Immunology and Allergies — MCQs
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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:
Which of the following is not found in DiGeorge's syndrome?
All are features of Wiskott-Aldrich syndrome, except which of the following?
Which of the following statements about Wiskott-Aldrich syndrome is false?
A 12-month-old infant with a history of recurrent infections, eczema, generalized edema, and easy bruising is diagnosed with an X-linked, recessive, congenital immunodeficiency, and the complete blood count shows thrombocytopenia. What is the most likely diagnosis?
The most common leukocytoclastic vasculitis affecting children is
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 3-month-old girl was referred for recurrent fever, pneumonia, diarrhea, chronic dermatitis, failure to thrive, and motor retardation. The patient was the daughter of consanguineous parents and had a female sibling who had died due to recurrent infections. She suffered from oral thrush and a diffuse brownish-colored macular rash on the trunk. Chest auscultation revealed bilateral crackles at the lower zones. Chest X-ray showed the absence of a thymus shadow, with para-cardiac infiltration and inferolateral squaring of the scapulae. Laboratory tests revealed mild anemia, profound lymphocytopenia, and hypogammaglobulinemia, with low adenosine deaminase (ADA) enzyme activities. What is the diagnosis?
A 4-year-old boy presents with a history of left ankle joint swelling and pain for four days, preceded by an upper respiratory infection. On examination, the left ankle is swollen and tender, and there is a petechial rash over the lower limbs. He is admitted two days later with bleeding per rectum. What is the most likely clinical diagnosis?
A 5-year-old child presents with perivascular IgA deposition and neutrophilic collection. There is an erythematous rash on the lower limbs and non-blanching purpura. The likely diagnosis in the child is:
Immunology and Allergies Indian Medical PG Practice Questions and MCQs
Question 131: 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 132: Which of the following is not found in DiGeorge's syndrome?
- A. Eczema (Correct Answer)
- B. Tetany
- C. T cell lymphopenia
- D. Mucocutaneous candidiasis
Explanation: ***Eczema*** - **Eczema** is NOT a recognized feature of **DiGeorge syndrome** (22q11.2 deletion syndrome). - While individuals with immunodeficiencies may experience various skin conditions, eczema is specifically associated with conditions like **Hyper-IgE syndrome, Wiskott-Aldrich syndrome**, or atopic disorders, not DiGeorge's. - DiGeorge's follows the **CATCH-22 mnemonic**: Cardiac defects, Abnormal facies, Thymic hypoplasia, Cleft palate, Hypocalcemia, 22q11 deletion. *Tetany* - **Tetany IS found** in DiGeorge's syndrome due to **hypocalcemia** from parathyroid gland hypoplasia or aplasia. - The lack of parathyroid hormone leads to **low serum calcium levels**, resulting in increased neuromuscular excitability and tetany. *T cell lymphopenia* - **T-cell lymphopenia IS found** in DiGeorge's syndrome due to **thymic hypoplasia or aplasia**. - The primary immunological defect is **T-cell deficiency**, leading to increased susceptibility to viral, fungal, and intracellular bacterial infections. - B-cell numbers are typically normal, though antibody responses may be impaired due to lack of T-cell help. *Mucocutaneous candidiasis* - **This IS found** in patients with DiGeorge's syndrome as an opportunistic infection due to **T-cell immunodeficiency**. - The impaired **cellular immunity** makes individuals highly susceptible to fungal infections like *Candida albicans* affecting mucous membranes and skin.
Question 133: All are features of Wiskott-Aldrich syndrome, except which of the following?
- A. Elevated IgE level
- B. Decreased ratio of CD4 and CD8 cells
- C. Decreased IgM level
- D. Decreased IgA level (Correct Answer)
Explanation: ***Decreased IgA level*** - Wiskott-Aldrich syndrome typically presents with **elevated IgA levels**, not decreased. - The characteristic humoral abnormalities include **low IgM** (most characteristic), **elevated IgA**, and **elevated IgE**. - IgG levels are variable (normal, elevated, or may decrease with disease progression). *Decreased IgM level* - This is the **most characteristic immunological feature** of Wiskott-Aldrich syndrome, contributing to susceptibility to encapsulated bacteria. - The defect in antibody production, particularly **IgM response to polysaccharide antigens**, is a hallmark of the disease. *Elevated IgE level* - High IgE levels are a common finding in Wiskott-Aldrich syndrome, often contributing to **eczema** and allergic manifestations. - This elevated IgE is part of the characteristic immunoglobulin pattern in WAS. *Decreased ratio of CD4 and CD8 cells* - This reflects **progressive T-cell dysfunction**, a central component of Wiskott-Aldrich syndrome. - Patients experience **gradual T-cell depletion** with decreased CD4/CD8 ratio, leading to impaired cell-mediated immunity.
Question 134: Which of the following statements about Wiskott-Aldrich syndrome is false?
- A. Autosomal Recessive disorder (Correct Answer)
- B. Impaired platelet aggregation in response to agonist
- C. Thrombocytopenia
- D. Eczematous Rash
Explanation: ***Autosomal Recessive disorder*** - **Wiskott-Aldrich Syndrome (WAS)** is an **X-linked recessive disorder**, not autosomal recessive. This statement is therefore false, making it the correct answer to the question. - It is caused by mutations in the WAS gene, which encodes the Wiskott-Aldrich syndrome protein (WASp) and is located on the X chromosome. *Eczematous Rash* - Patients with Wiskott-Aldrich syndrome frequently present with severe and persistent **eczematous rash**, which is a key component of the clinical triad. - This rash is often recalcitrant to standard treatments and can be widespread. *Impaired platelet aggregation in response to agonist* - Patients with WAS exhibit **abnormal platelet function**, specifically **impaired aggregation** in response to various agonists. - This functional defect contributes to the bleeding diathesis seen in the syndrome, alongside reduced platelet count. *Thrombocytopenia* - **Thrombocytopenia**, characterized by a low platelet count, is a hallmark feature of Wiskott-Aldrich syndrome. - The platelets are also typically very small in size (**microthrombocytopenia**), which is a distinctive finding.
Question 135: A 12-month-old infant with a history of recurrent infections, eczema, generalized edema, and easy bruising is diagnosed with an X-linked, recessive, congenital immunodeficiency, and the complete blood count shows thrombocytopenia. What is the most likely diagnosis?
- A. Isolated IgA deficiency
- B. Severe combined immunodeficiency
- C. Wiskott-Aldrich syndrome (Correct Answer)
- D. DiGeorge syndrome (22q11.2 deletion)
Explanation: ***Wiskott-Aldrich syndrome*** - Characterized by the **triad** of **eczema**, **thrombocytopenia**, and **immune deficiency**, aligning perfectly with the infant's symptoms [1]. - Patients often have a history of **easy bruising** due to low platelet count and increased susceptibility to infections [1]. *Isolated IgA deficiency* - Primarily results in **recurrent infections**, particularly **mucosal infections**, but does not manifest with **eczema** or **thrombocytopenia** [3]. - **IgA levels** are low, but other immunoglobulin levels (IgG, IgM) remain normal, unlike Wiskott-Aldrich syndrome [3]. *Severe combined immunodeficiency* - Presents with **infections** due to lack of both **T and B cell** function, but not typically associated with **eczema** or **thrombocytopenia** [4]. - Patients often have **failure to thrive** and significant **lymphopenia** on lab tests, which is not indicated here [2]. *DiGeorge syndrome* - Involves **thymic aplasia**, leading to **T-cell deficiency**, but presents with **cardiac defects** and **hypoparathyroidism**, along with infections [2]. - Typically associated with **hypocalcemia and facial dysmorphisms**, which are absent in this infant's presentation [2]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 250-251. [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. 167-168. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 249-250. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 247-248.
Question 136: The most common leukocytoclastic vasculitis affecting children is
- A. Takayasu arteritis
- B. Kawasaki disease
- C. Henoch-Schönlein purpura (Correct Answer)
- D. Polyarteritis nodosa
Explanation: ***Henoch-Schönlein purpura (HSP/IgA vasculitis)*** - This is the **most common systemic vasculitis in children**, primarily affecting small vessels, and is a classic example of **leukocytoclastic vasculitis**. - Characterized by the classic presentation of **palpable purpura** (non-thrombocytopenic), *arthralgia/arthritis*, *abdominal pain*, and *renal involvement* (hematuria/proteinuria). - IgA deposition in vessel walls is the hallmark pathological finding. *Takayasu arteritis* - This is a *large-vessel vasculitis* predominantly affecting the **aorta and its major branches**, leading to stenoses, occlusions, and aneurysms. - It primarily affects *young women* and is not characterized by leukocytoclastic vasculitis. *Kawasaki disease* - This is a *medium-vessel vasculitis* that primarily affects *infants and young children*, with a risk of **coronary artery aneurysms**. - While it causes vasculitis, it is not typically classified as a leukocytoclastic vasculitis and has distinct clinical features like fever, conjunctivitis, and rash. *Polyarteritis nodosa* - This is a *medium-sized vessel necrotizing vasculitis* that can affect multiple organ systems, but it is *rare in children* and more common in adults. - It is not considered the most common leukocytoclastic vasculitis in children and presents with different clinical manifestations, often involving the *kidneys*, *gut*, and *nerves*.
Question 137: 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 138: A 3-month-old girl was referred for recurrent fever, pneumonia, diarrhea, chronic dermatitis, failure to thrive, and motor retardation. The patient was the daughter of consanguineous parents and had a female sibling who had died due to recurrent infections. She suffered from oral thrush and a diffuse brownish-colored macular rash on the trunk. Chest auscultation revealed bilateral crackles at the lower zones. Chest X-ray showed the absence of a thymus shadow, with para-cardiac infiltration and inferolateral squaring of the scapulae. Laboratory tests revealed mild anemia, profound lymphocytopenia, and hypogammaglobulinemia, with low adenosine deaminase (ADA) enzyme activities. What is the diagnosis?
- A. Gout
- B. Dwarfism
- C. Intellectual disability
- D. Immunodeficiency (Correct Answer)
Explanation: ***Immunodeficiency*** - The constellation of **recurrent severe infections** (fever, pneumonia, diarrhea, oral thrush), **failure to thrive**, **chronic dermatitis**, profound **lymphocytopenia**, **hypogammaglobulinemia**, and **absent thymus shadow** on chest X-ray are classic signs of **Severe Combined Immunodeficiency (SCID)**. The low **adenosine deaminase (ADA)** activity specifically points to **ADA-SCID**. - The family history of a **sibling dying from recurrent infections** and **consanguineous parents** suggests an **autosomal recessive** inheritance pattern, further supporting a genetic immunodeficiency like ADA-SCID. *Gout* - **Gout** is a form of inflammatory arthritis caused by **urate crystals** in joints, primarily affecting adults. - The symptoms described—recurrent infections, absent thymus, lymphocytopenia—are not characteristic of gout. *Dwarfism* - **Dwarfism** refers to short stature due to genetic or hormonal conditions. - While chronic illness can impact growth, the primary presentation is severe immune dysfunction, making isolated dwarfism an insufficient diagnosis. *Intellectual disability* - **Intellectual disability** involves impaired cognitive and adaptive functioning. - Although some genetic syndromes causing immunodeficiency can affect neurodevelopment, the core life-threatening issue is profound immune system failure leading to severe infections.
Question 139: A 4-year-old boy presents with a history of left ankle joint swelling and pain for four days, preceded by an upper respiratory infection. On examination, the left ankle is swollen and tender, and there is a petechial rash over the lower limbs. He is admitted two days later with bleeding per rectum. What is the most likely clinical diagnosis?
- A. Acute rheumatic fever
- B. Henoch-Schönlein purpura (Correct Answer)
- C. Juvenile rheumatoid arthritis
- D. Pyogenic arthritis
Explanation: ***Henoch-Schönlein purpura (IgA vasculitis)*** - This diagnosis aligns with the **classic triad of symptoms in a child**: joint pain and swelling (arthritis), palpable **petechial rash on lower limbs**, and **gastrointestinal bleeding** (bleeding per rectum), often preceded by an upper respiratory infection. - The condition is a **leukocytoclastic vasculitis** affecting small blood vessels, leading to the observed multisystem involvement. *Acute rheumatic fever* - While it can present with **migratory polyarthritis** following a streptococcal infection, it typically does not cause a petechial rash or gastrointestinal bleeding. - Other major criteria like **carditis** or **chorea** would be expected in acute rheumatic fever. *Juvenile rheumatoid arthritis* - This condition primarily presents with **chronic arthritis** lasting longer than six weeks, and is not typically associated with an acute petechial rash or gastrointestinal bleeding. - Systemic forms can cause fever and rash, but the rash is usually evanescent and salmon-colored, not petechial. *Pyogenic arthritis* - This is a **bacterial joint infection** causing severe pain, swelling, and warmth in a single joint, often accompanied by fever and elevated inflammatory markers. - It would not typically present with a widespread petechial rash or gastrointestinal bleeding.
Question 140: A 5-year-old child presents with perivascular IgA deposition and neutrophilic collection. There is an erythematous rash on the lower limbs and non-blanching purpura. The likely diagnosis in the child is:
- A. Henoch - schonlein purpura (Correct Answer)
- B. Wegener's granulomatosis
- C. Giant cell vasculitis
- D. Kawasaki disease
Explanation: ***Henoch - schonlein purpura*** - Characterized by **perivascular IgA deposition** and **neutrophilic infiltrates** [1], leading to purpura, especially in children. - Presents with **non-blanching purpura** on lower extremities, often accompanied by abdominal pain and arthralgia. *Wegner's granulomatosis* - Typically affects **adults** and is associated with **granulomatous inflammation** and respiratory symptoms, not common in young children. - Involves the **upper and lower respiratory tracts**, along with renal manifestations, differing significantly from this presentation. *Kawasaki disease* - Primarily presents with **fever**, **rash**, and lymphadenopathy; coronary artery involvement is a key concern. - The rash in Kawasaki typically does **not present** as purpura and is not associated with prominent IgA deposition. *Giant cell vasculitis* - Generally affects older adults and presents with **temporal headaches**, vision changes, and scalp tenderness. - **Purpura** and IgA deposition are not features of this condition, making it inappropriate for this child's symptoms. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Cardiovascular Disease, pp. 278-279.
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Development of Immune System
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Primary Immunodeficiency Disorders
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Secondary Immunodeficiency Disorders
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Anaphylaxis
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