/L. What is the next best intervention for this patient’s treatment?
. Administration of broad spectrum IV antibiotics
. Irrigation and debridement in OR followed by broad spectrum IV antibiotics
. NSAIDS and observation with repeat ESR and CRP in 24 hours
. Joint aspiration and blood cultures

Correct Answer & Explanation

. Joint aspiration and blood cultures

Explanation

DISCUSSION: The patient is demonstrating signs of septic shock. Administration of antibiotics should not be delayed. Aspirating the knee joint and obtaining blood cultures can be rapidly accomplished to obtain accurate specimens. This should be followed immediately by administration of broad spectrum IV antibiotics. Patients with septic shock can be identified with a clinical construct of sepsis with persisting hypotension requiring vasopressors to maintain mean arterial pressure (MAP) ≥ 65 mmHg and having a serum lactate level > 2 mmol/L (18 mg/dL) despite adequate volume resuscitation. With these criteria, hospital mortality is in excess of 40%.

Question 367

Topic: Infection, Pharmacology & VTE
What is the typical MRI signal intensity of bone marrow affected by acute osteomyelitis?
. Decreased on T1-weighted imaging, increased on T1-weighted imaging with gadolinium enhancement, increased on T2-weighted imaging
. Decreased on T1-weighted imaging, increased on T1-weighted imaging with gadolinium enhancement, decreased on T2-weighted imaging
. Increased on T1-weighted imaging, increased on T1-weighted imaging with gadolinium enhancement, increased on T2-weighted imaging
. Increased on T1-weighted imaging, increased on T1-weighted imaging with gadolinium enhancement, decreased on T2-weighted imaging
. Increased on T1-weighted imaging, decreased on T1-weighted imaging with gadolinium enhancement, decreased on T2-weighted imaging

Correct Answer & Explanation

. Decreased on T1-weighted imaging, increased on T1-weighted imaging with gadolinium enhancement, increased on T2-weighted imaging

Explanation

DISCUSSION: The classic MRI findings of osteomyelitis are a decrease in the normally high signal intensity of marrow on T1-weighted images and normal or increased signal intensity on T2-weighted images. This is the result of replacement of marrow fat by inflammatory cells and edema, which causes lower signal intensity than fat on T1-weighted images and higher signal intensity than fat on T2-weighted images. The addition of gadolinium to a T1-weighted sequence reveals increased signal intensity in the hyperemic marrow.

Question 368

Topic: Infection, Pharmacology & VTE
What is the most common organism found following a nail puncture wound through tennis shoes in a host without immunocompromise?
. Methicillin-resistant Staphylococcus aureus
. Escherichia coli
. Enterobacter
. Pseudomonas aeruginosa
. Klebsiella pneumoniae

Correct Answer & Explanation

. Pseudomonas aeruginosa

Explanation

The association of a nail puncture wound with a gram-negative infection (Pseudomonas aeruginosa) has been attributed to the local environmental factors in shoes.

Question 369

Topic: Infection, Pharmacology & VTE
An 8-year-old boy has had pain and swelling around the right knee for the past 4 weeks. He recalls bumping it about 4 weeks ago. He has no pain in other joints and denies any fevers, chills, or other symptoms. A radiograph is shown in Figure 13. Laboratory studies show a WBC count of 9,700/mm³, an erythrocyte sedimentation rate of 18 mm/h, and a C-reactive protein level of 3.7 mg/L. What is the next most appropriate step in management?
. Chemotherapy and radiation therapy
. Intravenous antibiotics, protected weight bearing, and a repeat C-reactive protein after improvement
. Open biopsy and debridement of the site, followed by intravenous antibiotics
. Technetium Tc 99m bone scan
. Empiric oral antibiotics and repeat laboratory studies in 1 week

Correct Answer & Explanation

. Open biopsy and debridement of the site, followed by intravenous antibiotics

Explanation

The history and laboratory findings are consistent with osteomyelitis of the patella. The radiograph reveals bone destruction in the patella; therefore, the next most appropriate step is open biopsy and debridement of the site. Aspiration of the knee joint may be needed to rule out septic arthritis prior to patellar debridement. With this amount of bone destruction, surgical debridement is helpful to obtain cultures and to remove necrotic material. Administering antibiotics without any prior culture increases the risk of negative cultures later and a potentially incorrect choice of antibiotic. A neoplasm should be included in the differential. It would be inappropriate to initiate chemotherapy and radiation therapy without a biopsy-confirmed diagnosis. A bone scan is likely to demonstrate uptake, but radiographs have already localized the abnormality to the patella.

Question 370

Topic: Infection, Pharmacology & VTE

What antithrombotic agent is a selective factor I0a inhibitor? Review Topic

. Warfarin
. Low-molecular-weight heparin
. Rivaroxaban
. Aspirin

Correct Answer & Explanation

. Warfarin

Explanation

Rivaroxaban is a selective factor I0a inhibitor. Aspirin is a cyclooxygenase inhibitor. Low-molecular-weight heparin is a nonspecific anticoagulant. Warfarin is a vitamin K antagonist and reduces production of clotting factors II, VII, IX, and X.

Question 371

Topic: Infection, Pharmacology & VTE

What role does quorum sensing play in the development of a bacterial biofilm?

. Activates genes that produce virulence factors
. Creates planktonic bacteria
. Facilitates bacterial adhesion to a substrate
. Lowers antimicrobial resistance

Correct Answer & Explanation

. Activates genes that produce virulence factors

Explanation

The development of a bacterial biofilm is a 2-stage process. The first step is the adhesion of individual bacteria to a substrate regulated by adhesions. After several bacteria have attached, quorum sensing (cell-to-cell communication) allows maturation of the biofilm and expression of genes that activate virulence factors. This can also increase the antibacterial resistance of the bacteria. Planktonic bacteria are individual free-moving bacteria.

Question 372

Topic: Infection, Pharmacology & VTE

A 51-year-old man sustained an open fracture of his tibia in Korea 42 years ago. An infection developed and it was resolved with surgical treatment. For the past 6 months, an ulcer with mild drainage has developed over the medial tibia. The ulcer is small and there is minimal erythema at the ulcer site. A radiograph and MRI scan are shown in Figures 43a and Figure 43b. Initial cultures show Staphylococcus aureus susceptible to the most appropriate antibiotics. Laboratory studies show an erythrocyte sedimentation rate of 70 mm/h. What is the most appropriate surgical treatment at this time? Review Topic

. Irrigation and debridement of the cystic lesion and 6 weeks of IV antibiotics
. Curettage, debridement of nonviable bone, and placement of absorbable antibiotic beads, followed by a course of IV antibiotics from 1 to 4 weeks and a 6-week course of oral antibiotics
. Complete resection of the infected portion of bone, placement of an external fixator to stabilize the tibia, and 6 weeks of IV antibiotics
. Amputation
. Local debridement of bone and the overlying skin and soft tissues, 6 weeks of IV antibiotics, and free-flap wound coverage

Correct Answer & Explanation

. Irrigation and debridement of the cystic lesion and 6 weeks of IV antibiotics

Explanation

The patient has chronic tibial osteomyelitis that is due to low virulent bacteria. The history and studies do not suggest the need for an amputation or a free-flap procedure. This is a localized tibial infection that is in a healed bone; there is no need to resect the entire area of the tibia bone around the infection. The most appropriate treatment is curettage, debridement of nonviable bone, and placement of absorbable antibiotic beads, followed by a course of IV antibiotics from 1 to 4 weeks and a 6-week course of oral antibiotics. Studies have shown that in cases of localized osteomyelitis that are of low virulence, as little as 1 week of IV antibiotics followed by 6 weeks of oral antibiotics is successful.

Question 373

Topic: Infection, Pharmacology & VTE
Figure 40 shows the AP radiograph of a 55-year-old man who reports left knee pain. Which of the following conditions is least likely to produce this radiographic presentation?
. Hemochromatosis
. Alkaptonuria
. Wilson’s disease
. Septic arthritis
. Calcium pyrophosphate dihydrate crystal deposition

Correct Answer & Explanation

. Septic arthritis

Explanation

The radiograph reveals densities within the articular cartilage of the knee commonly referred to as chondrocalcinosis. The term chondrocalcinosis refers to the presence of calcium-containing crystals detected as radiodensities in cartilage. Calcium-containing crystals other than calcium pyrophosphate dihydrate may also deposit in articular cartilage and menisci, producing both radiographically detectable densities in cartilage and joint inflammation or degeneration. Hemochromatosis, alkaptonuria (ochronosis), and Wilson’s disease are characterized by cellular deposition of iron, calcium, and copper ions, respectively, into various tissues including articular cartilage and can give this appearance. Septic arthritis does not usually cause chondrocalcinosis.

Question 374

Topic: Infection, Pharmacology & VTE

Figure 71 is the MRI scan of a 2-year-old girl who has been febrile for 1 week and has refused to bear weight on her left lower extremity for 3 days. Her entire left lower extremity is markedly swollen. Doppler ultrasound shows a deep venous thrombosis of the internal iliac vein. Her white blood cell count is 19000/ µL (reference range, 4500-11000/ µL) and her C-reactive protein level is higher than 20 mg/L (reference range, 0.08-3.1 mg/L). If blood cultures yield positive results, what is the most likely organism? Review Topic

. Methicillin-resistant Staphylococcus aureus
. Salmonella typhii
. Escherichia coli
. Vancomycin-resistant Enterococcus

Correct Answer & Explanation

. Methicillin-resistant Staphylococcus aureus

Explanation

The clinical picture is one of infection and deep venous thrombosis. The MRI scan is consistent with osteomyelitis. Deep venous thrombosis in association with musculoskeletal infection is more common in osteomyelitis caused by methicillin-resistantStaphylococcus aureus. Presenting C-reactive protein levels generally are higher than 6 mg/L and are higher than with other causative organisms. The presence of the Panton-Valentine leukocidin gene encoded in strains of bacteria may explain the deep venous thrombosis.

Question 375

Topic: Infection, Pharmacology & VTE
A 7-year-old boy sustained a 2-cm laceration to the anterior aspect of his left knee after falling on a rock. Examination reveals that the joint surface is not visible through the wound. Radiographs show no evidence of a foreign body or free air in the joint. Management should consist of:
. debridement of the skin edges, closure of the wound, and administration of an oral cephalosporin for 10 days.
. a saline load test.
. arthroscopic examination of the knee.
. leaving the wound open, administration of an oral cephalosporin, and reevaluation in 48 hours.
. injection of contrast material into the laceration, followed by radiographic studies.

Correct Answer & Explanation

. a saline load test.

Explanation

DISCUSSION: The possibility of an open joint injury should be considered in any patient who has a small periarticular laceration. Failure to promptly diagnose and treat such injuries may lead to septic arthritis. The diagnosis of an open joint is easily made when there is visible communication of the joint through the traumatic wound, or when intra-articular air is present on a radiograph. In the absence of these findings, the diagnosis of an open joint may be established by the saline load test, in which a volume of saline is injected into the joint under sterile conditions. If fluid extravasates through the traumatic wound, the diagnosis of an open joint is established. REFERENCES: Voit GA, Irvine G, Beals RK: Saline load test for penetration of periarticular lacerations. J Bone Joint Surg Br 1996;78:732-733.

Question 376

Topic: Infection, Pharmacology & VTE
Linezolid exerts its antimicrobial action by inhibiting bacterial
. protein synthesis.
. peptidoglycan wall synthesis.
. DNA-gyrase activity.
. mitochondrial enzymes.
. oxidative phosphorylation.

Correct Answer & Explanation

. protein synthesis.

Explanation

Linezolid is the first agent of the oxazolidinone group of antibiotics and is very active against methicillin-sensitive Staphylococcus aureus, S. epidermidis, and vancomycin-resistant enterococci. The drug has no gram-negative activity. Linezolid inhibits protein synthesis by blocking formation of the 70S ribosomal translation complex. This mechanism of action is unique to the oxazolidinones.

Question 377

Topic: Infection, Pharmacology & VTE
A 51-year-old man sustained an open fracture of his tibia in Korea 42 years ago. An infection developed and it was resolved with surgical treatment. For the past 6 months, an ulcer with mild drainage has developed over the medial tibia. The ulcer is small and there is minimal erythema at the ulcer site. A radiograph and MRI scan are shown in Figures 43a and Figure 43b. Initial cultures show Staphylococcus aureus susceptible to the most appropriate antibiotics. Laboratory studies show an erythrocyte sedimentation rate of 70 mm/h. What is the most appropriate surgical treatment at this time?
. Irrigation and debridement of the cystic lesion and 6 weeks of IV antibiotics
. Curettage, debridement of nonviable bone, and placement of absorbable antibiotic beads, followed by a course of IV antibiotics from 1 to 4 weeks and a 6-week course of oral antibiotics
. Complete resection of the infected portion of bone, placement of an external fixator to stabilize the tibia, and 6 weeks of IV antibiotics
. Amputation
. Local debridement of bone and the overlying skin and soft tissues, 6 weeks of IV antibiotics, and free-flap wound coverage

Correct Answer & Explanation

. Curettage, debridement of nonviable bone, and placement of absorbable antibiotic beads, followed by a course of IV antibiotics from 1 to 4 weeks and a 6-week course of oral antibiotics

Explanation

The patient has chronic tibial osteomyelitis that is due to low virulent bacteria. The history and studies do not suggest the need for an amputation or a free-flap procedure. This is a localized tibial infection that is in a healed bone; there is no need to resect the entire area of the tibia bone around the infection. The most appropriate treatment is curettage, debridement of nonviable bone, and placement of absorbable antibiotic beads, followed by a course of IV antibiotics from 1 to 4 weeks and a 6-week course of oral antibiotics. Studies have shown that in cases of localized osteomyelitis that are of low virulence, as little as 1 week of IV antibiotics followed by 6 weeks of oral antibiotics is successful.

Question 378

Topic: Infection, Pharmacology & VTE

A researcher decides she wants to look at the current total number of patients who have methicillin-resistant Staphylococcus aureus (MRSA) infections in a hospital on 1 particular day. What is the researcher measuring?

. Correlation coefficient of MRSA
. Prevalence of MRSA
. Incidence of MRSA
. Relative risk of MRSA

Correct Answer & Explanation

. Prevalence of MRSA

Explanation

The prevalence of a disease is a measure of the number of cases of a disease at or during a specific time point or time period. In this case, the researcher wants to know the prevalence of disease on a given day. Incidence measures new cases of a disease or event per unit of time. Correlation coefficient is a measure of how 2 things correlate with one another, while relative risk is a statistical outcome that is often used in case-control or cohort studies to provide a measure of the risk of a particular disease occurring when a certain exposure has already occurred.

Question 379

Topic: Infection, Pharmacology & VTE

What is the plasma half-life of warfarin?

. 1 to 2 hours
. 4 to 6 hours
. 12 to 18 hours
. 36 to 42 hours

Correct Answer & Explanation

. 36 to 42 hours

Explanation

Warfarin, which is dosed daily, can take 72 to 96 hours to reach therapeutic levels. It has a plasma half-life of 36 to 42 hours. Low-molecular heparins have a plasma half-life of 4 to 5 hours, and fondaparinux has a half-life of 17 to 21 hours. Warfarin will not affect the International Normalized Ratio (INR) until 2 to 3 days after it is given. Patients on chronic warfarin therapy should have treatment stopped 3 to 5 days before elective surgery to allow the INR to normalize.

Question 380

Topic: Infection, Pharmacology & VTE
Clinical staging of osteomyelitis using the Cierney-Mader classification system takes into account which of the following factors?
. Age and gender of patient
. Fracture type and type of bacteria
. Host status and extent of infected bone
. Immune status and chronicity of infection
. Bacterial resistance and source of infection

Correct Answer & Explanation

. Host status and extent of infected bone

Explanation

DISCUSSION: The Cierney-Mader classification system takes into account host status (A: healthy, B: comorbidities, C: treatment morbidity > infection) and the extent of infected bone (type I: medullary, type II: superficial, type III: localized, type IV: diffuse).

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