Bacterial Skin Infections — MCQs

Bacterial Skin Infections Indian Medical PG Practice Questions and MCQs

Question 151: A sex worker presents with a discharging ulcer. Gram-negative diplococci are seen on microscopy, and growth is obtained on modified Thayer-Martin media. What is the most likely diagnosis?

A. Neisseria gonorrhoeae (Correct Answer)
B. Syphilis
C. Lymphogranuloma venereum
D. Chancroid

Explanation: ### Explanation The clinical presentation and laboratory findings point directly to **Neisseria gonorrhoeae**. **Why Option A is Correct:** * **Microscopy:** *Neisseria gonorrhoeae* is a classic **Gram-negative diplococcus** (kidney-bean shaped) often found within polymorphonuclear leukocytes. * **Culture:** **Modified Thayer-Martin (MTM) media** is a selective medium (containing vancomycin, colistin, nystatin, and trimethoprim) specifically designed to inhibit normal flora and allow the growth of *Neisseria* species. * **Clinical Context:** In females (especially high-risk groups like sex workers), gonorrhea often presents as cervicitis with purulent discharge, which can lead to skin ulcers or disseminated gonococcal infection (DGI). **Why Other Options are Incorrect:** * **B. Syphilis:** Caused by *Treponema pallidum* (a spirochete). It cannot be seen on Gram stain or grown on Thayer-Martin media; it requires dark-field microscopy or serology (VDRL/RPR). * **C. Lymphogranuloma venereum (LGV):** Caused by *Chlamydia trachomatis* (L1-L3). Chlamydia is an obligate intracellular bacterium that does not show up as Gram-negative diplococci and requires cell culture or NAAT for diagnosis. * **D. Chancroid:** Caused by *Haemophilus ducreyi*. While it is a Gram-negative rod, it typically presents as a "school of fish" or "railroad track" appearance on microscopy and requires specialized media (like Mueller-Hinton agar), not MTM. **High-Yield NEET-PG Pearls:** * **Gold Standard Diagnosis:** Nucleic Acid Amplification Test (NAAT) is now the gold standard for gonorrhea. * **Treatment:** Due to increasing resistance, the current CDC/WHO recommendation is usually a single dose of **IM Ceftriaxone**. * **Fitz-Hugh-Curtis Syndrome:** A complication of gonococcal (or chlamydial) PID involving peri-hepatitis ("violin-string" adhesions). * **Culture Media:** Remember **Chocolate Agar** is non-selective, while **Thayer-Martin** is selective for *Neisseria*.

Question 152: A young man presents with asymptomatic macules and erythematous painless lesions over the glans with generalized lymphadenopathy. What is the treatment of choice for this condition?

A. Ceftriaxone
B. Benzathine penicillin (Correct Answer)
C. Acyclovir
D. Fluconazole

Explanation: ### Explanation The clinical presentation of **painless erythematous lesions (chancres)** on the glans penis accompanied by **generalized lymphadenopathy** is classic for **Primary Syphilis**. Syphilis is caused by the spirochete *Treponema pallidum*. **1. Why Benzathine Penicillin is Correct:** Benzathine Penicillin G is the gold standard and treatment of choice for Syphilis. *Treponema pallidum* is highly sensitive to penicillin, and because the organism divides slowly, a long-acting repository formulation like Benzathine Penicillin (administered intramuscularly) ensures sustained treponemicidal levels in the blood. For primary, secondary, or early latent syphilis, a **single dose of 2.4 million units IM** is sufficient. **2. Why the Other Options are Incorrect:** * **Ceftriaxone (Option A):** While it has anti-treponemal activity and can be used as an alternative in penicillin-allergic patients, it is not the first-line "treatment of choice." * **Acyclovir (Option C):** This is an antiviral used for Herpes Simplex Virus (HSV). Genital herpes typically presents with **painful** vesicles or ulcers, unlike the painless lesions described here. * **Fluconazole (Option D):** This is an antifungal used for conditions like Candidal balanitis, which usually presents with itchy, white patches rather than painless indurated ulcers and generalized lymphadenopathy. **3. NEET-PG High-Yield Pearls:** * **The "P" Rule:** Syphilitic chancres are **P**ainless, **P**uriform (clean base), and **P**alpable (indurated). * **Diagnosis:** Dark-ground microscopy is the gold standard for early lesions; VDRL/RPR are used for screening (non-specific), and TPHA/FTA-ABS are confirmatory (specific). * **Jarisch-Herxheimer Reaction:** A common febrile reaction occurring within 24 hours of starting penicillin treatment due to the release of endotoxins from dying spirochetes. * **Drug of Choice in Pregnancy:** Penicillin remains the only recommended treatment; patients with allergies must undergo desensitization.

Question 153: A patient with borderline tuberculoid leprosy presents with the following findings. Which type of hypersensitivity reaction and nerve is enlarged?

A. Type 4 & greater auricular nerve (Correct Answer)
B. Type 1 & greater auricular nerve
C. Type 3 & anterior auricular nerve
D. Type 2 & greater auricular nerve

Explanation: ***Type 4 & greater auricular nerve*** - Borderline tuberculoid leprosy is characterized by a strong **cell-mediated immune response** against *Mycobacterium leprae*, which manifests as a **Type 4 (delayed-type) hypersensitivity** reaction leading to granuloma formation. - The image shows a thickened, cord-like structure in the neck, which is characteristic of an enlarged **greater auricular nerve**, the most commonly involved cutaneous nerve of the head and neck in leprosy. *Type 1 & greater auricular nerve* - **Type 1 hypersensitivity** is an immediate, **IgE-mediated** reaction (e.g., anaphylaxis) and is not the immunological basis for nerve damage or skin lesions in tuberculoid leprosy. - The pathogenesis of tuberculoid leprosy involves a **delayed-type** T-cell response, which takes days to develop, unlike the rapid onset of Type 1 reactions. *Type 2 & greater auricular nerve* - **Type 2 hypersensitivity** is an **antibody-dependent cytotoxic** reaction, which is not the primary mechanism in tuberculoid leprosy's pathology. - While immune reactions occur in leprosy, Type 2 is not the correct classification for the T-cell-mediated granulomatous inflammation seen in the tuberculoid form. *Type 3 & anterior auricular nerve* - **Type 3 hypersensitivity** involves **immune-complex deposition** and is characteristic of **Erythema Nodosum Leprosum (ENL)**, a complication typically seen in lepromatous leprosy, not borderline tuberculoid. - The enlarged nerve shown is clearly the **greater auricular nerve** due to its location crossing the sternocleidomastoid muscle; the **anterior auricular nerve** is located more anteriorly and is not typically affected this prominently.

Question 154: Identify the given condition and its treatment.

A. Erythema multiforme with steroids
B. Impetigo bullosa with antibiotics
C. Epidermolysis bullosa with bandaging
D. Staphylococcal scalded skin syndrome with Inj cephalexin (Correct Answer)

Explanation: ***Staphylococcal scalded skin syndrome with Inj cephalexin*** - This is a serious skin infection caused by **exfoliative toxins** produced by *Staphylococcus aureus*, leading to widespread erythema and desquamation. The image may represent the initial focus of infection. - Treatment involves systemic **anti-staphylococcal antibiotics**, such as cephalexin or nafcillin, to eliminate the toxin-producing bacteria, along with supportive care for the skin. *Epidermolysis bullosa with bandaging* - This is a group of inherited **genetic disorders** causing extreme skin fragility and blistering in response to minimal trauma, not an infection. - The clinical presentation involves **mechanically-induced bullae** and erosions, rather than the infectious pustules seen here. *Impetigo bullosa with antibiotics* - Bullous impetigo is a **localized skin infection** with flaccid bullae caused by *S. aureus* exotoxins, confined to the area of infection. - Staphylococcal scalded skin syndrome is a **systemic illness** where toxins circulate, causing widespread skin sloughing far from the initial infection site, and often presents with fever and irritability. *Erythema multiforme with steroids* - This is an immune-mediated **hypersensitivity reaction**, most commonly triggered by infections like **Herpes simplex virus** or medications. - The characteristic skin lesions are **targetoid papules** and plaques, which are morphologically distinct from the pustules shown in the image.

Question 155: A person with the H/o long-term sexual relationship presented with painful ulcers on his genitals with tender lymphadenopathy. What is the diagnosis?

A. LGV
B. Chlamydia
C. Gonorrhoea
D. Chancroid (Correct Answer)

Explanation: ***Chancroid*** - Caused by the bacterium **_Haemophilus ducreyi_**, it classically presents with one or more deep, painful genital ulcers that have ragged, undermined borders and a purulent base. - It is characteristically associated with tender, suppurative inguinal lymphadenopathy, often unilateral, which is consistent with the patient's presentation. *Gonorrhoea* - Caused by **_Neisseria gonorrhoeae_**, it typically presents as **purulent urethritis** or cervicitis with discharge and dysuria. - While it can cause systemic infection, painful genital ulcers are not a characteristic feature of a primary gonococcal infection. *Chlamydia* - Caused by **_Chlamydia trachomatis_** (serovars D-K), it is a leading cause of nongonococcal urethritis and is frequently asymptomatic, especially in women. - This infection does not typically cause painful genital ulcers; its presentation is more commonly urethritis, cervicitis, or pelvic inflammatory disease. *LGV* - Lymphogranuloma venereum (LGV) is caused by invasive serovars (L1, L2, L3) of **_Chlamydia trachomatis_**. - It typically begins with a small, transient, **painless** papule or ulcer, followed by the development of painful inguinal lymphadenopathy (buboes), which differentiates it from the painful ulcers of chancroid.

Question 156: A 45-year-old truck driver with a history of multiple sex partners presented to the dermatological department, as shown below. What is the likely diagnosis?

A. Secondary syphilis (Correct Answer)
B. Lichen planus
C. Scabies
D. Psoriasis

Explanation: ***Secondary syphilis*** - The image shows a classic **maculopapular rash** involving the **palms**, a hallmark feature of secondary syphilis, which is caused by the spirochete **Treponema pallidum**. - The patient's history of **multiple sex partners** is a significant risk factor, and other associated findings can include generalized lymphadenopathy, fever, and **condylomata lata**. *Lichen planus* - Characterized by the "6 P's": **pruritic, polygonal, planar, purple papules and plaques**, often with fine white lines on the surface known as **Wickham's striae**. - The lesions in the image lack these classic features and are not typically pruritic, distinguishing it from the presented case. *Scabies* - This is an intensely **pruritic** infestation caused by the mite **Sarcoptes scabiei**, which creates linear **burrows**, especially in the **interdigital web spaces**, wrists, and axillae. - The rash in secondary syphilis is classically non-pruritic, and the morphology is maculopapular rather than burrow-like. *Psoriasis* - Typically presents as **well-demarcated erythematous plaques** with a **silvery scale** on extensor surfaces like the elbows and knees. - While palmoplantar psoriasis occurs, it usually manifests as hyperkeratotic plaques or pustules, not the diffuse maculopapular rash seen here.

Question 157: A patient presents with erythematous streaks extending peripherally from a site of infection on the skin. Involvement of which of the following structures leads to this clinical presentation?

A. Superficial lymphatics (Correct Answer)
B. Skin
C. Superficial veins
D. Deep lymphatics

Explanation: ***Superficial lymphatics*** (Assuming the image shows signs of **lymphangitis** or **cellulitis**, characterized by **red streaks** spreading from an infected site.)- The classic presentation of **acute lymphangitis** involves **erythematous streaks** extending peripherally from a site of infection (often a wound or cellulitis), which are typically visible superficial structures.- This pattern suggests inflammation and infection tracking along the **superficial lymphatic vessels** which drain the peripheral skin and subcutaneous tissues.*Deep lymphatics*- Involvement of the **deep lymphatics** (e.g., those alongside major blood vessels) typically leads to **lymphedema** (swelling) of the entire limb, rather than the visible **red streaking** seen in acute superficial lymphangitis.- They are located deeper and their inflammation is less likely to produce the superficial, linear rash visible on the skin.*Superficial veins*- Inflammation and thrombosis of superficial veins (**superficial thrombophlebitis**) typically presents as a localized, **palpable, tender cord** rather than multiple linear streaks that spread over distance, which are characteristic of lymphatic tracing.- This condition would primarily involve blood flow obstruction, not the characteristic infection tracking seen in lymphangitis.*Skin*- Although the signs are *visible* on the skin, the primary pathological process causing the streaks is the infection spreading *within* the **lymphatic vessels** beneath the skin surface, not solely a primary skin disease (like **erysipelas** or **cellulitis** alone).- Cellulitis is often the source, but the visible tracking (streaks) follows the path of the **superficial lymphatics**.

Question 158: A 45-year-old man with multiple sexual partners presents with a palmoplantar rash as seen below. On examination, he has epitrochlear lymphadenopathy. Which of the following is the likely diagnosis?

A. Psoriasis
B. Secondary syphilis (Correct Answer)
C. Meningococcemia
D. Stevens-Johnson syndrome

Explanation: ***Secondary syphilis*** - The classic rash of secondary syphilis is a diffuse, maculopapular eruption that characteristically involves the **palms and soles**, as seen in the image. A history of multiple sexual partners is a major risk factor. - **Epitrochlear lymphadenopathy** is a highly suggestive, though not pathognomonic, sign of secondary syphilis. Other systemic symptoms may include fever, malaise, and **condylomata lata**. *Psoriasis* - While psoriasis can affect the palms and soles (**palmoplantar psoriasis**), it typically presents as well-demarcated, erythematous plaques with a silvery scale, which differs from the rash shown. - Psoriasis is an autoimmune condition and is not associated with **epitrochlear lymphadenopathy** or risk factors like multiple sexual partners. *Meningococcemia* - This is an acute, life-threatening infection that presents with a **petechial or purpuric rash** that can become necrotic, not a papular rash on the palms and soles. - Patients with **meningococcemia** are typically systemically unwell with high fever, hypotension, and signs of meningitis, which are absent in this presentation. *Steven Johnson syndrome* - SJS is a severe mucocutaneous reaction characterized by **targetoid lesions**, bullae, and epidermal detachment, which are not features of the rash shown. - A key feature of SJS is severe involvement of at least two **mucous membranes** (e.g., oral, ocular, genital), which is not mentioned in this case.

Question 159: A patient presents with an indurated plaque on the cheek with central atrophy. Chest X-ray reveals apical calcification. Which of the following tests is most appropriate to confirm the diagnosis?

A. Mantoux test
B. Slit skin smear
C. PCR (Correct Answer)
D. Probe test

Explanation: ***PCR*** - The clinical picture of an indurated plaque (often exhibiting **apple-jelly nodules** on diascopy) with central atrophy, coupled with radiological evidence of old pulmonary TB (apical calcification), strongly suggests **Lupus Vulgaris** (cutaneous tuberculosis). - **PCR (Polymerase Chain Reaction)** is the most sensitive and specific method for confirming the diagnosis by detecting *Mycobacterium tuberculosis* DNA, which is essential as Lupus Vulgaris is typically a **paucibacillary** condition where AFB staining and culture often fail. *Mantoux test* - The **Mantoux test** assesses delayed-type hypersensitivity (Type IV reaction) to tuberculin antigens and indicates prior exposure to TB or BCG vaccination. - It is useful for screening but **does not confirm active disease** (Lupus Vulgaris) and can be negative in immunocompromised patients or anergic forms. *Slit skin smear* - **Slit skin smear** is the diagnostic method primarily used to detect **acid-fast bacilli** (*M. leprae*) and classify **Leprosy** (Hansen's disease). - It is **not the investigation of choice** for diagnosing tuberculosis. *Probe test* - Nucleic acid **probe tests** (hybridization) are molecular techniques used to identify *M. tuberculosis* but are generally less sensitive than modern **PCR** assays, especially when dealing with limited tissue samples or low bacterial load. - **PCR** is the superior and more widely employed molecular diagnostic standard for confirming paucibacillary TB.

Question 160: A male presents with lesions as shown in the image and a history of unprotected sexual intercourse a few months ago. What is the most appropriate investigation to confirm the diagnosis?

A. Serology (Correct Answer)
B. Tzanck smear
C. KOH
D. Biopsy

Explanation: ***Serology*** - The clinical presentation (diffuse body rash, often involving the palms and soles, following recent unprotected sexual exposure) is highly suggestive of **Secondary Syphilis**. - **Serological tests** (Non-treponemal tests like RPR/VDRL and specific Treponemal tests like TPPA/FTA-ABS) are the definitive and most appropriate confirmatory investigation for syphilis. *Tzanck smear* - This test is used primarily for the rapid diagnosis of vesicular lesions caused by herpes viruses, such as **Herpes Simplex Virus (HSV)** or **Varicella-Zoster Virus (VZV)**. - It is not indicated for the diagnosis of the typical maculopapular rash seen in secondary syphilis. *KOH* - **Potassium hydroxide (KOH) preparation** is a direct microscopy test specifically used to identify structures like hyphae and spores in the diagnosis of **superficial fungal infections**. - The patient's presentation with a rash secondary to sexually transmitted infection is not typically investigated using KOH. *Biopsy* - While a skin biopsy might confirm the diagnosis histologically (showing characteristic perivascular infiltrate), it is **invasive** and generally reserved for cases where serology is equivocal or the presentation is atypical. - **Serology** provides a systemic assessment and is the standard initial confirmatory test for syphilis.

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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