Primary Immunodeficiency Disorders — MCQs
A child presents with recurrent episodes of sinopulmonary infections caused by bacteria with polysaccharide-rich capsules. Which immunoglobulin subclass deficiency is most commonly associated with these types of infections?
30-year male with recurrent sinopulmonary infections has low serum IgA. Most likely diagnosis?
Decreased T cell immunity is a feature of what?
A 6-month-old male infant presents with recurrent severe bacterial infections with encapsulated organisms (Streptococcus pneumoniae and Haemophilus influenzae). Laboratory findings reveal profound deficiency of all immunoglobulin classes (IgG, IgA, IgM) with absent mature B cells in peripheral blood. The most likely diagnosis is:
A patient with chronic granulomatous disease is most likely to have a defect in which enzyme?
A 46 year old lady on vegan diet for a decade presents with chief complaints of tingling and numbness in lower limbs for two months and a history of swaying while walking through narrow corridors. Which one of the following blood tests is advisable for diagnosis in this patient?
AIDS, secondary infection will be all except
Prophylaxis with Cotrimoxazole is recommended in the following situation except
A 3-year-old child presented with fatigue, malaise, fever, sore throat, headache, nausea, abdominal pain, and myalgia. On examination, generalized lymphadenopathy, hepatosplenomegaly, tonsillar enlargement, palatal petechiae, rashes, and edema of the eyelids were observed. Some unusual cells were seen in the peripheral blood. A specific serological test was performed. What is the receptor involved in the pathogenesis of the disease associated with these symptoms?
A 40-year old woman presented to the surgical OPD with features suggestive of colitis. She was on prolonged treatment with clindamycin. Fecal sample was positive for toxin produced by this agent. Her condition improved on treatment with metronidazole. The clinical condition is associated with -
Primary Immunodeficiency Disorders Indian Medical PG Practice Questions and MCQs
Question 1: A child presents with recurrent episodes of sinopulmonary infections caused by bacteria with polysaccharide-rich capsules. Which immunoglobulin subclass deficiency is most commonly associated with these types of infections?
- A. IgA deficiency
- B. IgG1 deficiency
- C. IgA + IgG2 deficiency
- D. IgG2 deficiency (Correct Answer)
Explanation: ***Correct: IgG2 deficiency*** - **IgG2** is the primary antibody subclass responsible for neutralizing **polysaccharide antigens** found on the capsules of bacteria like *Streptococcus pneumoniae* and *Haemophilus influenzae* - A deficiency in IgG2 leads to impaired opsonization and clearance of these encapsulated bacteria, resulting in **recurrent sinopulmonary infections** - IgG2 deficiency is the **most common selective IgG subclass deficiency** and classically presents with recurrent infections by encapsulated organisms *Incorrect: IgA deficiency* - While **IgA deficiency** is the most common primary immunodeficiency overall, it primarily affects **mucosal immunity**, leading to respiratory and gastrointestinal infections - IgA's role in clearing encapsulated bacteria is less prominent than IgG2's - Many patients with selective IgA deficiency remain asymptomatic *Incorrect: IgG1 deficiency* - **IgG1** is the most abundant IgG subclass and is crucial for responding to **protein antigens**, such as those from viruses and bacteria like diphtheria and tetanus - A deficiency in IgG1 typically causes more severe and widespread infections beyond just encapsulated bacteria - IgG1 deficiency is less common than IgG2 deficiency *Incorrect: IgA + IgG2 deficiency* - This combined deficiency would present with significant infections, including those from encapsulated bacteria, due to the IgG2 component - However, the question asks for the **most common immunoglobulin subclass deficiency** specifically associated with encapsulated bacterial infections - The single most specific answer is **IgG2 deficiency** alone
Question 2: 30-year male with recurrent sinopulmonary infections has low serum IgA. Most likely diagnosis?
- A. X-linked agammaglobulinemia
- B. Hyper IgM syndrome
- C. Selective IgA deficiency (Correct Answer)
- D. Common variable immunodeficiency
Explanation: ***Selective IgA deficiency*** - This condition is characterized by **recurrent sinopulmonary infections** and **low serum IgA levels** while other immunoglobulin levels are typically normal [1]. - Due to IgA's role in mucosal immunity, its deficiency predisposes to infections of the respiratory and gastrointestinal tracts [1]. *X-linked agammaglobulinemia* - This disorder is marked by a severe deficiency of **all immunoglobulin classes** (IgG, IgA, IgM) due to a defect in **B-cell maturation** [1]. - Patients typically present with severe recurrent bacterial infections in **early infancy**, which is earlier than the age of presentation in this case (30-year-old male) [1]. *Hyper IgM syndrome* - This condition is characterized by **normal or elevated IgM levels** but **low IgG, IgA, and IgE levels**, resulting from a defect in **class switching**. - It often involves recurrent infections, but the specific pattern of immunoglobulin levels differs significantly from the description. *Common variable immunodeficiency* - This is a heterogeneous disorder characterized by **low levels of IgG** (and often IgA and/or IgM) leading to recurrent infections [1]. - Unlike selective IgA deficiency, CVID involves a broader defect in humoral immunity, with significant reductions in **IgG** in addition to IgA [1].
Question 3: Decreased T cell immunity is a feature of what?
- A. Hyper IgM syndrome
- B. Severe congenital neutropenia
- C. Chronic granulomatous disease
- D. DiGeorge syndrome (Correct Answer)
Explanation: ***Digeorge syndrome*** - Characterized by **thymic hypoplasia**, leading to a significant reduction in **T cell production** and function. - Patients commonly present with **recurrent infections** and associated features like **hypoparathyroidism** and cardiac defects. *Hyper IgM syndrome* - Causes **defective antibody class switching**, resulting in elevated **IgM** levels and low levels of other immunoglobulins, but **T cell counts can be normal** [1]. - The main defect is in **B cell activation**, not T cell immunity, hence not relevant to decreased T cell immunity [1]. *Severe congenital neutropenia* - Primarily presents with **recurrent bacterial infections** due to low levels of **neutrophils**, rather than T cell dysfunction. - This condition does not directly affect T cell immunity but rather focuses on the **myeloid lineage's impairment** in white blood cells. *Chronic granulomatous disease* - Involves defective **respiratory burst in phagocytes**, leading to issues in engulfing certain types of bacteria, primarily affecting **neutrophil function**. - T cell immunity remains largely intact, as this disorder does not primarily involve T cell deficiency or dysfunction.
Question 4: A 6-month-old male infant presents with recurrent severe bacterial infections with encapsulated organisms (Streptococcus pneumoniae and Haemophilus influenzae). Laboratory findings reveal profound deficiency of all immunoglobulin classes (IgG, IgA, IgM) with absent mature B cells in peripheral blood. The most likely diagnosis is:
- A. X-linked agammaglobulinemia of Bruton (Correct Answer)
- B. DiGeorge's syndrome
- C. Isolated IgA deficiency
- D. Chronic granulomatous disease
Explanation: ***X-linked agammaglobulinemia of Bruton*** - Characterized by a **severe deficiency of immunoglobulins**, leading to frequent bacterial infections in infants [1][2]. - The absence of mature B cells in the peripheral blood is a hallmark [1], along with a positive family history due to its **X-linked recessive inheritance** [2]. *Chronic granulomatous disease* - Presents with recurrent **bacterial and fungal infections** due to a defect in **immune response**, but not primarily characterized by low immunoglobulin levels. - Typically involves **catalase-positive organisms**, which differs from the broad antibody deficiency seen in the correct diagnosis. *Isolated IgA deficiency* - Commonly manifests with **sinus and respiratory infections**, but patients often have normal **IgG and IgM levels**. - It does not usually cause severe or recurrent infections in infants, differentiating it from the severe immunodeficiency seen in X-linked agammaglobulinemia. *DiGeorge's syndrome* - Associated with **congenital heart defects** and **thyroid issues**, along with T-cell deficiency, but typically presents with **low T-cell counts rather than low B cells or immunoglobulins**. - The immunological profile is distinct from that of X-linked agammaglobulinemia, where B cells are severely affected [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 248-249. [2] 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. 165-166.
Question 5: A patient with chronic granulomatous disease is most likely to have a defect in which enzyme?
- A. Superoxide dismutase
- B. Catalase
- C. Myeloperoxidase
- D. NADPH oxidase (Correct Answer)
Explanation: ***NADPH oxidase*** - **Chronic granulomatous disease (CGD)** is characterized by a defect in **NADPH oxidase**, an enzyme critical for the formation of **superoxide radicals**. - Without a functional **NADPH oxidase**, phagocytes cannot mount a **respiratory burst** to kill certain bacteria and fungi, leading to recurrent infections and granuloma formation. *Superoxide dismutase* - This enzyme converts **superoxide** into **hydrogen peroxide** and oxygen, an essential step in detoxifying reactive oxygen species. - A defect here would lead to an accumulation of superoxide, but is not the primary cause of the susceptibility to specific infections seen in CGD. *Catalase* - **Catalase** breaks down **hydrogen peroxide** into water and oxygen, protecting cells from oxidative damage. - While important for reducing oxidative stress, its deficiency is not responsible for the impaired microbial killing in CGD, rather, it's involved in the *breakdown* of products generated by NADPH oxidase. *Myeloperoxidase* - **Myeloperoxidase (MPO)** combines **hydrogen peroxide** with chloride ions to produce **hypochlorous acid (bleach)**, a potent microbicidal agent. - Although crucial for killing, MPO can only function if NADPH oxidase first produces sufficient hydrogen peroxide; thus, its deficiency presents differently than CGD.
Question 6: A 46 year old lady on vegan diet for a decade presents with chief complaints of tingling and numbness in lower limbs for two months and a history of swaying while walking through narrow corridors. Which one of the following blood tests is advisable for diagnosis in this patient?
- A. Serum protein electrophoresis
- B. Vitamin 25(OH) D level
- C. Vitamin B12 levels (Correct Answer)
- D. Anti-gliadin antibodies
Explanation: ***Vitamin B12 levels*** - A **vegan diet** for an extended period puts patients at high risk for **vitamin B12 deficiency**, as B12 is primarily found in animal products [1]. - Symptoms like **tingling, numbness (paresthesias)**, and **impaired gait (ataxia)** are classic neurological manifestations of severe vitamin B12 deficiency, often due to **subacute combined degeneration** of the spinal cord [1]. *Serum protein electrophoresis* - This test is used to detect and quantify various proteins in the serum, primarily for suspected **monoclonal gammopathies** like multiple myeloma or Waldenström macroglobulinemia. - Her symptoms are primarily neurological and directly attributable to her dietary choices, making ser um protein electrophoresis less relevant as an initial diagnostic step. *Vitamin 25(OH) D level* - While vegans are at risk for **vitamin D deficiency** due to limited dietary sources and insufficient sun exposure, the primary symptoms of vitamin D deficiency are typically **bone pain, muscle weakness**, or fatigue, not the present neurological signs [2]. - Although vitamin D deficiency can cause non-specific neurological symptoms, the specific combination of paresthesia and ataxia in a long-term vegan points more strongly to B12 deficiency. *Anti-gliadin antibodies* - These antibodies are ordered to screen for **celiac disease**, an autoimmune disorder triggered by gluten consumption. - While celiac disease can present with neurological symptoms, there is no information in the patient's history to suggest a malabsorption disorder other than dietary restrictions, and her strict vegan diet directly points to a lack of B12.
Question 7: AIDS, secondary infection will be all except
- A. Candida
- B. Kaposi's sarcoma (Correct Answer)
- C. HSV
- D. Rubella
Explanation: ***Kaposi's sarcoma*** - Kaposi's sarcoma is a **cancer** caused by human herpesvirus 8 (HHV-8) [2] that is common in patients with AIDS, but it is a **malignancy**, not a secondary infection [2],[3]. - While it arises due to immune suppression, it represents abnormal cell proliferation rather than direct microbial invasion. *Candida* - **Candidiasis** (e.g., oral thrush, esophageal candidiasis) is a common opportunistic fungal infection in AIDS patients due to their **impaired cellular immunity** [1]. - It often presents as **white plaques** on mucous membranes and is a clear example of a secondary infection. *HSV* - **Herpes Simplex Virus (HSV)** infections, including oral and genital herpes, are common and often severe in AIDS patients. - Due to immunocompromise, these infections can be **more widespread**, chronic, or recur frequently, qualifying as secondary infections. *Rubella* - **Rubella (German measles)** is a viral infection that is generally mild and self-limiting in immunocompetent individuals. - It is **not considered an opportunistic infection** or a common secondary infection specifically associated with AIDS; rather, it is listed as a differential diagnosis for the primary HIV infection rash [1].
Question 8: Prophylaxis with Cotrimoxazole is recommended in the following situation except
- A. For all HIV-infected infants under 1 year of age
- B. For all symptomatic HIV-infected children over 5 years of age without considering CD4 count (Correct Answer)
- C. For all HIV-exposed infants until HIV infection is excluded
- D. As prophylaxis after treatment for Pneumocystis carinii pneumonia (PCP)
Explanation: For all symptomatic HIV-infected children over 5 years of age without considering CD4 count - Cotrimoxazole prophylaxis in symptomatic HIV-infected children over 5 years of age should be guided by CD4 count, typically indicated when CD4 < 200 cells/mm3 or CD4 percentage < 15%. [1] - Administering prophylaxis without considering the CD4 count in this age group is not the standard recommendation, as it could lead to unnecessary drug exposure and potential resistance. [1] For all HIV-infected infants under 1 year of age - All HIV-infected infants should receive Cotrimoxazole prophylaxis regardless of their CD4 count due to their high risk of Pneumocystis jirovecii pneumonia (PCP) and other bacterial infections. [2] - This recommendation is based on the significant morbidity and mortality associated with PCP in this vulnerable age group. [2] For all HIV-exposed infants until HIV infection is excluded - Cotrimoxazole prophylaxis is recommended for all HIV-exposed infants starting at 4-6 weeks of age until HIV infection is definitively excluded. [2] - This proactive measure protects infants who may be HIV-infected from opportunistic infections, particularly PCP, during the diagnostic window period. As prophylaxis after treatment for Pneumocystis carinii pneumonia (PCP) - Following successful treatment for PCP, Cotrimoxazole is highly recommended as secondary prophylaxis to prevent recurrence of the infection. [2] - This continuation of therapy is crucial because individuals who have had PCP are at very high risk for future episodes. [2]
Question 9: A 3-year-old child presented with fatigue, malaise, fever, sore throat, headache, nausea, abdominal pain, and myalgia. On examination, generalized lymphadenopathy, hepatosplenomegaly, tonsillar enlargement, palatal petechiae, rashes, and edema of the eyelids were observed. Some unusual cells were seen in the peripheral blood. A specific serological test was performed. What is the receptor involved in the pathogenesis of the disease associated with these symptoms?
- A. CD21 (Correct Answer)
- B. CD20
- C. CD19
- D. CD117
Explanation: ***CD21*** - The constellation of symptoms (fatigue, fever, sore throat, lymphadenopathy, hepatosplenomegaly, tonsillar enlargement, palatal petechiae, edema of eyelids, and atypical lymphocytes) in a child strongly suggests **infectious mononucleosis**, which is most commonly caused by the **Epstein-Barr Virus (EBV)** [1]. - EBV primarily infects **B lymphocytes** by binding to the **CD21 receptor** (also known as complement receptor type 2, CR2) on the B cell surface. *CD20* - **CD20** is another transmembrane protein found on the surface of B lymphocytes, but it is not the primary receptor used by EBV for entry. - It plays a role in B cell activation and is a target for immunotherapy in some B cell malignancies. *CD19* - **CD19** is a B-cell specific surface marker that is part of a receptor complex involved in B cell activation and growth. - While present on B cells, it is not the direct receptor that EBV uses to enter the cell. *CD117* - **CD117** (c-Kit receptor) is a receptor tyrosine kinase primarily found on hematopoietic stem cells, mast cells, and interstitial cells of Cajal. - It is not expressed on B lymphocytes and is therefore not involved in EBV infection.
Question 10: A 40-year old woman presented to the surgical OPD with features suggestive of colitis. She was on prolonged treatment with clindamycin. Fecal sample was positive for toxin produced by this agent. Her condition improved on treatment with metronidazole. The clinical condition is associated with -
- A. Listeria monocytogenes
- B. Bacillus anthracis
- C. Clostridium difficile (Correct Answer)
- D. Acinetobacter baumannii
Explanation: ***Clostridium difficile*** - The history of **clindamycin use**, followed by **colitis symptoms**, a **positive fecal toxin test**, and improvement with **metronidazole**, are classic indicators of *Clostridium difficile* infection (CDI) [1]. - *C. difficile* produces toxins (Toxin A and Toxin B) that cause **pseudomembranous colitis**, often after antibiotic disruption of normal gut flora [1]. *Listeria monocytogenes* - This bacterium is primarily a cause of **foodborne illness**, leading to febrile gastroenteritis, meningitis, or sepsis, particularly in immunocompromised individuals, pregnant women, and neonates. - It is not typically associated with **antibiotic-associated colitis** or treated with metronidazole as a primary agent for bowel infection. *Bacillus anthracis* - This is the causative agent of **anthrax**, which can manifest as cutaneous, inhalational, or gastrointestinal forms. - **Gastrointestinal anthrax** causes severe abdominal pain, vomiting, bloody diarrhea, and fever, but it is rare and not linked to antibiotic use or toxin detection in stool in the context described. *Acinetobacter baumannii* - *Acinetobacter baumannii* is an important **opportunistic pathogen** often associated with hospital-acquired infections, such as pneumonia, urinary tract infections, and bloodstream infections, particularly in critically ill patients. - It is not a known cause of **antibiotic-associated colitis** due to toxin production, nor is metronidazole the primary treatment.
Want unlimited practice?
Get full access to all questions, explanations, and performance tracking.
Start For Free