Soft Tissue Infections — MCQs
An 18-month-old child presents with cellulitis of the leg and SpO2 of 88%. There is no prior history of hospitalization or illness. What is the most probable organism?
A child with fever presents with multiple tender erythematous skin lesions, and on microscopic examination, the skin lesions are found to have neutrophilic infiltration in the dermis. What is the diagnosis?
Which type of necrosis is characterized by deposition of immune complexes and fibrin in the walls of blood vessels?
Which of the following is not included in the Asepsis score?
A 45-year-old construction worker suffers a penetrating wound of the left leg, which is cleaned and sutured. Three days later, the patient presents with sudden onset of severe pain at the site of injury. Physical examination shows darkening of the surrounding skin, hemorrhage, and cutaneous necrosis. The wound shows a thick serosanguinous discharge with gas bubbles and a foul-smelling odor. Which of the following is the most likely etiology of this patient's wound infection?
What is the first-line treatment for gas gangrene?
What is the most common complication of a felon?
A diabetic patient presents with sudden-onset perineal pain. On examination, foul-smelling discharge and necrotic tissue are noted. Which of the following is the most characteristic feature of this condition?
What is the most appropriate treatment for a patient with a suspected Brodie's abscess?
Preferred time for prophylactic antibiotic administration for surgery?
Soft Tissue Infections Indian Medical PG Practice Questions and MCQs
Question 1: An 18-month-old child presents with cellulitis of the leg and SpO2 of 88%. There is no prior history of hospitalization or illness. What is the most probable organism?
- A. MRSA
- B. Streptococcus pyogenes
- C. Streptococcus pneumoniae (Correct Answer)
- D. All of the options
Explanation: ***Streptococcus pneumoniae*** - **Streptococcus pneumoniae** is the most probable organism given the clinical presentation of cellulitis with **hypoxia (SpO2 88%)** in a previously healthy 18-month-old child. - The key finding is the **low oxygen saturation**, which suggests **concurrent pneumonia or bacteremia** with respiratory involvement, not just isolated skin infection. - **Pneumococcal bacteremia** in young children commonly presents with distant site infections (including cellulitis) along with primary respiratory manifestations—explaining both the leg cellulitis and the desaturation. - This age group (18 months) is particularly susceptible to invasive pneumococcal disease, especially if not fully vaccinated or if vaccine coverage is incomplete. *Streptococcus pyogenes* - **Streptococcus pyogenes** (Group A Streptococcus) is indeed a common cause of **cellulitis** in children and can cause rapid local spread. - However, it typically does NOT cause significant **hypoxia** unless there is extensive tissue destruction (necrotizing fasciitis) or toxic shock syndrome, which would present with additional features like severe toxicity, shock, or multi-organ involvement. - The isolated finding of SpO2 88% with cellulitis is more consistent with a pathogen that commonly affects both skin and respiratory system simultaneously. *MRSA* - **MRSA (Methicillin-resistant Staphylococcus aureus)** is a significant cause of skin and soft tissue infections, particularly abscesses and furuncles. - While MRSA can cause severe cellulitis, the **hypoxia** would be unusual unless there is concurrent necrotizing pneumonia or sepsis with ARDS, which is less common in an otherwise healthy child with no prior hospitalization. - The absence of prior healthcare exposure makes community-acquired MRSA possible, but it doesn't explain the respiratory compromise as well as pneumococcus does. *All of the options* - While multiple organisms can cause pediatric cellulitis, the **specific clinical picture** with significant hypoxia points most strongly to **Streptococcus pneumoniae**. - The combination of cellulitis + respiratory compromise is characteristic of pneumococcal bacteremia in this age group, making it the MOST probable single organism.
Question 2: A child with fever presents with multiple tender erythematous skin lesions, and on microscopic examination, the skin lesions are found to have neutrophilic infiltration in the dermis. What is the diagnosis?
- A. Sweet syndrome (Correct Answer)
- B. Behcet's syndrome
- C. Pyoderma gangrenosum
- D. Leukemia cutis
Explanation: ***Sweet syndrome*** - **Sweet syndrome**, also known as acute febrile neutrophilic dermatosis, presents with **fever**, **tender erythematous plaques**, and a characteristic histology of **dense neutrophilic infiltrate in the dermis** without vasculitis. - It is often triggered by **infection**, malignancy, or drugs and is more common in women, though it can occur in children. *Behçet's syndrome* - **Behçet's syndrome** is a multisystem vasculitis characterized by **recurrent oral and genital ulcers**, uveitis, and skin lesions such as erythema nodosum or papulopustular lesions, but not typically the specific neutrophilic dermatosis seen here. - The hallmark is **recurrent aphthous ulceration**, which is not mentioned in the patient's presentation. *Pyoderma gangrenosum* - **Pyoderma gangrenosum** presents as rapidly enlarging, **painful necrotic ulcers** with undermined purplish borders, often associated with inflammatory bowel disease or hematological disorders. - While it also involves neutrophilic infiltration, the clinical presentation of **tender erythematous plaques without ulceration** is not typical. *Leukemia cutis* - **Leukemia cutis** refers to infiltration of the skin by leukemic cells, which can present as papules, nodules, or plaques with **neutrophilic (myeloid) infiltration** on histology. - However, it typically occurs in patients with **known or occult hematologic malignancy**, and the lesions are usually **non-tender** and may have a violaceous hue, unlike the tender erythematous plaques of Sweet syndrome. - Sweet syndrome itself can be **paraneoplastic** and associated with myeloid malignancies, making the distinction important.
Question 3: Which type of necrosis is characterized by deposition of immune complexes and fibrin in the walls of blood vessels?
- A. Liquefactive necrosis
- B. Coagulative necrosis
- C. Caseous necrosis
- D. Fibrinoid necrosis (Correct Answer)
Explanation: ***Fibrinoid necrosis*** - This type of necrosis is classically associated with **immune-mediated vascular damage**, where antigen-antibody complexes are deposited in arterial walls [2]. - The microscopic appearance is characterized by bright pink, amorphous material composed of **fibrin and immune complexes**, giving a fibrin-like staining pattern [1]. *Liquefactive necrosis* - Characterized by the **dissolution of dead cells into a viscous liquid mass**, often seen in bacterial infections or brain infarcts. - The necrotic tissue is replaced by inflammatory cells and fluid, rather than immune complex deposits. *Coagulative necrosis* - Occurs due to **ischemia**, leading to protein denaturation and preservation of cell outlines for a period. - It does not involve the deposition of immune complexes or fibrin in vessel walls. *Caseous necrosis* - A form of coagulative necrosis associated with **tuberculosis**, characterized by a friable, "cheese-like" appearance. - It primarily involves granulomatous inflammation and macrophage accumulation, not immune complex deposition in blood vessels. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of Infancy and Childhood, pp. 514-518. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 214-242.
Question 4: Which of the following is not included in the Asepsis score?
- A. Purulent exudate
- B. Erythema
- C. Serous discharge
- D. Induration (Correct Answer)
Explanation: ***Induration*** - The **ASEPSIS score** is a tool used to quantify surgical wound infection, and it assesses signs like **erythema**, serous discharge, and purulent exudate. - **Induration** is not a primary component directly scored within the ASEPSIS system; rather, it is a sign of inflammation but not specifically enumerated in the score's basic criteria. *Erythema* - **Erythema** (redness) is a key sign of inflammation and a component assessed in the **ASEPSIS score** to indicate wound infection severity. - The extent of erythema around the wound edges contributes to the scoring. *Serous discharge* - The presence and amount of **serous discharge** from a surgical wound is an important parameter in the **ASEPSIS score**. - Excessive or prolonged serous discharge can indicate a potential wound healing problem or infection. *Purulent exudate* - **Purulent exudate** (pus) is a definitive sign of infection and carries a high score within the **ASEPSIS system**. - Its presence significantly increases the overall ASEPSIS score, indicating a more severe wound infection.
Question 5: A 45-year-old construction worker suffers a penetrating wound of the left leg, which is cleaned and sutured. Three days later, the patient presents with sudden onset of severe pain at the site of injury. Physical examination shows darkening of the surrounding skin, hemorrhage, and cutaneous necrosis. The wound shows a thick serosanguinous discharge with gas bubbles and a foul-smelling odor. Which of the following is the most likely etiology of this patient's wound infection?
- A. Clostridium perfringens (Correct Answer)
- B. Staphylococcus epidermidis
- C. Staphylococcus aureus
- D. Clostridium botulinum
Explanation: ***Clostridium perfringens*** - The sudden onset of severe pain, **darkening of skin**, **hemorrhage**, **cutaneous necrosis**, and especially the presence of **gas bubbles** and a **fragrant odor** (often described as sweet/putrid) point directly to **gas gangrene**, caused primarily by *Clostridium perfringens*. - This bacterium is a **gram-positive, anaerobic rod** that produces powerful **exotoxins**, leading to rapid tissue destruction and gas production. *Staphylococcus epidermidis* - This bacterium is a common **commensal skin organism** and typically causes **indolent infections** associated with foreign bodies (e.g., catheters, prosthetic joints), not rapidly progressing necrosis and gas. - While it can form **biofilms**, it does not produce the extensive tissue destruction, gas, or characteristic odor seen here. *Staphylococcus aureus* - *S. aureus* causes a variety of infections, including cellulitis, abscesses, and necrotizing fasciitis, but typically does **not produce gas** in tissues or the characteristic fragrant odor. - While it can cause rapid progression and necrosis, the specific feature of **gas bubbles** strongly differentiates it from *Clostridium perfringens*. *Clostridium botulinum* - *Clostridium botulinum* causes **botulism**, a neuroparalytic disease, through its potent neurotoxin. - It does **not typically cause wound infections** with severe local tissue destruction, gas production, or a fragrant discharge.
Question 6: What is the first-line treatment for gas gangrene?
- A. Debridement & antibiotics (Correct Answer)
- B. Hyperbaric oxygen
- C. Polyvalent gas gangrene antitoxin
- D. Amputation
Explanation: ***Debridement & antibiotics*** - **Aggressive surgical debridement** to remove necrotic tissue and reduce bacterial load is the most critical initial step. - **Broad-spectrum antibiotics**, particularly penicillin G, are essential to target the causative *Clostridium perfringens* and prevent systemic spread. *Hyperbaric oxygen* - While **hyperbaric oxygen therapy** can be a useful adjunct by inhibiting bacterial growth and toxin production in anaerobic environments, it is not the *first-line* or sole treatment. - It should be used in conjunction with debridement and antibiotics, not as a standalone initial therapy. *Polyvalent gas gangrene antitoxin* - **Antitoxins** are generally not recommended due to their limited efficacy and potential for severe allergic reactions. - The primary treatment focuses on removing the source of infection and killing the bacteria, not neutralizing toxins alone. *Amputation* - **Amputation** is a drastic measure typically reserved for cases where the limb is irreversibly damaged, infection is uncontrollable by other means, or there is a threat to life. - It is not the initial treatment but may be necessary in advanced or complicated cases.
Question 7: What is the most common complication of a felon?
- A. Osteomyelitis (Correct Answer)
- B. Subungual hematoma
- C. Infective arthritis
- D. No complications
Explanation: ***Osteomyelitis*** - A **felon** is a severe infection of the **distal pulp space** of the fingertip, which has numerous fibrous septa. - The tightly compartmentalized nature of this space can lead to increased pressure, compromising blood supply and facilitating the spread of infection to the underlying **phalanx bone**, causing **osteomyelitis**. *Subungual hematoma* - A **subungual hematoma** is a collection of blood under the nail, usually resulting from direct trauma. - It is not a complication of an infection like a felon, but rather a separate traumatic injury. *Infective arthritis* - **Infective arthritis** involves the joint space, typically resulting from direct inoculation, hematogenous spread, or spread from adjacent soft tissue infection. - While possible, it is less common for a felon to directly spread to the **distal interphalangeal joint** compared to the more immediate risk of bone involvement. *No complications* - A **felon** is a serious infection that, if left untreated, almost always leads to complications due to the unique anatomy of the fingertip pulp space. - The high pressure within the compartments of the distal pulp makes it prone to necrosis and spread of infection to adjacent structures.
Question 8: A diabetic patient presents with sudden-onset perineal pain. On examination, foul-smelling discharge and necrotic tissue are noted. Which of the following is the most characteristic feature of this condition?
- A. Mixed aerobic and anaerobic infection (Correct Answer)
- B. Urinary diversion may be considered in severe cases
- C. Bilateral orchidectomy is not routinely required
- D. Anti-gas gangrene serum is indicated only in specific cases
Explanation: **Mixed aerobic and anaerobic infection** - Fournier's gangrene is a polymicrobial infection typically involving a **synergistic mixture of aerobic and anaerobic bacteria**. - This mixed infection contributes to the rapid progression and tissue destruction seen in this condition, leading to the **foul-smelling discharge** due to anaerobic metabolism. *Anti-gas gangrene serum is indicated only in specific cases.* - Anti-gas gangrene serum is specifically for **Clostridium perfringens** infections, which can cause gas gangrene but is usually a distinct clinical entity from Fournier's. - While Clostridium species can be present in Fournier's gangrene, it is not the sole causative agent, and **broader antimicrobial therapy** is the mainstay of treatment, not antitoxin serum. *Urinary diversion may be considered in severe cases.* - Urinary diversion, such as a **suprapubic catheter**, may be necessary when the urethra or perineum is extensively involved or to prevent ongoing contamination of the surgical site. - However, it's not a primary treatment for the infection itself but rather an **adjunctive measure** to manage complicated cases of Fournier's gangrene. *Bilateral orchidectomy is not routinely required.* - **Testicular involvement** in Fournier's gangrene is rare due to the separate blood supply of the testes. - **Orchidectomy** is only performed if the testes themselves are affected by necrosis, which is uncommon and occurs in critically severe cases; routine removal is not indicated.
Question 9: What is the most appropriate treatment for a patient with a suspected Brodie's abscess?
- A. IV antibiotics only
- B. Curettage and drainage (Correct Answer)
- C. Amputation
- D. Radiotherapy
Explanation: ***Correct: Curettage and drainage*** - **Brodie's abscess** is a subacute or chronic form of osteomyelitis involving a localized collection of pus in the bone - **Surgical intervention** with curettage and drainage is necessary to remove infected tissue and decompress the lesion - This approach directly addresses the localized bone infection, removes necrotic debris, and allows for local antibiotic delivery or culture-guided systemic therapy - Promotes healing and prevents recurrence by eliminating the sequestrum and poorly vascularized tissue *Incorrect: IV antibiotics only* - While antibiotics are crucial for treating osteomyelitis, **IV antibiotics alone** are insufficient for Brodie's abscess - The abscess creates an environment with **poor blood supply** to the central necrotic tissue, limiting antibiotic penetration and efficacy - Surgical debridement is essential to remove the avascular focus and allow antibiotics to work effectively *Incorrect: Amputation* - **Amputation** is an extreme measure reserved for severe, chronic, and uncontrollable osteomyelitis with extensive soft tissue damage or sepsis - Only considered when limb salvage procedures have failed or in cases of life-threatening infection - Not appropriate for a localized Brodie's abscess, which typically responds well to less invasive surgical methods *Incorrect: Radiotherapy* - **Radiotherapy** uses high-energy radiation to treat malignancies - Has **no role** in treating bacterial infections like Brodie's abscess - Would be inappropriate and potentially harmful in this clinical context
Question 10: Preferred time for prophylactic antibiotic administration for surgery?
- A. 1 day before surgery
- B. At the time of induction of anaesthesia (Correct Answer)
- C. I.V. during surgery
- D. I.M. 6 hrs before surgery
Explanation: ***At the time of induction of anaesthesia*** - This timing ensures that a **therapeutic concentration** of the antibiotic is present in the tissues at the time of the initial surgical incision, when the risk of bacterial contamination is highest. - Administering the antibiotic too early or too late can reduce its effectiveness in preventing **surgical site infections (SSIs)**. *1 day before surgery* - Administering antibiotics a day before surgery would lead to the drug being **metabolized and eliminated** from the body before the surgical incision is made, rendering it ineffective for prophylaxis. - This timing also increases the risk of **antibiotic resistance** development without providing adequate protection against SSIs. *I.V. during surgery* - Administering the antibiotic intravenously during surgery means that the drug will not have reached sufficient **tissue concentrations** at the crucial moment of the initial incision. - The protective effect is largely dependent on adequate tissue levels **prior to contamination**, which would not be achieved by administration only during the procedure. *I.M. 6 hrs before surgery* - While closer to the optimal timing than 1 day before, administering intramuscularly 6 hours prior may result in **suboptimal drug levels** at the time of incision, especially for drugs with shorter half-lives. - Intramuscular administration can also have variable absorption rates compared to intravenous, potentially delaying peak tissue concentration and reducing reliability for **prophylactic efficacy**.
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