Bacterial Skin Infections Practice Questions

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: 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].

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: A 40-year-old woman presents with a painless ulcer on her genitalia and reports a recent new sexual partner. What is the most likely diagnosis?

Syphilis. Syphilis - **Primary syphilis** is characterized by a **painless chancre** (ulcer) at the site of infection [1], which typically appears 10 to 90 days after exposure. - The history of a new sexual partner increases the likelihood of acquiring a sexually transmitted infection like syphilis [2]. *Gonorrhea* - Primarily causes **urethritis** in men and **cervicitis** in women, leading to symptoms like discharge and dysuria, not typically a painless ulcer. - While it can cause pharyngitis or proctitis, a painless genital ulcer is not its classic presentation. *Chlamydia* - Often causes **asymptomatic infections** or symptoms similar to gonorrhea, such as **cervicitis** or **urethritis**, with discharge and dysuria [2]. - It does not typically present with a **painless genital ulcer**. *Genital herpes* - Characterized by **painful vesicles** and **ulcers** [3], usually preceded by prodromal symptoms like tingling or burning. - The ulcers associated with herpes are typically *painful* [4], which contrasts with the symptom presented in the question.

Q: Which of the following is the treatment of choice for chancroid?

Azithromycin. ***Azithromycin*** - **Azithromycin** 1 gram orally in a **single dose** is a highly effective and convenient treatment for chancroid caused by *Haemophilus ducreyi*. - Its long half-life allows for single-dose administration, which improves **patient adherence** and reduces the risk of further transmission. *Ceftriaxone* - **Ceftriaxone** is primarily used to treat **gonorrhea** [1] and is also effective against other bacterial infections. While it has some activity against *Haemophilus ducreyi*, **azithromycin** or **ciprofloxacin** are generally preferred for chancroid. *Penicillin* - **Penicillin** is the cornerstone of treatment for **syphilis**, caused by *Treponema pallidum*. - It is **not effective** against *Haemophilus ducreyi*, the causative agent of chancroid. *Doxycycline* - **Doxycycline** is a broad-spectrum antibiotic used to treat various infections, including **chlamydia** and **syphilis** (as an alternative to penicillin). - It is **not the preferred first-line treatment** for chancroid; single-dose azithromycin or ceftriaxone are generally more effective.

Q: A 30-year-old male presents with a history of a painless genital ulcer followed by a generalized rash and mucous patches in the mouth. What is the appropriate treatment?

Penicillin G. Penicillin G - The clinical presentation of a **painless genital ulcer** (chancre) followed by a **generalized rash** [1] and **mucous patches** in the mouth is classic for **secondary syphilis**. [3] - **Penicillin G benzathine** is the treatment of choice for all stages of syphilis, effectively eradicating the causative organism, *Treponema pallidum*. [2] *Azithromycin* - Azithromycin is a macrolide antibiotic primarily used for treating **atypical pneumonia**, **chlamydia**, and some **bacterial gastroenteritis**. - It is not effective against *Treponema pallidum* and is not recommended for the treatment of syphilis due to increasing resistance. *Doxycycline* - Doxycycline is a tetracycline antibiotic used for various bacterial infections, including **Lyme disease**, **Rocky Mountain spotted fever**, and **chlamydia**. - While it can be used as an alternative treatment for syphilis in patients **allergic to penicillin**, penicillin G is the preferred first-line agent due to its superior efficacy. *Acyclovir* - Acyclovir is an **antiviral medication** used to treat **herpes simplex virus (HSV)** infections, such as genital herpes and cold sores. - It has no antibacterial activity and is therefore ineffective against syphilis, which is caused by a bacterium.

Question 1

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 2

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 3

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 4

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 5

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 6

Which of the following is a hallmark of tertiary syphilis?

Accepted Answer

Aortic aneurysm

Answer

Chancre

Answer

Condylomata lata

Answer

Maculopapular rash

Question 7

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

Accepted Answer

Doxycycline

Answer

Penicillin

Answer

Ceftriaxone

Answer

Metronidazole

Question 8

A 40-year-old woman presents with a painless ulcer on her genitalia and reports a recent new sexual partner. What is the most likely diagnosis?

Accepted Answer

Syphilis

Answer

Gonorrhea

Answer

Chlamydia

Answer

Genital herpes

Question 9

Which of the following is the treatment of choice for chancroid?

Accepted Answer

Azithromycin

Answer

Ceftriaxone

Answer

Penicillin

Answer

Doxycycline

Question 10

A 30-year-old male presents with a history of a painless genital ulcer followed by a generalized rash and mucous patches in the mouth. What is the appropriate treatment?

Accepted Answer

Penicillin G

Answer

Azithromycin

Answer

Doxycycline

Answer

Acyclovir

Bacterial Skin Infections — MCQs

Bacterial Skin Infections — MCQs

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