Skin and soft tissue infections — MCQs

10 questions

A 7-year-old girl is brought to the pediatrician by her parents for red papules over her left thigh and swelling in the right axilla for the past few days. Her parents say that she had a cat bite on her left thigh 2 weeks ago. Her temperature is 38.6°C (101.4°F), pulse is 90/min, and respirations are 22/min. On her physical examination, hepatosplenomegaly is present with a healing area of erythema on her left thigh. Her laboratory studies show: Hemoglobin 12.9 gm/dL Leukocyte count 9,300/mm3 Platelet count 167,000/mm3 ESR 12 mm/hr Which of the following is the most appropriate next step in management?

A 72-year-old woman comes to the physician because of a 3-day history of redness and swelling of her right leg and fever. She says the leg is very painful and the redness over it has become larger. She appears ill. Her temperature is 39.3°C (102.7°F), pulse is 103/min, and blood pressure is 138/90 mm Hg. Cardiopulmonary examination shows no abnormalities. Examination shows an area of diffuse erythema and swelling over her anterior right lower leg; it is warm and tender to touch. Squeezing of the calf does not elicit tenderness. There is swelling of the right inguinal lymph nodes. Pedal pulses are palpable bilaterally. Which of the following is the strongest predisposing factor for this patient's condition?

A 62-year-old woman presents to the emergency department for evaluation of a spreading skin infection that began from an ulcer on her foot. The patient has type 2 diabetes mellitus that is poorly controlled. On examination, there is redness and erythema to the lower limb with skin breakdown along an extensive portion of the leg. The patient’s tissues separate readily from the fascial plane, prompting a diagnosis of necrotizing fasciitis. What is the exotoxin most likely associated with this patient’s presentation?

A 74-year-old woman presents to the clinic for evaluation of an erythematous and edematous skin rash on her right leg that has progressively worsened over the last 2 weeks. The medical history is significant for hypertension and diabetes mellitus type 2. She takes prescribed lisinopril and metformin. The vital signs include: blood pressure 152/92 mm Hg, heart rate 76/min, respiratory rate 12/min, and temperature 37.8°C (100.1°F). On physical exam, the patient appears alert and oriented. Observation of the lesion reveals a poorly demarcated region of erythema and edema along the anterior aspect of the right tibia. Within the region of erythema is a 2–3 millimeter linear break in the skin that does not reveal any serous or purulent discharge. Tenderness to palpation and warmth is associated with the lesion. There are no vesicles, pustules, papules, or nodules present. Ultrasound of the lower extremity is negative for deep vein thrombosis or skin abscess. The blood cultures are pending. Which of the following is the most likely diagnosis based on history and physical examination?

A 19-year-old woman presents to the family medicine clinic after noticing swelling of her right index finger a few hours ago. She has no past medical history and takes no prescription medications. She takes ibuprofen occasionally, as needed. She says that she has smoked a few cigarettes a day for the last year. On further questioning, the patient says that she has a dog and a cat at home. Her blood pressure is 108/67 mm Hg, heart rate is 94/min, respiratory rate is 12/min, and temperature is 37.8°C (100.1°F). On physical examination, the physician notices 2 clean puncture wounds with localized erythema and induration on the dorsum of the right second digit. Capillary refill is 2 seconds. Sensory and motor function are intact bilaterally. Which of the following is the most appropriate treatment choice for this patient?

A 35-year-old man comes to the emergency room for severe left leg pain several hours after injuring himself on a gardening tool. His temperature is 39°C (102.2°F) and his pulse is 105/min. Physical examination of the left leg shows a small laceration on the ankle surrounded by dusky skin and overlying bullae extending to the posterior thigh. There is a crackling sound when the skin is palpated. Surgical exploration shows necrosis of the gastrocnemius muscles and surrounding tissues. Tissue culture shows anaerobic gram-positive rods and a double zone of hemolysis on blood agar. Which of the following best describes the mechanism of cellular damage caused by the responsible pathogen?

A 28-year-old male presents to his primary care physician with complaints of intermittent abdominal pain and alternating bouts of constipation and diarrhea. His medical chart is not significant for any past medical problems or prior surgeries. He is not prescribed any current medications. Which of the following questions would be the most useful next question in eliciting further history from this patient?

Two days after hospital admission and surgical treatment for a cut on his right thigh from a sickle, a 35-year-old man has fever, chills, and intense pain. The wound is swollen. He had a similar injury 4 months ago that resolved following treatment with bacitracin ointment and daily dressings. He works on a farm on the outskirts of the city. He appears anxious. His temperature is 38.5°C (101.3°F), pulse is 103/min, and blood pressure is 114/76 mm Hg. Examination shows a 6-cm edematous deep, foul-smelling wound on the medial surface of the right thigh. The skin over the thigh appears darker than the skin on the lower leg. There are multiple blisters around the wound. Light palpation around the wound causes severe pain; crepitus is present. Which of the following is the most likely causal organism?

A 43-year-old man is brought to the emergency department 40 minutes after falling off a 10-foot ladder. He has severe pain and swelling of his right ankle and is unable to walk. He did not lose consciousness after the fall. He has no nausea. He appears uncomfortable. His temperature is 37°C (98.6°F), pulse is 98/min, respirations are 16/min, and blood pressure is 110/80 mm Hg. He is alert and oriented to person, place, and time. Examination shows multiple abrasions over both lower extremities. There is swelling and tenderness of the right ankle; range of motion is limited by pain. The remainder of the examination shows no abnormalities. An x-ray of the ankle shows an extra-articular calcaneal fracture. Intravenous analgesia is administered. Which of the following is the most appropriate next step in the management of this patient?

Q10

A 6-month-old girl presents with recurring skin infections. Past medical history is significant for 3 episodes of acute otitis media since birth. The patient was born at 39 weeks via an uncomplicated, spontaneous transvaginal delivery, but there was delayed umbilical cord separation. She has met all developmental milestones. On physical examination, the skin around her mouth is inflamed and red. Which of the following is most likely responsible for this child’s clinical presentation?

Skin and soft tissue infections US Medical PG Practice Questions and MCQs

Question 1: A 7-year-old girl is brought to the pediatrician by her parents for red papules over her left thigh and swelling in the right axilla for the past few days. Her parents say that she had a cat bite on her left thigh 2 weeks ago. Her temperature is 38.6°C (101.4°F), pulse is 90/min, and respirations are 22/min. On her physical examination, hepatosplenomegaly is present with a healing area of erythema on her left thigh. Her laboratory studies show: Hemoglobin 12.9 gm/dL Leukocyte count 9,300/mm3 Platelet count 167,000/mm3 ESR 12 mm/hr Which of the following is the most appropriate next step in management?

A. Azithromycin as a single agent (Correct Answer)
B. No treatment is required
C. Doxycycline + rifampin
D. Surgical excision of the lymph node
E. Rifampin + azithromycin

Explanation: ***Azithromycin as a single agent*** - This patient presents with symptoms consistent with **cat-scratch disease (CSD)**, including a history of cat bite, regional lymphadenopathy (swelling in the right axilla), and fever. Azithromycin is the **recommended first-line treatment** for CSD, especially in children, due to its efficacy and favorable safety profile. - While CSD is often self-limiting, antibiotic treatment with azithromycin can **shorten the duration** and **reduce the severity** of symptoms, including painful lymphadenopathy, and help prevent disseminated disease. *No treatment is required* - While CSD can be self-limiting, the patient presents with **significant symptoms** including fever, tender lymphadenopathy, and hepatosplenomegaly, suggesting a more severe course that warrants intervention. - Administering antibiotics like azithromycin can **alleviate symptoms** and **prevent complications**, such as disseminated infection, particularly in immunocompromised patients, though this child's immune status is not specified. *Doxycycline + rifampin* - **Doxycycline** is generally avoided in children under 8 years due to the risk of **permanent tooth discoloration** and inhibition of bone growth, making it an inappropriate first-line choice for this 7-year-old. - While **rifampin** can be used for CSD, particularly in refractory cases or disseminated disease, it is not typically given as a primary agent, and the combination with doxycycline is not the preferred initial therapy due to the age contraindication. *Surgical excision of the lymph node* - **Surgical excision** of lymph nodes is generally **not recommended** for uncomplicated CSD due to the risk of scarring and potential complications. - It is typically reserved for cases with **suppurative or fluctuant lymph nodes** that fail to respond to antibiotic therapy, or to rule out other diagnoses if malignancy is suspected. *Rifampin + azithromycin* - While **rifampin** is an alternative for CSD, especially in severe or disseminated cases, **azithromycin alone** is usually sufficient as the first-line treatment. - There is no clinical evidence to suggest a significant benefit of combination therapy with rifampin and azithromycin over azithromycin monotherapy for initial management of typical CSD in immunocompetent children.

Question 2: A 72-year-old woman comes to the physician because of a 3-day history of redness and swelling of her right leg and fever. She says the leg is very painful and the redness over it has become larger. She appears ill. Her temperature is 39.3°C (102.7°F), pulse is 103/min, and blood pressure is 138/90 mm Hg. Cardiopulmonary examination shows no abnormalities. Examination shows an area of diffuse erythema and swelling over her anterior right lower leg; it is warm and tender to touch. Squeezing of the calf does not elicit tenderness. There is swelling of the right inguinal lymph nodes. Pedal pulses are palpable bilaterally. Which of the following is the strongest predisposing factor for this patient's condition?

A. Cigarette smoking
B. Graves disease
C. Tinea pedis (Correct Answer)
D. Rheumatoid arthritis
E. Immobility

Explanation: ***Tinea pedis*** - The patient's presentation of **unilateral leg redness, swelling, warmth, tenderness, and fever** is highly suggestive of **bacterial cellulitis**. - **Tinea pedis (athlete's foot)** causes breaks in the skin barrier, allowing bacteria (typically *Streptococcus pyogenes* or *Staphylococcus aureus*) to enter and cause infection. *Cigarette smoking* - While smoking has numerous negative health effects, it is **not a direct predisposing factor for cellulitis**. - Smoking can impair wound healing and immune function generally, but it does not specifically increase the risk of skin barrier breakdown in the way fungal infections do. *Graves disease* - **Graves disease** is an autoimmune condition causing hyperthyroidism and is not directly linked to an increased risk of cellulitis. - It can cause **pretibial myxedema**, which involves skin changes but does not typically lead to skin breakdown and bacterial infection. *Rheumatoid arthritis* - **Rheumatoid arthritis** is a chronic inflammatory autoimmune disease primarily affecting joints. - While patients on immunosuppressive therapy for RA may have a higher risk of infections in general, RA itself does not directly predispose to cellulitis by causing skin barrier disruption. *Immobility* - **Immobility** can lead to conditions like **deep vein thrombosis (DVT)** or **pressure ulcers**, but it is not the strongest direct predisposing factor for cellulitis in this clinical scenario. - While immobility often accompanies conditions that impair skin integrity (e.g., venous insufficiency), it doesn't directly cause the primary break in the skin that leads to cellulitis as Tinea pedis does.

Question 3: A 62-year-old woman presents to the emergency department for evaluation of a spreading skin infection that began from an ulcer on her foot. The patient has type 2 diabetes mellitus that is poorly controlled. On examination, there is redness and erythema to the lower limb with skin breakdown along an extensive portion of the leg. The patient’s tissues separate readily from the fascial plane, prompting a diagnosis of necrotizing fasciitis. What is the exotoxin most likely associated with this patient’s presentation?

A. Streptococcal pyogenic exotoxin A
B. TSST-1
C. Diphtheria toxin
D. Exfoliative toxin
E. Streptococcal pyogenic exotoxin B (Correct Answer)

Explanation: ***Streptococcal pyogenic exotoxin B*** - **Streptococcal pyogenic exotoxin B** is a **cysteine protease** that directly degrades tissue, including collagen and fibronectin, leading to the rapid tissue destruction characteristic of **necrotizing fasciitis**. - This exotoxin is frequently associated with **Group A Streptococcus (GAS)** infections, a common cause of severe soft tissue infections, especially in immunocompromised individuals like diabetics. *Streptococcal pyogenic exotoxin A* - This exotoxin acts as a **superantigen**, primarily causing symptoms of **streptococcal toxic shock syndrome** (STSS), characterized by fever, rash, and organ failure. - While GAS can cause necrotizing fasciitis, Exotoxin A is more closely linked to toxic shock phenomena rather than direct tissue destruction. *TSST-1* - **Toxic Shock Syndrome Toxin-1 (TSST-1)** is produced by **Staphylococcus aureus** and is a classic cause of **staphylococcal toxic shock syndrome**. - It acts as a **superantigen** but is not directly responsible for the extensive tissue necrosis seen in necrotizing fasciitis caused by streptococci. *Diphtheria toxin* - **Diphtheria toxin**, produced by *Corynebacterium diphtheriae*, inhibits **protein synthesis** by inactivating elongation factor-2 (EF-2), leading to cell death. - It causes diphtheria, characterized by a **pseudomembrane** in the throat and myocarditis, not necrotizing fasciitis. *Exfoliative toxin* - **Exfoliative toxins A and B** are produced by **Staphylococcus aureus** and are responsible for **Staphylococcal Scalded Skin Syndrome (SSSS)**. - These toxins cause cleavage of desmoglein-1 in the epidermis, leading to widespread blistering and desquamation, not deep tissue necrosis.

Question 4: A 74-year-old woman presents to the clinic for evaluation of an erythematous and edematous skin rash on her right leg that has progressively worsened over the last 2 weeks. The medical history is significant for hypertension and diabetes mellitus type 2. She takes prescribed lisinopril and metformin. The vital signs include: blood pressure 152/92 mm Hg, heart rate 76/min, respiratory rate 12/min, and temperature 37.8°C (100.1°F). On physical exam, the patient appears alert and oriented. Observation of the lesion reveals a poorly demarcated region of erythema and edema along the anterior aspect of the right tibia. Within the region of erythema is a 2–3 millimeter linear break in the skin that does not reveal any serous or purulent discharge. Tenderness to palpation and warmth is associated with the lesion. There are no vesicles, pustules, papules, or nodules present. Ultrasound of the lower extremity is negative for deep vein thrombosis or skin abscess. The blood cultures are pending. Which of the following is the most likely diagnosis based on history and physical examination?

A. Irritant contact dermatitis
B. Gas gangrene
C. Folliculitis
D. Erysipelas
E. Cellulitis (Correct Answer)

Explanation: **Cellulitis** - The patient's presentation with a **poorly demarcated**, erythematous, and edematous rash on the lower leg, accompanied by warmth, tenderness, and a low-grade fever, is highly consistent with **cellulitis**. The linear skin break provides a potential port of entry for bacteria. - Her history of **diabetes mellitus** is a significant risk factor for cellulitis due to impaired immune function and compromised peripheral circulation. The absence of vesicles or pustules further supports this diagnosis. *Irritant contact dermatitis* - This condition is typically characterized by **pruritus (itching)** and a rash that develops after exposure to an irritant, which is not described. - While it can cause redness and edema, contact dermatitis usually does not present with significant **warmth**, tenderness, or fever. *Gas gangrene* - This is a severe, rapidly progressing infection characterized by **crepitus** (gas in the tissues), severe pain, and often a foul-smelling discharge, none of which are noted in the patient's presentation. - The patient's symptoms are localized and do not suggest the systemic toxicity and rapid tissue necrosis associated with gas gangrene. *Folliculitis* - Folliculitis involves inflammation of hair follicles, presenting as small, **pustular lesions centered on hair follicles**, which are explicitly stated to be absent in this case. - The extensive, diffuse erythema and edema described are not typical features of folliculitis. *Erysipelas* - Erysipelas is a superficial skin infection that typically presents with a **sharply demarcated**, raised border, unlike the "poorly demarcated" lesion described. - While it shares some features with cellulitis (erythema, edema), the distinct border is a key differentiator, and erysipelas is also more likely to affect the face.

Question 5: A 19-year-old woman presents to the family medicine clinic after noticing swelling of her right index finger a few hours ago. She has no past medical history and takes no prescription medications. She takes ibuprofen occasionally, as needed. She says that she has smoked a few cigarettes a day for the last year. On further questioning, the patient says that she has a dog and a cat at home. Her blood pressure is 108/67 mm Hg, heart rate is 94/min, respiratory rate is 12/min, and temperature is 37.8°C (100.1°F). On physical examination, the physician notices 2 clean puncture wounds with localized erythema and induration on the dorsum of the right second digit. Capillary refill is 2 seconds. Sensory and motor function are intact bilaterally. Which of the following is the most appropriate treatment choice for this patient?

A. Doxycycline
B. Amoxicillin
C. Azithromycin
D. Amoxicillin–clavulanate (Correct Answer)
E. Clindamycin

Explanation: ***Amoxicillin–clavulanate*** - This patient presents with a **cat or dog bite** wound, manifesting as puncture wounds, erythema, and induration on the finger, indicating a **localized infection**. - **Amoxicillin–clavulanate** is the recommended first-line prophylactic and therapeutic antibiotic for animal bites due to its coverage of common pathogens like *Pasteurella multocida*, *Staphylococcus aureus*, and anaerobes. *Doxycycline* - While doxycycline has broad-spectrum activity, it is typically used as an alternative for animal bites in cases of **penicillin allergy** or for specific infections like **tularemia**. - It does not offer the same comprehensive coverage for typical animal bite pathogens as amoxicillin-clavulanate. *Amoxicillin* - **Amoxicillin alone** lacks coverage against **beta-lactamase producing bacteria**, which are commonly found in animal oral flora and can cause infections in bite wounds. - The addition of clavulanate is crucial to inhibit beta-lactamase and broaden the spectrum of coverage. *Azithromycin* - Azithromycin is a macrolide that is generally **not recommended** as a first-line agent for animal bite infections due to inconsistent coverage against primary bite pathogens. - It might be considered in specific cases of **penicillin allergy** but is less effective than amoxicillin-clavulanate or even doxycycline. *Clindamycin* - Clindamycin offers good coverage against **anaerobes** and some gram-positive bacteria, particularly **Staphylococcus** species. - However, it has **poor gram-negative coverage** and would need to be combined with another agent (e.g., a fluoroquinolone) to provide adequate empirical coverage for animal bite infections.

Question 6: A 35-year-old man comes to the emergency room for severe left leg pain several hours after injuring himself on a gardening tool. His temperature is 39°C (102.2°F) and his pulse is 105/min. Physical examination of the left leg shows a small laceration on the ankle surrounded by dusky skin and overlying bullae extending to the posterior thigh. There is a crackling sound when the skin is palpated. Surgical exploration shows necrosis of the gastrocnemius muscles and surrounding tissues. Tissue culture shows anaerobic gram-positive rods and a double zone of hemolysis on blood agar. Which of the following best describes the mechanism of cellular damage caused by the responsible pathogen?

A. Inhibition of neurotransmitter release by protease
B. Inactivation of elongation factor by ribosyltransferase
C. Lipopolysaccharide-induced complement and macrophage activation
D. Degradation of cell membranes by phospholipase (Correct Answer)
E. Increase of intracellular cAMP by adenylate cyclase

Explanation: ***Degradation of cell membranes by phospholipase*** - The clinical presentation (severe leg pain, dusky skin, bullae, crepitus, muscle necrosis, anaerobic gram-positive rods, double zone of hemolysis) is highly suggestive of **gas gangrene** caused by *Clostridium perfringens*. - *Clostridium perfringens* produces **alpha-toxin**, a **phospholipase C** (lecithinase) that degrades cell membranes, leading to red blood cell lysis, tissue necrosis, and organ damage. *Inhibition of neurotransmitter release by protease* - This mechanism is characteristic of **botulinum toxin** (produced by *Clostridium botulinum*) and **tetanus toxin** (produced by *Clostridium tetani*), both of which are neurotoxins that cleave SNARE proteins. - These toxins primarily affect neurological function and do not cause the extensive tissue necrosis and gas formation seen in gas gangrene. *Inactivation of elongation factor by ribosyltransferase* - This is the mechanism of action of **diphtheria toxin** (produced by *Corynebacterium diphtheriae*) and **Pseudomonas exotoxin A**. - These toxins inhibit protein synthesis, leading to cell death, but they do not cause the rapid and widespread tissue destruction and gas production observed in this case. *Lipopolysaccharide-induced complement and macrophage activation* - **Lipopolysaccharide (LPS)** is a component of the outer membrane of **Gram-negative bacteria**, leading to a strong inflammatory response (e.g., in sepsis). - The pathogen described is a **Gram-positive rod**, indicating that LPS is not the primary mechanism of pathogenicity here. *Increase of intracellular cAMP by adenylate cyclase* - This mechanism is employed by toxins like **cholera toxin** (from *Vibrio cholerae*) and **pertussis toxin** (from *Bordetella pertussis*), leading to fluid and electrolyte imbalances. - These toxins typically cause diarrheal diseases or respiratory symptoms and do not explain the localized, fulminant tissue necrosis seen in the patient's leg.

Question 7: A 28-year-old male presents to his primary care physician with complaints of intermittent abdominal pain and alternating bouts of constipation and diarrhea. His medical chart is not significant for any past medical problems or prior surgeries. He is not prescribed any current medications. Which of the following questions would be the most useful next question in eliciting further history from this patient?

A. "Does the diarrhea typically precede the constipation, or vice-versa?"
B. "Is the diarrhea foul-smelling?"
C. "Please rate your abdominal pain on a scale of 1-10, with 10 being the worst pain of your life"
D. "Are the symptoms worse in the morning or at night?"
E. "Can you tell me more about the symptoms you have been experiencing?" (Correct Answer)

Explanation: ***Can you tell me more about the symptoms you have been experiencing?*** - This **open-ended question** encourages the patient to provide a **comprehensive narrative** of their symptoms, including details about onset, frequency, duration, alleviating/aggravating factors, and associated symptoms, which is crucial for diagnosis. - In a patient presenting with vague, intermittent symptoms like alternating constipation and diarrhea, allowing them to elaborate freely can reveal important clues that might not be captured by more targeted questions. *Does the diarrhea typically precede the constipation, or vice-versa?* - While knowing the sequence of symptoms can be helpful in understanding the **pattern of bowel dysfunction**, it is a very specific question that might overlook other important aspects of the patient's experience. - It prematurely narrows the focus without first obtaining a broad understanding of the patient's overall symptomatic picture. *Is the diarrhea foul-smelling?* - Foul-smelling diarrhea can indicate **malabsorption** or **bacterial overgrowth**, which are important to consider in some gastrointestinal conditions. - However, this is a **specific symptom inquiry** that should follow a more general exploration of the patient's symptoms, as it may not be relevant if other crucial details are missed. *Please rate your abdominal pain on a scale of 1-10, with 10 being the worst pain of your life* - Quantifying pain intensity is useful for assessing the **severity of discomfort** and monitoring changes over time. - However, for a patient with intermittent rather than acute, severe pain, understanding the **character, location, and triggers** of the pain is often more diagnostically valuable than just a numerical rating initially. *Are the symptoms worse in the morning or at night?* - Diurnal variation can be relevant in certain conditions, such as inflammatory bowel diseases where nocturnal symptoms might be more concerning, or functional disorders whose symptoms might be stress-related. - This is another **specific question** that should come after gathering a more complete initial picture of the patient's symptoms to ensure no key information is overlooked.

Question 8: Two days after hospital admission and surgical treatment for a cut on his right thigh from a sickle, a 35-year-old man has fever, chills, and intense pain. The wound is swollen. He had a similar injury 4 months ago that resolved following treatment with bacitracin ointment and daily dressings. He works on a farm on the outskirts of the city. He appears anxious. His temperature is 38.5°C (101.3°F), pulse is 103/min, and blood pressure is 114/76 mm Hg. Examination shows a 6-cm edematous deep, foul-smelling wound on the medial surface of the right thigh. The skin over the thigh appears darker than the skin on the lower leg. There are multiple blisters around the wound. Light palpation around the wound causes severe pain; crepitus is present. Which of the following is the most likely causal organism?

A. Staphylococcus aureus
B. Clostridium perfringens (Correct Answer)
C. Pseudomonas aeruginosa
D. Rhizopus oryzae
E. Pasteurella multocida

Explanation: ***Clostridium perfringens*** - The rapid onset of severe pain, **foul-smelling discharge**, **crepitus** (due to gas production), **edema**, and **blisters** in a deep wound are classic signs of **gas gangrene**, most commonly caused by *Clostridium perfringens*. - This organism is a **spore-forming anaerobe** commonly found in soil, consistent with the patient's farm work and the nature of the injury (sickle cut leading to a deep wound). *Staphylococcus aureus* - While *Staphylococcus aureus* can cause wound infections, it typically presents with **abscess formation**, **purulent drainage**, and **erythema** without crepitus or the rapid, severe tissue destruction seen here. - It is not associated with the **foul-smelling discharge** or **gas production** characteristic of gas gangrene. *Pseudomonas aeruginosa* - *Pseudomonas aeruginosa* infections often occur in **burns**, puncture wounds (especially through shoes), and in immunocompromised patients, producing a **grape-like odor** and a **blue-green pigment**. - It does not typically cause gas gangrene with crepitus or the rapid tissue necrosis described in the patient. *Rhizopus oryzae* - *Rhizopus oryzae* is a **fungus** that causes **mucormycosis**, primarily affecting immunocompromised individuals, usually presenting as rhinocerebral, pulmonary, or cutaneous infections. - It is not a bacterial cause of acute, rapidly spreading wound infections with gas production like the one described. *Pasteurella multocida* - *Pasteurella multocida* is typically associated with **animal bites** or scratches, causing rapid-onset cellulitis and local infection. - While it can cause soft tissue infection, it does not produce gas or the profound tissue destruction and foul odor seen in gas gangrene.

Question 9: A 43-year-old man is brought to the emergency department 40 minutes after falling off a 10-foot ladder. He has severe pain and swelling of his right ankle and is unable to walk. He did not lose consciousness after the fall. He has no nausea. He appears uncomfortable. His temperature is 37°C (98.6°F), pulse is 98/min, respirations are 16/min, and blood pressure is 110/80 mm Hg. He is alert and oriented to person, place, and time. Examination shows multiple abrasions over both lower extremities. There is swelling and tenderness of the right ankle; range of motion is limited by pain. The remainder of the examination shows no abnormalities. An x-ray of the ankle shows an extra-articular calcaneal fracture. Intravenous analgesia is administered. Which of the following is the most appropriate next step in the management of this patient?

A. Short leg splint and orthopedic consultation
B. Broad-spectrum antibiotic therapy
C. MRI of the right ankle
D. Open reduction and internal fixation
E. X-ray of the spine (Correct Answer)

Explanation: ***X-ray of the spine*** - A **high-energy calcaneal fracture** (especially from a fall from height) is often associated with other injuries, particularly to the **spine**, due to axial loading. - Approximately **10% of calcaneal fractures** are associated with **lumbar spine compression fractures**, making imaging of the spine an essential next step to rule out this potentially serious concomitant injury. *Short leg splint and orthopedic consultation* - While a **short leg splint** is appropriate for initial immobilization and pain control of the ankle fracture, and **orthopedic consultation** is necessary, these steps do not address the immediate need to exclude other critical injuries like spinal fractures in high-impact trauma. - This option represents definitive management of the ankle rather than comprehensive early trauma assessment in a high-risk patient. *Broad-spectrum antibiotic therapy* - **Antibiotic therapy** is primarily indicated for **open fractures** to prevent infection, or in cases of significant soft tissue injury with high contamination risk; the provided information describes an extra-articular fracture with abrasions, but not explicitly an open fracture requiring immediate broad-spectrum antibiotics. - The focus should first be on skeletal integrity elsewhere and definitive fracture management rather than presumptive infection prevention unless an open fracture is confirmed. *MRI of the right ankle* - While an **MRI** can provide detailed imaging of soft tissues, ligaments, and cartilage, and may be useful later for surgical planning or to assess subtle injuries, a plain **X-ray has already confirmed a calcaneal fracture**. - The immediate priority after a high-energy trauma is to rule out other significant, potentially disabling or life-threatening bony injuries, particularly to the spine, rather than further detailed imaging of the already-identified ankle fracture. *Open reduction and internal fixation* - **Open reduction and internal fixation (ORIF)** is a surgical procedure for definitive management of certain fractures; however, it is not the **immediate next step** in the emergency department for initial patient assessment following trauma. - Before surgical intervention, a comprehensive assessment to rule out other injuries (especially spinal fractures) and to thoroughly plan the specific surgical approach is required.

Question 10: A 6-month-old girl presents with recurring skin infections. Past medical history is significant for 3 episodes of acute otitis media since birth. The patient was born at 39 weeks via an uncomplicated, spontaneous transvaginal delivery, but there was delayed umbilical cord separation. She has met all developmental milestones. On physical examination, the skin around her mouth is inflamed and red. Which of the following is most likely responsible for this child’s clinical presentation?

A. Deficiency in NADPH oxidase
B. IL-12 receptor deficiency
C. Absence of CD18 molecule on the surface of leukocytes (Correct Answer)
D. A microtubule dysfunction
E. Defect in tyrosine kinase

Explanation: ***Absence of CD18 molecule on the surface of leukocytes*** - The combination of **recurrent bacterial skin infections**, **otitis media**, and **delayed umbilical cord separation** is highly characteristic of **leukocyte adhesion deficiency type 1 (LAD-1)**. - LAD-1 is caused by a defect in the **CD18 subunit of integrins**, leading to impaired leukocyte extravasation to sites of infection. *Deficiency in NADPH oxidase* - This defect is associated with **chronic granulomatous disease (CGD)**, which presents with recurrent infections by **catalase-positive organisms** and granuloma formation. - While recurrent infections occur, **delayed umbilical cord separation** is not a typical feature of CGD. *IL-12 receptor deficiency* - This deficiency leads to impaired cellular immunity, particularly against **intracellular bacteria (e.g., mycobacteria)** and **fungi**. - It does not typically present with the specific combination of **pyogenic infections** and **delayed umbilical cord separation** seen in this patient. *A microtubule dysfunction* - Microtubule dysfunction can be seen in conditions like **Chédiak-Higashi syndrome**, which involves impaired lysosomal trafficking and leads to **recurrent pyogenic infections**, **oculocutaneous albinism**, and **neuropathy**. - **Delayed umbilical cord separation** is not a characteristic feature of Chédiak-Higashi syndrome. *Defect in tyrosine kinase* - Defects in tyrosine kinase, such as **Bruton's tyrosine kinase (BTK)**, cause **X-linked agammaglobulinemia**, leading to recurrent infections with **encapsulated bacteria** due to impaired B cell development. - This condition is characterized by a lack of mature B cells and **low immunoglobulin levels**, but it does not typically present with **delayed umbilical cord separation**.

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