Immunology and Allergies Practice Questions

Q: A child admitted with meningitis is found to have gram-negative diplococci on examination. The child has a history of similar infections with the same organism. Which of the following should be suspected?

Complement deficiency. **Explanation:** The clinical presentation of recurrent meningitis caused by **Gram-negative diplococci** (*Neisseria meningitidis*) is a classic hallmark of **Terminal Complement Deficiency (C5–C9)**. **1. Why Complement Deficiency is Correct:** The complement system is vital for the clearance of encapsulated bacteria. Specifically, the **Membrane Attack Complex (MAC)**, formed by components **C5b through C9**, is essential for the lysis of *Neisseria* species. Patients with deficiencies in these terminal components (or the alternative pathway components like Properdin) have a significantly increased risk (up to 10,000-fold) of systemic neisserial infections. A history of recurrent episodes with the same organism strongly points toward a defect in this specific lytic pathway. **2. Why Other Options are Incorrect:** * **B and D (Immunoglobulin/B-cell Deficiency):** While these lead to recurrent infections with encapsulated bacteria (e.g., *S. pneumoniae, H. influenzae*), they typically present with sinopulmonary infections (pneumonia, otitis media) and involve a broader range of pathogens rather than isolated, recurrent *Neisseria*. * **C (T-cell Deficiency):** These deficiencies typically present early in infancy with opportunistic infections (fungal like *Candida*, viral, or *Pneumocystis jirovecii*), rather than recurrent pyogenic bacterial meningitis. **Clinical Pearls for NEET-PG:** * **C1, C2, C4 deficiency:** Strongly associated with **SLE** and other autoimmune diseases (due to failure of immune complex clearance). * **C3 deficiency:** The most severe; leads to recurrent infections with all pyogenic bacteria. * **C1 Esterase Inhibitor deficiency:** Causes **Hereditary Angioedema** (characterized by low C4 levels). * **CH50 Assay:** The best initial screening test for suspected complement deficiency.

Q: Most common rheumatic disease in children is:

Juvenile idiopathic arthritis. ### Explanation **Correct Answer: A. Juvenile Idiopathic Arthritis (JIA)** **Why it is correct:** Juvenile Idiopathic Arthritis (JIA) is the **most common chronic rheumatic disease of childhood**, with an estimated prevalence of approximately 1 in 1,000 children. It is defined as arthritis of unknown etiology beginning before the age of 16 years and persisting for at least 6 weeks. It encompasses a heterogeneous group of disorders characterized by chronic synovial inflammation. **Why the other options are incorrect:** * **B. Juvenile Ankylosing Spondylitis:** This is a subtype of Enthesitis-Related Arthritis (ERA). While significant, it is far less common than the overall incidence of JIA. * **C. Systemic Lupus Erythematosus (SLE):** Childhood-onset SLE is a serious multi-system autoimmune disease, but its prevalence is significantly lower (approx. 10–20 per 100,000 children) compared to JIA. * **D. Morphea:** Also known as localized scleroderma, this is the most common form of scleroderma in children. However, it is a localized skin disease and is much rarer than JIA. **High-Yield Clinical Pearls for NEET-PG:** * **Subtypes:** The most common subtype of JIA is **Oligoarticular JIA** (affects ≤4 joints in the first 6 months). * **Uveitis:** Chronic asymptomatic **anterior uveitis** is a major complication, especially in girls with oligoarticular JIA who are **ANA positive**. Regular slit-lamp exams are mandatory. * **Systemic JIA (Still’s Disease):** Characterized by daily "quotidian" spiking fevers, evanescent (salmon-pink) rashes, and hepatosplenomegaly. It is often associated with Macrophage Activation Syndrome (MAS). * **First-line Treatment:** NSAIDs are used for symptom control, but **Methotrexate** is the most common disease-modifying antirheumatic drug (DMARD) used.

Q: An 11-year-old boy presents with multiple abscesses on his face, chest, and back, along with a history of recurrent respiratory infections. Physical examination reveals atopic excoriating skin and multiple cold abscesses on his back. What is the most probable diagnosis?

Hyper IgE syndrome. ### **Explanation** The clinical presentation of recurrent skin and respiratory infections, atopic dermatitis, and the hallmark **"cold abscesses"** (abscesses lacking typical signs of inflammation like warmth or redness) is diagnostic of **Hyper IgE Syndrome (Job Syndrome)**. **1. Why Hyper IgE Syndrome is Correct:** This is a primary immunodeficiency, most commonly caused by a **STAT3 mutation** (Autosomal Dominant). This mutation leads to a failure of Th17 cell differentiation. Since Th17 cells are crucial for recruiting neutrophils to sites of infection, their absence results in a lack of inflammatory response, leading to "cold" staphylococcal abscesses. Laboratory findings typically show **markedly elevated IgE levels** (>2000 IU/mL) and eosinophilia. **2. Why Incorrect Options are Wrong:** * **Hyper IgM Syndrome:** Characterized by a defect in CD40L, leading to an inability to class-switch from IgM. Patients present with recurrent sinopulmonary infections and opportunistic infections (e.g., *Pneumocystis jirovecii*), but not cold abscesses or extreme IgE elevation. * **Carcinoid Syndrome:** A paraneoplastic syndrome (usually from neuroendocrine tumors) presenting with flushing, diarrhea, and wheezing due to serotonin excess. It has no primary immunological basis. * **Wiskott-Aldrich Syndrome:** Defined by the triad of **T**hrombocytopenia (small platelets/bleeding), **E**czema, and **R**ecurrent infections (**mnemonic: WATER**). While it involves eczema, the presence of cold abscesses specifically points toward Hyper IgE. **3. NEET-PG High-Yield Pearls (FATED Mnemonic):** To remember the features of Job Syndrome, use **FATED**: * **F**acies (coarse facial features: prominent forehead, deep-set eyes). * **A**bscesses (Cold Staphylococcal abscesses). * **T**eeth (retention of primary/deciduous teeth). * **E**levated IgE. * **D**ermatological problems (Eczema). * *Bonus:* Fractures from minor trauma are also common.

Q: A 3-year-old male presents with a skin rash and epistaxis. He has experienced several severe sinopulmonary infections. A careful history reveals that his maternal uncle died of bleeding complications following an emergency cholecystectomy. What additional findings are likely in this case?

Low platelet count and low serum IgM levels. The clinical presentation of **recurrent sinopulmonary infections, skin rash (eczema), and bleeding (epistaxis)** in a young male, combined with an X-linked family history (maternal uncle), is classic for **Wiskott-Aldrich Syndrome (WAS)**. ### **1. Why Option D is Correct** WAS is caused by a mutation in the *WASP* gene, which leads to defects in the actin cytoskeleton of hematopoietic cells. The hallmark triad is **Immunodeficiency, Eczema, and Thrombocytopenia**. * **Microthrombocytopenia:** Patients have a low platelet count with characteristically **small platelets** (low Mean Platelet Volume). * **Immunoglobulins:** The typical pattern is **low IgM**, normal to high IgG, and **elevated IgA and IgE**. Low IgM levels contribute to the susceptibility to encapsulated organisms (e.g., *S. pneumoniae*). ### **2. Why Other Options are Incorrect** * **Option A:** A CD4/CD8 ratio < 1.5:1 is non-specific and often seen in viral infections or HIV. While T-cell function declines over time in WAS, it is not the diagnostic hallmark. * **Option B:** Cerebellar ataxia is the hallmark of **Ataxia-Telangiectasia**, which also presents with immunodeficiency but features telangiectasias and sensitivity to ionizing radiation, not microthrombocytopenia. * **Option C:** WAS is characterized by **thrombocytopenia** (low count), not thrombocytosis. Furthermore, IgM is typically low, not high. ### **3. NEET-PG High-Yield Pearls** * **Mnemonic (WATER):** **W**iskott-**A**ldrich, **T**hrombocytopenia, **E**czema, **R**ecurrent infections. * **Inheritance:** X-linked Recessive (affects males). * **Platelet Morphology:** It is the **only** condition where small platelets (low MPV) are a primary diagnostic feature. * **Complications:** Increased risk of **autoimmune hemolytic anemia** and **B-cell lymphomas**. * **Definitive Treatment:** Hematopoietic stem cell transplant.

Q: A 4-year-old child presented with palpable purpura and polyarthralgia without frank arthritis, along with colicky abdominal pain associated with nausea, vomiting, diarrhea, and the passage of blood and mucus per rectum. Urine examination revealed proteinuria and microscopic hematuria. Laboratory studies revealed mild leukocytosis, normal platelet count, normal PT and aPTT, eosinophilia, normal serum complement components, and elevated IgA levels. Skin biopsy specimen was taken. What is the most likely diagnosis?

Henoch-Schonlein purpura (HSP). ### Explanation **Henoch-Schönlein Purpura (HSP)**, also known as IgA Vasculitis, is the most common systemic vasculitis in children. It is a small-vessel vasculitis characterized by the deposition of **IgA-dominant immune complexes**. **Why Option C is Correct:** The diagnosis is based on the classic clinical tetrad presented in the question: 1. **Palpable Purpura:** Non-thrombocytopenic (normal platelet count) lesions, typically on the lower extremities/buttocks. 2. **Arthralgia:** Migratory pain without permanent joint deformity. 3. **Abdominal Pain:** Colicky pain due to bowel wall edema/hemorrhage (can lead to intussusception). 4. **Renal Involvement:** Proteinuria and hematuria (IgA nephropathy). The laboratory findings of **elevated IgA levels** and **normal platelet/coagulation profiles** (PT/aPTT) are pathognomonic for HSP in this clinical context. **Why Other Options are Incorrect:** * **A. Clotting disorder:** Ruled out by the normal PT, aPTT, and platelet count. * **B. Septic emboli:** Usually associated with high-grade fever, splinter hemorrhages, and positive blood cultures; the specific IgA elevation and renal involvement point toward vasculitis. * **C. Urticarial vasculitis:** Presents primarily with wheals lasting >24 hours and often involves low complement levels (hypocomplementemia), unlike the normal complement levels seen here. **High-Yield Clinical Pearls for NEET-PG:** * **Pathology:** Leukocytoclastic vasculitis with IgA and C3 deposition on immunofluorescence. * **Trigger:** Often follows an Upper Respiratory Tract Infection (URTI). * **Complication:** Intussusception (usually ileo-ileal) is the most common GI complication. * **Prognosis:** Generally excellent, but long-term morbidity depends on the severity of renal involvement.

Question 1

What are the diagnostic criteria for Juvenile Rheumatoid Arthritis (JRA)?

Accepted Answer

Disease persisting for 6 weeks or longer

Answer

Onset before 16 years of age

Answer

Arthritis involving more than 5 joints

Answer

Polyarticular JRA Anti-nuclear antibody (ANA) is positive

Question 2

A 3-year-old male child presents with recurrent infections despite proper treatment and hygiene. The child has had multiple infections with S. aureus, Pseudomonas, and E. coli. Which of the following tests would be most useful to diagnose the child's condition?

Accepted Answer

Negative nitroblue-tetrazolium test

Answer

Positive nitroblue-tetrazolium test

Answer

Increased IgM, Decreased IgG, IgA, and IgE

Answer

Increased IgE and IgA, Decreased IgM

Question 3

In a 4-year-old boy with a history of recurrent pyogenic infections caused by bacteria with polysaccharide-rich capsules, which of the following immunoglobulin deficiencies is most likely?

Accepted Answer

IgA and IgG2 deficiency

Answer

IgA deficiency

Answer

IgG1 deficiency

Answer

IgG2 deficiency

Question 4

A child is receiving corticosteroids for medical therapy. Which of the following conditions is NOT a contraindication for receiving a live viral vaccine in this child?

Accepted Answer

Chronic asthmatic child receiving low-dose inhaled steroid for 10 months

Answer

Receiving 2 mg/kg of prednisolone for at least 2 weeks at present

Answer

Received 2 mg/kg of prednisolone for at least 2 weeks in the past one month

Answer

Receiving 4 mg/kg of prednisolone for 4 weeks, prior to 2 weeks

Question 5

A child admitted with meningitis is found to have gram-negative diplococci on examination. The child has a history of similar infections with the same organism. Which of the following should be suspected?

Accepted Answer

Complement deficiency

Answer

Immunoglobulin deficiency

Answer

T cell deficiency

Answer

B cell deficiency

Question 6

Most common rheumatic disease in children is:

Accepted Answer

Juvenile idiopathic arthritis

Answer

Juvenile ankylosing spondylitis

Answer

Systemic lupus erythematosus

Answer

Morphea

Question 7

An 11-year-old boy presents with multiple abscesses on his face, chest, and back, along with a history of recurrent respiratory infections. Physical examination reveals atopic excoriating skin and multiple cold abscesses on his back. What is the most probable diagnosis?

Accepted Answer

Hyper IgE syndrome

Answer

Hyper IgM syndrome

Answer

Carcinoid syndrome

Answer

Wiskott Aldrich syndrome

Question 8

A 3-year-old male presents with a skin rash and epistaxis. He has experienced several severe sinopulmonary infections. A careful history reveals that his maternal uncle died of bleeding complications following an emergency cholecystectomy. What additional findings are likely in this case?

Accepted Answer

Low platelet count and low serum IgM levels

Answer

A CD4/CD8 ratio of < 1.5:1

Answer

Cerebellar ataxia

Answer

Elevated platelet count and high serum IgG, IgA, and IgE levels

Question 9

Which of the following is a characteristic of Henoch-Schonlein Purpura?

Accepted Answer

Blood in stool

Answer

Thrombocytopenia

Answer

Intracranial hemorrhage

Answer

Susceptibility to infection

Question 10

A 4-year-old child presented with palpable purpura and polyarthralgia without frank arthritis, along with colicky abdominal pain associated with nausea, vomiting, diarrhea, and the passage of blood and mucus per rectum. Urine examination revealed proteinuria and microscopic hematuria. Laboratory studies revealed mild leukocytosis, normal platelet count, normal PT and aPTT, eosinophilia, normal serum complement components, and elevated IgA levels. Skin biopsy specimen was taken. What is the most likely diagnosis?

Accepted Answer

Henoch-Schonlein purpura (HSP)

Answer

Clotting disorder

Answer

Septic emboli

Answer

Urticarial vasculitis

Immunology and Allergies — MCQs

Immunology and Allergies — MCQs

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