Bacterial Skin Infections — MCQs
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What is the minimum number of bacilli per gram of tissue required for a positive slit skin smear for Hansen's disease?
Lupus vulgaris is a form of which of the following?
Manifestations of erythema nodosum leprosum (ENL) include all of the following except:
What is a Globi?
Bacillary angiomatosis is caused by which organism?
What is the first consideration in the differential diagnosis of a painless palatal perforation?
A farmer presents with a lesion on the leg. Which of the following is the most likely diagnosis?
The Ridley-Jopling classification of leprosy is a type of?
Apple jelly nodules on diascopy are characteristic of which condition?
A penile ulcer is painful in which of the following conditions?
Bacterial Skin Infections Indian Medical PG Practice Questions and MCQs
Question 61: What is the minimum number of bacilli per gram of tissue required for a positive slit skin smear for Hansen's disease?
- A. 10 bacilli/gram of tissue
- B. 102 bacilli/gram of tissue
- C. 103 bacilli/gram of tissue
- D. 104 bacilli/gram of tissue (Correct Answer)
Explanation: **Explanation:** The **Slit Skin Smear (SSS)** is a fundamental diagnostic tool in Leprosy (Hansen’s disease) used to detect *Mycobacterium leprae*. The correct answer is **10⁴ bacilli/gram of tissue** because this represents the threshold of sensitivity for the microscopic examination of a Ziehl-Neelsen stained smear. * **Why 10⁴ is correct:** *M. leprae* are acid-fast bacilli (AFB). For a pathologist to reliably visualize at least one bacillus under an oil-immersion lens during a routine examination, there must be a minimum concentration of approximately **10,000 (10⁴) organisms per gram** of skin tissue. If the bacterial load is lower than this, the smear will likely be reported as negative (Bacteriological Index 0), even if the patient has paucibacillary disease. * **Why other options are incorrect:** Options **A (10¹)**, **B (10²)**, and **C (10³)** represent bacterial loads that are too low for detection via standard light microscopy. At these concentrations, the probability of a bacillus appearing in the small sample of serum and tissue pulp collected during a slit-skin procedure is statistically negligible. **High-Yield Clinical Pearls for NEET-PG:** * **Bacteriological Index (BI):** Measured on Ridley’s Logarithmic Scale (1+ to 6+). A BI of 1+ corresponds to 1–10 bacilli per 100 oil-immersion fields. * **Morphological Index (MI):** Represents the percentage of **solidly stained** (viable) bacilli. It is used to assess the efficacy of Multi-Drug Therapy (MDT). * **Sites for SSS:** Usually taken from 4–6 sites, including both earlobes and active skin lesions. * **Classification:** SSS is negative in Tuberculoid (TT) leprosy and strongly positive in Lepromatous (LL) leprosy.
Question 62: Lupus vulgaris is a form of which of the following?
- A. Skin tuberculosis (Correct Answer)
- B. Pulmonary tuberculosis
- C. Lymph-node tuberculosis
- D. Kidney tuberculosis
Explanation: **Explanation:** **Lupus Vulgaris (LV)** is the most common clinical variant of **cutaneous (skin) tuberculosis**. It occurs in individuals with a high degree of cell-mediated immunity who have been previously sensitized to *Mycobacterium tuberculosis*. The infection typically spreads to the skin via the hematogenous, lymphatic, or contiguous route from an underlying internal focus. * **Why Option A is correct:** Lupus vulgaris is specifically defined as a chronic, progressive form of **Skin Tuberculosis**. It is characterized by the classic "apple-jelly" nodules seen on diascopy. * **Why Options B, C, and D are incorrect:** While tuberculosis can affect the lungs (Pulmonary), lymph nodes (Scrofuloderma/Lymphadenitis), and kidneys (Renal), the term "Lupus Vulgaris" refers exclusively to the dermatological manifestation. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** It presents as reddish-brown plaques, most commonly on the **face** (nose and cheeks) in a "butterfly" distribution. * **Diascopy:** A diagnostic bedside test where pressing a glass slide against the lesion reveals **"Apple-jelly nodules"** (pale brownish-yellow spots). * **Complication:** The most dreaded long-term complication of chronic Lupus Vulgaris is the development of **Squamous Cell Carcinoma** (Marjolin’s ulcer) within the scar. * **Histopathology:** Shows well-formed tuberculoid granulomas with central caseation necrosis (though caseation may be minimal due to high immunity).
Question 63: Manifestations of erythema nodosum leprosum (ENL) include all of the following except:
- A. Pancreatitis (Correct Answer)
- B. Fever
- C. Hepatitis
- D. All of the above
Explanation: **Explanation:** **Erythema Nodosum Leprosum (ENL)**, also known as a **Type 2 Lepra Reaction**, is a systemic immune-complex-mediated (Type III hypersensitivity) reaction occurring primarily in patients with lepromatous (LL) or borderline lepromatous (BL) leprosy. It is characterized by the deposition of immune complexes in various tissues, leading to widespread inflammatory manifestations. 1. **Why Pancreatitis is the correct answer:** While ENL is a multisystem disorder, **pancreatitis is not a recognized manifestation**. The inflammation typically targets the skin, nerves, eyes, joints, and certain internal organs like the liver, kidneys, and testes. Pancreatitis is not part of the clinical spectrum of Type 2 reactions. 2. **Analysis of incorrect options:** * **Fever:** ENL is a systemic illness. High-grade fever, malaise, and constitutional symptoms are hallmark features of the reaction. * **Hepatitis:** The immune complex deposition can involve internal organs. Hepatosplenomegaly and transient hepatitis (elevated liver enzymes) are documented systemic features of severe ENL. 3. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Triad:** Tender, evanescent (short-lived) erythematous nodules + Fever + Systemic involvement. * **Common Sites:** Extensor surfaces of limbs and the face. * **Other Systemic Features:** Iridocyclitis (eye), Orchitis (testes—can lead to sterility), Glomerulonephritis (kidney), Arthritis, and Lymphadenopathy. * **Drug of Choice:** **Thalidomide** is the most effective treatment for severe ENL. Prednisolone and Clofazimine are also used. * **Trigger:** Often triggered by the initiation of MDT (due to rapid antigen release), pregnancy, or stress.
Question 64: What is a Globi?
- A. Histiocyte containing acid-fast bacillus (Correct Answer)
- B. Lymphocyte containing acid-fast bacillus
- C. Neutrophil containing acid-fast bacillus
- D. Large lymphocyte containing acid-fast bacillus
Explanation: **Explanation:** A **Globi** is a characteristic histopathological feature found in **Lepromatous Leprosy (LL)**. It refers to a large, foamy macrophage (histiocyte) that is packed with numerous *Mycobacterium leprae* bacilli. These bacilli are often arranged in parallel bundles, resembling "cigars in a box." **Why the correct answer is right:** * **Option A:** In Lepromatous Leprosy, the host's cell-mediated immunity (CMI) is severely depressed. This allows *M. leprae* to multiply uncontrollably within **histiocytes** (macrophages). As the bacilli multiply, they form dense clusters or "globi" within the cytoplasm of these cells, which often take on a foamy appearance due to lipid accumulation (Virchow cells). **Why the incorrect options are wrong:** * **Options B, C, and D:** While lymphocytes and neutrophils are part of the inflammatory infiltrate in various stages of leprosy, they do not function as the primary host cells for the intracellular replication of *M. leprae*. The hallmark of the disease is the involvement of the mononuclear phagocyte system (histiocytes). **High-Yield NEET-PG Pearls:** * **Virchow’s Cells (Lepracytes):** These are the foamy histiocytes that contain the globi. * **Fite-Faraco Stain:** This is the preferred modified acid-fast stain used to visualize *M. leprae* in tissue sections, as the bacilli are less acid-fast than *M. tuberculosis*. * **Bacteriological Index (BI):** Globi are typically seen in patients with a high BI (4+ to 6+), signifying a high bacterial load. * **Grenz Zone:** In Lepromatous Leprosy, a clear band of uninvolved dermis (Grenz zone) is usually seen between the epidermis and the dermal infiltrate of foamy histiocytes.
Question 65: Bacillary angiomatosis is caused by which organism?
- A. Bartonella henselae (Correct Answer)
- B. Hansen's bacillus
- C. Koch's bacillus
- D. Haemophilus ducreyi
Explanation: **Explanation:** **Bacillary Angiomatosis (BA)** is a vascular proliferative disease caused by Gram-negative rickettsial organisms of the genus *Bartonella*. It primarily affects immunocompromised individuals, particularly those with HIV/AIDS (CD4 count <200 cells/mm³). 1. **Why Option A is correct:** The primary causative agents are **Bartonella henselae** (transmitted via cat scratches/bites) and **Bartonella quintana** (transmitted via the human body louse). These bacteria induce endothelial cell proliferation, leading to the characteristic "mulberry-like" friable, red-to-purple vascular papules and nodules that can mimic Kaposi Sarcoma. 2. **Why other options are incorrect:** * **Option B (Hansen’s bacillus):** This refers to *Mycobacterium leprae*, the causative agent of Leprosy, characterized by hypopigmented patches and nerve thickening. * **Option C (Koch’s bacillus):** This refers to *Mycobacterium tuberculosis*, which causes Tuberculosis (e.g., Lupus vulgaris or Scrofuloderma in the skin). * **Option D (Haemophilus ducreyi):** This is the causative agent of **Chancroid**, characterized by painful genital ulcers and inguinal lymphadenopathy (buboes). **High-Yield Clinical Pearls for NEET-PG:** * **Histopathology:** Shows lobular proliferation of capillaries with **neutrophilic infiltrate** and "amphophilic granular clumps" (which are the bacteria). * **Special Stain:** **Warthin-Starry silver stain** is used to visualize the bacilli. * **Differential Diagnosis:** Must be distinguished from **Kaposi Sarcoma** (which shows a lymphocytic infiltrate and spindle cells). * **Treatment of Choice:** **Erythromycin** or Doxycycline.
Question 66: What is the first consideration in the differential diagnosis of a painless palatal perforation?
- A. Syphilis (Correct Answer)
- B. Histoplasmosis
- C. Scrofuloderma
- D. Actinomycosis
Explanation: **Explanation:** The correct answer is **Syphilis (Option A)**. Palatal perforation is a classic manifestation of **Tertiary Syphilis**, specifically due to the formation of a **Gumma**. A gumma is a localized, chronic granulomatous lesion characterized by a "rubbery" consistency. When it involves the hard palate, it leads to endarteritis obliterans, resulting in tissue necrosis and eventual painless perforation. In the context of NEET-PG, any painless, destructive midline granuloma of the palate should first raise suspicion of Syphilis or Wegener’s Granulomatosis. **Analysis of Incorrect Options:** * **Histoplasmosis (Option B):** While it can cause oral ulcers (often painful) in immunocompromised patients, it typically presents as a proliferative or vegetative growth rather than a clean palatal perforation. * **Scrofuloderma (Option C):** This is a form of cutaneous tuberculosis resulting from the breakdown of skin over an underlying infected lymph node or bone. It typically involves the neck (cervical lymph nodes) and presents with "string of beads" ulcers and sinus tracts, not palatal perforation. * **Actinomycosis (Option D):** Known for "lumpy jaw," it presents with multiple draining sinuses and "sulfur granules" in the pus. It involves the mandible more commonly than the palate and is usually associated with painful swelling. **High-Yield Clinical Pearls for NEET-PG:** * **Gumma:** The hallmark of late benign syphilis; most common sites are the skin, bone (tibia/palate), and liver. * **Differential Diagnosis of Palatal Perforation:** Syphilis (Gumma), Wegener’s Granulomatosis (GPA), NK/T-cell lymphoma (Lethal Midline Granuloma), and chronic cocaine abuse. * **Treatment of Choice:** For Tertiary Syphilis (without neurosyphilis), the treatment is Benzathine Penicillin G, 2.4 million units IM weekly for 3 weeks.
Question 67: A farmer presents with a lesion on the leg. Which of the following is the most likely diagnosis?
- A. Verruca vulgaris
- B. Tuberculosis verrucosa cutis (Correct Answer)
- C. Mycetoma
- D. Lichen planus hypertrophicus
Explanation: ***Tuberculosis verrucosa cutis*** - **Farmer's occupation** creates high risk for inoculation injury with **Mycobacterium tuberculosis**, leading to this **verrucous, warty skin lesion** typically on exposed areas like legs. - Characterized by **hyperkeratotic, warty plaques** with minimal inflammation, often called "**prosector's wart**" when occurring in healthcare workers. *Verruca vulgaris* - Caused by **human papillomavirus (HPV)**, not associated with occupational farming activities or tuberculosis exposure. - Typically presents as **well-demarcated papules** with **black dots** (thrombosed capillaries), unlike the hyperkeratotic appearance of TVC. *Mycetoma* - Presents as **chronic granulomatous infection** with **multiple sinuses** discharging colored grains, not a single verrucous lesion. - Caused by **fungi or actinomycetes**, typically affecting the **foot** (Madura foot) rather than presenting as warty leg lesions. *Lichen planus hypertrophicus* - **Autoimmune condition** with **violaceous, polygonal papules** showing **Wickham's striae**, unrelated to occupational exposure. - Typically affects **flexural surfaces** and mucous membranes, not associated with farming or tuberculosis infection.
Question 68: The Ridley-Jopling classification of leprosy is a type of?
- A. Clinical, bacteriological, immunological, and epidemiological classification
- B. Clinical, bacteriological, immunological, and therapeutic classification
- C. Clinical, bacteriological, immunological, and histological classification (Correct Answer)
- D. Operational classification
Explanation: The **Ridley-Jopling classification** is the gold standard for classifying leprosy (Hansen’s disease) because it reflects the dynamic relationship between the host’s cell-mediated immunity (CMI) and the *Mycobacterium leprae* bacilli. ### Why Option C is Correct The Ridley-Jopling system is a **five-group classification** (TT, BT, BB, BL, LL) based on four specific parameters: 1. **Clinical:** Number and morphology of skin lesions and nerve involvement. 2. **Bacteriological:** The Bacterial Index (BI) observed on slit-skin smears. 3. **Immunological:** The status of the patient’s CMI (measured by the Lepromin test). 4. **Histological:** Specific pathological findings on skin biopsy (e.g., well-formed granulomas in TT vs. foamy macrophages/Virchow cells in LL). ### Why Other Options are Incorrect * **Option A & B:** While epidemiology and therapy are crucial for public health, they are **not** criteria used to define the Ridley-Jopling scales. Therapy is a *consequence* of the classification, not a defining feature. * **Option D:** The **Operational Classification** is the WHO system (Paucibacillary vs. Multibacillary), which is used primarily for treatment allocation in the field based on the number of lesions, without requiring biopsy or smears. ### High-Yield Clinical Pearls for NEET-PG * **Stable Poles:** Tuberculoid (TT) and Lepromatous (LL) are the stable polar forms. * **Unstable Form:** Mid-borderline (BB) is the most unstable form and can shift toward either pole (upgrading/downgrading reactions). * **Lepromin Test:** Strongly positive in TT (high CMI) and negative in LL (low CMI). It is used for **prognosis and classification**, not for diagnosis. * **Indeterminate Leprosy:** This is the earliest stage and is not included in the five-tier Ridley-Jopling scale.
Question 69: Apple jelly nodules on diascopy are characteristic of which condition?
- A. Lupus vulgaris (Correct Answer)
- B. Tinea versicolor
- C. Erythrasma
- D. Vitiligo
Explanation: **Explanation:** **Lupus Vulgaris (Correct Answer):** Lupus vulgaris is the most common form of chronic, progressive cutaneous tuberculosis. It occurs in individuals with a high degree of cell-mediated immunity. The characteristic lesion is a reddish-brown plaque that expands peripherally. When a glass slide is pressed against the lesion (**diascopy**), the vascular congestion is blanched, revealing yellowish-brown, translucent foci known as **"apple jelly nodules."** These nodules represent the underlying granulomatous pathology (tubercles) in the dermis. **Incorrect Options:** * **Tinea versicolor:** A fungal infection caused by *Malassezia furfur*. It presents as hypo- or hyperpigmented scaly macules. Diagnosis is confirmed by a "spaghetti and meatballs" appearance on KOH mount or yellow-orange fluorescence under Wood’s lamp. * **Erythrasma:** A bacterial infection caused by *Corynebacterium minutissimum*. It typically involves intertriginous areas and shows a characteristic **coral-red fluorescence** under Wood’s lamp due to porphyrin production. * **Vitiligo:** An autoimmune condition causing depigmentation. Diascopy is not diagnostic; however, Wood’s lamp examination shows a bright "milk-white" fluorescence. **High-Yield Clinical Pearls for NEET-PG:** * **Diascopy:** Used to differentiate between purpura (extravasated blood, does not blanch) and erythema (dilated capillaries, blanches). * **Lupus Vulgaris Complication:** The most serious long-term complication is the development of **Squamous Cell Carcinoma** (Marjolin’s ulcer) within the scar. * **Other "Apple Jelly" associations:** While classic for Lupus Vulgaris, apple jelly nodules can also be seen in **Sarcoidosis** and **Leishmaniasis**.
Question 70: A penile ulcer is painful in which of the following conditions?
- A. Syphilis
- B. Lymphogranuloma venereum (LGV)
- C. Donovanosis
- D. Chancroid (Correct Answer)
Explanation: ### Explanation The key to differentiating genital ulcers in NEET-PG is identifying the presence or absence of pain and the characteristics of the ulcer base. **1. Why Chancroid is Correct:** Chancroid, caused by **_Haemophilus ducreyi_**, is classically characterized by a **painful**, soft ulcer (Soft Chancre). The ulcers are often multiple, have ragged/undermined edges, and a necrotic purulent base. The pain is a hallmark feature that distinguishes it from most other sexually transmitted infections (STIs). **2. Why the Other Options are Incorrect:** * **Syphilis (Option A):** Caused by *Treponema pallidum*, the primary chancre is characteristically **painless**, indurated (hard), and clean-based. * **Lymphogranuloma venereum (Option B):** Caused by *Chlamydia trachomatis* (L1-L3), the initial primary lesion is a **painless** transient papule or ulcer that often heals before the patient seeks medical attention. The clinical focus is usually the painful "Groove sign" in the lymph nodes. * **Donovanosis (Option C):** Also known as Granuloma Inguinale (caused by *Klebsiella granulomatis*), it presents as **painless**, beefy-red, velvety ulcers that bleed easily on touch. **3. High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Painful Ulcers:** "**H**elp **H**im" → **H**erpes and **H**aemophilus (*H. ducreyi* / Chancroid) are the painful ones. * **School of Fish Appearance:** Characteristic Gram stain finding for *H. ducreyi*. * **Donovan Bodies:** Safety-pin appearance within macrophages seen in Donovanosis (Wright-Giemsa stain). * **Treatment of Choice:** For Chancroid, the first-line treatment is **Azithromycin (1g orally, single dose)** or Ceftriaxone.
Practice by Chapter
Impetigo
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Folliculitis, Furuncles, and Carbuncles
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Ecthyma
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Erysipelas and Cellulitis
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Staphylococcal Scalded Skin Syndrome
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Necrotizing Fasciitis
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Cutaneous Tuberculosis
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Leprosy
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Lyme Disease
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Syphilis
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Antibiotic Resistance in Dermatology
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Prophylaxis and Management
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