Bacterial Skin Infections Practice Questions

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: Which is the most commonly affected nerve in leprosy?

Ulnar nerve. **Explanation:** Leprosy (*Hansen’s Disease*), caused by *Mycobacterium leprae*, has a unique predilection for peripheral nerves. The bacteria thrive at temperatures slightly lower than the core body temperature (around 30-33°C). Consequently, nerves that are located superficially—where the temperature is cooler—are most frequently affected. **1. Why Ulnar Nerve is Correct:** The **ulnar nerve** is the most commonly involved nerve in leprosy worldwide. It is particularly vulnerable at the elbow, where it passes superficially through the ulnar groove (retro-epicondylar). Involvement typically leads to "claw hand" (ape-like deformity of the medial two fingers) and sensory loss over the ulnar distribution. **2. Analysis of Incorrect Options:** * **Median Nerve:** While frequently involved (leading to "ape thumb" deformity), it is generally the second most common nerve affected in the upper limb, not the first. * **Radial Nerve:** This nerve is less commonly involved than the ulnar or median nerves. When affected, it typically occurs late in the disease, resulting in wrist drop. * **Sciatic Nerve:** This is a deep-seated nerve. Because of its deep location and higher surrounding temperature, it is almost never involved in leprosy. **Clinical Pearls for NEET-PG:** * **Most common nerve in the Lower Limb:** Common Peroneal Nerve (leads to foot drop). * **Most common Cranial Nerve:** Facial Nerve (leads to lagophthalmos). * **Great Auricular Nerve:** Often cited as the most common nerve to be *visibly* enlarged or palpated in the neck. * **Nerve Abscess:** Most commonly seen in the ulnar nerve in paucibacillary cases. * **Cardinal Sign:** Thickened, tender nerves associated with sensory loss or muscle weakness is a diagnostic hallmark of leprosy.

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.

Q: The lichenoid eruption known as 'Tuberculids' is seen in which of the following skin conditions?

Lichen scrofulosorum. **Explanation:** **Lichen scrofulosorum** is the correct answer because it is a classic example of a **Tuberculid**. Tuberculids are hypersensitivity reactions in the skin to an internal focus of *Mycobacterium tuberculosis*. Unlike true cutaneous tuberculosis, tuberculids are characterized by a **negative culture** (paucibacillary) and the absence of bacilli on histopathology, but a strongly positive Mantoux test. Clinical presentation involves asymptomatic, grouped, lichenoid (follicular), skin-colored to reddish-brown papules, typically found on the trunk of children or young adults with systemic TB (often lymph node or skeletal TB). **Analysis of Incorrect Options:** * **Lupus vulgaris (A):** This is the most common form of **chronic, progressive secondary cutaneous TB** in sensitized individuals. It is characterized by "apple-jelly" nodules on diascopy, not a lichenoid tuberculid eruption. * **Scrofuloderma (B):** This is a **contiguous spread** of TB to the skin from an underlying infected structure (like a lymph node or bone). It presents with cold abscesses and sinus tracts. * **Tuberculosis Cutis Orificialis (D):** This is a rare form of TB occurring at mucosal orifices (mouth, anus) due to **autoinoculation** from advanced internal organ TB (e.g., pulmonary or intestinal TB). **High-Yield Clinical Pearls for NEET-PG:** * **Tuberculids Trio:** 1. Lichen scrofulosorum (Lichenoid), 2. Papulonecrotic tuberculid (Necrotic papules on extensors), 3. Erythema induratum of Bazin (Nodules on calves). * **Lichen scrofulosorum** is the most common tuberculid in children. * **Histology:** Shows non-caseating granulomas around hair follicles and sweat glands. * **Treatment:** It responds rapidly to standard Anti-Tubercular Therapy (ATT).

Q: Which drug is NOT used in Type 1 Lepra reaction?

Thalidomide. **Explanation:** The management of Lepra reactions is a high-yield topic in NEET-PG. To answer this correctly, one must distinguish between Type 1 and Type 2 reactions. **Why Thalidomide is the Correct Answer:** **Thalidomide** is the drug of choice for **Type 2 Lepra Reaction** (Erythema Nodosum Leprosum/ENL). It acts by inhibiting TNF-alpha. However, it has **no role in Type 1 reactions**, which are delayed-type hypersensitivity (Type IV) reactions involving a change in cell-mediated immunity. Using Thalidomide in Type 1 reactions is ineffective and clinically inappropriate. **Analysis of Incorrect Options:** * **Antileprotics (A):** In Type 1 reactions, Multi-Drug Therapy (MDT) should **never be stopped**. If the reaction occurs during treatment, MDT is continued; if it occurs after completion, it is not restarted unless a relapse is suspected. * **Analgesics (B):** These are used for symptomatic relief of nerve pain and joint aches associated with the inflammation in Type 1 reactions. * **Corticosteroids (C):** Systemic steroids (like Prednisolone) are the **mainstay of treatment** for Type 1 reactions. they are essential to prevent permanent nerve damage and manage acute neuritis. **High-Yield Clinical Pearls for NEET-PG:** * **Type 1 Reaction (Reversal Reaction):** Seen in Borderline cases (BT, BB, BL). Characterized by "upgrading" or "downgrading" of lesions (erythema, edema) and **neuritis**. * **Type 2 Reaction (ENL):** Seen in Multibacillary cases (BL, LL). Characterized by tender evanescent nodules, fever, and systemic involvement. * **Drug of Choice Summary:** * Type 1: **Corticosteroids**. * Type 2: **Thalidomide** (except in women of childbearing age due to teratogenicity/Phocomelia) or **Clofazimine**.

Question 1

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 2

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 3

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 4

Which is the most commonly affected nerve in leprosy?

Accepted Answer

Ulnar nerve

Answer

Median nerve

Answer

Radial nerve

Answer

Sciatic nerve

Question 5

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 6

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

Accepted Answer

Erysipelas

Answer

Cellulitis

Answer

Lymphangitis

Answer

Abscess

Question 7

Which of the following is true of lepromatous leprosy?

Accepted Answer

Involvement of earlobes

Answer

Bacterial index + to ++

Answer

Symmetrical involvement

Answer

Only a few bacilli are seen in the lesion

Question 8

What is the characteristic finding in a case of leprosy?

Accepted Answer

Long contact with tuberculoid leprosy can transmit the disease.

Answer

Culture test is positive in 2-3 months in LT media

Answer

Cell-mediated immunity (CMI) is seen in Lepromatous leprosy

Answer

Macule lesions heal spontaneously

Question 9

The lichenoid eruption known as 'Tuberculids' is seen in which of the following skin conditions?

Accepted Answer

Lichen scrofulosorum

Answer

Lupus vulgaris

Answer

Scrofuloderma

Answer

Tuberculosis Cutis Orificialis

Question 10

Which drug is NOT used in Type 1 Lepra reaction?

Accepted Answer

Thalidomide

Answer

Antileprotics

Answer

Analgesics

Answer

Corticosteroids

Bacterial Skin Infections — MCQs

Bacterial Skin Infections — MCQs

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