Bacterial Skin Infections Practice Questions

Q: A 25-year-old male presents with multiple painful genital ulcers and tender inguinal lymphadenopathy. The likely diagnosis is:

Chancroid. **Chancroid** - **Chancroid** presents with **multiple, painful, ragged genital ulcers** with a grayish base and associated **tender inguinal lymphadenopathy** (buboes) [1]. - It is caused by the bacterium *Haemophilus ducreyi*. *Primary syphilis* - Primary syphilis typically presents as a **single, painless chancre** with a firm, indurated base and usually non-tender, rubbery regional lymphadenopathy. - The ulcers described are multiple and painful, which is inconsistent with a syphilic chancre. *Genital herpes* - Genital herpes causes **multiple, painful vesicles** that progress to shallow ulcers, often preceded by a prodrome of tingling or burning [2]. - While painful, herpes lesions are typically vesicular initially and do not commonly present with the deep, ragged ulcers and classic tender buboes seen in chancroid [1]. *Lymphogranuloma venereum* - LGV typically starts as a **small, painless papule or ulcer** that often goes unnoticed, followed by the development of **large, often suppurative, unilateral inguinal lymphadenopathy** (buboes) in later stages [1]. - The initial lesion in LGV is often transient and painless, unlike the prominent, painful ulcers described here.

Q: A 25-year-old man presents with non-anesthetic hypopigmented macules on his arm and has a family history of leprosy. What is the most appropriate diagnostic test?

Skin biopsy. ***Skin biopsy*** - A **skin biopsy** of the affected lesion, particularly the edge, is the most appropriate diagnostic test to confirm leprosy by identifying **acid-fast bacilli (AFB)** or characteristic histological changes like granulomas and nerve involvement. - It allows for the differentiation of leprosy from other hypopigmenting conditions and classification into specific types based on the **Ridley-Jopling classification**. *KOH mount* - A **KOH mount** is primarily used to diagnose **fungal infections** by dissolving keratinocytes and allowing visualization of fungal elements. - It would not be useful for identifying the acid-fast bacilli of *Mycobacterium leprae* or for assessing nerve involvement. *PCR for Mycobacterium leprae* - While **PCR is highly sensitive** for detecting *M. leprae* DNA, it is not the **first-line diagnostic test** and is usually reserved for cases where conventional methods are inconclusive or for research purposes. - It may not always correlate with disease activity or viability of the bacilli, and false positives can occur. *Slit skin smear* - A **slit skin smear** is used to determine the **bacterial index (BI)** and **morphological index (MI)** in leprosy, particularly in patients with multiple lesions or suspected lepromatous leprosy [1]. - However, in cases of **paucibacillary leprosy** (tuberculoid type), the smear may be negative, making a biopsy more reliable for diagnosis and classification, especially with **non-anesthetic hypopigmented macules** [1].

Q: A young man presents with asymptomatic macules and erythematous lesions on the glans, accompanied by generalized lymphadenopathy. What condition is being described?

Secondary Syphilis. ***Secondary Syphilis*** - **Asymptomatic macules** and **erythematous lesions** on the glans, along with **generalized lymphadenopathy**, are classic manifestations of secondary syphilis. - The rash can be highly variable and may affect palms and soles, often described as a **coppery or ham-colored macular rash**. *Herpes Simplex* - Characterized by painful **vesicles** and **ulcers**, not asymptomatic macules and erythematous lesions. - While it can cause local lymphadenopathy, it typically does not lead to **generalized lymphadenopathy**. *Candidiasis* - Presents as **pruritic (itchy)** red patches, sometimes with **satellite lesions** and a **white discharge**, primarily associated with fungal infection. - It does not typically cause generalized lymphadenopathy. *Gonorrhea* - Primarily causes **urethritis** with **purulent discharge** in men. - **Skin lesions** are rare and usually manifest as pustules or hemorrhagic lesions in cases of disseminated infection, not asymptomatic macules on the glans.

Q: A newborn presents with large areas of denuded skin, blisters, and a positive Nikolsky's sign. What is the most likely diagnosis?

Staphylococcal scalded skin syndrome. ***Staphylococcal scalded skin syndrome*** - This condition is characterized by **large areas of denuded skin**, **fragile blisters**, and a **positive Nikolsky's sign**, which are all classic presentations in neonates. - It is caused by **exfoliative toxins** produced by *Staphylococcus aureus* that cleave desmoglein-1 in the epidermis. *Bullous impetigo* - While it presents with **blisters**, they are typically **localized**, smaller, and less extensive than in SSSS. - It does not usually cause such widespread **denudation** or a generalized positive Nikolsky's sign. *Toxic epidermal necrolysis* - This is a severe drug-induced reaction typically seen in **older children or adults**, not in newborns. - It involves extensive epidermal detachment similar to a **severe burn**, but the etiology and age of onset differ significantly. *Congenital epidermolysis bullosa* - This is a group of **genetic disorders** characterized by extremely fragile skin and blister formation, often present at birth. - While it can cause extensive blistering and denudation, the key differentiating factor is its **congenital nature** and underlying genetic defect, rather than a bacterial toxin.

Q: Which sexually transmitted infection is associated with the formation of condylomata lata?

Secondary syphilis. ***Secondary syphilis*** - **Condylomata lata** are highly infectious, flat-topped, moist, fleshy papules that are characteristic lesions of **secondary syphilis**, often found in warm, moist areas like the anogenital region [1]. - They represent a mucocutaneous manifestation of widespread **spirochete dissemination** during the secondary stage [1]. *Genital herpes* - Genital herpes is characterized by painful **vesicles** and **ulcers**, not flat, warty lesions like condylomata lata [1]. - It is caused by the **herpes simplex virus (HSV)**, predominantly HSV-2. *Lymphogranuloma venereum* - This infection presents with a transient, often unnoticed, primary lesion followed by **inguinal lymphadenopathy** (buboes) and associated systemic symptoms. - It is caused by specific serovars of **_Chlamydia trachomatis_** and does not typically involve condylomata lata. *Primary syphilis* - Primary syphilis is characterized by a single, painless lesion called a **chancre** at the site of inoculation [1]. - This stage precedes the disseminated manifestations, including condylomata lata, seen in secondary syphilis [1].

Q: Which of the following conditions can present as a painless genital ulcer?

Primary syphilis. ***Primary syphilis*** - A **chancre**, the hallmark lesion of primary syphilis, is typically a **painless, indurated ulcer** with a clean base. - This characteristic makes it a common cause of painless genital ulcers. *Genital herpes* - Genital herpes typically presents with **multiple, painful vesicular lesions** [1] that can rupture and form shallow ulcers. - Pain is a distinguishing feature, making it less likely to be a painless ulcer [1]. *Chancroid* - Chancroid is caused by *Haemophilus ducreyi* and produces **painful, ragged-edged ulcers** with a grayish base [2]. - The ulcers are usually accompanied by **tender, suppurative lymphadenopathy** [2]. *Lymphogranuloma venereum* - The primary lesion of LGV can be a **small, painless vesicle or ulcer**, but it is often fleeting and unnoticed [2]. - The more prominent and characteristic presentation involves **painful, often suppurative inguinal lymphadenopathy** (buboes) [2].

Q: A patient presents with a painless ulcer and a positive RPR test. What is the most likely diagnosis?

Primary syphilis. **Primary syphilis** - The presence of a **painless ulcer**, known as a **chancre**, is the classic hallmark of primary syphilis [1]. - A **positive RPR test** (Rapid Plasma Reagin) indicates active syphilis infection [1]. *Chancroid* - Caused by **Haemophilus ducreyi**, chancroid typically presents with **multiple, painful, and tender ulcers**. - The RPR test would be **negative**, as it is not a test for chancroid. *Lymphogranuloma venereum* - Initial lesion is often a **transient, painless papule or vesicle** that may go unnoticed, followed by painful **inguinal lymphadenopathy (buboes)**. - While it can be associated with genital ulcers, they are usually not the primary diagnostic feature, and the RPR test would be negative. *Genital herpes* - Characterized by **multiple, painful vesicular or ulcerative lesions** on an erythematous base [1]. - The RPR test would be **negative** as it is a viral infection, not bacterial [1].

Q: A 50-year-old male presents with a painless genital ulcer and non-tender inguinal lymphadenopathy. The initial RPR is negative, but there is a high suspicion for syphilis. What is the next best diagnostic test?

FTA-ABS. ***FTA-ABS*** - **Fluorescent Treponemal Antibody Absorption (FTA-ABS)** is a **treponemal test** that remains positive for life and is useful in confirming syphilis in cases of high suspicion, especially when non-treponemal tests like RPR are negative (e.g., in early stages or due to the **prozone phenomenon**) [1]. - It directly detects antibodies specific to *Treponema pallidum* and is more sensitive than RPR in early syphilis [1]. *Dark field microscopy* - **Dark field microscopy** directly visualizes spirochetes from a chancre [1], but its utility is limited by the need for fresh samples and specialized equipment. - While it offers immediate diagnosis, a negative result does not rule out syphilis, especially if the lesion is healing or if antibiotics have been used. *PCR for T. pallidum* - **PCR for *T. pallidum*** is highly sensitive and specific but is not routinely available in all clinical settings, and its use is typically reserved for challenging cases or research. - While it can be useful in detecting DNA from the bacteria, it's not the initial confirmatory test of choice when a treponemal serum assay is widely available and appropriate. *HIV test* - An **HIV test** is crucial for patients with syphilis as coinfection is common, but it does not directly diagnose syphilis. - While important for comprehensive patient care, it does not address the immediate diagnostic question regarding syphilis itself.

Q: What is the most appropriate treatment for a patient diagnosed with lymphogranuloma venereum?

Doxycycline. ***Doxycycline*** - **Doxycycline** is the recommended first-line treatment for **lymphogranuloma venereum (LGV)** due to its effectiveness against *Chlamydia trachomatis* serovars L1, L2, and L3, which cause LGV. - Treatment typically involves a 21-day course to ensure complete eradication of the infection and resolution of symptoms like **lymphadenopathy** and **genital ulcers** [1]. *Penicillin* - **Penicillin** is primarily used to treat bacterial infections like **syphilis**, **streptococcal pharyngitis**, and certain **gonococcal infections**. - It is **ineffective** against *Chlamydia trachomatis*, the causative agent of LGV. *Ceftriaxone* - **Ceftriaxone** is a third-generation cephalosporin commonly used for treating **gonorrhea**, **meningitis**, and other severe bacterial infections [1]. - It has **poor activity** against *Chlamydia trachomatis* and is not an appropriate treatment for LGV. *Metronidazole* - **Metronidazole** is an antimicrobial highly effective against **anaerobic bacteria** and **protozoa**, commonly used for conditions like **trichomoniasis**, **bacterial vaginosis**, and **amebiasis**. - It has **no activity** against *Chlamydia trachomatis* and is therefore not used for LGV.

Q: Which of the following is a hallmark of tertiary syphilis?

Aortic aneurysm. ***Aortic aneurysm*** – **Aortic aneurysm** (specifically **thoracic aortic aneurysm**) is a classic manifestation of tertiary syphilis, resulting from chronic inflammation of the vasa vasorum leading to weakening of the aortic wall. – It can also manifest as **neurosyphilis** (e.g., tabes dorsalis, general paresis) or **gummas** (granulomatous lesions) affecting various organs [1]. *Chancre* – A **chancre** is a **painless ulcerative lesion** that characterizes the **primary stage** of syphilis [1]. – It typically appears at the site of infection about 3 weeks after exposure and resolves spontaneously [1]. *Condylomata lata* – **Condylomata lata** are **wart-like lesions** that appear in the **secondary stage** of syphilis, often in moist areas like the anogenital region or skin folds [1]. – They are highly infectious and contain numerous spirochetes. *Maculopapular rash* – A **maculopapular rash** is a common and distinctive feature of **secondary syphilis**, often affecting the palms and soles [1]. – This rash is typically non-itchy and can appear a few weeks to months after the chancre has resolved [1].

Question 1

A 25-year-old male presents with multiple painful genital ulcers and tender inguinal lymphadenopathy. The likely diagnosis is:

Accepted Answer

Chancroid

Answer

Primary syphilis

Answer

Genital herpes

Answer

Lymphogranuloma venereum

Question 2

A 25-year-old man presents with non-anesthetic hypopigmented macules on his arm and has a family history of leprosy. What is the most appropriate diagnostic test?

Accepted Answer

Skin biopsy

Answer

KOH mount

Answer

PCR for Mycobacterium leprae

Answer

Slit skin smear

Question 3

A young man presents with asymptomatic macules and erythematous lesions on the glans, accompanied by generalized lymphadenopathy. What condition is being described?

Accepted Answer

Secondary Syphilis

Answer

Herpes Simplex

Answer

Candidiasis

Answer

Gonorrhea

Question 4

A newborn presents with large areas of denuded skin, blisters, and a positive Nikolsky's sign. What is the most likely diagnosis?

Accepted Answer

Staphylococcal scalded skin syndrome

Answer

Toxic epidermal necrolysis

Answer

Bullous impetigo

Answer

Congenital epidermolysis bullosa

Question 5

Which sexually transmitted infection is associated with the formation of condylomata lata?

Accepted Answer

Secondary syphilis

Answer

Genital herpes

Answer

Lymphogranuloma venereum

Answer

Primary syphilis

Question 6

Which of the following conditions can present as a painless genital ulcer?

Accepted Answer

Primary syphilis

Answer

Genital herpes

Answer

Chancroid

Answer

Lymphogranuloma venereum

Question 7

A patient presents with a painless ulcer and a positive RPR test. What is the most likely diagnosis?

Accepted Answer

Primary syphilis

Answer

Chancroid

Answer

Lymphogranuloma venereum

Answer

Genital herpes

Question 8

A 50-year-old male presents with a painless genital ulcer and non-tender inguinal lymphadenopathy. The initial RPR is negative, but there is a high suspicion for syphilis. What is the next best diagnostic test?

Accepted Answer

FTA-ABS

Answer

Dark field microscopy

Answer

PCR for T. pallidum

Answer

HIV test

Question 9

What is the most appropriate treatment for a patient diagnosed with lymphogranuloma venereum?

Accepted Answer

Doxycycline

Answer

Penicillin

Answer

Ceftriaxone

Answer

Metronidazole

Question 10

Which of the following is a hallmark of tertiary syphilis?

Accepted Answer

Aortic aneurysm

Answer

Chancre

Answer

Condylomata lata

Answer

Maculopapular rash

Bacterial Skin Infections — MCQs

Bacterial Skin Infections — MCQs

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