Infectious Diseases — MCQs

A 32 year old man presents with a 3-month history of weight loss, night sweats, a productive cough with blood-tinged sputum, anorexia, general malaise, and a low grade fever. A PPD skin test shows > 10 mm of induration. If the area of induration were biopsied, which of the following type of reactive cells would be found?

Q137

Stain used for direct microscopic examination of fungal culture is -

Q138

Which of the following statements about rabies is true?

Q139

Characteristic of amebiasis is:

Q140

Lepra cells are -

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 131: True statement regarding pathology of pneumocystis jiroveci pneumonia:

A. Alveoli are filled with foamy exudates (Correct Answer)
B. Interstitial pneumonitis with foamy vacuoles
C. Necrotising hemorrhage
D. Pleural effusion

Explanation: ***Alveoli are filled with foamy exudates*** - This is a hallmark pathological finding in **Pneumocystis jiroveci pneumonia (PJP)**, where the alveoli are filled with an **eosinophilic, foamy, or honeycomb-like material** composed of organisms and host proteins [1]. - This exudate is rich in **trophozoites and cysts** of *P. jiroveci*, which stain well with special stains like Gomori methenamine silver (GMS) [1]. *Interstitial pneumonitis with foamy vacuoles* - While PJP does cause **interstitial inflammation**, the characteristic "foamy vacuoles" are actually the **alveolar exudate**, not an isolated interstitial finding. - The interstitial changes typically involve **lymphoplasmacytic infiltration**, but the primary accumulation of organisms and debris is intra-alveolar. *Necrotising hemorrhage* - **Necrotizing hemorrhage** is not a typical pathological feature of PJP. - This finding is more commonly associated with severe bacterial pneumonias, fungal infections like **aspergillosis**, or vasculitic processes [1]. *Pleural effusion* - **Pleural effusion** is an infrequent finding in uncomplicated PJP, occurring in less than 5% of cases. - When present, it often suggests a co-infection or other underlying pathology, rather than being a characteristic feature of PJP itself. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Respiratory Tract Disease, pp. 318-319.

Question 132: Which of the following is true regarding globi in a patient with lepromatous leprosy?

A. Consists of lipid-laden macrophages
B. Consists of neutrophils filled with bacteria
C. Consists of macrophages filled with AFB (Correct Answer)
D. Consists of activated lymphocytes

Explanation: ***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.

Question 133: A 45-year old patient presented with fever, night sweats and weight loss. On X-ray, a mass was seen in apical lobe. On histopathology, caseous necrosis was present. What is the name of underlying process?

A. Decreased supply of growth factor
B. Acute decrease in blood supply
C. Enzymatic degeneration
D. Granulomatous inflammation (Type IV hypersensitivity) (Correct Answer)

Explanation: ***Granulomatous inflammation (Type IV hypersensitivity)*** - The presence of **caseous necrosis** on histopathology, combined with symptoms like fever, night sweats, and weight loss, and an apical lung mass, is highly characteristic of **tuberculosis** [1]. - Tuberculosis is a classic example of a **type IV hypersensitivity reaction** involving **epithelioid macrophages** (modified macrophages), **lymphocytes**, and **Langhans giant cells** forming **granulomas** with central **caseous necrosis** [2], [3]. - This represents **granulomatous inflammation**, which is the hallmark histopathological finding in tuberculosis [1]. *Decreased supply of growth factor* - This typically leads to **atrophy** or **apoptosis**, which are distinct from the inflammatory and necrotic process described. - It does not explain the characteristic histological finding of **caseous necrosis** or the systemic symptoms. *Acute decrease in blood supply* - An acute decrease in blood supply (ischemia or infarction) would lead to **coagulative necrosis** in most tissues, not the **caseous necrosis** seen in this presentation. - While infarction can cause tissue death, the specific histological and clinical picture points away from simple ischemia. *Enzymatic degeneration* - **Enzymatic degeneration**, particularly from pancreatic enzymes, is typical of **fat necrosis** (e.g., in acute pancreatitis), where fat cells are broken down. - This process does not produce the characteristic **caseous necrosis** and granulomatous inflammation seen in the patient's lung. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 383-384. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, p. 109. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, p. 360.

Question 134: Histopathological feature of HIV encephalitis is/are-

A. Microglial nodules (Correct Answer)
B. Lewy body
C. Fibrillary plaque
D. Negri body

Explanation: ***Microglial nodules*** - **Microglial nodules** are a hallmark histopathological feature of **HIV encephalitis**, representing clusters of activated microglia and macrophages in the brain parenchyma [2]. - These nodules often contain **multinucleated giant cells**, which are believed to be formed by the fusion of HIV-infected macrophages and are pathognomonic for HIV encephalitis [1]. *Lewy body* - **Lewy bodies** are abnormal aggregates of protein (primarily **alpha-synuclein**) that develop inside nerve cells, primarily associated with **Parkinson's disease** and **Lewy body dementia**. - They are not characteristic of HIV encephalitis or other viral infections of the brain. *Fibrillary plaque* - **Fibrillary plaques**, specifically **amyloid plaques**, are extracellular deposits of aggregated **beta-amyloid protein** found in the brains of individuals with **Alzheimer's disease**. - These are a key feature of neurodegenerative conditions but are not seen in HIV encephalitis. *Negri body* - **Negri bodies** are eosinophilic, sharply demarcated neuronal cytoplasmic inclusions found in the pyramidal cells of the hippocampus and Purkinje cells of the cerebellum in individuals with **rabies**. - They are specific to rabies infection and are not associated with HIV encephalitis. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Manifestations Of Central And Peripheral Nervous System Disease, pp. 711-712. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Peripheral Nerves and Skeletal Muscles, pp. 1255-1256.

Question 135: What is the infraclavicular lesion of tuberculosis known as?

A. Assman's focus
B. Ghon's focus
C. Puhl's focus
D. Simon's focus (Correct Answer)

Explanation: ***Simon's focus*** - **Simon's focus** refers to a tuberculous lesion in the **apical region** (infraclavicular area) that is typically found in adults - It is considered an initial lesion of **secondary pulmonary tuberculosis**, often arising from reactivation or endogenous reinfection - Located in the **upper lung zones**, particularly the apical and posterior segments *Assmann's focus* - **Assmann's focus** describes tuberculosis lesions that are typically found in the **apices of the upper lobes** or the superior segment of the lower lobes - These are often **early infiltrative lesions** in post-primary tuberculosis - Similar location to Simon's focus but represents a different stage of disease *Ghon's focus* - A **Ghon's focus** is a primary tuberculous lesion, usually located in the **mid-zone of the lungs**, and is typically subpleural - It is the initial lesion that develops after **primary infection** with *Mycobacterium tuberculosis* - Part of the **Ghon complex** (Ghon focus + associated lymph node involvement) *Puhl's focus* - **Puhl's focus** represents a **small, circumscribed tuberculous lesion** often found in the **lower lobes** - It is another term for a benign, usually calcified lesion in the context of tuberculosis

Question 136: A 32 year old man presents with a 3-month history of weight loss, night sweats, a productive cough with blood-tinged sputum, anorexia, general malaise, and a low grade fever. A PPD skin test shows > 10 mm of induration. If the area of induration were biopsied, which of the following type of reactive cells would be found?

A. Eosinophil
B. T lymphocyte (Correct Answer)
C. B lymphocyte
D. Mast cell

Explanation: ***T lymphocyte*** - The clinical picture (weight loss, night sweats, productive cough with blood-tinged sputum, positive PPD) is highly suggestive of **tuberculosis**, a **Type IV hypersensitivity reaction** [1], [2]. - **Type IV hypersensitivity reactions** are cell-mediated, involving the activation of **T lymphocytes**, which migrate to the site of antigen exposure (like a PPD test site or a tuberculous granuloma) and release cytokines, leading to induration and inflammation [1], [2]. *Eosinophil* - **Eosinophils** are primarily involved in allergic reactions and defense against parasitic infections [3]. - They are not the predominant reactive cells in a **Type IV hypersensitivity** response like that seen in tuberculosis [1]. *Mast cell* - **Mast cells** play a critical role in immediate hypersensitivity reactions (Type I), releasing histamine and other mediators [4]. - They are not the primary cells involved in the delayed-type hypersensitivity response elicited by tuberculin purified protein derivative (PPD) [2]. *B lymphocyte* - **B lymphocytes** are responsible for humoral immunity by producing antibodies [3]. - While they contribute to overall immune responses, they are not the main effector cells in a cell-mediated **Type IV hypersensitivity reaction** characteristic of a positive PPD test [1], [2]. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 173-174. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, p. 218. [3] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 195-196. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 208-210.

Question 137: Stain used for direct microscopic examination of fungal culture is -

A. Gomori methenamine silver (GMS)
B. Von kossa
C. PAS
D. Lactophenol cotton blue stain (Correct Answer)

Explanation: ***Lactophenol cotton blue stain*** - This is the **standard stain** for direct microscopic examination of fungal cultures and clinical specimens - The **lactophenol component** acts as a mounting fluid and killing agent, preserving fungal morphology - The **cotton blue** stains the **chitin in fungal cell walls**, making hyphae, spores, and other structures clearly visible - Widely used in **mycology laboratories** for identification of fungi based on morphological features *Gomori methenamine silver (GMS)* - GMS is a **histological stain** used to demonstrate fungi in **tissue sections**, not for direct culture examination [1] - Silver impregnation causes fungal cell walls to stain black against a green background [1] - Primarily used in **surgical pathology** for biopsy specimens [1] *Von Kossa* - This stain is used to identify **calcium salts** in tissue sections - Commonly used for visualizing bone, calcified cartilage, and pathological calcification - Not used for fungal detection *PAS (Periodic Acid-Schiff)* - PAS stains **carbohydrates and glycoproteins** and can highlight fungal elements in **tissue sections** - It is a general histological stain, not specific for direct fungal culture examination - Less specific than GMS for fungi, but useful for demonstrating fungal cell walls in tissues **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Lung, p. 717.

Question 138: Which of the following statements about rabies is true?

A. Presence of meningitis suggests against the diagnosis of rabies
B. Convulsions are generally not seen in a patient with rabies
C. Incubation period is approximately 20 to 80 days
D. Intracytoplasmic eosinophilic inclusion bodies are seen in brain cells (Correct Answer)

Explanation: ***Intracytoplasmic eosinophilic inclusion bodies are seen in brain cells*** - **Negri bodies** are pathognomonic **intracytoplasmic eosinophilic inclusion bodies** found in rabies infection [1] - They are seen in **neurons (nerve cells) of the brain**, particularly in the **hippocampus (Ammon's horn)**, **cerebellum (Purkinje cells)**, and **brainstem** [1] - Neurons are brain cells, making this statement **correct and accurate** - Negri bodies are found in approximately **50-80% of rabies cases** and are diagnostic when present *Incubation period is approximately 20 to 80 days* - The incubation period for rabies is highly variable and typically ranges from **1-3 months (30-90 days)** - The range can extend from **as short as 5 days to several years** in rare cases - The statement "20 to 80 days" is **too narrow** and doesn't capture the typical range accurately - Variability depends on bite location, viral load, and host factors *Presence of meningitis suggests against the diagnosis of rabies* - This is **incorrect** - rabies primarily causes **encephalitis**, but meningeal signs can be present - Rabies can present with **meningismus and CSF pleocytosis** - The presence of meningeal symptoms does **not rule out rabies** *Convulsions are generally not seen in a patient with rabies* - This is **false** - **seizures and convulsions are common** in rabies, especially in the **furious form** - Neurological manifestations include **muscle spasms**, **seizures**, **hydrophobia**, and **aerophobia** - The severe CNS inflammation leads to frequent convulsive episodes **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Central Nervous System, pp. 1279-1280.

Question 139: Characteristic of amebiasis is:

A. Ulcers with raised margins
B. Skip lesion
C. Flask shaped ulcer (Correct Answer)
D. Longitudinal ulcer

Explanation: ***Flask shaped ulcer*** - The "flask-shaped" ulcer is a **pathognomonic lesion** of intestinal amebiasis, caused by the ***Entamoeba histolytica*** trophozoites invading the colonic mucosa [1]. - This characteristic shape results from the **pinpoint entry** through the mucosa, followed by **lateral extension** and undermining of the submucosa [1]. *Ulcers with raised margins* - Ulcers with **raised, heaped-up margins** are more characteristic of **malignant lesions**, such as neoplastic ulcers in the gastrointestinal tract. - While some inflammatory ulcers can have raised edges, the *distinct* flask shape is specific to amebiasis. *Skip lesion* - **Skip lesions** are discontinuous areas of inflammation, with sections of normal tissue in between affected areas. - This pattern is a hallmark finding in **Crohn's disease**, a type of inflammatory bowel disease, and is not typical of amebic colitis. *Longitudinal ulcer* - **Longitudinal ulcers** (ulcers that run along the length of the bowel) are commonly seen in **inflammatory bowel diseases**, particularly **Crohn's disease**. - They are often associated with fissures and deep ulcerations along the mesenteric border, distinct from the flask shape of amebic ulcers. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Alimentary System Disease, pp. 364-365.

Question 140: Lepra cells are -

A. Neutrophils
B. Plasma cells
C. Histiocytes (Correct Answer)
D. Lymphocytes

Explanation: ***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.

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