Immunology and Allergies Practice Questions

Q: True about Severe Combined Immunodeficiency (SCID) in children is:

It is due to adenosine deaminase deficiency. **Explanation:** Severe Combined Immunodeficiency (SCID) is a pediatric emergency characterized by a profound defect in both **T-cell and B-cell** function. **1. Why Option A is Correct:** Adenosine Deaminase (ADA) deficiency is the **second most common cause** of SCID (autosomal recessive). ADA is an enzyme required to break down toxic metabolites (deoxyadenosine) within lymphocytes. Without it, these toxins accumulate, leading to the death of T, B, and NK cells. The most common cause overall is the **X-linked SCID** (IL-2 receptor gamma chain mutation). **2. Why Other Options are Incorrect:** * **Option B:** In SCID, **both** cellular (T-cell) and humoral (B-cell) immunity are severely affected. While B-cells may be present in some forms, they are non-functional due to the lack of T-cell help. * **Option C:** Live vaccines (e.g., BCG, OPV, MMR) are **strictly contraindicated** in SCID patients as they can cause fatal systemic infections. Even non-live vaccines are generally ineffective due to the inability to mount an immune response. * **Option D:** A hallmark of SCID is **thymic hypoplasia or dysplasia**. On a chest X-ray, the absence of a thymic shadow is a classic diagnostic clue. **Clinical Pearls for NEET-PG:** * **Presentation:** Recurrent severe infections (pneumonia, diarrhea, thrush), failure to thrive, and persistent lymphopenia (<1500 cells/mm³). * **Diagnosis:** Low absolute lymphocyte count and flow cytometry showing absent T-cells. * **Treatment:** Hematopoietic Stem Cell Transplant (HSCT) is the definitive treatment. ADA deficiency can also be treated with Enzyme Replacement Therapy (ERT) or Gene Therapy. * **Screening:** TRECs (T-cell Receptor Excision Circles) are used in newborn screening to detect SCID early.

Q: A 4-year-old male presents with a recent onset of rash, urticaria, and fever of 101°F. The mother reports the child has been complaining of bone pain. Physical examination reveals mild lymphadenopathy. The patient recently completed a 10-day course of cefaclor suspension for an upper respiratory infection. How should this patient be treated?

Oral prednisone and diphenhydramine. ### **Explanation** The clinical presentation of fever, urticaria, lymphadenopathy, and arthralgia (bone pain) following the administration of a medication (cefaclor) is classic for **Serum Sickness-Like Reaction (SSLR)**. **Why Option D is Correct:** SSLR is a Type III hypersensitivity reaction caused by the deposition of immune complexes in small vessels. Unlike true Serum Sickness, it does not involve circulating immune complexes or low complement levels. The mainstay of treatment is **symptomatic relief** and removal of the offending agent. * **Antihistamines (Diphenhydramine):** Used to manage pruritus and urticaria. * **Corticosteroids (Oral Prednisone):** Indicated in moderate to severe cases, especially when there is significant joint pain (arthralgia) or high fever, to rapidly reduce inflammation. **Why Other Options are Incorrect:** * **Option A:** **Aspirin** is contraindicated in children with viral-like symptoms or febrile illnesses due to the risk of **Reye Syndrome**. * **Option B:** **Erythromycin** is an antibiotic. SSLR is an immunological reaction, not an active infection; adding another antibiotic may complicate the clinical picture. * **Option C:** **Penicillin** is a common trigger for SSLR. Administering it would worsen the hypersensitivity reaction. **High-Yield Clinical Pearls for NEET-PG:** * **Common Triggers:** Cefaclor (most common in children), Penicillins, and Sulfa drugs. * **Timing:** Symptoms typically appear **7–21 days** after drug exposure. * **Key Differentiator:** Unlike true Serum Sickness, SSLR lacks renal involvement (no proteinuria/hematuria) and complement levels (C3, C4) remain **normal**. * **Prognosis:** Excellent; symptoms usually resolve within 1–2 weeks of drug discontinuation.

Q: Physical examination that finds multiple palpable purpuric lesions on the legs of a 7-year-old boy is most suggestive of what condition?

Hemorrhage secondary to hypersensitivity vasculitis. **Explanation:** The clinical presentation of **palpable purpura** in a child, particularly localized to the lower extremities, is the hallmark of **Henoch-Schönlein Purpura (HSP)**, the most common form of **hypersensitivity vasculitis** in children. 1. **Why Option B is Correct:** Palpable purpura occurs when there is inflammation of small blood vessels (vasculitis), leading to vessel wall damage and the leakage of red blood cells into the dermis (**hemorrhage**). Unlike flat petechiae, these lesions are palpable because the inflammatory process causes localized edema and cellular infiltration. In HSP, this is typically an IgA-mediated immune complex deposition in the vessel walls. 2. **Why Incorrect Options are Wrong:** * **Option A:** Excess corticosteroids typically cause skin thinning, easy bruising (ecchymosis), and striae due to collagen breakdown, but not inflammatory palpable purpura. * **Option C:** Erythema from active hyperemia (increased blood flow) blanches under pressure (diascopy). Purpura does not blanch because the blood is extravasated outside the vessels. * **Option D:** Telangiectasias are permanent dilatations of pre-existing small blood vessels. They are blanchable, non-palpable, and do not represent acute hemorrhage. **NEET-PG High-Yield Pearls:** * **HSP Tetrad:** Palpable purpura (without thrombocytopenia), arthritis/arthralgia, abdominal pain (intussusception risk), and renal involvement (IgA nephropathy). * **Diagnosis:** Primarily clinical. If a biopsy is done, it shows **leukocytoclastic vasculitis** with IgA deposition on immunofluorescence. * **Platelet Count:** Crucially, the platelet count in HSP is **normal**; this distinguishes it from Immune Thrombocytopenic Purpura (ITP), where purpura is non-palpable and platelets are low.

Q: Which of the following is NOT true about cartilage-hair hypoplasia syndrome?

Non-functioning T cells. **Explanation:** **Cartilage-Hair Hypoplasia (CHH)**, also known as McKusick type metaphyseal chondrodysplasia, is an autosomal recessive disorder caused by mutations in the **RMRP gene**. 1. **Why Option C is the correct answer (The "NOT true" statement):** While CHH is characterized by a cellular immunodeficiency, it typically involves a **reduction in the number of T cells** (lymphopenia) rather than a total absence of function. The T cells that are present usually retain some level of functionality, although there is impaired proliferation. Therefore, stating that the T cells are "non-functioning" is medically inaccurate in the context of this syndrome. 2. **Analysis of Incorrect Options:** * **Option A (Neutropenia):** This is a **true** clinical feature of CHH. Patients frequently present with cyclic or persistent neutropenia, which contributes to their increased susceptibility to infections. * **Option B (Depigmented hair):** This is a **true** hallmark of the disease. The "hair hypoplasia" aspect manifests as fine, sparse, light-colored (hypopigmented/depigmented), and brittle hair due to a reduction in the hair shaft diameter. **Clinical Pearls for NEET-PG:** * **Triad:** Short-limbed dwarfism (metaphyseal dysplasias), sparse/light hair, and immunodeficiency. * **Genetics:** Mutation in the **RMRP gene** (encodes the RNA component of RNase MRP enzyme). * **Key Complications:** High risk of severe **Varicella** infections, increased incidence of malignancies (especially lymphomas), and Hirschsprung disease. * **Radiology:** Metaphyseal flaring and irregularities, particularly at the knees.

Q: A 9-year-old child presents with multiple itchy erythematous wheals all over the body for 2 days, with no respiratory difficulty. What is the most appropriate treatment?

Antihistamines. ### Explanation **Correct Option: C (Antihistamines)** The clinical presentation of itchy, erythematous wheals (hives) without systemic involvement is diagnostic of **Acute Urticaria**. The underlying pathophysiology involves Type I Hypersensitivity, where mast cell degranulation releases histamine, leading to vasodilation and increased capillary permeability. **Second-generation H1-antihistamines** (e.g., Cetirizine, Loratadine) are the first-line treatment as they effectively block H1 receptors, reducing itching and wheal formation with minimal sedation. **Why other options are incorrect:** * **A. Antihelminthics:** While parasitic infections (like *Ascaris*) can cause urticaria, they are not the immediate treatment for an acute symptomatic presentation. They are considered only if the history suggests infestation or if urticaria becomes chronic. * **B. Systemic Corticosteroids:** These are reserved for severe cases, refractory urticaria, or when associated with angioedema. They are not first-line for simple, uncomplicated wheals. * **D. Adrenaline:** This is the life-saving drug of choice for **Anaphylaxis**. Since the patient has no respiratory difficulty (no airway compromise or wheezing) and no hemodynamic instability, adrenaline is not indicated. **Clinical Pearls for NEET-PG:** * **Acute vs. Chronic:** Urticaria is "acute" if it lasts 6 weeks. * **Drug of Choice:** Non-sedating H1 blockers are preferred over first-generation antihistamines (like Pheniramine) due to a better safety profile. * **Anaphylaxis Red Flags:** Always check for "ABC" (Airway, Breathing, Circulation) compromise. If present, the immediate step is **Intramuscular Adrenaline (1:1000)**. * **Common Triggers:** In children, viral infections are the most common cause of acute urticaria, followed by food and medications.

Question 1

True about Severe Combined Immunodeficiency (SCID) in children is:

Accepted Answer

It is due to adenosine deaminase deficiency

Answer

Humoral immunity is predominantly affected

Answer

Child should receive double dose of all vaccines

Answer

Patients with SCID have normal thymus

Question 2

A 4-year-old male presents with a recent onset of rash, urticaria, and fever of 101°F. The mother reports the child has been complaining of bone pain. Physical examination reveals mild lymphadenopathy. The patient recently completed a 10-day course of cefaclor suspension for an upper respiratory infection. How should this patient be treated?

Accepted Answer

Oral prednisone and diphenhydramine

Answer

Aspirin and diphenhydramine

Answer

Erythromycin and diphenhydramine

Answer

Intravenous penicillin and diphenhydramine

Question 3

A 9-year-old girl presents with a 6-month history of difficulty combing her hair and climbing upstairs. She exhibits a positive Gower's sign and a maculopapular rash over her metacarpophalangeal joints. What is the most appropriate next investigation?

Accepted Answer

Creatine Kinase (CK)

Answer

Erythrocyte Sedimentation Rate (ESR)

Answer

Rheumatoid Factor (RA factor)

Answer

Electromyography (EMG)

Question 4

A 20-year-old male presented with eczema, recurrent skin abscesses, and recurrent lung infections. There is eosinophilia and high serum levels of IgE. What is the most likely diagnosis?

Accepted Answer

Job's syndrome

Answer

Shwachman's disease

Answer

Wiskott-Aldrich syndrome

Answer

Nezelof syndrome

Question 5

Physical examination that finds multiple palpable purpuric lesions on the legs of a 7-year-old boy is most suggestive of what condition?

Accepted Answer

Hemorrhage secondary to hypersensitivity vasculitis

Answer

Bleeding secondary to excess corticosteroids

Answer

Erythema secondary to active hyperemia

Answer

Telangiectasia secondary to a congenital malformation

Question 6

Which of the following is NOT true about cartilage-hair hypoplasia syndrome?

Accepted Answer

Non-functioning T cells

Answer

Neutropenia

Answer

Depigmented hair

Answer

None of the above

Question 7

A 9-year-old boy presented with high fever, pruritic erythematous rash, joint pain, and lymph node enlargement. He had a history of upper respiratory tract infection for which he was on cefaclor for 7 days, completing a 10-day course. What is the most likely diagnosis?

Accepted Answer

Serum sickness-like illness

Answer

Hemolytic-uremic syndrome

Answer

Kawasaki disease

Answer

Type III hypersensitivity

Question 8

A child with an obvious rash presents with recurrent infections. Investigations revealed a decreased platelet count and reduced IgM. Which of the following is the most likely diagnosis?

Accepted Answer

Wiskott-Aldrich Syndrome

Answer

Idiopathic Thrombocytopenic Purpura

Answer

Thrombotic Thrombocytopenic Purpura

Answer

DiGeorge anomaly

Question 9

Which of the following conditions is characterized by immunoglobulin deficiency?

Accepted Answer

All of the above

Answer

Wiskott Aldrich syndrome

Answer

X linked hypogammaglobulinemia

Answer

Kawasaki disease

Question 10

A 9-year-old child presents with multiple itchy erythematous wheals all over the body for 2 days, with no respiratory difficulty. What is the most appropriate treatment?

Accepted Answer

Antihistamines

Answer

Antihelminthics

Answer

Systemic corticosteroids

Answer

Adrenaline

Immunology and Allergies — MCQs

Immunology and Allergies — MCQs

On this page

Practice by Chapter

Want unlimited practice?