Infectious Disease Pathology in Immunocompromised Hosts — MCQs
A patient with AIDS presents with meningitis. India ink staining shows encapsulated yeasts. Which organism is most likely?
Given the immunologic abnormalities of normal serum IgG, normal serum IgA, normal serum IgM, decreased T-cell function, and decreased parathyroid function, which clinical presentation is most likely?
A person with AIDS related complex is most likely suffering from:
Which of the following is NOT seen in an HIV patient with a CD4 count less than 100 per microliter, who has a non-productive cough?
Which of the following conditions is least commonly associated with Pneumocystis carinii in AIDS?
In HIV patients, Kaposi's sarcoma is most likely caused by which of the following?
Which infection is not common in HIV patients?
What is a limitation of the case fatality rate?
Which of the following can be prevented by transfusing irradiated RBCs?
The following pathological features are associated with Plasmodium falciparum except-
Infectious Disease Pathology in Immunocompromised Hosts Indian Medical PG Practice Questions and MCQs
Question 1: A patient with AIDS presents with meningitis. India ink staining shows encapsulated yeasts. Which organism is most likely?
- A. Candida albicans
- B. Cryptococcus neoformans (Correct Answer)
- C. Histoplasma capsulatum
- D. Coccidioides immitis
Explanation: ***Cryptococcus neoformans*** - This fungus is a common cause of **meningitis in AIDS patients** and characteristically appears as **encapsulated yeasts** on India ink staining of CSF. - The capsule excludes the ink, creating a distinct **halo** around the yeast cell, which is diagnostic. *Candida albicans* - While *Candida* can cause systemic infections, including meningitis, it typically presents as **pseudohyphae** or budding yeast without an obvious capsule on India ink stain. - *Candida meningitis* is less common in AIDS patients compared to *Cryptococcus*. *Histoplasma capsulatum* - This is a dimorphic fungus that causes **histoplasmosis**, often disseminated in AIDS patients, but typically manifests as **pulmonary disease** or hepatosplenomegaly. - It appears as small, **intracellular yeasts** within macrophages and would not show an encapsulated form on India ink stain in CSF. *Coccidioides immitis* - This dimorphic fungus causes **coccidioidomycosis**, which can lead to meningitis, particularly in immunocompromised individuals. - In CSF, it is seen as **spherules containing endospores**, not encapsulated yeasts, which is a distinct morphological feature.
Question 2: Given the immunologic abnormalities of normal serum IgG, normal serum IgA, normal serum IgM, decreased T-cell function, and decreased parathyroid function, which clinical presentation is most likely?
- A. A 1-year-old boy with severe eczema, recurrent middle-ear infections, lymphopenia, and thrombocytopenia
- B. A 9-year-old boy with an eczema-like rash and recurrent severe staphylococcal infections
- C. A 5-year-old boy who, after 3 months of age, developed recurrent otitis media, pneumonia, diarrhea, and sinusitis, often with simultaneous infections at two or more disparate sites
- D. A distinctive-appearing 8-month-old boy with an interrupted aortic arch, hypocalcemia, and cleft palate (Correct Answer)
Explanation: ***A distinctive-appearing 8-month-old boy with an interrupted aortic arch, hypocalcemia, and cleft palate*** - This presentation is highly suggestive of **DiGeorge syndrome**, characterized by **thymic hypoplasia** (leading to decreased T-cell function) and **parathyroid hypoplasia** (causing hypocalcemia). - **Cardiac defects** (like an interrupted aortic arch) and **facial anomalies** (including cleft palate) are also classic features of this disorder, which involves a deletion on chromosome 22q11.2. *A 1-year-old boy with severe eczema, recurrent middle-ear infections, lymphopenia, and thrombocytopenia* - This clinical picture describes **Wiskott-Aldrich syndrome**, an X-linked disorder characterized by the triad of eczema, thrombocytopenia (with small platelets), and immunodeficiency leading to recurrent infections. - While it involves immunodeficiency and lymphopenia, it does not typically present with decreased parathyroid function. *A 9-year-old boy with an eczema-like rash and recurrent severe staphylococcal infections* - This presentation is characteristic of **hyper-IgE syndrome** (Job's syndrome), an immunodeficiency characterized by extremely elevated IgE levels, recurrent staphylococcal skin infections, and eczema. - The immunologic abnormalities described in the stem (normal Ig levels, decreased T-cell function, decreased parathyroid function) do not match the key features of hyper-IgE syndrome. *A 5-year-old boy who, after 3 months of age, developed recurrent otitis media, pneumonia, diarrhea, and sinusitis, often with simultaneous infections at two or more disparate sites* - This description is consistent with **X-linked agammaglobulinemia (XLA)**, where B-cell maturation is blocked, leading to a profound deficiency of all immunoglobulin classes. - The stem mentions normal serum IgG, IgA, and IgM, which rules out XLA.
Question 3: A person with AIDS related complex is most likely suffering from:
- A. Opportunistic infection (Correct Answer)
- B. Generalized lymphadenopathy
- C. Cancer related to AIDS
- D. Herpes zoster
Explanation: ***Opportunistic infection*** - AIDS-related complex (ARC) describes symptoms experienced by individuals with **HIV infection** before the full onset of AIDS, often including systemic symptoms and increased susceptibility to infections. - The immunocompromised state in ARC makes patients highly vulnerable to **opportunistic infections**, which are common presentations during this phase [1]. *Generalized lymphadenopathy* - While **generalized lymphadenopathy** is a common feature of HIV infection and can be part of ARC, it is a symptom or sign, not the primary "suffering" that defines much of the morbidity [1]. - **Persistent generalized lymphadenopathy (PGL)** is characterized by enlarged lymph nodes in two or more extrainguinal sites for over three months, often seen in early HIV infection, but it *doesn't fully encompass* "suffering" as broadly as opportunistic infections do [1]. *Cancer related to AIDS* - **AIDS-defining cancers** (e.g., Kaposi's sarcoma, non-Hodgkin lymphoma) are more characteristic of full-blown AIDS, when the immune system is severely compromised (CD4 count typically < 200 cells/µL). - While the risk of certain cancers increases with HIV, and some may occur in ARC, **opportunistic infections** are a more ubiquitous and defining feature of the "suffering" associated with the ARC stage [1]. *Herpes zoster* - **Herpes zoster**, or shingles, results from reactivation of the varicella-zoster virus and is more prevalent and often more severe in HIV-positive individuals, including those with ARC [1]. - However, it represents *one specific type* of opportunistic infection or condition, and the question asks what the person is "most likely suffering from" in a general sense within ARC, for which opportunistic infections are the overarching category.
Question 4: Which of the following is NOT seen in an HIV patient with a CD4 count less than 100 per microliter, who has a non-productive cough?
- A. Mycoplasma pneumoniae (Correct Answer)
- B. Pneumocystis jirovecii
- C. Cryptococcal infection
- D. Mycobacterium tuberculosis
Explanation: ***Mycoplasma pneumoniae*** - *Mycoplasma pneumoniae* is an atypical bacterium that causes **community-acquired pneumonia** in immunocompetent individuals. - While it can cause a non-productive cough, it is **not considered an opportunistic infection** in HIV patients with advanced immunosuppression (CD4 < 100), as its incidence is not significantly higher or more severe in this population compared to the general population. *Pneumocystis jirovecii* - **Pneumocystis pneumonia (PCP)** is a classic opportunistic infection in HIV patients, especially when the **CD4 count is below 200 cells/µL** [1]. - It commonly presents with a **non-productive cough**, fever, and dyspnea, and is a strong consideration in this clinical scenario [2]. *Cryptococcal infection* - **Pulmonary cryptococcosis**, caused by *Cryptococcus neoformans*, is an opportunistic infection in advanced HIV disease (CD4 < 100 cells/µL). - It often presents with **non-specific respiratory symptoms** including a non-productive cough, and can disseminate to the central nervous system. *Mycobacterium tuberculosis* - **Tuberculosis (TB)** is a common and serious opportunistic infection in HIV patients, particularly with **advanced immunosuppression** [1]. - Pulmonary TB can present with a **non-productive or productive cough**, fever, and weight loss, and is a significant cause of morbidity and mortality in this population [1].
Question 5: Which of the following conditions is least commonly associated with Pneumocystis carinii in AIDS?
- A. Meningitis
- B. Otic polypoid mass (Correct Answer)
- C. Pneumonia
- D. Ophthalmic choroid lesion
Explanation: ***Otic polypoid mass*** - While *Pneumocystis jirovecii* (formerly *carinii*) can cause **extrapulmonary disease** in immunocompromised patients, an **otic polypoid mass** is an extremely rare and atypical presentation. - Extrapulmonary manifestations usually involve organs with rich vascular supply, but ear involvement in this form is not a characteristic feature. *Pneumonia* - **Pneumocystis pneumonia (PCP)** is the **most common opportunistic infection** and AIDS-defining illness caused by *Pneumocystis jirovecii* in individuals with AIDS [1]. - It typically manifests as **fever, cough, and dyspnea** with characteristic imaging findings [1]. *Ophthalmic choroid lesion* - **Choroid lesions** due to *Pneumocystis jirovecii* are a recognized, albeit less common, **extrapulmonary manifestation** in immunocompromised patients, particularly those with AIDS. - These lesions are usually **asymptomatic** and discovered incidentally on funduscopic examination. *Meningitis* - Although *Pneumocystis jirovecii* causing **meningitis** is rare, it has been reported in severely immunocompromised individuals with AIDS, often as part of disseminated disease. - Central nervous system involvement signifies **widespread dissemination** and advanced immunosuppression.
Question 6: In HIV patients, Kaposi's sarcoma is most likely caused by which of the following?
- A. Bacteria
- B. Parasite
- C. Fungus
- D. Virus (Correct Answer)
Explanation: ***Virus*** - The image likely depicts **Kaposi's sarcoma**, a common lesion in HIV patients, which is caused by **Human Herpesvirus 8 (HHV-8)**. - Other viral infections like **Herpes Simplex Virus (HSV)** can also cause mucocutaneous lesions in immunocompromised individuals. *Bacteria* - While HIV patients are susceptible to bacterial infections (e.g., **Staphylococcus aureus** causing skin abscesses), the described lesion type is not characteristic of common bacterial skin infections. - Bacterial lesions often present as pustules, cellulitis, or ulcers with purulent discharge, which differ from typical Kaposi's sarcoma. *Parasite* - Parasitic infections can occur in HIV patients (e.g., **scabies** or **leishmaniasis**), but these typically present with different dermatological features like intensely itchy papules or nodular ulcerative lesions. - Lesions caused by parasites do not usually manifest as the violaceous, nodular, or plaque-like appearances seen in Kaposi's sarcoma. *Fungus* - Fungal infections in HIV patients can cause skin lesions (e.g., **candidiasis** with oral thrush or esophagitis, or **cryptococcosis** with molluscum-like lesions). - However, the morphology of these fungal lesions generally differs from the classic appearance of Kaposi's sarcoma or other common viral lesions in HIV.
Question 7: Which infection is not common in HIV patients?
- A. Atypical mycobacterial infection
- B. Candidiasis
- C. Cryptosporidiosis
- D. Aspergillosis (Correct Answer)
Explanation: ***Aspergillosis*** - While *Aspergillus* can cause infection in severely immunocompromised individuals, it is **less common** in HIV patients compared to other opportunistic infections listed, especially in the era of effective antiretroviral therapy (ART). - Its prevalence in HIV patients is significantly lower than in other populations, such as those with **neutropenia** or following **organ transplantation**. *Cryptosporidiosis* - This is a well-known **opportunistic infection** in HIV patients, especially those with low CD4 counts, causing **severe, chronic diarrhea** [1]. - It often leads to significant **malabsorption** and weight loss, representing a characteristic manifestation of advanced HIV disease [1]. *Atypical mycobacterial infection* - Infections by **Mycobacterium avium complex (MAC)** are very common in HIV patients with advanced immunosuppression (CD4 count <50 cells/µL) [1]. - MAC can cause **disseminated disease**, including fever, night sweats, weight loss, and anemia [1]. *Candidiasis* - **Oropharyngeal** and **esophageal candidiasis** are extremely common in HIV patients, often indicating immune suppression [1]. - While generally not life-threatening, it can be a significant cause of **discomfort** and difficulty eating for individuals with HIV [1].
Question 8: What is a limitation of the case fatality rate?
- A. Not useful in acute infectious disease
- B. Not related to virulence
- C. Time period not specified (Correct Answer)
- D. It is not related to survival rate
Explanation: ***Time period not specified*** - The **case fatality rate (CFR)** is sometimes presented without a clear time frame, making it difficult to compare across different studies or diseases. - A CFR calculated over **24 hours** is vastly different from one calculated over **30 days** or **one year**, yet both could be presented simply as "CFR" *Not useful in acute infectious disease* - The CFR is highly **useful** in acute infectious diseases, as it directly measures the **severity** and immediate impact of an outbreak. - It helps public health officials understand the **lethality** of an infectious agent and aids in resource allocation and intervention strategies. *Not related to virulence* - **Case fatality rate** is directly related to **virulence**, as it reflects the proportion of affected individuals who die from the disease. - A higher CFR indicates a more **virulent pathogen** or a more severe disease process. *It is not related to survival rate* - The **case fatality rate** is inherently linked to the **survival rate**; they are complementary measures. - If the CFR is X%, then the associated survival rate is (100 - X)%, representing the proportion of cases that do not die from the disease.
Question 9: Which of the following can be prevented by transfusing irradiated RBCs?
- A. Graft versus host disease (Correct Answer)
- B. HLA Alloimmunization
- C. Transfusion Related Acute Lung Injury (TRALI)
- D. Immunomodulation
Explanation: Graft versus host disease - **Irradiation** of red blood cell (RBC) products inactivates proliferating donor **T-lymphocytes**, which are responsible for mediating transfusion-associated **graft-versus-host disease (TA-GVHD)**. - TA-GVHD is a severe and often fatal complication where donor immune cells attack recipient tissues. *HLA Alloimmunization* - **HLA alloimmunization** is prevented by **leukoreduction**, which removes donor leukocytes expressing HLA antigens, not by irradiation. - Irradiation targets the proliferative capacity of T-lymphocytes, but does not remove the cells themselves or prevent the presentation of HLA antigens. *Transfusion Related Acute Lung Injury (TRALI)* - **TRALI** is primarily associated with **donor antibodies** (anti-HLA or anti-HNA) in plasma that react with recipient neutrophils, leading to lung injury. - It is prevented by selecting plasma donors who have not been pregnant or by using male-only plasma, not by irradiating RBCs. *Immunomodulation* - **Transfusion-related immunomodulation (TRIM)** is a broad effect associated with multiple blood components, including cytokines and biological response modifiers in the transfused products. - While leukoreduction may reduce some aspects of TRIM, irradiation is not specifically used to prevent or reduce this phenomenon.
Question 10: The following pathological features are associated with Plasmodium falciparum except-
- A. Cytoadherence
- B. Sequestration
- C. Rosetting
- D. Tissue phase (Correct Answer)
Explanation: ***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.
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