Bacterial Skin Infections Practice Questions

Q: A truck driver presents with a single painless genital ulcer that appeared 3 weeks after an unprotected sexual encounter. There is associated non-tender inguinal lymphadenopathy. What is the most likely diagnosis?

Primary syphilis. ***Primary syphilis*** - The classic presentation is a **chancre**, which is a **solitary, painless, indurated ulcer** that typically appears 2-4 weeks after infection with *Treponema pallidum*. - It is commonly associated with **rubbery, firm, non-tender inguinal lymphadenopathy** occurring shortly after the ulcer develops. *Chancroid* - Caused by *Haemophilus ducreyi*, it presents with a **painful, ragged ulcer** with a purulent base, distinguishing it from the painless chancre of syphilis. - Lymphadenopathy in chancroid is typically **painful, suppurative, and matted** (buboes), unlike the non-tender node in this patient. *Genital herpes* - Caused by HSV-1 or HSV-2, this typically presents as **grouped, painful vesicles** that progress to shallow ulcers with an erythematous base. - Patients often report significant **local pain, burning, or itching** and systemic constitutional symptoms, which are absent in this presentation. *Lymphogranuloma venereum* - Caused by *Chlamydia trachomatis* (serovars L1-L3), it typically presents as a **small, transient, painless papule** or ulcer that may go unnoticed. - The hallmark clinical feature is **painful, massive, fluctuant inguinal lymphadenopathy** (groin buboes), which is distinct from the non-tender findings described.

Q: A patient presents with multiple painful genital ulcers associated with tender cervical/inguinal lymphadenopathy. The ulcers are soft and irregular as shown in the image. What is the most likely causative organism?

Haemophilus ducreyi. ***Haemophilus ducreyi*** - This organism causes **chancroid**, which classically presents as **multiple, painful, necrotic ulcers** with irregular borders and a gray/yellowish exudate. - It is further characterized by severe, tender **inguinal lymphadenopathy** (buboes) which may rupture, helping to distinguish it from the painless ulcers of syphilis. *Chlamydia trachomatis* - Serovars L1-L3 of *C. trachomatis* cause **lymphogranuloma venereum (LGV)**, which typically presents with a small, painless primary ulcer that often goes unnoticed. - The hallmark of LGV is painful, matted, **inguinal lymphadenopathy** (the 'groove sign'), appearing weeks after the primary lesion rather than concurrent with a painful ulcer. *Klebsiella granulomatis* - This bacterium is the causative agent of **granuloma inguinale (donovanosis)**, characterized by painless, beefy-red, friable ulcerations. - It is not associated with significant **lymphadenopathy**, as it primarily manifests as a slowly progressive, chronic granulomatous disease. *Treponema pallidum* - This organism causes **syphilis**, where the primary lesion (chancre) typically presents as a single, painless, indurated ulcer with clean, raised borders. - Unlike chancroid, the clinical presentation of primary syphilis involves non-tender regional **lymphadenopathy** and lacks the soft, irregular, painful ulcer characteristics described.

Q: A female presents with greenish frothy discharge; whiff test and Amsel’s criteria are negative. What microscopy feature is expected?

Motile flagellates. ***Motile flagellates*** - The presentation of **greenish, frothy vaginal discharge** is a classic clinical feature of **trichomoniasis**, caused by the protozoan parasite *Trichomonas vaginalis*. - Microscopic examination of a **wet mount** will reveal the characteristic **motile, pear-shaped flagellated trophozoites**. *Pseudohyphae* - These are indicative of a **Candida albicans** (yeast) infection, which typically presents with **thick, white, curd-like discharge**. - While pruritus is common with candidiasis, the discharge is not classically described as greenish or frothy. *Clue cells* - These represent **bacterial vaginosis** (BV), characterized by epithelial cells coated with *Gardnerella vaginalis*. - The prompt explicitly states that **Amsel’s criteria** and the **whiff test** are negative, which effectively rules out a diagnosis of BV. *Gram-negative diplococci* - This finding is associated with **Neisseria gonorrhoeae** infection, which often presents with **purulent cervical discharge** and cervicitis. - While *N. gonorrhoeae* can cause discharge, it does not match the specific description of frothy green discharge or the expected microscopic findings of a protozoan infection.

Q: Which subtype of leprosy has the maximum number of TH1 cells?

Tuberculoid (TT). In leprosy, the clinical presentation is determined by the host's **Cell-Mediated Immunity (CMI)** against *Mycobacterium leprae*. This response is governed by the balance between **Th1** and **Th2** helper T-cells. ### Why Tuberculoid (TT) is Correct: **Tuberculoid Leprosy (TT)** represents the high-resistance end of the Ridley-Jopling spectrum. In these patients, the body mounts a vigorous **Th1-mediated immune response**. Th1 cells secrete pro-inflammatory cytokines like **IL-2 and IFN-γ**, which activate macrophages to kill the bacilli. Because the Th1 response is at its peak, the bacterial load is very low (paucibacillary), and the Mitsuda skin test is strongly positive. ### Why the Other Options are Incorrect: * **Lepromatous (LL):** This is the opposite end of the spectrum. Here, the immune response is dominated by **Th2 cells**, which secrete cytokines like **IL-4, IL-5, and IL-10**. This suppresses CMI and promotes antibody production, which is ineffective against intracellular *M. leprae*, leading to high bacterial loads (multibacillary). * **Borderline (BB) and Borderline Leprosy:** These represent the immunologically unstable middle of the spectrum. They have a mixture of Th1 and Th2 responses but never reach the maximal Th1 levels seen in polar Tuberculoid leprosy. ### High-Yield Clinical Pearls for NEET-PG: * **Th1 Response (TT):** High CMI, low bacilli, positive Lepromin test, cytokines: **IL-2, IFN-γ, IL-12**. * **Th2 Response (LL):** Low CMI, high bacilli, negative Lepromin test, cytokines: **IL-4, IL-5, IL-10**. * **Histology:** TT shows well-formed granulomas with epithelioid cells and many lymphocytes; LL shows "foamy macrophages" (Virchow cells) packed with bacilli (globi). * **Mnemonic:** **T**uberculoid = **T**h1 = **T**ight (strong) immunity.

Q: A young boy has a single scaly, hypoanaesthetic patch over the hand plus thickened ulnar nerve. What is the diagnosis?

Tuberculoid leprosy. ### Explanation The clinical presentation of a **single, well-defined, hypoanaesthetic patch** associated with a **thickened peripheral nerve** is the classic hallmark of **Tuberculoid Leprosy (TT)**. #### Why Tuberculoid Leprosy is Correct: In the Ridley-Jopling classification, Tuberculoid Leprosy represents the pole with **high cell-mediated immunity (CMI)**. The body’s strong immune response limits the disease to a few lesions (usually 1–3). * **Skin Lesion:** Typically a single, large, erythematous or hypopigmented patch with well-defined borders and a scaly surface. * **Sensory Loss:** Due to intense inflammation within the dermal nerves, anesthesia (loss of sensation) is early and profound. * **Nerve Involvement:** Asymmetric, early, and severe nerve thickening is characteristic. #### Why Other Options are Incorrect: * **Lepromatous Leprosy (LL):** Represents the low CMI pole. It presents with **multiple, symmetrical** macules, papules, or nodules. Sensory loss and nerve thickening occur very late in the disease. * **Indeterminate Leprosy:** This is the earliest stage. It usually presents as a single, vaguely defined hypopigmented macule with **no or minimal sensory loss** and no nerve thickening. * **Borderline Leprosy (BT/BB/BL):** These cases show more numerous lesions (usually 3–10) than TT. While BT (Borderline Tuberculoid) is similar to TT, the presence of a single lesion and profound anesthesia strongly points toward the polar Tuberculoid end. #### NEET-PG High-Yield Pearls: * **Cardinal Signs of Leprosy (WHO):** 1. Hypopigmented/erythematous patch with loss of sensation; 2. Thickened peripheral nerves; 3. Positive skin smear for Acid Fast Bacilli. * **Lepromin Test:** Strongly **positive** in Tuberculoid (TT) and **negative** in Lepromatous (LL). * **First Sensation Lost:** Temperature (cold followed by hot), followed by touch, pain, and deep pressure. * **Most Common Nerve Involved:** Ulnar nerve.

Q: What is most important in establishing the diagnosis of leprosy?

Slit smear for AFB. **Explanation:** The diagnosis of leprosy (Hansen’s disease) is primarily clinical, but the gold standard for **definitive confirmation** and classification is the demonstration of *Mycobacterium leprae*. **Why Slit Skin Smear (SSS) is the correct answer:** While leprosy is often diagnosed based on clinical signs, the **Slit Skin Smear for Acid-Fast Bacilli (AFB)** provides objective bacteriological evidence. It is essential for calculating the Bacteriological Index (BI) and Morphological Index (MI), which help distinguish between Paucibacillary (PB) and Multibacillary (MB) cases, thereby guiding the duration of Multi-Drug Therapy (MDT). **Analysis of Incorrect Options:** * **Evidence of neural involvement:** While thickened nerves and sensory loss are cardinal signs of leprosy, they can also occur in other neuropathies (e.g., diabetes, amyloidosis). It is a diagnostic criterion but less definitive than visualizing the bacilli. * **Hypopigmented patches:** This is a common presenting feature but is non-specific. Differential diagnoses include Pityriasis alba, Vitiligo, and Tinea versicolor. * **Positive Lepromin Test:** This is **not a diagnostic test**. It is used to measure the patient's cell-mediated immunity (CMI) against *M. leprae* to classify the type of leprosy (positive in Tuberculoid, negative in Lepromatous) and determine prognosis. **High-Yield Clinical Pearls for NEET-PG:** * **WHO Cardinal Signs:** (1) Hypopigmented/reddish patches with loss of sensation, (2) Thickened peripheral nerves, (3) Positive SSS for AFB. Presence of any **one** is diagnostic. * **Most common nerve involved:** Ulnar nerve. * **Biopsy Gold Standard:** Nerve biopsy is the most definitive for Pure Neuritic Leprosy. * **Staining:** Modified Ziehl-Neelsen stain (using 5% $H_2SO_4$ instead of 20% as *M. leprae* is less acid-fast than *M. tuberculosis*).

Q: Milian's ear sign is seen in which of the following conditions?

Erysipelas. **Explanation:** **Milian’s Ear Sign** is a classic clinical diagnostic feature used to differentiate between **Erysipelas** and **Cellulitis**. 1. **Why Erysipelas is correct:** Erysipelas is a superficial bacterial infection (most commonly caused by Group A *Streptococcus*) involving the upper dermis and superficial lymphatics. Because the pinna of the ear consists of skin tightly bound to cartilage with **no subcutaneous fat**, it can only be involved by superficial infections like erysipelas. When the ear is involved, it is called Milian’s Ear Sign. 2. **Why other options are incorrect:** * **Cellulitis:** This is a deeper infection involving the deep dermis and **subcutaneous fat**. Since the pinna lacks subcutaneous fat, cellulitis cannot involve the earlobe or pinna. This distinction is the primary utility of Milian’s sign. * **Lymphangitis:** This refers to the inflammation of lymphatic channels, typically presenting as red, tender streaks extending proximally from a site of infection. * **Abscess:** This is a localized collection of pus within the dermis or deeper tissues, characterized by fluctuance, rather than the well-demarcated, "butterfly" distribution seen in facial erysipelas. **High-Yield Clinical Pearls for NEET-PG:** * **Erysipelas:** Characterized by a "Step-ladder" rise in temperature, a "Peau d'orange" appearance, and **sharply demarcated borders**. * **Common Site:** Lower limbs are most common; the face is the second most common. * **Treatment of Choice:** Penicillin (as it is primarily Streptococcal). * **Differential Diagnosis:** In Cellulitis, the borders are **ill-defined** and not raised, as the infection is deeper.

Question 1

A truck driver presents with a single painless genital ulcer that appeared 3 weeks after an unprotected sexual encounter. There is associated non-tender inguinal lymphadenopathy. What is the most likely diagnosis?

Accepted Answer

Primary syphilis

Answer

Chancroid

Answer

Genital herpes

Answer

Lymphogranuloma venereum

Question 2

A patient presents with multiple painful genital ulcers associated with tender cervical/inguinal lymphadenopathy. The ulcers are soft and irregular as shown in the image. What is the most likely causative organism?

Accepted Answer

Haemophilus ducreyi

Answer

Chlamydia trachomatis

Answer

Klebsiella granulomatis

Answer

Treponema pallidum

Question 3

A female presents with greenish frothy discharge; whiff test and Amsel’s criteria are negative.
What microscopy feature is expected?

Accepted Answer

Motile flagellates

Answer

Pseudohyphae

Answer

Clue cells

Answer

Gram-negative diplococci

Question 4

A 38-year-old man with a known history of well-controlled plaque psoriasis on his elbows and knees presents for a routine review. He mentions his nails have become unsightly and occasionally painful. Examination of the hands is performed and the findings are shown (Image 3). Which histopathological finding in the nail unit is most directly responsible for the proximal nail plate changes visible in this image?

Accepted Answer

B. Parakeratotic foci in the nail matrix with retention of nuclei in the keratogenous zone

Answer

A. Spongiosis of the nail matrix epithelium with exocytosis of lymphocytes

Answer

C. Subungual acantholysis with suprabasal cleft formation in the hyponychium

Answer

D. Interface vacuolar degeneration at the nail matrix basement membrane

Question 5

A patient presents with multiple hypopigmented and hypesthetic patches on the lateral aspect of the forearm, with abundant acid-fast bacilli (AFB) and granulomatous inflammation on histology. What is the most likely diagnosis?

Accepted Answer

Borderline leprosy

Answer

Tuberculoid leprosy

Answer

Intermediate leprosy

Answer

Lepromatous leprosy

Question 6

What is the worldwide accepted minimum dose of penicillin for latent syphilis?

Accepted Answer

7.0 million units

Answer

4.8 million units

Answer

6.0 million units

Answer

10 units

Question 7

Which subtype of leprosy has the maximum number of TH1 cells?

Accepted Answer

Tuberculoid (TT)

Answer

Bande (BB)

Answer

Lepromatous (LL)

Answer

Borderline leprosy

Question 8

A young boy has a single scaly, hypoanaesthetic patch over the hand plus thickened ulnar nerve. What is the diagnosis?

Accepted Answer

Tuberculoid leprosy

Answer

Lepromatous leprosy

Answer

Indeterminate leprosy

Answer

Borderline leprosy

Question 9

What is most important in establishing the diagnosis of leprosy?

Accepted Answer

Slit smear for AFB

Answer

Evidence of neural involvement

Answer

Hypopigmented patches

Answer

Positive lepromin test

Question 10

Milian's ear sign is seen in which of the following conditions?

Accepted Answer

Erysipelas

Answer

Cellulitis

Answer

Lymphangitis

Answer

Abscess

Bacterial Skin Infections — MCQs

Bacterial Skin Infections — MCQs

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