Bacterial Skin Infections Practice Questions

Q: A patient presents with genital ulcer disease. Which of the following combinations correctly matches the pain characteristics with the causative organism?

Multiple painful - HSV. ***Multiple painful - HSV*** - **Herpes Simplex Virus (HSV)** typically causes a constellation of **multiple, superficial, painful ulcers**, often preceded by tingling or burning sensations [1]. - These lesions evolve from vesicles to pustules and then to ulcers, making them highly characteristic of HSV infection [1]. *Painless - H. ducreyi* - **_Haemophilus ducreyi_** is the causative agent of **chancroid**, which classically presents as **painful, ragged, undermined ulcers** with erythematous bases, not painless ones [1]. - The descriptor "painless" is characteristic of the chancre of syphilis caused by _Treponema pallidum_. *Single painful - C. trachomatis* - **_Chlamydia trachomatis_** (specifically serovars L1-L3) causes **lymphogranuloma venereum (LGV)**, which initially presents with a **small, often painless, transient ulcer or papule** that can go unnoticed, followed by painful inguinal lymphadenopathy [1]. - A single painful ulcer is not the typical presentation for _Chlamydia trachomatis_ in the context of genital ulcer disease. *Painful - T. pallidum* - **_Treponema pallidum_**, the bacterium responsible for **syphilis**, causes a primary lesion known as a **chancre**, which is typically a **single, firm, painless ulcer** with raised, indurated borders [1]. - Painful ulcers are uncharacteristic of primary syphilis.

Q: In a patient with primary syphilis, which of the following indicates the need for CSF examination?

Neurological symptoms. Detailed examination of the central nervous system involvement in syphilis focuses on clinical indicators and diagnostic procedures. ***Neurological symptoms*** - The presence of **neurological symptoms** such as headache, altered mental status, or cranial nerve palsies in a patient with syphilis indicates potential **neurosyphilis** affecting the central nervous system. - A **CSF examination** is crucial in this scenario to assess for pleocytosis, elevated protein, and a reactive VDRL, which are diagnostic of neurosyphilis [1]. *Recent HIV exposure* - While HIV co-infection can alter the course of syphilis and increase the risk of neurosyphilis, recent exposure alone without symptoms or established HIV infection does not automatically necessitate a **CSF examination** in primary syphilis. - HIV-positive patients with syphilis typically require CSF examination only if they have symptoms, high RPR titers, or treatment failure. *Positive VDRL test* - A positive **VDRL test** (Venereal Disease Research Laboratory) is a common serological marker for syphilis infection and is expected in primary syphilis. - It indicates systemic infection but does not specifically point to **CNS involvement** without accompanying neurological symptoms or other risk factors. *High RPR titers* - **Rapid Plasma Reagin (RPR)** titers indicate the activity of the syphilis infection and typically correlate with disease burden. High titers are common in primary syphilis. - While very high RPR titers (e.g., ≥1:32) in HIV-infected individuals, or in non-HIV individuals who fail to respond to treatment, can be an indication for **CSF examination**, high titers alone in primary syphilis without other indicators are not sufficient.

Q: Choose the INCORRECT statement about lymphogranuloma venereum (LGV):

Doxycycline is contraindicated. ***Doxycycline is contraindicated*** - This statement is **incorrect** because **doxycycline** is the **first-line treatment** for lymphogranuloma venereum (LGV), typically administered for a 21-day course. - It is highly effective against *Chlamydia trachomatis* serovars L1, L2, and L3, which cause LGV. *Fistulas are common in late stage* - This statement is **correct**. If left untreated, LGV can progress to a late stage characterized by **chronic inflammation**, **strictures**, and the formation of **fistulas** involving the rectum, vagina, or perineum. - These complications result from extensive tissue damage and scarring, often following the rupture of inflamed lymph nodes. *Primary lesion may be painless* - This statement is **correct**. The primary lesion of LGV is often a **small, painless papule, vesicle, or ulcer** (chancre) that appears at the site of inoculation. - It often goes unnoticed because of its transient and asymptomatic nature, preceding the more prominent lymphadenopathy. *Caused by L1, L2, L3 serovars* - This statement is **correct**. Lymphogranuloma venereum is specifically caused by the **L1, L2, and L3 serovars** of *Chlamydia trachomatis* [1]. - These serovars have a greater invasive capacity compared to other *Chlamydia trachomatis* serovars, leading to systemic infection and severe lymphadenopathy.

Q: Which pattern suggests secondary syphilis rather than pityriasis rosea?

Palmoplantar involvement. ***Palmoplantar involvement*** - **Secondary syphilis** characteristically presents with a rash that affects the **palms and soles**, a distribution that is rare in most other dermatological conditions, including pityriasis rosea. - This specific finding is a crucial diagnostic clue differentiating it from a wide range of other skin eruptions. *Christmas tree distribution* - The "Christmas tree" pattern, characterized by oval lesions following the **Langer's lines** on the trunk, is a classic presentation of **pityriasis rosea**. - This linear orientation is not typical for the rash of secondary syphilis. *Collarette scaling* - **Collarette scaling**, where fine scales are present just inside the periphery of a lesion, is a common feature of the individual lesions in **pityriasis rosea**. - While some scaling can be seen in syphilis, the distinctive collarette pattern is more indicative of pityriasis rosea. *Herald patch presence* - The appearance of a **herald patch** (or mother patch) — a single, larger, oval lesion that precedes the generalized rash — is a pathognomonic sign of **pityriasis rosea**. - No such precursor lesion is typically found in secondary syphilis.

Q: Which nerve biopsy is taken to diagnose neuritic leprosy?

Radial cutaneous nerve. ***Radial cutaneous nerve*** - The **radial cutaneous nerve** (superficial branch of radial nerve) is the **preferred nerve for biopsy** in suspected neuritic leprosy - It is a **purely sensory nerve** with minimal functional consequences if damaged, making it the safest choice for diagnostic biopsy - This nerve is **superficially located** at the wrist and easily accessible for biopsy procedures - Provides excellent diagnostic yield as it is commonly involved in leprosy neuritis *Ulnar nerve* - While the ulnar nerve is frequently **thickened and tender** in leprosy and can be easily palpated, it is **NOT preferred for biopsy** [1] - Contains both **motor and sensory fibers**, so biopsy carries significant risk of functional impairment including weakness of intrinsic hand muscles - Clinical examination and nerve thickening is sufficient for diagnosis; biopsy is avoided due to morbidity risk *Median nerve* - The median nerve can be affected in leprosy but is **not suitable for biopsy** due to its critical motor and sensory functions - Biopsy would risk severe hand dysfunction including loss of thumb opposition and sensory loss in the lateral palm - Deep location also makes it less accessible compared to superficial cutaneous nerves *Radial nerve* - The **main radial nerve trunk** is a mixed nerve with important motor functions (wrist and finger extension) - Its deep location and functional importance make it **unsuitable for diagnostic biopsy** - Risk of wrist drop and significant morbidity makes this an inappropriate biopsy site **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, p. 386.

Q: Most specific sign of secondary syphilis is:

Condyloma lata. ***Condyloma lata*** - These are **flat-topped, moist, wart-like lesions** that appear in warm, moist areas like the anogenital region or skin folds. They are highly contagious and are considered the most specific sign of secondary syphilis due to their unique appearance and association. - Their distinct morphology and location help differentiate them from other dermatological conditions, making them a key diagnostic feature. *Mucous patches* - While **mucous patches** are characteristic of secondary syphilis, appearing as painless, whitish lesions on mucous membranes, they are less specific as similar lesions can be seen in other conditions. - They are often overlooked or mistaken for other oral or genital lesions, making them less distinct than condyloma lata for specific diagnosis. *Copper colored rash* - A **diffuse, copper-colored macular or papular rash** is a common manifestation of secondary syphilis, often affecting the trunk and extremities. - However, similar rashes can be seen in various viral exanthems or drug reactions, making it less specific than condyloma lata. *Palm/sole lesions* - **Lesions on the palms and soles** are a highly suggestive, though not entirely specific, sign of secondary syphilis, presenting as macules or papules. - While very characteristic, other conditions like Rocky Mountain spotted fever or hand-foot-and-mouth disease can also cause palmoplantar lesions, reducing their specificity compared to condyloma lata.

Q: Which feature best differentiates folliculitis from furuncle?

Depth of involvement. ***Depth of involvement*** - **Folliculitis** is a superficial infection involving only the **hair follicle ostium**. - A **furuncle** (boil) is a deeper infection that extends into the **dermis** and subcutaneous tissue, often originating from a hair follicle. *Age of presentation* - Both conditions can occur at **any age**, although certain types of folliculitis (e.g., hot tub folliculitis) might be more common in specific age groups due to exposure. - Age itself is **not a distinguishing factor** in terms of disease pathology or differentiation. *Causative organism* - Both folliculitis and furuncles are **most commonly caused by *Staphylococcus aureus***. - While other organisms can sometimes cause folliculitis (e.g., *Pseudomonas* for hot tub folliculitis), the primary causative agent is similar for both. *Site of occurrence* - Both folliculitis and furuncles typically occur in **hair-bearing areas** of the body. - The site of occurrence does not inherently differentiate between a superficial infection of the follicle and a deeper, more extensive infection.

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 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 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.

Question 1

A patient presents with genital ulcer disease. Which of the following combinations correctly matches the pain characteristics with the causative organism?

Accepted Answer

Multiple painful - HSV

Answer

Painless - H. ducreyi

Answer

Single painful - C. trachomatis

Answer

Painful - T. pallidum

Question 2

In a patient with primary syphilis, which of the following indicates the need for CSF examination?

Accepted Answer

Neurological symptoms

Answer

Recent HIV exposure

Answer

Positive VDRL test

Answer

High RPR titers

Question 3

Choose the INCORRECT statement about lymphogranuloma venereum (LGV):

Accepted Answer

Doxycycline is contraindicated

Answer

Fistulas are common in late stage

Answer

Primary lesion may be painless

Answer

Caused by L1, L2, L3 serovars

Question 4

Which pattern suggests secondary syphilis rather than pityriasis rosea?

Accepted Answer

Palmoplantar involvement

Answer

Christmas tree distribution

Answer

Collarette scaling

Answer

Herald patch presence

Question 5

Which nerve biopsy is taken to diagnose neuritic leprosy?

Accepted Answer

Radial cutaneous nerve

Answer

Median nerve

Answer

Radial nerve

Answer

Ulnar nerve

Question 6

Most specific sign of secondary syphilis is:

Accepted Answer

Condyloma lata

Answer

Mucous patches

Answer

Copper colored rash

Answer

Palm/sole lesions

Question 7

Which feature best differentiates folliculitis from furuncle?

Accepted Answer

Depth of involvement

Answer

Age of presentation

Answer

Causative organism

Answer

Site of occurrence

Question 8

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 9

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 10

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

Bacterial Skin Infections — MCQs

Bacterial Skin Infections — MCQs

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