Bacterial Skin Infections — MCQs
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Cutaneous tuberculosis secondary to underlying infected tissue, such as lymph nodes, is called as?
Apple jelly nodules are seen in which condition?
Lepra bacilli are mainly transmitted by?
Tuberculoid leprosy is characterized by which of the following?
Which of the following is a type of cutaneous tuberculosis?
Leonine facies is seen in which type of leprosy?
What is the treatment for Lucio phenomenon?
A diabetic male presents with a red, tender, and painful swelling on the right buttock with multiple discharging points. The swelling is hard and indurated, accompanied by high-grade fever and malaise. What is the most likely diagnosis?
Apple jelly nodules are characteristic of which condition?
In which type of cutaneous tuberculosis, caseation is most commonly seen?
Bacterial Skin Infections Indian Medical PG Practice Questions and MCQs
Question 21: Cutaneous tuberculosis secondary to underlying infected tissue, such as lymph nodes, is called as?
- A. Lupus Vulgaris
- B. Scrofuloderma (Correct Answer)
- C. Spina Ventosa
- D. Tuberculous Verrucosa Cutis
Explanation: **Explanation:** **Scrofuloderma (Tuberculosis Colliquativa Cutis)** is the correct answer. It represents a **pericontiguous spread** of tuberculosis to the overlying skin from an underlying infected focus, most commonly a **tuberculous lymph node** (especially cervical), but also from infected bones or joints. It typically presents as firm, painless subcutaneous nodules that eventually break down to form ulcers and sinus tracts with a characteristic "watery" or "cheesy" discharge. **Analysis of Incorrect Options:** * **Lupus Vulgaris:** This is the most common chronic form of cutaneous TB in adults. It occurs via hematogenous, lymphatic, or contiguous spread in individuals with high immunity. The hallmark clinical sign is the **"Apple-jelly nodule"** seen on diascopy. * **Spina Ventosa:** This refers to **tuberculous dactylitis**, involving the short bones of the hands or feet. While it can lead to scrofuloderma of the overlying skin, the term itself refers to the bone pathology, not the cutaneous manifestation. * **Tuberculous Verrucosa Cutis (TVC):** Also known as "Prosector’s wart," this is a form of **exogenous inoculation** TB occurring in previously sensitized individuals with high immunity. It presents as a solitary, warty (verrucous) plaque, usually on the hands. **High-Yield Clinical Pearls for NEET-PG:** * **Classification:** Cutaneous TB is classified based on the bacterial load (**Multibacillary** vs. **Paucibacillary**) and the route of infection. * **Paucibacillary forms:** Lupus Vulgaris, TVC, and Tuberculids. * **Multibacillary forms:** Scrofuloderma, Orificial TB, and Miliary TB. * **Most common type in India:** Lupus Vulgaris (overall), though Scrofuloderma is very common in children.
Question 22: Apple jelly nodules are seen in which condition?
- A. Ichthyosis vulgaris
- B. Lichen planus
- C. Lupus vulgaris (Correct Answer)
- D. Lupus erythematosus
Explanation: **Explanation:** **Lupus Vulgaris (Correct Answer):** Lupus vulgaris is the most common form of **cutaneous tuberculosis** in adults, occurring in individuals with high immunity against *Mycobacterium tuberculosis*. The characteristic clinical finding is a plaque composed of "tubercles." When a glass slide is pressed against the lesion (**Diascopy**), the background erythema blanches, revealing yellowish-brown, translucent, granulomatous foci that resemble **apple jelly**. This is a classic diagnostic sign for Lupus vulgaris. **Why other options are incorrect:** * **Ichthyosis vulgaris:** A genetic disorder of keratinization characterized by dry, fish-like scales, particularly on the extensors. It does not involve granulomatous inflammation or apple jelly nodules. * **Lichen planus:** An inflammatory condition characterized by the "6 Ps" (Planar, Purple, Polygonal, Pruritic, Papules, and Plaques). A key diagnostic feature here is **Wickham striae** (whitish reticular lines), not apple jelly nodules. * **Lupus erythematosus (LE):** While Systemic LE or Discoid LE can present with various skin rashes (like the malar rash or scarred plaques), they are autoimmune in nature. Diascopy in LE does not reveal apple jelly nodules. **NEET-PG High-Yield Pearls:** * **Diascopy:** Used to differentiate purpura (does not blanch) from erythematous lesions (blanch). In Lupus vulgaris and Sarcoidosis, it reveals the "apple jelly" appearance. * **Most common site:** Face and neck (earlobes are a classic site). * **Complication:** Long-standing Lupus vulgaris carries a risk of developing **Squamous Cell Carcinoma** (Marjolin’s ulcer). * **Histopathology:** Shows well-formed non-caseating granulomas with peripheral lymphocytes.
Question 23: Lepra bacilli are mainly transmitted by?
- A. Skin contact
- B. Droplets (Correct Answer)
- C. Stool
- D. Urine
Explanation: **Explanation:** **1. Why Droplets is Correct:** The primary mode of transmission for *Mycobacterium leprae* is via **respiratory droplets** (aerosolized secretions) from the nasal mucosa of untreated patients with lepromatous leprosy. The nasal mucosa is a major reservoir, shedding millions of bacilli daily. Infection occurs when a susceptible individual inhales these droplets during prolonged, close contact. **2. Why Other Options are Incorrect:** * **Skin Contact:** While historically believed to be the main route, skin-to-skin contact is now considered an **inefficient** mode of transmission. Intact skin is an effective barrier; transmission only occurs if there is contact between broken skin and a high load of bacilli, which is rare compared to the respiratory route. * **Stool and Urine:** *M. leprae* is not an enteric or urinary pathogen. There is no evidence of fecal-oral or urogenital transmission in humans. **3. Clinical Pearls for NEET-PG:** * **Incubation Period:** Leprosy has a very long incubation period, averaging **3 to 5 years** (can range from 6 months to 20 years). * **Target Cells:** The bacilli have a predilection for **Schwann cells** (leading to nerve damage) and **macrophages**. * **Temperature Sensitivity:** *M. leprae* grows best at **30°C**, which explains its preference for cooler body parts like the nose, ears, and peripheral nerves. * **Infectivity vs. Pathogenicity:** Leprosy has **high infectivity but low pathogenicity**; most people (approx. 95%) have natural immunity and do not develop the disease even after exposure. * **Armadillos:** In certain regions (like the Southern US), the nine-banded armadillo is a known zoonotic reservoir.
Question 24: Tuberculoid leprosy is characterized by which of the following?
- A. Non-caseating granuloma in nerves (Correct Answer)
- B. Subepidermal clear zone
- C. Numerous bacilli in the skin
- D. Caseation in the skin
Explanation: **Explanation:** Tuberculoid Leprosy (TT) represents the high-resistance end of the Ridley-Jopling scale, where a robust **Type 1 (Th1) cell-mediated immunity** effectively contains the infection. **1. Why Option A is Correct:** In Tuberculoid leprosy, the immune response is so vigorous that it forms well-defined **epithelioid cell granulomas**. These granulomas characteristically extend along the neurovascular bundles and invade the dermal nerves. The hallmark of TT is the destruction of these nerves by **non-caseating granulomas**, leading to early, profound anesthesia and nerve thickening. **2. Why the other options are incorrect:** * **Option B (Subepidermal clear zone):** Also known as the **Grenz zone**, this is a feature of **Lepromatous Leprosy (LL)**. In LL, the granuloma does not reach the epidermis, leaving a clear band of collagen. In TT, the granuloma often "erodes" or touches the basal layer of the epidermis. * **Option C (Numerous bacilli):** TT is **paucibacillary**. Due to high immunity, Acid-Fast Bacilli (AFB) are rarely, if ever, found in skin smears or biopsies (Bacteriological Index = 0). Numerous bacilli are seen in LL (multibacillary). * **Option D (Caseation in the skin):** While caseation can occasionally occur within the *nerves* (nerve abscess) in TT, it is **not** a feature of the skin lesions themselves. **High-Yield Clinical Pearls for NEET-PG:** * **Lepromin Test:** Strongly positive in TT (indicates high CMI); negative in LL. * **Clinical Presentation:** Usually a single or few (1-3) well-defined, anesthetic, hypo-pigmented patches with hair loss. * **Nerve Involvement:** Early, asymmetrical, and severe. * **Cytokine Profile:** Th1 response (IL-2, IFN-γ, IL-12).
Question 25: Which of the following is a type of cutaneous tuberculosis?
- A. Pemphigus vulgaris
- B. Scrofuloderma (Correct Answer)
- C. Lupus pernio
- D. Lupus panniculitis
Explanation: **Explanation:** **Scrofuloderma** (Tuberculosis colliquativa cutis) is a common form of **cutaneous tuberculosis** seen in individuals with moderate immunity. It occurs due to the **contiguous spread** of infection to the overlying skin from an underlying tuberculous focus, most commonly a cervical lymph node, bone, or joint. Clinically, it presents as painless, firm subcutaneous nodules that eventually break down to form ulcers and sinus tracts discharging caseous material. **Analysis of Incorrect Options:** * **Pemphigus vulgaris (A):** This is an **autoimmune** intraepidermal blistering disorder caused by IgG antibodies against desmoglein 3 (and sometimes 1), not an infection. * **Lupus pernio (C):** This is a pathognomonic cutaneous manifestation of **Sarcoidosis**. It presents as violaceous, indurated plaques on the nose, cheeks, and ears. (Note: Do not confuse this with *Lupus vulgaris*, which is a form of cutaneous TB). * **Lupus panniculitis (D):** Also known as Lupus erythematosus profundus, this is a variant of **Lupus Erythematosus** involving the subcutaneous fat. **High-Yield Clinical Pearls for NEET-PG:** * **Lupus Vulgaris:** The most common form of cutaneous TB in adults; shows "apple-jelly nodules" on diascopy. * **Tuberculosis Verrucosa Cutis (TVC):** Known as "Prosector’s wart," it occurs due to exogenous inoculation in a previously sensitized individual. * **Tuberculids:** These are hypersensitivity reactions to internal TB (e.g., Erythema induratum of Bazin, Lichen scrofulosorum). * **Diagnosis:** Histopathology typically shows granulomatous inflammation with caseous necrosis.
Question 26: Leonine facies is seen in which type of leprosy?
- A. Tuberculoid
- B. Borderline
- C. Lepromatous (Correct Answer)
- D. Borderline tuberculoid
Explanation: **Explanation:** **Leonine facies** (lion-like appearance) is a classic clinical hallmark of **Lepromatous Leprosy (LL)**. This occurs due to the hematogenous spread of *Mycobacterium leprae* in a host with low cell-mediated immunity (CMI). The high bacterial load leads to diffuse infiltration of the facial skin, resulting in: * Thickening and furrowing of the forehead and cheeks. * Widening of the nose. * Pendulous earlobes. * Loss of eyebrows (Madarosis), particularly the lateral one-third. **Analysis of Options:** * **Tuberculoid (TT):** Characterized by high CMI and few lesions (paucibacillary). Lesions are well-defined, anesthetic, and do not cause diffuse facial infiltration. * **Borderline Tuberculoid (BT):** Similar to TT but with more lesions and more nerve involvement; it does not present with the massive infiltration seen in LL. * **Borderline (BB):** An unstable form of leprosy that acts as a transition point. While it has more lesions than TT, it lacks the characteristic diffuse infiltration required to produce leonine facies. **High-Yield Clinical Pearls for NEET-PG:** * **Grenz Zone:** A clear sub-epidermal zone seen on histopathology in Lepromatous Leprosy (absent in TT). * **Globi:** Large clusters of acid-fast bacilli (AFB) found within **Virchow cells** (foamy macrophages) in LL. * **Bacteriological Index (BI):** Highest in LL (4+ to 6+), whereas it is 0 in TT. * **Differential Diagnosis:** Leonine facies can also be seen in **Post-Kala-azar Dermal Leishmaniasis (PKDL)**, Mycosis Fungoides (Cutaneous T-cell Lymphoma), and Sarcoidosis.
Question 27: What is the treatment for Lucio phenomenon?
- A. Steroids
- B. Lenalidomide
- C. Clofazimine
- D. Exchange transfusion (Correct Answer)
Explanation: **Explanation:** **Lucio phenomenon** is a rare, life-threatening variant of Type 2 Lepra reaction (ENL) seen exclusively in patients with diffuse lepromatous leprosy (Lucio leprosy). It is characterized by widespread necrotizing vasculitis, leading to hemorrhagic infarcts and large, jagged ulcerations. **Why Exchange Transfusion is the Correct Answer:** The pathogenesis involves a severe hypercoagulable state and massive immune complex deposition leading to vascular occlusion. **Exchange transfusion** is considered the treatment of choice in severe cases as it rapidly removes circulating immune complexes, inflammatory cytokines, and improves the rheological properties of blood, thereby preventing further tissue necrosis and multi-organ failure. **Analysis of Incorrect Options:** * **A. Steroids:** While steroids are the mainstay for Type 1 and standard Type 2 (ENL) reactions, they are often ineffective in Lucio phenomenon and may worsen the risk of secondary sepsis from large ulcers. * **B. Lenalidomide:** This is not a standard treatment for Lepra reactions. Thalidomide (the parent drug) is the drug of choice for ENL but is notably **ineffective** in Lucio phenomenon. * **C. Clofazimine:** While used in the management of ENL due to its anti-inflammatory properties, it acts too slowly to manage the acute, necrotizing crisis of Lucio phenomenon. **High-Yield Clinical Pearls for NEET-PG:** * **Geographic association:** Most commonly reported in Mexico and Central America. * **Clinical triad:** Diffuse non-nodular infiltration of skin, alopecia of eyebrows/eyelashes, and necrotizing skin lesions. * **Histopathology:** Characterized by ischemic necrosis of the epidermis and superficial dermis, with massive invasion of blood vessel walls by *M. lepromatosis* or *M. leprae*. * **Key distinction:** Unlike ENL, Lucio phenomenon typically lacks systemic symptoms like high fever in the early stages, focusing primarily on cutaneous infarcts.
Question 28: A diabetic male presents with a red, tender, and painful swelling on the right buttock with multiple discharging points. The swelling is hard and indurated, accompanied by high-grade fever and malaise. What is the most likely diagnosis?
- A. Folliculitis
- B. Furuncle
- C. Carbuncle (Correct Answer)
- D. Impetigo
Explanation: ### Explanation The correct diagnosis is **Carbuncle**. **1. Why Carbuncle is correct:** A carbuncle is a deep-seated, inflammatory mass formed by a cluster of interconnecting furuncles. The hallmark clinical feature described—**multiple discharging points** (often likened to a "sieve-like" appearance)—is pathognomonic. It typically occurs in areas with thick skin like the nape of the neck or buttocks. The patient’s profile (diabetic male) is a classic risk factor, as immunocompromised states predispose individuals to deeper, more severe staphylococcal infections. The presence of systemic symptoms like high-grade fever and malaise further points toward this deeper, more extensive infection compared to localized folliculitis. **2. Why other options are incorrect:** * **Folliculitis:** This is a superficial inflammation of the hair follicle. It presents as small, itchy pustules without significant induration or systemic symptoms. * **Furuncle (Boil):** This is a deep-seated infection of a *single* hair follicle. While painful and tender, it presents with a single pointing head, not multiple discharging sinuses. * **Impetigo:** A superficial bacterial infection (usually *S. aureus* or *S. pyogenes*). It presents as honey-colored crusts (non-bullous) or fragile blisters (bullous), typically in children, and lacks deep induration or multiple drainage points. **3. Clinical Pearls for NEET-PG:** * **Etiology:** Most common causative organism is *Staphylococcus aureus*. * **Classic Sign:** The **"Sieve-like" appearance** due to multiple follicular openings discharging pus. * **Predisposing Factors:** Diabetes Mellitus (most common), malnutrition, and immunosuppression. * **Treatment:** Requires systemic antibiotics (e.g., Cloxacillin or Cephalosporins) and often surgical incision and drainage. * **Differential:** Always rule out Hidradenitis Suppurativa if lesions are recurrent in axillary or inguinal regions.
Question 29: Apple jelly nodules are characteristic of which condition?
- A. Syphilis
- B. Scleroma
- C. Lupus vulgaris (Correct Answer)
- D. Leprosy
Explanation: **Explanation:** **Lupus Vulgaris (LV)** is the most common clinical variant of cutaneous tuberculosis, occurring in individuals with high immunity against *Mycobacterium tuberculosis*. The characteristic clinical finding is the **"Apple Jelly Nodule."** 1. **Why it is correct:** When a glass slide is pressed against the lesion (a technique called **diascopy**), the background erythema/vascularity blanches, revealing small, yellowish-brown, translucent foci. These resemble apple jelly. Histologically, these represent dermal granulomas. LV typically presents as a slowly progressive, plaque-like lesion that can lead to significant scarring and destruction (mutilation) of the nose or ears. 2. **Why other options are incorrect:** * **Syphilis:** Primary syphilis presents with a painless chancre; secondary syphilis shows "raw ham" colored papulosquamous lesions. It does not show apple jelly nodules. * **Scleroma (Rhinoscleroma):** Caused by *Klebsiella rhinoscleromatis*, it presents with woody hard swelling of the nose. Histology shows Mikulicz cells and Russell bodies. * **Leprosy:** Presents with hypopigmented patches, nerve thickening, and sensory loss. While granulomatous, it does not exhibit the apple jelly sign on diascopy. **High-Yield Clinical Pearls for NEET-PG:** * **Diascopy:** The diagnostic bedside test used to elicit apple jelly nodules. * **Common Site:** The face (especially the nose and cheeks) is the most common site for Lupus Vulgaris. * **Complication:** Long-standing Lupus Vulgaris carries a risk of developing **Squamous Cell Carcinoma** (Marjolin’s ulcer). * **Other "Apple Jelly" associations:** While classic for Lupus Vulgaris, similar nodules can occasionally be seen in **Sarcoidosis** and **Leishmaniasis**.
Question 30: In which type of cutaneous tuberculosis, caseation is most commonly seen?
- A. Papulonecrotic
- B. Scrofuloderma
- C. Lupus vulgaris (Correct Answer)
- D. Erythema nodosum
Explanation: **Explanation:** **Lupus Vulgaris (LV)** is the most common form of cutaneous tuberculosis in adults. It occurs in individuals with a high degree of cell-mediated immunity (CMI) and high tuberculin sensitivity. Histologically, it is characterized by well-formed **tuberculoid granulomas** located in the upper dermis. While caseation necrosis is often minimal or absent in many paucibacillary forms, among the options provided, **Lupus Vulgaris** classically demonstrates focal areas of **caseation necrosis** within the center of the granulomas. **Analysis of Incorrect Options:** * **Papulonecrotic Tuberculid:** This is a "tuberculid" reaction (a hypersensitivity response). While it shows wedge-shaped necrosis, it is typically characterized by vasculitis rather than classic caseating granulomas. * **Scrofuloderma:** This results from the direct extension of TB from an underlying structure (like a lymph node). While it involves massive necrosis and abscess formation, the histological hallmark is more focused on the cold abscess and sinus tracts rather than the discrete caseating granulomas seen in LV. * **Erythema Nodosum:** This is a non-specific septal panniculitis. It is a hypersensitivity reaction and does **not** show granulomas or caseation. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Sign:** The classic "Apple-jelly nodules" seen on diascopy are pathognomonic for Lupus Vulgaris. * **Risk of Malignancy:** Long-standing Lupus Vulgaris carries a risk of developing **Squamous Cell Carcinoma** (Marjolin’s ulcer). * **Classification:** LV is a **paucibacillary** form (difficult to find AFB on staining), whereas Scrofuloderma is **multibacillary**.
Practice by Chapter
Impetigo
Practice Questions
Folliculitis, Furuncles, and Carbuncles
Practice Questions
Ecthyma
Practice Questions
Erysipelas and Cellulitis
Practice Questions
Staphylococcal Scalded Skin Syndrome
Practice Questions
Necrotizing Fasciitis
Practice Questions
Cutaneous Tuberculosis
Practice Questions
Leprosy
Practice Questions
Lyme Disease
Practice Questions
Syphilis
Practice Questions
Antibiotic Resistance in Dermatology
Practice Questions
Prophylaxis and Management
Practice Questions
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