Bacterial Skin Infections Practice Questions

Q: Erythema nodosum leprosum is seen in a 16-year-old boy. This is a feature of which of the following types of leprosy?

Lepromatous. **Explanation:** **Erythema Nodosum Leprosum (ENL)**, also known as a **Type 2 Lepra Reaction**, is a classic example of a **Type III hypersensitivity reaction** (immune-complex mediated). It occurs due to the deposition of antigen-antibody complexes in tissues, leading to systemic inflammation. 1. **Why Lepromatous (Option A) is correct:** ENL occurs almost exclusively in patients with a high bacterial load (multibacillary) and high humoral (antibody) response. It is most commonly seen in **Lepromatous Leprosy (LL)** and sometimes in **Borderline Lepromatous (BL)** leprosy. It is triggered by the rapid killing of *M. leprae* (often after starting MDT), which releases large amounts of fragmented bacterial antigens into the bloodstream. 2. **Why other options are incorrect:** * **Tuberculoid (TT) and Borderline Tuberculoid (BT):** These are paucibacillary forms with high cell-mediated immunity (CMI) and very low bacterial load. Type 2 reactions (ENL) do not occur here; instead, these patients are prone to **Type 1 Lepra Reactions** (Delayed Hypersensitivity). * **Borderline (BB):** While borderline cases can shift, ENL is specifically associated with the "lepromatous end" of the spectrum where the bacillary index is high. **Clinical Pearls for NEET-PG:** * **Clinical Features:** Characterized by sudden onset of tender, evanescent, erythematous nodules, high-grade fever, malaise, and systemic involvement (neuritis, orchitis, iridocyclitis, and glomerulonephritis). * **Drug of Choice:** **Thalidomide** is the most effective treatment for ENL. Systemic corticosteroids and Clofazimine are also used. * **Timing:** Unlike Type 1 reactions (which occur early), ENL typically occurs later in the course of treatment.

Q: In secondary syphilis, which one of the following features is not found?

Aortitis. **Explanation:** The correct answer is **C. Aortitis**. Syphilis, caused by *Treponema pallidum*, progresses through distinct clinical stages [1]. Understanding the timing of systemic involvement is crucial for the NEET-PG exam. **1. Why Aortitis is the correct answer:** Aortitis is a manifestation of **Tertiary Syphilis** (Late Syphilis), occurring typically 10–30 years after the initial infection. It results from *vasa vasorum* inflammation (endarteritis obliterans), leading to medial necrosis and weakening of the aortic wall [1]. This can result in aortic aneurysms or aortic regurgitation. It is **not** a feature of the secondary stage. **2. Why the other options are incorrect:** * **Maculopapular rashes (Option A):** This is the most common cutaneous manifestation of Secondary Syphilis. The rash is typically widespread, symmetrical, and characteristically involves the **palms and soles** [1]. * **Generalized non-tender lymphadenopathy (Option B):** Secondary syphilis is a systemic spirochaetemic stage. Rubbery, discrete, and non-tender enlargement of lymph nodes (especially epitrochlear nodes) is a hallmark finding. * **Follicular syphilides (Option C):** These are small, papular lesions localized around hair follicles, often seen in secondary syphilis. They can lead to "moth-eaten" alopecia. **Clinical Pearls for NEET-PG:** * **Secondary Syphilis** is known as "The Great Imitator" and is the most florid stage. * **Condyloma Lata:** Highly infectious, moist, flat-topped papules in intertriginous areas (Secondary stage) [1]. * **Lues Maligna:** A severe pleomorphic form of secondary syphilis seen in HIV patients. * **Drug of Choice:** Benzathine Penicillin G remains the gold standard for all stages, though dosages vary.

Q: A single hypopigmented anesthetic patch with a satellite lesion on the forearm is likely diagnosed as which of the following?

Tuberculoid leprosy. **Explanation:** The clinical presentation of a **single hypopigmented, anesthetic patch** associated with **satellite lesions** is a classic hallmark of **Tuberculoid Leprosy (TT)**. In Tuberculoid Leprosy, the host possesses high cell-mediated immunity (CMI). This strong immune response localizes the infection to a single or very few lesions (usually 1–3). The hallmark features include well-defined margins, complete loss of sensation (anesthesia) due to nerve damage within the patch, and hair loss (alopecia). **Satellite lesions** (smaller macules or papules near the periphery of the main patch) are characteristic of the polar tuberculoid spectrum. **Analysis of Incorrect Options:** * **Indeterminate Leprosy:** This is the earliest stage. It typically presents as a single hypopigmented macule with *vague* margins and *partial* (not complete) sensory loss. Satellite lesions are not seen here. * **Neuritic Leprosy:** This form involves purely neurological symptoms (nerve thickening, pain, and sensory loss) in the distribution of a nerve, but it is characterized by the **absence** of any visible skin patches. * **Lupus Vulgaris:** This is a form of cutaneous tuberculosis. While it presents as a plaque, it is typically reddish-brown ("apple-jelly" nodules on diascopy) and is **not anesthetic**. **High-Yield Clinical Pearls for NEET-PG:** * **Ridley-Jopling Classification:** TT is the most stable form with the highest CMI. * **Nerve Involvement:** In TT, nerves are often thickened asymmetrically (e.g., ulnar or greater auricular nerve). * **Lepromin Test:** Strongly **positive** in Tuberculoid Leprosy (reflecting high CMI) and negative in Lepromatous Leprosy. * **Histopathology:** Shows well-formed non-caseating granulomas with rare or absent Acid-Fast Bacilli (paucibacillary).

Q: Multibacillary leprosy is characterized by which of the following?

Bacteriological index of 2 or greater. **Explanation:** The classification of Leprosy is a high-yield topic for NEET-PG, primarily following the **WHO Operational Classification**, which simplifies treatment protocols into Paucibacillary (PB) and Multibacillary (MB) types. **Why Option B is Correct:** According to the WHO classification, **Multibacillary (MB) leprosy** is defined by a high bacterial load. A **Bacteriological Index (BI) of ≥ 2+** at any site (using slit-skin smears) is a definitive diagnostic criterion for MB leprosy. Even if a patient has few skin lesions, a positive smear automatically classifies them as MB to ensure they receive the more robust 12-month MDT regimen. **Analysis of Incorrect Options:** * **Option A:** Under the WHO criteria, MB leprosy is characterized by having **more than five ( >5 ) lesions**. The presence of exactly five lesions would still be classified as Paucibacillary (PB), which covers 1 to 5 lesions. * **Option C:** Indeterminate leprosy is typically characterized by a single hypopigmented macule with vague margins and is almost always classified and treated as **Paucibacillary (PB)** due to the low bacterial load. **High-Yield Clinical Pearls for NEET-PG:** * **WHO Classification Criteria for MB Leprosy:** 1. > 5 skin lesions. 2. > 1 nerve involvement (some guidelines state ≥ 2 nerves). 3. Positive skin smear (BI ≥ 2+). * **MDT Regimen for MB:** Rifampicin (600mg once monthly), Clofazimine (300mg once monthly + 50mg daily), and Dapsone (100mg daily) for **12 months**. * **Cardinal Signs:** Definite loss of sensation, thickened nerves, and presence of *M. leprae* on skin smear. * **Ridley-Jopling Scale:** MB typically corresponds to Mid-borderline (BB), Borderline Lepromatous (BL), and Lepromatous Leprosy (LL).

Q: All of the following are true about bullous impetigo EXCEPT?

Lesions have an erythematous base. **Explanation:** Bullous impetigo is a localized form of staphylococcal scalded skin syndrome (SSSS). The hallmark of this condition is the formation of large, flaccid bullae due to the action of **Exfoliative Toxin A** produced by *Staphylococcus aureus*. **Why Option D is the Correct Answer (The Exception):** Unlike non-bullous impetigo, the bullae in bullous impetigo typically arise on **normal-appearing skin** and lack a surrounding halo of erythema. When these bullae rupture, they leave behind a moist, red, "varnish-like" erosive surface, but the base is generally **not erythematous** in the initial stages. **Analysis of Other Options:** * **Option A:** It is caused exclusively by *Staphylococcus aureus* (Phage group II, type 71). This differs from non-bullous impetigo, which can be caused by both *S. aureus* and *S. pyogenes*. * **Option B:** It is most common in neonates (where it is known as Pemphigus neonatorum) and young children due to lack of immunity against the toxin and immature renal clearance. * **Option C:** While it can occur anywhere, the face is a very common site, along with intertriginous areas like the axilla and groin. **NEET-PG High-Yield Pearls:** * **Target Protein:** The exfoliative toxin cleaves **Desmoglein-1** (found in the upper epidermis), leading to subcorneal splitting. * **Nikolsky Sign:** Usually negative in bullous impetigo (localized), but positive in SSSS (generalized). * **Treatment:** Topical Mupirocin for localized lesions; oral anti-staphylococcal antibiotics (e.g., Dicloxacillin or Cephalexin) for extensive cases.

Q: All of the following skin infections are caused by Staphylococcus aureus, EXCEPT:

Erysipelas. **Explanation:** The primary distinction in bacterial skin infections lies in the causative organism and the depth of involvement. **1. Why Erysipelas is the correct answer:** Erysipelas is a superficial form of cellulitis characterized by sharp, well-demarcated borders and prominent lymphatic involvement. It is classically caused by **Group A Beta-hemolytic Streptococci (Streptococcus pyogenes)**, not *Staphylococcus aureus*. It typically affects the upper dermis and superficial lymphatics. **2. Why the other options are incorrect:** * **Folliculitis:** This is a superficial infection of the hair follicle. **Staphylococcus aureus** is the most common causative agent. * **Furuncle (Boil):** This is a deeper, necrotizing infection of the hair follicle and surrounding tissue, forming an abscess. It is almost exclusively caused by **Staphylococcus aureus**. * **Cellulitis:** While both *Streptococcus* and *Staphylococcus* can cause cellulitis, **Staphylococcus aureus** is a major cause, especially when associated with an open wound, trauma, or abscess. **3. Clinical Pearls for NEET-PG:** * **Erysipelas vs. Cellulitis:** Erysipelas has **raised, sharply defined edges** (superficial), whereas Cellulitis has **indistinct, flat borders** (deep dermis/subcutaneous fat). * **Staphylococcal Scalded Skin Syndrome (SSSS):** Caused by exfoliative toxins (A and B) from *S. aureus*; targets Desmoglein-1. * **Impetigo:** *S. aureus* is the most common cause of both bullous and non-bullous impetigo (though *S. pyogenes* also causes non-bullous). * **Ecthyma:** A deeper form of impetigo extending into the dermis, often caused by *Streptococcus*.

Q: Staphylococcal infection causes all the following diseases except:

Erysipelas. **Explanation:** The core concept in this question is differentiating between infections caused by **Staphylococcus aureus** and **Streptococcus pyogenes** (Group A Streptococcus). **Why Erysipelas is the correct answer:** Erysipelas is a superficial form of cellulitis characterized by sharp, well-demarcated borders and intense erythema. It is classically caused by **Group A Beta-hemolytic Streptococci**. Unlike Staphylococcal infections, which tend to be localized and abscess-forming, Streptococcal infections often spread through tissue planes via enzymes like hyaluronidase. **Analysis of incorrect options:** * **Impetigo:** Can be caused by both *S. aureus* and *S. pyogenes*. However, **Bullous Impetigo** is exclusively caused by *S. aureus* (due to exfoliative toxins). * **Ecthyma:** This is a deeper, "punched-out" ulcerative form of impetigo. While it can be caused by Streptococcus, *S. aureus* is frequently isolated as a primary or co-infecting pathogen. * **Scalded Skin Syndrome (SSSS):** This is caused specifically by **Staphylococcal exfoliative toxins** (ETA and ETB) which target Desmoglein-1 in the stratum granulosum. **High-Yield Clinical Pearls for NEET-PG:** 1. **Golden Crust:** Pathognomonic for non-bullous impetigo (Staph or Strep). 2. **Nikolsky Sign:** Positive in Staphylococcal Scalded Skin Syndrome (SSSS) but negative in Bullous Impetigo. 3. **Depth of Infection:** Erysipelas involves the upper dermis and superficial lymphatics, whereas Cellulitis (often Staph) involves the deep dermis and subcutaneous fat. 4. **Toxin-Mediated Staph Diseases:** SSSS, Toxic Shock Syndrome (TSS), and Bullous Impetigo.

Q: Which of the following conditions present with draining sinuses?

Mycetoma and Scrofula. **Explanation:** The presence of **draining sinuses** (chronic tracks connecting deep-seated infections to the skin surface) is a hallmark of specific chronic granulomatous and suppurative conditions. **1. Why the Correct Answer is Right:** * **Mycetoma (Madura Foot):** This is a chronic granulomatous infection (fungal or bacterial) characterized by a clinical triad of **localized swelling, painless subcutaneous nodules, and multiple discharging sinuses** that extrude characteristic "grains." * **Scrofula (Scrofuloderma):** This is a form of cutaneous tuberculosis resulting from the breakdown of skin over an underlying tuberculous focus (usually a lymph node or bone). It presents as firm, painless nodules that ulcerate and form **chronic discharging sinus tracks** with watery or caseous discharge. **2. Why Other Options are Wrong:** * **Lupus Vulgaris:** This is the most common chronic form of cutaneous TB in previously sensitized individuals. It typically presents as "apple-jelly" nodules on diascopy and plaques, but it **does not** typically form draining sinuses. * **Pediculosis:** This is a superficial infestation by lice (head, body, or pubic). It presents with pruritus and excoriations, not deep-seated sinus formation. **Clinical Pearls for NEET-PG:** * **Actinomycetoma vs. Eumycetoma:** Actinomycetoma (bacterial) usually progresses faster and has more numerous sinuses compared to Eumycetoma (fungal). * **Other conditions with sinuses:** Actinomycosis (lumpy jaw with sulfur granules) and Hidradenitis Suppurativa (intertriginous areas). * **Scrofuloderma** is the most common cause of cold abscesses in the neck leading to sinus formation.

Q: The 'bubos' form is characteristic of which stage of Lymphogranuloma venereum (LGV)?

Secondary. Lymphogranuloma venereum (LGV) is a systemic sexually transmitted infection caused by **Chlamydia trachomatis serovars L1, L2, and L3**. The disease typically progresses through three distinct clinical stages: 1. **Secondary Stage (Correct Answer):** Also known as the **inguinal syndrome**, this stage occurs 2–6 weeks after the primary lesion [1]. It is characterized by painful regional lymphadenopathy, most commonly in the inguinal and femoral nodes [1]. These enlarged, inflamed nodes are termed **"bubos."** A classic clinical sign during this stage is the **"Groove sign,"** where the inguinal ligament divides the matted nodes into upper and lower groups. 2. **Primary Stage:** This stage involves a small, painless, transient papule or ulcer at the site of inoculation (genitals) [1]. It often goes unnoticed because it heals rapidly without scarring. 3. **Tertiary Stage:** Known as the **anogenital syndrome**, this stage involves chronic inflammation leading to complications like proctocolitis, rectal strictures, fistulae, and lymphatic obstruction (elephantiasis of the genitalia, also known as *esthiomene*). 4. **Latent Stage:** While LGV can have periods of subclinical infection, "bubos" are an active inflammatory manifestation of the secondary stage, not a feature of latency. **High-Yield Clinical Pearls for NEET-PG:** * **Causative Agent:** *C. trachomatis* (L1-L3). * **Groove Sign:** Pathognomonic for LGV (seen in only 15-20% of cases). * **Treatment of Choice:** **Doxycycline** (100 mg BID for 21 days). Erythromycin is the alternative for pregnant patients. * **Diagnosis:** Frei’s test (historical); Nucleic Acid Amplification Test (NAAT) is the modern gold standard.

Question 1

What is the treatment of choice for late cardiovascular syphilis?

Accepted Answer

Benzathine penicillin 7.2 million units in three divided doses

Answer

Benzathine penicillin 2.4 million units single dose

Answer

Benzylpenicillin 12-24 million units for 21 days

Answer

Tetracycline 2g daily

Question 2

Erythema nodosum leprosum is seen in a 16-year-old boy. This is a feature of which of the following types of leprosy?

Accepted Answer

Lepromatous

Answer

Borderline

Answer

Tuberculoid

Answer

Borderline tuberculoid

Question 3

In secondary syphilis, which one of the following features is not found?

Accepted Answer

Aortitis

Answer

Maculopapular rashes

Answer

Generalized non-tender lymphadenopathy

Answer

Follicular syphilides

Question 4

A single hypopigmented anesthetic patch with a satellite lesion on the forearm is likely diagnosed as which of the following?

Accepted Answer

Tuberculoid leprosy

Answer

Indeterminate leprosy

Answer

Neuritic leprosy

Answer

Lupus vulgaris

Question 5

Multibacillary leprosy is characterized by which of the following?

Accepted Answer

Bacteriological index of 2 or greater

Answer

Presence of five lesions

Answer

Indeterminate leprosy

Answer

All of the above

Question 6

All of the following are true about bullous impetigo EXCEPT?

Accepted Answer

Lesions have an erythematous base

Answer

Caused by Staphylococcus aureus

Answer

Common in neonates and infants

Answer

Lesions commonly occur on the face

Question 7

All of the following skin infections are caused by Staphylococcus aureus, EXCEPT:

Accepted Answer

Erysipelas

Answer

Folliculitis

Answer

Furuncle

Answer

Cellulitis

Question 8

Staphylococcal infection causes all the following diseases except:

Accepted Answer

Erysipelas

Answer

Impetigo

Answer

Ecthyma

Answer

Scalded skin syndrome

Question 9

Which of the following conditions present with draining sinuses?

Accepted Answer

Mycetoma and Scrofula

Answer

Mycetoma and Lupus vulgaris

Answer

Mycetoma and Pediculosis

Answer

Scrofula and Lupus vulgaris

Question 10

The 'bubos' form is characteristic of which stage of Lymphogranuloma venereum (LGV)?

Accepted Answer

Secondary

Answer

Primary

Answer

Tertiary

Answer

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Bacterial Skin Infections — MCQs

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