Bacterial Skin Infections — MCQs

A young male presented with a hypoesthetic patch on the right forearm. On examination, a thickened peripheral nerve was palpable. Skin biopsy histopathology shows well-formed epithelioid granulomas with Langhans giant cells, dense lymphocytic infiltrate, and perineural infiltration. What is the most likely diagnosis?

Bacterial Skin Infections Indian Medical PG Practice Questions and MCQs

Question 41: Erysipeloid is transmitted by what means?

A. Droplet
B. Feco-oral
C. Mosquito bite
D. Contact with animal (Correct Answer)

Explanation: **Explanation:** **Erysipeloid** is an occupational zoonotic infection caused by the Gram-positive bacillus ***Erysipelothrix rhusiopathiae***. **Why Option D is Correct:** The infection is primarily transmitted through **direct contact with infected animals** or their products. The bacteria enter the skin through minor abrasions or puncture wounds, typically on the hands. It is most commonly seen in individuals handling raw meat, poultry, or fish (e.g., butchers, fishermen, and veterinarians), earning it the nickname "Whale finger" or "Seal finger." **Why Other Options are Incorrect:** * **A. Droplet:** This is the mode of transmission for respiratory infections (e.g., Tuberculosis, Meningitis). Erysipeloid does not involve the respiratory tract. * **B. Feco-oral:** This route is typical for enteric pathogens (e.g., Typhoid, Hepatitis A). *E. rhusiopathiae* is not transmitted via contaminated food or water ingestion in humans. * **C. Mosquito bite:** Vector-borne transmission is characteristic of diseases like Malaria or Dengue. Erysipeloid requires direct cutaneous inoculation. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** Presents as a well-demarcated, **violaceous (purplish)**, painful, non-pitting inflammatory plaque, usually on the fingers or hands. * **Distinctive Feature:** Unlike Erysipelas (caused by *S. pyogenes*), Erysipeloid typically lacks fever and systemic symptoms. * **Cultural Characteristic:** On culture, it may show a characteristic "test-tube brush" appearance in gelatin stabs. * **Treatment of Choice:** **Penicillin** is the first-line treatment. Note that the organism is intrinsically resistant to Vancomycin (a common trap in exams).

Question 42: Which type of leprosy is characterized by the presence of Virchow's cells?

A. Lepromatous leprosy (Correct Answer)
B. Tuberculoid leprosy
C. Borderline lepromatous leprosy
D. Intermediate leprosy

Explanation: **Explanation:** The presence of **Virchow’s cells** (also known as Lepra cells) is the hallmark histopathological feature of **Lepromatous Leprosy (LL)**. 1. **Why Lepromatous Leprosy is correct:** In LL, the patient has low cell-mediated immunity (CMI). This allows *Mycobacterium leprae* to multiply unchecked within macrophages. These macrophages become heavily laden with bacilli and undergo fatty degeneration, resulting in a "foamy" or vacuolated appearance. These foamy macrophages are called Virchow’s cells. Under Fite-Faraco staining, they reveal numerous acid-fast bacilli arranged in clumps called **globi**. 2. **Why other options are incorrect:** * **Tuberculoid Leprosy (TT):** Characterized by high CMI. Histology shows well-formed granulomas with epithelioid cells and Langhans giant cells, but bacilli are rare or absent (paucibacillary). * **Borderline Lepromatous (BL):** While some foamy macrophages may be present, the classic, ubiquitous "Virchow cell" description specifically defines the polar LL end of the spectrum. * **Indeterminate Leprosy:** This is the early stage where specific features haven't developed; histology usually shows only non-specific lymphocytic infiltration around dermal appendages. **NEET-PG High-Yield Pearls:** * **Grenz Zone:** A clear subepidermal band of normal collagen found in LL (absent in TT). * **Leonine Facies:** The characteristic facial appearance in LL due to diffuse infiltration and nodule formation. * **Bacteriological Index (BI):** Highest in LL (4+ to 6+), reflecting the high bacterial load (multibacillary). * **Lepromin Test:** Strongly negative in LL (due to lack of CMI) and positive in TT.

Question 43: The commonest focus of Scrofuloderma is?

A. Lung
B. Lymph node (Correct Answer)
C. Larynx
D. Skin

Explanation: **Explanation:** **Scrofuloderma** (also known as Tuberculosis Colliquativa Cutis) is a form of secondary cutaneous tuberculosis. It occurs due to the **direct extension** of an underlying tuberculous focus into the overlying skin. 1. **Why Lymph Node is Correct:** The most common underlying focus for scrofuloderma is a **tuberculous lymph node**, particularly the **cervical lymph nodes** (scrofula). The infection spreads by contiguity from the infected node to the skin, leading to the formation of painless, cold abscesses, which eventually rupture to form undermined ulcers and sinus tracts that heal with characteristic **puckered (bridged) scars**. 2. **Why other options are incorrect:** * **Lung:** While the lungs are the primary site for systemic TB, scrofuloderma specifically requires a focus immediately beneath the skin. Lung involvement leads to hematogenous spread (e.g., Lupus Vulgaris or Miliary TB) rather than direct extension. * **Larynx:** Laryngeal TB is a rare site and does not typically involve the skin via direct extension. * **Skin:** Scrofuloderma is by definition a secondary infection; the primary focus is almost always an underlying structure like a lymph node, bone, or joint, not the skin itself. **Clinical Pearls for NEET-PG:** * **Commonest site:** Cervical region (neck), followed by axillary and inguinal regions. * **Pathogenesis:** Direct extension (Contiguity). * **Clinical Feature:** Painless "cold abscess," sinus tracts, and **bridged scars**. * **Mantoux Test:** Usually strongly positive. * **Differential Diagnosis:** Actinomycosis (which also presents with multiple discharging sinuses but usually involves the jaw).

Question 44: What is the most reliable test for chancroid detection?

A. Skin test
B. Biopsy
C. Gram-stained smear (Correct Answer)
D. Clinical examination

Explanation: ### Explanation **Chancroid** is a sexually transmitted infection caused by the Gram-negative coccobacillus ***Haemophilus ducreyi***. **Why Gram-stained smear is the correct answer:** The diagnosis of chancroid is primarily clinical, but among the laboratory investigations provided, the **Gram-stained smear** is the most reliable and rapid bedside test. When a smear is taken from the base of the ulcer, it reveals small, Gram-negative bacilli arranged in parallel rows or chains. This characteristic morphology is classically described as the **"School of Fish"** or **"Railroad Track"** appearance. While culture is the definitive gold standard, it is technically difficult and requires enriched media (like Nairobi medium); thus, the Gram stain remains the most high-yield diagnostic tool in an exam context. **Analysis of Incorrect Options:** * **A. Skin Test:** The Ito-Reenstierna test (a delayed hypersensitivity reaction) was used historically but is no longer used due to low sensitivity and the fact that it remains positive for years after infection. * **B. Biopsy:** While a biopsy shows three distinct zones of inflammation, it is invasive and rarely necessary for a diagnosis of chancroid. It is usually reserved to rule out malignancy or Donavanosis. * **D. Clinical Examination:** Although chancroid has a classic presentation (painful, soft, "dirty" ulcers with undermined edges), clinical diagnosis alone is often inaccurate as it mimics other genital ulcer diseases like Syphilis or Herpes. **NEET-PG High-Yield Pearls:** * **Clinical Triad:** Painful ulcer + Painful inguinal lymphadenopathy (Bubo) + Suppuration. * **Key Mnemonic:** "Ducreyi makes you cry" (because the ulcer is painful, unlike the painless chancre of Syphilis). * **Treatment of Choice:** A single dose of **Azithromycin (1g orally)** or Ceftriaxone (250mg IM). * **Differential:** Unlike Syphilis (indurated/hard), Chancroid is non-indurated (soft chancre).

Question 45: A 12-year-old boy presented with a gradually progressive plaque on his buttock for the last 3 years. The plaque was 15 cm in diameter, annular in shape, with crusting and induration at the periphery and scarring at the center. What is the most likely diagnosis?

A. Tinea corporis
B. Granuloma annulare
C. Lupus vulgaris (Correct Answer)
D. Borderline leprosy

Explanation: **Explanation:** The clinical presentation of a long-standing, slowly progressive, annular plaque with peripheral induration and central scarring is a classic description of **Lupus Vulgaris (LV)**. **1. Why Lupus Vulgaris is correct:** Lupus vulgaris is the most common form of **cutaneous tuberculosis** in adults and children, occurring in individuals with high immunity against *Mycobacterium tuberculosis*. It typically presents as a solitary plaque that spreads peripherally while healing with central scarring (atrophic scarring). The "apple-jelly" appearance on diascopy is a pathognomonic sign. The buttocks and lower extremities are common sites in the Indian subcontinent. **2. Why other options are incorrect:** * **Tinea corporis:** While it presents with annular lesions and peripheral scaling, it is an acute/subacute fungal infection. It would not persist for 3 years without significant inflammation or resolution and does not typically cause induration or scarring. * **Granuloma annulare:** This is a necrobiotic disorder presenting as asymptomatic annular plaques. However, it lacks the crusting, induration, and significant scarring seen in this case. * **Borderline leprosy:** While it presents with annular plaques, these are typically anesthetic or hypoesthetic. While central clearing occurs, the characteristic "crusting" and "induration" of LV are not features of leprosy. **Clinical Pearls for NEET-PG:** * **Most common site (Global):** Face (nose and cheeks). * **Most common site (India):** Buttocks and lower limbs. * **Diascopy:** Shows "Apple-jelly nodules." * **Complication:** Long-standing LV can lead to **Squamous Cell Carcinoma** (Marjolin’s ulcer). * **Histopathology:** Shows well-formed tuberculoid granulomas with minimal caseation necrosis.

Question 46: A 3-year-old child presents with multiple isolated lesions on the face and neck. Physical examination reveals lesions up to 4 cm in diameter with golden crusts, and in other areas, small blisters and weeping are observed. What is the most likely diagnosis?

A. Aphthous ulcers
B. Erysipelas
C. Herpes simplex I
D. Impetigo (Correct Answer)

Explanation: **Explanation:** The clinical presentation of a young child with **golden-yellow (honey-colored) crusts** on the face and neck is the classic hallmark of **Impetigo**, specifically the non-bullous variety. This is a highly contagious superficial bacterial infection of the epidermis, most commonly caused by *Staphylococcus aureus* or *Streptococcus pyogenes*. The "weeping" and small blisters (vesicles) represent the early stage before the exudate dries into the characteristic crust. **Why other options are incorrect:** * **Aphthous ulcers:** These are painful, shallow ulcers found on the **oral mucosa** (inside the mouth), not on the external skin of the face with crusting. * **Erysipelas:** This is a deeper infection (upper dermis) characterized by a **sharply demarcated**, bright red, edematous, and painful plaque, often accompanied by fever. It does not typically present with isolated honey-colored crusts. * **Herpes simplex I:** While it can cause vesicles on the face, they are usually **grouped (herpetiform)** on an erythematous base and are often associated with tingling or burning pain. While they can crust, the classic "golden crust" of impetigo is distinct. **High-Yield Clinical Pearls for NEET-PG:** * **Etiology:** *S. aureus* is now the most common cause of both bullous and non-bullous impetigo. * **Bullous Impetigo:** Caused by Staphylococcal **exfoliative toxins (ETA, ETB)** targeting Desmoglein 1. * **Complication:** Non-bullous impetigo (Streptococcal) can lead to **Post-Streptococcal Glomerulonephritis (PSGN)**, but notably, it does *not* lead to Rheumatic Fever. * **Treatment:** Topical **Mupirocin** is the drug of choice for localized lesions. For systemic involvement, use oral Cloxacillin or Amoxicillin-Clavulanate.

Question 47: Which of the following is NOT true regarding erysipelas?

A. It is an acute spreading inflammation of the outer dermis.
B. Superficial lymphatics are typically involved.
C. The rash is primarily due to exotoxin produced by Streptococcus pyogenes.
D. The scrotum and hands are the most common sites affected. (Correct Answer)

Explanation: **Erysipelas** is a distinct clinical variant of cellulitis characterized by its superficial nature and sharp demarcation. ### **Explanation of Options** * **Why D is the correct answer (The False Statement):** The most common site for erysipelas is the **lower limbs** (approx. 80%), followed by the **face** (butterfly distribution). The scrotum and hands are rarely involved. In contrast, Fournier’s gangrene is the necrotizing infection typically associated with the scrotum. * **Option A:** This is true. Erysipelas is an acute inflammatory condition specifically involving the **upper/outer dermis**. This superficial location results in the characteristic "raised" edge and "orange-peel" (peau d'orange) texture. * **Option B:** This is true. The infection characteristically involves the **superficial lymphatics**, leading to prominent lymphatic obstruction and regional lymphadenopathy. * **Option C:** This is true. The primary causative agent is **Group A Beta-hemolytic Streptococci (Streptococcus pyogenes)**. The rapid spread and systemic symptoms (fever, chills) are mediated by bacterial **exotoxins**. ### **High-Yield Clinical Pearls for NEET-PG** * **Milian’s Ear Sign:** A classic clinical sign where erysipelas involves the pinna (ear). Since the pinna lacks deep dermis/subcutaneous tissue, true cellulitis cannot occur there, making erysipelas the definitive diagnosis. * **Clinical Appearance:** Characterized by a "shiny, red, edematous, and tender plaque" with **sharply defined borders** (unlike cellulitis, which has diffuse borders). * **Drug of Choice:** Oral or IV **Penicillin** remains the treatment of choice due to the high sensitivity of *S. pyogenes*. * **Predisposing Factors:** Lymphedema, tinea pedis (serving as a portal of entry), and venous insufficiency.

Question 48: A 30-year-old female presents with a painful, red, warm nail fold of 7 days duration. The patient has tried home remedies such as turmeric powder and warm saline compressions without relief. What is the most probable diagnosis?

A. Ingrowing fingernail
B. Acute paronychia (Correct Answer)
C. Chronic paronychia
D. Onychomycosis

Explanation: **Explanation:** The clinical presentation of a painful, red, and warm nail fold of short duration (7 days) is classic for **Acute Paronychia**. This is a localized inflammatory process of the proximal or lateral nail folds, most commonly caused by bacterial infection (predominantly *Staphylococcus aureus*). It often follows minor trauma, such as nail-biting, aggressive manicuring, or hangnails, which breaches the protective barrier between the nail plate and the fold. **Analysis of Options:** * **Acute Paronychia (Correct):** Characterized by rapid onset (<6 weeks), intense pain, erythema, and edema. It is typically bacterial and may progress to abscess formation. * **Chronic Paronychia:** This is an irritant/allergic inflammatory condition (often involving *Candida*) lasting >6 weeks. It presents with boggy swelling, loss of the cuticle, and "bolster-like" hypertrophy of the nail fold, usually without the acute, throbbing pain seen here. * **Ingrowing fingernail:** While common in toes (Onychocryptosis), it is rare in fingernails. It involves the nail plate piercing the lateral fold, leading to granulation tissue rather than generalized fold inflammation. * **Onychomycosis:** This is a fungal infection of the nail plate itself, presenting with discoloration, thickening (subungual hyperkeratosis), and onycholysis, rather than acute inflammation of the surrounding skin. **High-Yield Clinical Pearls for NEET-PG:** * **Most common organism:** *Staphylococcus aureus* (Acute); *Candida albicans* (Chronic). * **Management:** Warm compresses and topical/oral antibiotics for early cases; **Incision and Drainage (I&D)** if an abscess (fluctuance) is present. * **Differential:** Herpetic Whitlow (caused by HSV) can mimic paronychia but presents with grouped vesicles and should *not* be incised.

Question 49: What is the treatment of choice for a nerve abscess in tuberculoid leprosy?

A. Incision and drainage (Correct Answer)
B. High dose clofazimine
C. Steroids
D. Thalidomide

Explanation: **Explanation:** In **Tuberculoid Leprosy (TT)**, the host exhibits high cell-mediated immunity (CMI). This intense immune response can lead to the formation of a **nerve abscess**, most commonly involving the ulnar or common peroneal nerves. 1. **Why Incision and Drainage (I&D) is correct:** A nerve abscess is a localized collection of caseous material within the nerve sheath. Because the abscess is an anatomical collection under pressure, medical management alone is insufficient. **Longitudinal incision and drainage** (neurolysis) is the treatment of choice to instantly relieve intraneural pressure, preventing irreversible ischemic damage and permanent nerve palsy. 2. **Why other options are incorrect:** * **Steroids:** While systemic steroids are the mainstay for Lepra reactions and "silent" neuritis, they cannot drain a physical collection of caseous pus. They may be used as an adjunct post-surgery to reduce inflammation. * **High dose Clofazimine:** This is used primarily for Type 2 Lepra Reactions (ENL) due to its anti-inflammatory properties; it has no role in treating a localized abscess. * **Thalidomide:** This is the drug of choice for severe **Type 2 Lepra Reactions (ENL)**, which occurs in lepromatous poles, not tuberculoid leprosy. **High-Yield Clinical Pearls for NEET-PG:** * **Most common nerve involved in Leprosy:** Ulnar nerve. * **Most common nerve involved in Nerve Abscess:** Ulnar nerve. * **Pure Neuritic Leprosy:** Presents with nerve involvement without skin lesions; diagnosis is confirmed by nerve biopsy or FNAC from the nerve. * **Silent Neuritis:** Sudden motor or sensory loss without clinical signs of inflammation; treated with a standard course of tapering Prednisolone.

Question 50: A young male presented with a hypoesthetic patch on the right forearm. On examination, a thickened peripheral nerve was palpable. Skin biopsy histopathology shows well-formed epithelioid granulomas with Langhans giant cells, dense lymphocytic infiltrate, and perineural infiltration. What is the most likely diagnosis?

A. Tuberculoid Leprosy (Correct Answer)
B. Lepromatous Leprosy
C. Lymphoma
D. Histiocytosis

Explanation: ***Tuberculoid Leprosy*** - The combination of a **hypoesthetic patch** with a **palpable thickened nerve** is pathognomonic for tuberculoid leprosy, representing the **TT pole** of Hansen's disease. - Histopathology shows **well-formed epithelioid granulomas** with **Langhans giant cells** and **perineural infiltration**, characteristic of the strong cell-mediated immune response in tuberculoid leprosy. *Lepromatous Leprosy* - Clinical presentation includes **multiple symmetrical lesions** without significant nerve thickening or hypoesthesia in early stages. - Histopathology shows **foamy macrophages** (Virchow cells) filled with **acid-fast bacilli** and **no true granuloma formation** due to poor cell-mediated immunity. *Lymphoma* - Would present with **lymphadenopathy** and **B-symptoms** (fever, night sweats, weight loss) rather than isolated hypoesthetic patches. - Histopathology would show **malignant lymphoid cells** with **monoclonal proliferation**, not granulomatous inflammation with nerve involvement. *Histiocytosis* - Typically presents with **multiple organ involvement** including bone lesions, skin rash, and hepatosplenomegaly in children. - Histopathology shows **Langerhans cells** with **Birbeck granules** and positive **CD1a/CD68** staining, distinct from epithelioid granulomas.

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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