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Infection, Pharmacology & VTE MCQs

Practice Set 65 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 1281

Topic: Infection, Pharmacology & VTE

A 52-year-old man with poorly controlled diabetes mellitus presents with a 3-week history of purulent drainage from a medial ulcer on his right great toe. On examination, a sterile blunt probe is easily advanced through the ulcer to a hard, gritty surface. Which of the following is the most accurate statement regarding this clinical finding?

. It has a high negative predictive value for osteomyelitis
. It has a high positive predictive value for osteomyelitis
. It indicates the need for immediate below-knee amputation
. It confirms the presence of a deep venous thrombosis
. It is pathognomonic for Charcot neuroarthropathy

Correct Answer & Explanation

. It has a high positive predictive value for osteomyelitis

Explanation

Correct Answer: BThe "probe-to-bone" test is a simple, cost-effective clinical examination maneuver used in the evaluation of diabetic foot ulcers. A positive test occurs when a sterile blunt probe can be advanced through the ulcer to palpate a hard, gritty bony surface. In the setting of an infected diabetic foot ulcer, a positive probe-to-bone test has a high positive predictive value (PPV), often cited around 89%, for the presence of underlying osteomyelitis. While it is highly predictive, a negative test does not definitively rule out osteomyelitis (lower negative predictive value), and further imaging, such as MRI, may be warranted if clinical suspicion remains high.

Question 1282

Topic: Infection, Pharmacology & VTE

A 52-year-old diabetic man is admitted with a deep, purulent ulcer on the medial aspect of his right great toe and confirmed osteomyelitis. He has not received any recent antibiotics. A bone biopsy is performed for culture prior to initiating antimicrobial therapy. Which of the following organisms is most commonly isolated in this clinical scenario?

. Pseudomonas aeruginosa
. Staphylococcus aureus
. Streptococcus pyogenes
. Bacteroides fragilis
. Escherichia coli

Correct Answer & Explanation

. Staphylococcus aureus

Explanation

Correct Answer: BDiabetic foot infections, including osteomyelitis, can be polymicrobial, especially in chronic, deep, or previously treated ulcers. However, Staphylococcus aureus is the single most common pathogen isolated from bone biopsies in patients with diabetic foot osteomyelitis. While Gram-negative organisms (like Pseudomonas aeruginosa and Escherichia coli) and anaerobes (like Bacteroides fragilis) are frequently found in mixed infections, particularly in ischemic or necrotic wounds, S. aureus remains the predominant organism. Empiric antibiotic therapy for severe diabetic foot infections must always include coverage for S. aureus, including MRSA if risk factors are present, along with broad-spectrum coverage for Gram-negative and anaerobic bacteria until culture results are available.

Question 1283

Topic: Infection, Pharmacology & VTE

A 65-year-old male with poorly controlled diabetes presents with a deep ulcer on the plantar aspect of his right heel. During the clinical examination, a sterile blunt probe is introduced into the ulcer and easily palpates hard, gritty bone at the base. What is the clinical significance of a positive probe-to-bone test in this setting?

. It is highly sensitive but poorly specific for diagnosing osteomyelitis.
. It has a high positive predictive value for osteomyelitis in the setting of an infected diabetic foot ulcer.
. It indicates the need for immediate below-knee amputation.
. It confirms the presence of Charcot arthropathy.
. It rules out the presence of peripheral arterial disease.

Correct Answer & Explanation

. It has a high positive predictive value for osteomyelitis in the setting of an infected diabetic foot ulcer.

Explanation

Correct Answer: BThe probe-to-bone test is a valuable clinical tool for assessing diabetic foot ulcers. In the setting of a clinically infected ulcer, a positive probe-to-bone test has a high positive predictive value (PPV) for underlying osteomyelitis. While imaging (like MRI) and bone biopsy are definitive, a positive probe-to-bone test strongly suggests osteomyelitis and guides initial management, often precluding the immediate need for advanced imaging if the clinical picture is clear.

Question 1284

Topic: Infection, Pharmacology & VTE

A 68-year-old male with diabetes presents with a foot ulcer. Examination reveals a deep ulcer penetrating to the joint capsule, but there is no evidence of abscess, osteomyelitis, or gangrene. According to the Wagner classification system for diabetic foot ulcers, what grade is this lesion?

. Grade 0
. Grade 1
. Grade 2
. Grade 3
. Grade 4

Correct Answer & Explanation

. Grade 2

Explanation

Correct Answer: CThe Wagner classification for diabetic foot ulcers is as follows: Grade 0: Pre-ulcerative lesion, healed ulcer, or presence of bony deformity. Grade 1: Superficial ulcer without subcutaneous tissue involvement. Grade 2: Deep ulcer penetrating to tendon, bone, or joint capsule, but without deep infection (abscess or osteomyelitis). Grade 3: Deep ulcer with osteomyelitis, abscess, or joint sepsis. Grade 4: Localized gangrene (e.g., forefoot or heel). Grade 5: Extensive gangrene involving the entire foot. The patient's ulcer penetrates to the joint capsule without infection, making it a Grade 2.

Question 1285

Topic: Infection, Pharmacology & VTE

A 60-year-old diabetic male presents with a red, swollen foot. You are trying to differentiate acute Charcot neuroarthropathy from osteomyelitis using MRI. Which of the following MRI findings is most specific for diagnosing osteomyelitis rather than Charcot arthropathy?

. Subchondral bone marrow edema on T2-weighted images
. Presence of periarticular soft tissue fluid collections
. Decreased signal on T1 that normalizes entirely post-contrast
. Replacement of marrow fat with fluid signal on T1 and T2
. Presence of the "ghost sign" where bone morphology is indistinct on T1 but reappears post-contrast

Correct Answer & Explanation

. Presence of the "ghost sign" where bone morphology is indistinct on T1 but reappears post-contrast

Explanation

The "ghost sign" on MRI is highly specific for osteomyelitis. It occurs when the morphologic features of the bone become indistinct on T1-weighted images but reappear on T2-weighted or post-contrast sequences. Charcot typically presents with subchondral edema without this complete loss of T1 architecture.

Question 1286

Topic: Infection, Pharmacology & VTE

A diabetic patient presents with a deep foot ulcer penetrating to the joint capsule and deep fascia. Clinical exam and imaging reveal no abscess or osteomyelitis. According to the Wagner classification system, what is the grade of this ulcer?

. Grade 0
. Grade 1
. Grade 2
. Grade 3
. Grade 4

Correct Answer & Explanation

. Grade 2

Explanation

Wagner Grade 2 is defined as a deep ulcer penetrating to ligament, tendon, joint capsule, or deep fascia without abscess or osteomyelitis. Grade 1 is superficial, and Grade 3 involves deep infection like osteomyelitis or deep abscess.

Question 1287

Topic: Infection, Pharmacology & VTE

A 60-year-old diabetic male presents with a limb-threatening, deep foot infection accompanied by systemic toxicity. Which of the following empirical intravenous antibiotic regimens is most appropriate while awaiting deep tissue cultures?

. Cefazolin monotherapy
. Clindamycin monotherapy
. Vancomycin and piperacillin-tazobactam
. Ciprofloxacin and metronidazole
. Linezolid monotherapy

Correct Answer & Explanation

. Vancomycin and piperacillin-tazobactam

Explanation

Severe, limb-threatening diabetic foot infections are typically polymicrobial and carry a high risk for MRSA. Empiric therapy must be broad-spectrum, classically utilizing IV vancomycin (for MRSA) and piperacillin-tazobactam (for Gram-negative and anaerobic coverage).

Question 1288

Topic: Infection, Pharmacology & VTE

A 64-year-old diabetic patient presents with a chronic plantar midfoot ulcer. During examination, a sterile metal probe is passed through the ulcer and contacts hard, gritty bone. In a population with a high prevalence of osteomyelitis, what is the most accurate statement regarding the probe-to-bone (PTB) test?

. It has a high negative predictive value but low positive predictive value.
. It confirms the need for immediate proximal amputation.
. It has a highly positive predictive value for underlying osteomyelitis.
. It requires immediate MRI confirmation before initiating empirical antibiotics.
. It is only valid if the ulcer is Wagner Grade 1.

Correct Answer & Explanation

. It has a highly positive predictive value for underlying osteomyelitis.

Explanation

In patients with a high pre-test probability (such as those with chronic diabetic foot ulcers in a specialized clinic), a positive probe-to-bone test has a highly positive predictive value for osteomyelitis. It strongly correlates with the presence of bone infection and often guides biopsy and treatment.

Question 1289

Topic: Infection, Pharmacology & VTE

A 52-year-old diabetic female presents with a plantar foot ulcer. Examination reveals the ulcer extends through the subcutaneous tissue to the deep fascia, with exposed tendon and bone. There is no evidence of osteomyelitis, abscess, or gangrene. According to the Wagner classification system, what grade is this ulcer?

. Grade 1
. Grade 2
. Grade 3
. Grade 4
. Grade 5

Correct Answer & Explanation

. Grade 2

Explanation

A Wagner Grade 2 ulcer is a deep ulcer penetrating to ligament, tendon, joint capsule, or deep fascia without active osteomyelitis or abscess. Grade 3 involves deep infection (osteomyelitis, abscess), while Grade 1 is superficial.

Question 1290

Topic: Infection, Pharmacology & VTE

Radiographs of an infant reveal severe stippling of the epiphyses (chondrodysplasia punctata). A careful maternal history should be taken, as which teratogenic exposure produces a clinical phenocopy of this condition?

. Lithium
. Warfarin
. Valproic acid
. Thalidomide
. Phenytoin

Correct Answer & Explanation

. Warfarin

Explanation

Fetal warfarin syndrome mimics chondrodysplasia punctata (stippled epiphyses). Warfarin inhibits vitamin K-dependent proteins (like osteocalcin), severely disrupting normal bone mineralization during development.

Question 1291

Topic: Infection, Pharmacology & VTE

Differentiating between acute Charcot neuroarthropathy and osteomyelitis in a diabetic foot can be challenging. Which of the following MRI findings is most specific for diagnosing osteomyelitis over acute Charcot arthropathy?

. Bone marrow edema in the cuboid and cuneiforms
. Subchondral cysts and large joint effusion
. Diffuse surrounding soft tissue edema
. Presence of a sinus tract extending to the bone
. Periarticular bone fragmentation

Correct Answer & Explanation

. Presence of a sinus tract extending to the bone

Explanation

Both acute Charcot and osteomyelitis present with prominent bone marrow edema and soft tissue swelling on MRI. However, the presence of a sinus tract, replacement of subchondral fat (ghost sign), and adjacent ulceration are highly specific for osteomyelitis.

Question 1292

Topic: Infection, Pharmacology & VTE

A 2-year-old boy presents with refusal to bear weight on the right leg and low-grade fever. Blood work shows a normal WBC count and mildly elevated CRP. Joint aspiration shows 45,000 WBCs. If the pathogen is a fastidious Gram-negative coccobacillus, what is the optimal method for isolation?

. Standard agar plating
. Inoculation of joint fluid into blood culture bottles
. Lowenstein-Jensen medium
. Thayer-Martin agar
. Sabouraud dextrose agar

Correct Answer & Explanation

. Inoculation of joint fluid into blood culture bottles

Explanation

Kingella kingae is a common cause of pediatric septic arthritis and osteomyelitis in children under 4. It is a fastidious organism that is best isolated by inoculating the synovial fluid directly into aerobic blood culture bottles.

Question 1293

Topic: Infection, Pharmacology & VTE

A 70-year-old man develops a chronic infection around his total hip arthroplasty, and cultures grow Staphylococcus epidermidis. Which phase of biofilm formation is characterized by the production of an extracellular polymeric substance (EPS) that creates a physical barrier against antibiotics?

. Initial reversible attachment
. Irreversible attachment and aggregation
. Maturation and glycocalyx formation
. Planktonic dispersion
. Quorum sensing initiation

Correct Answer & Explanation

. Maturation and glycocalyx formation

Explanation

During the maturation phase of biofilm development, bacteria secrete an extracellular polymeric substance (glycocalyx) that encases the colony. This EPS matrix acts as a robust physical and chemical barrier against both host immune cells and systemic antibiotics.

Question 1294

Topic: Infection, Pharmacology & VTE

A 2-year-old boy presents with a 3-day history of right knee swelling, limp, and low-grade fever. Synovial fluid aspiration shows a WBC count of 65,000/microL. Routine cultures at 48 hours are negative. Which of the following is the most likely causative organism and the best method for its detection?

. Staphylococcus aureus; prolonged culture
. Kingella kingae; polymerase chain reaction (PCR)
. Neisseria gonorrhoeae; Thayer-Martin agar
. Borrelia burgdorferi; Western blot
. Streptococcus pyogenes; rapid antigen test

Correct Answer & Explanation

. Kingella kingae; polymerase chain reaction (PCR)

Explanation

Kingella kingae is a leading cause of pediatric septic arthritis and osteomyelitis in children under 4 years old. Because it is fastidious and difficult to culture on standard media, PCR is the most sensitive and rapid diagnostic method.

Question 1295

Topic: Infection, Pharmacology & VTE

A 6-month-old infant is brought to the emergency department for irritability and refusal to move the left leg. Ultrasound reveals a left hip effusion. Which of the following features most strongly dictates the need for immediate surgical drainage of the hip joint?

. Erythrocyte sedimentation rate > 40 mm/hr
. Positive blood cultures for Staphylococcus aureus
. Aspiration yielding purulent fluid with > 50,000 WBCs/microL
. Radiographic evidence of joint space widening
. C-reactive protein > 20 mg/L

Correct Answer & Explanation

. Aspiration yielding purulent fluid with > 50,000 WBCs/microL

Explanation

A purulent joint aspirate with a WBC count > 50,000/microL confirms septic arthritis, which is a surgical emergency. Immediate arthrotomy and irrigation of the infant hip are required to prevent irreversible cartilage destruction and avascular necrosis.

Question 1296

Topic: Infection, Pharmacology & VTE

A 7-year-old girl from Connecticut presents with a massive right knee effusion. Surprisingly, she bears weight with a minimal limp and has only mild discomfort with range of motion. Joint aspiration reveals 40,000 WBCs/microL with 80% neutrophils. What is the most appropriate next step in management?

. Immediate arthroscopic irrigation and debridement
. Intravenous vancomycin and ceftriaxone
. Serological testing with an ELISA and confirmatory Western blot
. Intra-articular corticosteroid injection
. Open arthrotomy and washout

Correct Answer & Explanation

. Serological testing with an ELISA and confirmatory Western blot

Explanation

Lyme arthritis commonly presents with a massive knee effusion, but patients paradoxically maintain weight-bearing and have minimal pain compared to those with bacterial septic arthritis. Diagnosis requires two-tiered serologic testing, and it is primarily managed medically rather than with urgent surgical washout.

Question 1297

Topic: Infection, Pharmacology & VTE

A 9-year-old boy is admitted with severe, multifocal MRSA osteomyelitis and an associated deep vein thrombosis (DVT) of the affected extremity. The severity of this infection and the development of DVT are most strongly associated with which bacterial virulence factor?

. Panton-Valentine leukocidin (PVL)
. Toxic shock syndrome toxin-1 (TSST-1)
. Exfoliative toxin A
. Protein A
. Alpha-hemolysin

Correct Answer & Explanation

. Panton-Valentine leukocidin (PVL)

Explanation

Panton-Valentine leukocidin (PVL) is a cytotoxin produced by community-acquired MRSA strains that destroys leukocytes and causes severe tissue necrosis. PVL-positive strains are strongly associated with multifocal disease, aggressive osteomyelitis, and adjacent deep vein thrombosis.

Question 1298

Topic: Infection, Pharmacology & VTE
A 2-year-old child presents with a limp, fever, and a swollen knee. Aspiration yields purulent synovial fluid with a WBC of 65,000. Standard aerobic and anaerobic cultures on solid media are negative at 48 hours. What technique would have best optimized the isolation of the most likely responsible organism?
. Extended incubation of anaerobic cultures for 14 days
. Addition of acid-fast bacilli (AFB) stains
. Direct inoculation of synovial fluid into BACTEC blood culture vials
. Polymerase chain reaction (PCR) targeting Neisseria gonorrhoeae
. Culturing the fluid specifically on MacConkey agar

Correct Answer & Explanation

. Direct inoculation of synovial fluid into BACTEC blood culture vials

Explanation

Kingella kingae is a highly fastidious organism and the most common cause of septic arthritis in children under 4 years old. Isolation is significantly enhanced by inoculating synovial fluid directly into aerobic BACTEC blood culture vials.

Question 1299

Topic: Infection, Pharmacology & VTE

Staphylococcus epidermidis frequently causes chronic prosthetic joint infections due to its ability to form a robust biofilm. Which specific structural component produced by this bacteria is primarily responsible for adherence and biofilm architecture?

. Protein A
. Polysaccharide intercellular adhesin (PIA)
. Panton-Valentine leukocidin (PVL)
. Alpha-toxin
. Toxic shock syndrome toxin-1 (TSST-1)

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA)

Explanation

S. epidermidis secures itself to orthopaedic implants via a biofilm composed of an exopolysaccharide matrix. The critical structural component of this glycocalyx is polysaccharide intercellular adhesin (PIA).

Question 1300

Topic: Infection, Pharmacology & VTE
A 14-month-old presents with acute knee swelling and refusal to bear weight. Aspiration yields cloudy fluid. Routine synovial cultures on blood agar are negative at 48 hours. What is the optimal method to isolate the most likely organism in this specific age group?
. Fungal culture isolation
. Acid-fast bacilli smear and culture
. Inoculation into aerobic blood culture vials
. Lowenstein-Jensen medium plating
. Thayer-Martin agar plating

Correct Answer & Explanation

. Inoculation into aerobic blood culture vials

Explanation

Kingella kingae is a fastidious Gram-negative organism and a leading cause of septic arthritis in children under 4 years of age. It is best isolated by inoculating synovial fluid directly into BACTEC blood culture vials or via PCR testing.

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