Infectious Diseases Practice Questions

Q: Which of the following is the most likely cause in a case of granuloma with positive AFB?

Tuberculosis. ***Tuberculosis*** - **Mycobacterium tuberculosis** is the classic cause of **granulomatous inflammation** with **positive AFB** staining in histopathology. - TB is the most common mycobacterial infection worldwide, and **AFB staining** is routinely positive in tissue specimens, making it the standard association for granuloma + AFB. *Leprosy* - While **Mycobacterium leprae** is acid-fast, **AFB positivity** is variable and often requires special techniques for demonstration. - Leprosy is much less common globally, and AFB demonstration in routine histopathology is less reliable compared to tuberculosis. *Syphilis* - Syphilis is caused by **Treponema pallidum**, a **spirochete** that is not acid-fast. - Although syphilis can cause granulomatous inflammation (**gummas**), **AFB staining** would be negative. *Cat scratch disease* - Cat scratch disease is caused by **Bartonella henselae**, a **Gram-negative bacterium**. - While it causes **granulomatous lymphadenitis**, **Bartonella** is not acid-fast, so **AFB** would be negative.

Q: Cellulitis is characterized as:

Nonsuppurative and invasive. ***Nonsuppurative and invasive*** - Cellulitis is considered **nonsuppurative** as it typically lacks macroscopic pus formation, distinguishing it from abscesses. - It is **invasive** because it involves the dermal and subcutaneous tissues, spreading through fascial planes. *Suppurative and invasive* - This description is more indicative of conditions like an **abscess**, which involves localized collections of pus. - While abscesses are invasive, cellulitis characteristically lacks the discrete pus collection. *Nonsuppurative and non-invasive* - Conditions that are nonsuppurative and non-invasive might include self-limiting skin rashes or superficial inflammatory processes. - Cellulitis involves deeper tissue infection, which inherently makes it invasive. *Suppurative and non-invasive* - A condition that is suppurative but non-invasive would be rare and contradictory, as pus formation often indicates a tissue response that is at least locally invasive. - Superficial pustules might be considered suppurative and relatively non-invasive, but cellulitis clearly extends beyond such superficial lesions.

Q: Which of the following infectious diseases is the most likely cause of granuloma formation?

Leprosy. ***Leprosy*** - Leprosy is a classic example of a chronic infection that leads to **granuloma formation**, particularly in its tuberculoid and borderline tuberculoid forms [1]. - The immune response to *Mycobacterium leprae* involves the formation of **macrophage-rich granulomas** to contain the infection, often affecting the skin and nerves [2]. *Syphilis* - While syphilis can cause **gummas**, which are granulomatous lesions, these are typically seen in tertiary syphilis and are less characteristic of granuloma formation across all stages compared to leprosy [3]. - Gummas are often **necrotic** and can be widespread, but the primary pathology of syphilis involves vasculitis and inflammation rather than classic granulomatous tissue reaction. *Cat scratch disease* - Caused by *Bartonella henselae*, this infection typically leads to **lymphadenopathy** with **stellate microabscesses** and sometimes epithelioid granulomas, but the granulomas are usually less prominent and distinct than those seen in leprosy. - The histological features are dominated by **suppurative necrosis** within lymphoid tissue rather than well-formed, non-caseating granulomas. *Trench fever* - Trench fever, caused by *Bartonella quintana*, primarily presents with **fever**, **bone pain**, and a **maculopapular rash**. - It does not typically cause **granuloma formation**; the pathology is more related to bacteremia and inflammation of vascular endothelium. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 385-386. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Disorders Involving Inflammatory And Haemopoietic Cells, pp. 638-639. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, p. 360.

Q: In spinal tuberculosis, the commoner route of spread is:

Blood. ***Blood*** - Spinal tuberculosis, also known as **Pott's disease**, primarily spreads via the **hematogenous route** [1] from a primary infection elsewhere, most commonly the lungs [1]. - Bacilli reach the vertebral bodies through the **arterial circulation** or via the **paravertebral (Batson's) venous plexus**, which allows retrograde spread without passing through the lungs. - The rich vascular supply of the vertebral bodies, particularly the **metaphyseal regions adjacent to intervertebral discs**, facilitates the deposition and growth of **Mycobacterium tuberculosis**. - This accounts for the typical involvement of two adjacent vertebrae with disc destruction in spinal TB [2]. *Lymphatics* - While lymphatic spread is important in other forms of tuberculosis, it is **not the primary route** for the initial seeding of the spine. - Lymphatic involvement tends to be secondary to established bony lesions or occurs in cases of extensive soft tissue involvement with paravertebral abscess formation. *Direct spread* - Direct spread is **rare** in spinal tuberculosis and typically occurs from an adjacent infected structure, such as a psoas abscess that erodes into the spine or from mediastinal lymph nodes. - It is not the most common initial mode of dissemination to the vertebrae. *All of the options* - While other routes like lymphatics and direct spread can contribute in specific circumstances, **hematogenous spread (via blood)** is overwhelmingly the most common and primary route for spinal tuberculosis. - The question asks for the "commoner route," which is definitively the bloodstream. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 379-380. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, pp. 1197-1198.

Q: The following pathological features are associated with Plasmodium falciparum except-

Tissue phase. ***Tissue phase*** (Correct Answer - NOT associated with P. falciparum) - While *Plasmodium falciparum* does have a **hepatic (liver) phase** in its life cycle, the term "**tissue phase**" specifically refers to the **persistent dormant liver stage (hypnozoites)** seen in **relapsing malarias** [1]. - **Hypnozoites** are found in *Plasmodium vivax* and *Plasmodium ovale* but **NOT in *P. falciparum***. - These dormant forms can reactivate months or years later, causing relapse—a feature absent in *P. falciparum* infection. *Cytoadherence* (Incorrect - IS associated with P. falciparum) - This is a **key virulence factor** of *P. falciparum*, where **infected red blood cells (iRBCs)** bind to the **vascular endothelium** via adhesion molecules (PfEMP1) [1]. - This binding leads to **sequestration** in deep capillaries and avoidance of splenic clearance, contributing to severe malaria pathology [1]. *Sequestration* (Incorrect - IS associated with P. falciparum) - Refers to the confinement of **iRBCs** in the **deep microvasculature** of vital organs such as the brain, lungs, and kidneys. - Results from **cytoadherence** and is the primary mechanism behind severe complications like **cerebral malaria** in *P. falciparum*. *Rosetting* (Incorrect - IS associated with P. falciparum) - Involves **iRBCs** binding to uninfected red blood cells, forming **rosette structures**. - This phenomenon impedes blood flow in capillaries and contributes to **microvascular obstruction** and tissue hypoxia in severe *P. falciparum* infections. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 398-400.

Q: Which of the following is a special stain used to diagnose fungal hyphae in tissues-

Silver methenamine. ***Silver methenamine*** - **Grocott's methenamine silver (GMS) stain** is widely used to visualize **fungal elements** in tissue sections. - It works by staining the **polysaccharides** in the fungal cell walls, making them appear **black** against a green or grayish-green background. *Masson trichome* - This stain is primarily used to differentiate **collagen fibers** from smooth muscle and other tissues. - It stains **collagen blue or green**, cytoplasm red, and nuclei black, and is not suitable for identifying fungi. *Congo Red* - **Congo Red stain** is used to identify **amyloid deposits** in tissues, which appear red-pink and show apple-green birefringence under polarized light [1]. - It does not specifically stain fungal hyphae. *Alizarin Red* - **Alizarin Red S stain** is used to demonstrate the presence of **calcium deposits** in tissues. - It stains calcium salts **orange-red** or scarlet, and is not utilized for fungal identification. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 268-269.

Q: Which of the following is true regarding globi in a patient with lepromatous leprosy?

Consists of macrophages filled with AFB. ***Consists of macrophages filled with AFB*** - **Globi** are characteristic microscopic structures found in lepromatous leprosy, representing large aggregates of **Mycobacterium leprae** within **macrophages** [1]. - These macrophages are heavily parasitized with **acid-fast bacilli (AFB)**, which are the bacteria causing leprosy [1]. *Consists of lipid-laden macrophages* - While macrophages in leprosy can contain lipids, **globi** specifically refer to the aggregation of these macrophages *filled primarily with bacteria*, not just lipid droplets [1]. - The lipid content is secondary to the bacterial accumulation and degradation, not the defining characteristic of a globus. *Consists of neutrophils filled with bacteria* - **Neutrophils** are the primary phagocytes in acute bacterial infections, but they are generally less involved in chronic granulomatous diseases like leprosy compared to macrophages [2]. - **Globi** are fundamentally macrophage-derived structures, not neutrophil-derived. *Consists of activated lymphocytes* - **Lymphocytes** are crucial for the immune response in leprosy, particularly in the tuberculoid form, but they do not form globi [1]. - **Globi** represent bacterial burden within host cells, which are typically macrophages, not aggregates of lymphocytes [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 385-386. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, p. 360.

Q: Lepra cells are -

Histiocytes. ***Histiocytes*** - **Histiocytes** (a type of **macrophage**) are the primary cells infected by *Mycobacterium leprae* [1]. - Within these cells, the bacteria can multiply and form large aggregates, leading to the characteristic foamy appearance of **"lepra cells"** when viewed microscopically [1]. *Neutrophils* - **Neutrophils** are primarily involved in the acute inflammatory response and phagocytosis of bacteria, but they are not the main host cell for *Mycobacterium leprae*. - They are typically associated with pyogenic infections rather than chronic granulomatous diseases like leprosy. *Plasma cells* - **Plasma cells** are differentiated B lymphocytes responsible for producing antibodies. - While they play a role in the immune response to various infections, they are not directly infected by *Mycobacterium leprae* or involved in the formation of lepra cells. *Lymphocytes* - **Lymphocytes** (T and B cells) are crucial for adaptive immunity and the cell-mediated immune response in leprosy. - However, they are not the cells that directly harbor and are transformed into "lepra cells" by the *Mycobacterium leprae* bacteria. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 385-386.

Q: "Medlar bodies" are seen in

Chromblastomycosis. ***Chromblastomycosis*** - "**Medlar bodies**" (also known as muriform cells or sclerotic bodies) are characteristic findings in the tissue biopsy of patients with **chromoblastomycosis**. - These are thick-walled, septate, dark brown fungal cells that reproduce by septation and are crucial for the diagnosis of this chronic fungal infection. *Coccidiomycosis* - This deep fungal infection is characterized by thick-walled **spherules containing endospores** in tissue, rather than Medlar bodies [1]. - It primarily affects the lungs but can disseminate to other organs. *Sporotrichosis* - The classic histological finding in sporotrichosis is the presence of **cigar-shaped budding yeasts** in tissue, especially in the suppurative granulomas. - **Asteroid bodies**, which are yeasts surrounded by eosinophilic material, may also be seen. *Histoplasmosis* - This fungal infection is identified by small, **intracellular budding yeasts** (2-4 µm) found within macrophages in tissue samples [1]. - It commonly affects the lungs and can disseminate, particularly in immunocompromised individuals [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Lung, p. 717.

Question 1

Which of the following is the most likely cause in a case of granuloma with positive AFB?

Accepted Answer

Tuberculosis

Answer

Syphilis

Answer

Cat scratch disease

Answer

Leprosy

Question 2

Cellulitis is characterized as:

Accepted Answer

Nonsuppurative and invasive

Answer

Suppurative and invasive

Answer

Nonsuppurative and non-invasive

Answer

Suppurative and non-invasive

Question 3

Which of the following infectious diseases is the most likely cause of granuloma formation?

Accepted Answer

Leprosy

Answer

Syphilis

Answer

Cat scratch disease

Answer

Trench fever

Question 4

Earliest feature of TB:

Accepted Answer

Lymphocytosis

Answer

Caseation

Answer

Granuloma

Answer

Langerhans' Giant cells

Question 5

In spinal tuberculosis, the commoner route of spread is:

Accepted Answer

Blood

Answer

Lymphatics

Answer

All of the options

Answer

Direct spread

Question 6

The following pathological features are associated with Plasmodium falciparum except-

Accepted Answer

Tissue phase

Answer

Cytoadherence

Answer

Sequestration

Answer

Rosetting

Question 7

Which of the following is a special stain used to diagnose fungal hyphae in tissues-

Accepted Answer

Silver methenamine

Answer

Masson trichrome

Answer

Congo Red

Answer

Alizarin Red

Question 8

Which of the following is true regarding globi in a patient with lepromatous leprosy?

Accepted Answer

Consists of macrophages filled with AFB

Answer

Consists of lipid-laden macrophages

Answer

Consists of neutrophils filled with bacteria

Answer

Consists of activated lymphocytes

Question 9

Lepra cells are -

Accepted Answer

Histiocytes

Answer

Neutrophils

Answer

Plasma cells

Answer

Lymphocytes

Question 10

"Medlar bodies" are seen in

Accepted Answer

Chromblastomycosis

Answer

Coccidiomycosis

Answer

Sporotrichosis

Answer

Histoplasmosis

Infectious Diseases — MCQs

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