Bacterial Skin Infections Practice Questions

Q: A 25-year-old man develops hypopigmented atrophic patches with diminished sensation on his face. What is the most likely diagnosis?

Indeterminate leprosy. ***Indeterminate leprosy*** - This is the earliest stage of leprosy, characterized by **hypopigmented or erythematous patches** with **diminished or absent sensation** (hypesthesia or anesthesia). - The lesions are typically **few in number** (1-5), ill-defined, and may show subtle **atrophy** due to involvement of dermal nerves and adnexal structures. - **Loss of sensation** is the key diagnostic feature that distinguishes leprosy from other hypopigmentary disorders. In early cases, sensory loss may be subtle and require careful examination. - The face is a common site for leprosy lesions due to the cooler temperature preferred by *Mycobacterium leprae*. *Pityriasis alba* - Presents with **hypopigmented patches with fine scales**, commonly seen in children and adolescents on the face. - Lesions have **normal sensation** (not anesthetic) and are **not atrophic**. - Generally resolves spontaneously without treatment. *Pityriasis versicolor* - Caused by **Malassezia yeast**, presenting as hypo- or hyperpigmented patches with fine scales. - Lesions have **normal sensation** and are typically found on the **trunk and proximal extremities**. - Not atrophic and can be confirmed with KOH examination showing "spaghetti and meatballs" appearance. *Borderline leprosy* - Represents mid-spectrum disease with **multiple, well-defined plaques** showing clear asymmetry. - Shows **definite anesthesia** with demonstrable nerve thickening. - Lesions are more numerous and polymorphic compared to indeterminate leprosy, with clearer immunological classification.

Q: A 27-year-old man presents with a painless genital ulcer and non-tender inguinal lymphadenopathy. The VDRL test is positive. What is the next step in management?

Confirm with FTA-ABS. ***Confirm with FTA-ABS*** - A positive **VDRL test** (a non-treponemal test) for syphilis should always be confirmed with a **treponemal-specific test** like **FTA-ABS** (fluorescent treponemal antibody absorption) due to the possibility of false positives [1]. - The combination of a **painless genital ulcer** (chancre) and **non-tender inguinal lymphadenopathy** is highly suggestive of **primary syphilis**, making confirmation crucial before treatment. *Empirical treatment with benzathine penicillin* - While syphilis is treated with **benzathine penicillin**, empirical treatment without confirmation is generally not recommended, especially given the availability of confirmatory tests. - This approach could lead to unnecessary antibiotic exposure if the VDRL result is a **false positive**, and would miss an opportunity for definitive diagnosis [1]. *PCR for HSV* - **Herpes simplex virus (HSV)** typically causes painful, vesicular lesions that ulcerate, which is different from the described painless ulcer [2]. - Although HSV can cause genital ulcers, a positive VDRL specifically points towards syphilis, making HSV testing less relevant as the *next* step [2]. *Dark field microscopy for syphilis diagnosis* - **Dark-field microscopy** is a method for directly visualizing **Treponema pallidum** from chancre exudate, providing an immediate diagnosis. - However, it requires specialized equipment and expertise that may not be readily available, and a confirmatory serological test like **FTA-ABS** is still necessary for a complete diagnostic workup.

Q: A 26-year-old woman presents with a painless, indurated genital ulcer, and VDRL is positive. What is the first-line treatment?

Benzathine penicillin G. Benzathine penicillin G - A painless, indurated genital ulcer combined with a positive VDRL strongly indicates primary syphilis [1]. - Benzathine penicillin G administered as a single intramuscular dose is the first-line treatment for primary, secondary, and early latent syphilis due to its efficacy and extended action. *Doxycycline* - While doxycycline is an alternative treatment for penicillin-allergic patients with early syphilis, it is not the first-line therapy due to penicillin's superior efficacy and single-dose convenience. - It would require a 14-day course of treatment, which is less convenient than a single penicillin injection. *Azithromycin* - Azithromycin is typically used for treating chlamydia or gonorrhea, but it is not effective for treating syphilis due to increasing resistance and inferior efficacy compared to penicillin. - It is not recommended as a primary or alternative treatment for syphilis by current guidelines. *Ceftriaxone* - Ceftriaxone is primarily used for the treatment of gonorrhea, bacterial meningitis, and other severe bacterial infections. - While it has some activity against Treponema pallidum, it is not the recommended first-line treatment for syphilis and its efficacy has not been as thoroughly established as penicillin.

Q: 28 year old female complaints of foul smelling yellowish urethral discharge since 4 days. History of burning micturation. History of sexual contact with multiple partners 2 days before the onset of symptoms. Most likely diagnosis is ?

Gonococcal urethritis. ***Gonococcal urethritis*** - The presentation of **foul-smelling, yellowish urethral discharge** and **burning micturition** shortly after unprotected sexual contact with multiple partners is highly suggestive of **gonorrhea**. [1] - Symptoms in females are often mild or asymptomatic, but when present, include **dysuria** and vaginal discharge that can be purulent. [2] *Chlamydia* - While *Chlamydia* can cause urethritis with similar symptoms, the discharge is typically **less purulent and yellowish** and more often *mucoid or clear*. [1] - The incubation period for *Chlamydia* is generally **longer (1-3 weeks)** compared to the 2-day onset in this case. [1] *Chancroid* - Characterized by **painful genital ulcers with suppurative inguinal lymphadenopathy** (buboes), rather than urethral discharge and dysuria. - It is caused by *Haemophilus ducreyi*, and ulcer formation is the primary symptom. *Non-infective urethritis* - Non-infective urethritis would present with similar symptoms but would lack the history of **recent unprotected sexual contact** with multiple partners. - This diagnosis is typically considered after excluding infectious causes, especially in sexually active individuals. [1]

Q: Which of the following is the least preferred treatment for impetigo?

Topical gentamicin. ***Topical gentamicin*** - **Gentamicin** is an **aminoglycoside** with a broad spectrum of activity, and it is usually reserved for serious infections due to its potential for **ototoxicity** and **nephrotoxicity**. - While it has antibacterial properties, it is not a first-line treatment for impetigo due to the availability of safer and equally effective topical antibiotics. *Topical mupirocin* - **Mupirocin** is a highly effective topical antibiotic for **impetigo**, particularly against **Staphylococcus aureus** and **Streptococcus pyogenes**. - It is often considered a **first-line therapy** for localized impetigo due to its low systemic absorption and favorable safety profile. *Systemic erythromycin* - **Erythromycin** is a **macrolide antibiotic** that can be used for impetigo, especially in cases of extensive involvement or when topical treatments are insufficient. - It was once a common choice, but its use has decreased due to increasing **bacterial resistance** and the emergence of other effective systemic options. *Systemic cephalosporins* - **Systemic cephalosporins**, such as **cephalexin**, are effective oral antibiotics for impetigo, particularly in cases of widespread disease or when topical therapy fails. - They are generally well-tolerated and provide good coverage against the typical causative organisms of impetigo.

Q: Dose of benzathine penicillin G to be given in patients with latent syphilis without penicillin allergy and normal CSF findings is

2.4 million units (mU) IM / week for 3 weeks. ***2.4 million units (mU) IM / week for 3 weeks*** - This is the **standard CDC-recommended regimen** for treating **latent syphilis** in patients without penicillin allergy and normal CSF findings. - The extended duration and specific dosage ensure adequate drug levels to eradicate the infection in its latent phase. *1.8 million units (mU) IM / week for 3 weeks* - This dose is **insufficient** for the treatment of latent syphilis. - Subtherapeutic dosing can lead to treatment failure and progression of the disease. *2.0 million units (mU) IM / week for 3 weeks* - While closer to the correct dose, 2.0 mU is **not the recommended standard** for latent syphilis. - Adherence to established guidelines is crucial for effective treatment of syphilis. *3.0 million units (mU) IM / week for 3 weeks* - This dosage is **higher than necessary** for latent syphilis and could potentially increase the risk of side effects, although usually not severe with single dose. - Overdosing does not offer additional therapeutic benefit for latent syphilis compared to the standard regimen.

Q: What is the most common renal manifestation associated with leprosy?

Membranous glomerulonephritis. ***Membranous glomerulonephritis*** - **Membranous glomerulonephritis** is the most frequently reported renal lesion in leprosy, often associated with a **lepromatous form** of the disease. [2] - This is due to the deposition of **immune complexes** containing *Mycobacterium leprae* antigens in the glomerular basement membrane. [2] *Acute glomerulonephritis* - While possible in some infections, **acute glomerulonephritis** is not specifically or most commonly linked to leprosy. - It’s often characterized by **abrupt onset** of hematuria, proteinuria, and renal dysfunction. [1] *Membranoproliferative glomerulonephritis* - **Membranoproliferative glomerulonephritis** is a less common renal manifestation in leprosy. - It results from immune complex deposition causing mesangial and endothelial cell proliferation, often associated with other chronic infections but less so with leprosy specifically. [3] *Mesangioproliferative glomerulonephritis* - **Mesangioproliferative glomerulonephritis** involves proliferation of mesangial cells and can be seen in various conditions. - However, it is not the dominant or most common renal finding in patients with leprosy, which primarily involves subepithelial immune complex deposition.

Q: A 5-year-old child presents with a honey-colored crusted lesion on their face. What is the most likely causative organism?

Streptococcus pyogenes. ***Streptococcus pyogenes*** - *Streptococcus pyogenes* (Group A Streptococcus) is the **most common causative organism** of **non-bullous impetigo**, which characteristically presents with **honey-colored crusted lesions**. - Non-bullous impetigo accounts for **70% of all impetigo cases** and typically affects the face, particularly around the mouth and nose. - The honey-colored crusts form when the serous exudate from ruptured vesicles dries on the skin surface. - **Important complication:** Post-streptococcal glomerulonephritis can occur 1-3 weeks after skin infection. *Staphylococcus aureus* - *S. aureus* is the primary cause of **bullous impetigo** (30% of cases), which presents with **fluid-filled bullae** rather than honey-colored crusts. - While *S. aureus* can co-infect with *S. pyogenes* in non-bullous impetigo, it is **not the primary pathogen** in the classic honey-crusted presentation described. - *S. aureus* produces exfoliative toxins that cause bullae formation in bullous impetigo. *Pseudomonas aeruginosa* - *Pseudomonas aeruginosa* is typically associated with **hot tub folliculitis**, infections in immunocompromised individuals, or puncture wounds. - Infections characteristically produce **bluish-green pus** with a fruity odor, not honey-colored crusts. - Not a typical cause of impetigo in healthy children. *Candida albicans* - *Candida albicans* causes **fungal infections** such as oral thrush, diaper dermatitis, or intertrigo in skin folds. - Presents with **erythematous patches with satellite lesions**, not honey-colored crusts. - The lesions are typically moist, macerated, and pruritic rather than crusted.

Q: Bullous impetigo is primarily caused by which of the following?

Staphylococcus aureus. ***Staphylococcus aureus*** - **Bullous impetigo** is a distinct form of impetigo characterized by **blisters or bullae**, caused by specific strains of *Staphylococcus aureus* that produce **exfoliative toxins**. - These toxins target **desmoglein 1**, an adhesion protein, leading to epidermal cleavage and the formation of superficial blisters. *Streptococcus pyogenes* - This bacterium is the primary cause of **non-bullous impetigo** (impetigo contagiosa), which presents as small vesicles that rupture and form honey-colored crusts. - While it can cause other skin infections, it does not typically produce the exfoliative toxins responsible for bullous impetigo. *Escherichia coli* - **Escherichia coli** is a common inhabitant of the **gastrointestinal tract** and a frequent cause of urinary tract infections, sepsis, and diarrheal diseases. - It is not associated with impetigo or other primary skin infections in immunocompetent individuals. *Yersinia pestis* - **Yersinia pestis** is the causative agent of **plague**, a severe infectious disease that manifests as bubonic, pneumonic, or septicemic forms. - This bacterium is transmitted by **fleas** and is not implicated in causing impetigo.

Question 1

A 25-year-old man develops hypopigmented atrophic patches with diminished sensation on his face. What is the most likely diagnosis?

Accepted Answer

Indeterminate leprosy

Answer

Pityriasis alba

Answer

Pityriasis versicolor

Answer

Borderline leprosy

Question 2

A 27-year-old man presents with a painless genital ulcer and non-tender inguinal lymphadenopathy. The VDRL test is positive. What is the next step in management?

Accepted Answer

Confirm with FTA-ABS

Answer

PCR for HSV

Answer

Empirical treatment with benzathine penicillin

Answer

Dark field microscopy for syphilis diagnosis

Question 3

A 26-year-old woman presents with a painless, indurated genital ulcer, and VDRL is positive. What is the first-line treatment?

Accepted Answer

Benzathine penicillin G

Answer

Doxycycline

Answer

Azithromycin

Answer

Ceftriaxone

Question 4

28 year old female complaints of foul smelling yellowish urethral discharge since 4 days. History of burning micturation. History of sexual contact with multiple partners 2 days before the onset of symptoms. Most likely diagnosis is ?

Accepted Answer

Gonococcal urethritis

Answer

Chlamydia

Answer

Chancroid

Answer

Non-infective urethritis

Question 5

Which of the following is the least preferred treatment for impetigo?

Accepted Answer

Topical gentamicin

Answer

Topical mupirocin

Answer

Systemic erythromycin

Answer

Systemic cephalosporins

Question 6

Dose of benzathine penicillin G to be given in patients with latent syphilis without penicillin allergy and normal CSF findings is

Accepted Answer

2.4 million units (mU) IM / week for 3 weeks

Answer

1.8 million units (mU) IM / week for 3 weeks

Answer

2.0 million units (mU) IM / week for 3 weeks

Answer

3.0 million units (mU) IM / week for 3 weeks

Question 7

What is the most common renal manifestation associated with leprosy?

Accepted Answer

Membranous glomerulonephritis

Answer

Acute glomerulonephritis

Answer

Membranoproliferative glomerulonephritis

Answer

Mesangioproliferative glomerulonephritis

Question 8

A 10-year-old boy presents with an ulcerated lesion with undermined edges over the upper chest, accompanied by a satellite lesion in the anterior axillary fold for two months. Axillary lymph nodes are palpable. Histopathology reveals a dermal abscess with ill-defined histiocytes. AFB staining of the tissue is positive. Chest X-ray shows infiltrations and cavities. Mantoux test is positive. What is the most likely diagnosis?

Accepted Answer

Scrofuloderma

Answer

Skin abscess

Answer

Furuncle

Answer

Cellulitis

Answer

Erysipelas

Question 9

A 5-year-old child presents with a honey-colored crusted lesion on their face. What is the most likely causative organism?

Accepted Answer

Streptococcus pyogenes

Answer

Staphylococcus aureus

Answer

Candida albicans

Answer

Pseudomonas aeruginosa

Question 10

Bullous impetigo is primarily caused by which of the following?

Accepted Answer

Staphylococcus aureus

Answer

Streptococcus pyogenes

Answer

Escherichia coli

Answer

Yersinia pestis

Bacterial Skin Infections — MCQs

Bacterial Skin Infections — MCQs

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