Immunology and Allergies Practice Questions

Q: 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?

IgG2 deficiency. ***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

Q: A child presented with non-blanching purpura in the lower limb and recurrent abdominal pain. Which condition is characterized by the deposition of IgA?

Henoch-Schönlein purpura. ***Henoch-Schönlein purpura*** - This condition is a **leukocytoclastic vasculitis** [1] primarily affecting small vessels, characterized by palpable **purpura**, **abdominal pain** [2], and often **arthralgia** and **renal involvement**. - It is defined by the deposition of **IgA immune complexes** in affected small vessels, a key diagnostic feature. *Granulomatosis with polyangiitis* - This is an **ANCA-associated vasculitis** [1] characterized by granulomatous inflammation of the respiratory tract and necrotizing vasculitis, typically affecting small to medium-sized vessels. - It is associated with **antineutrophil cytoplasmic antibodies (ANCA)**, specifically **c-ANCA**, and does not involve IgA deposition. *Kawasaki syndrome* - This is an **acute febrile illness** primarily in young children [3], characterized by inflammation of medium-sized arteries, most notably the **coronary arteries**. - It presents with fever, rash, **conjunctivitis**, and **lymphadenopathy**, but not IgA deposition [3]. *Takayasu arteritis* - This is a **large-vessel vasculitis** [1] primarily affecting the **aorta** and its major branches, leading to stenoses, occlusions, and aneurysms. - It usually presents in young women with symptoms related to **ischemia** of affected organs, and is not associated with IgA deposition or purpura in the lower limbs.

Q: A 5-year-old child presents with non-blanching macules and papules on the skin. Skin biopsy reveals a perivascular IgA deposition. Which of the following is the most likely diagnosis?

Henoch-Schönlein purpura. ***Henoch-Schönlein purpura*** - This condition commonly presents in children with **non-blanching macules and papules** (palpable purpura), often on the lower extremities and buttocks. - Skin biopsy showing **perivascular IgA deposition** is the hallmark diagnostic finding for Henoch-Schönlein purpura. *Wegener's granulomatosis* - This is a **systemic vasculitis** (now called Granulomatosis with Polyangiitis) primarily affecting the respiratory tract and kidneys. - It is typically associated with **antineutrophil cytoplasmic antibodies (ANCA)**, specifically c-ANCA, and does not feature IgA deposition. *Kawasaki disease* - Characterized by **fever, rash, conjunctivitis, oral mucosal changes**, and **cervical lymphadenopathy** in young children. - While it is a form of vasculitis, it does not typically present with IgA deposition on skin biopsy and has a distinct clinical presentation. *Drug-induced vasculitis* - This condition is caused by an adverse reaction to a medication and can present with various skin lesions, including purpura. - Although it can cause vasculitis, the specific finding of **IgA deposition** is more characteristic of Henoch-Schönlein purpura than general drug-induced vasculitis.

Q: 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?

Immunodeficiency. ***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.

Q: A 7-year-old boy presents with a palpable, non-blanching rash that started 3 days prior and involves the lower limbs and buttocks, following a previous viral upper respiratory tract infection. His blood pressure is normal, and kidney function tests are normal. What is the diagnosis?

Henoch-Schonlein purpura. ***Henoch-Schönlein purpura (IgA vasculitis)*** - The classic presentation of a **palpable, non-blanching purpuric rash** on the lower limbs and buttocks, especially after a viral upper respiratory infection in a child, is highly characteristic of Henoch-Schönlein purpura (HSP), now termed **IgA vasculitis**. - Although HSP can involve the kidneys, the **normal kidney function tests** and blood pressure here are consistent with early or mild disease, or prior to the development of renal manifestations which can occur later. - HSP is a **small vessel vasculitis** characterized by IgA immune complex deposition affecting skin, joints, GI tract, and kidneys. *Meningococcemia* - While meningococcemia can cause a **non-blanching rash**, it is typically accompanied by signs of severe illness such as **fever, altered mental status, and hemodynamic instability**, which are absent in this child. - The rash in meningococcemia often progresses rapidly to **petechiae and purpura**, but the distribution and association with a prior viral URI are less specific than in HSP. *Hemolytic uremic syndrome* - This condition involves the triad of **microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury**, often following a diarrheal illness (e.g., E. coli O157:H7). - The patient's **normal kidney function tests** and the rash pattern are not consistent with HUS; rash in HUS is not typically a prominent feature. *Cutis marmorata* - This is a harmless, temporary phenomenon characterized by a **lace-like, reticulated reddish-blue discoloration of the skin** that occurs in response to cold exposure due to vasomotor instability. - Unlike the described rash, cutis marmorata **blanches with pressure** and is not a palpable purpuric rash associated with a systemic illness.

Q: A neonate presents with recurrent seizures, hypocalcemia, and recurrent infections. What is the diagnosis?

DiGeorge syndrome (22q11.2 deletion syndrome). ***DiGeorge syndrome (22q11.2 deletion syndrome)*** - This syndrome is characterized by **thymic hypoplasia/aplasia** (leading to **T-cell immunodeficiency** and recurrent infections) and **parathyroid hypoplasia/aplasia** (leading to **hypocalcemia** and seizures). - Other common features include **cardiac anomalies** (especially conotruncal defects) and distinctive **facial features**. *Bardet-Biedl syndrome* - This is a rare genetic disorder characterized by **retinal dystrophy**, **polydactyly**, **obesity**, **renal dysfunction**, and **intellectual disability**. - It does not typically present with the combination of severe immunodeficiency, hypocalcemia, and seizures as primary symptoms in neonates. *Gitelman syndrome (hypokalemic metabolic alkalosis)* - This is a renal tubular disorder characterized by **hypokalemia**, **hypomagnesemia**, and **metabolic alkalosis**, usually presenting in late childhood or adulthood. - It involves impaired reabsorption of sodium chloride in the distal convoluted tubule and is not associated with recurrent infections or hypocalcemia presenting as seizures in neonates. *Idiopathic hypercalciuria (calcium wasting)* - This condition involves excessive **calcium excretion in the urine** without an apparent cause and can lead to kidney stones or osteoporosis in older individuals. - It does not cause hypocalcemia, recurrent infections, or seizures in neonates; in fact, the name implies a loss of calcium from the body through urine, not a deficiency in the blood.

Q: 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?

Henoch-Schönlein purpura. ***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 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?

Accepted Answer

IgG2 deficiency

Answer

IgA deficiency

Answer

IgG1 deficiency

Answer

IgA + IgG2 deficiency

Question 2

A child presented with non-blanching purpura in the lower limb and recurrent abdominal pain. Which condition is characterized by the deposition of IgA?

Accepted Answer

Henoch-Schönlein purpura

Answer

Granulomatosis with polyangiitis

Answer

Kawasaki syndrome

Answer

Takayasu arteritis

Question 3

A 5-year-old child presents with non-blanching macules and papules on the skin. Skin biopsy reveals a perivascular IgA deposition. Which of the following is the most likely diagnosis?

Accepted Answer

Henoch-Schönlein purpura

Answer

Wegener's granulomatosis

Answer

Kawasaki disease

Answer

Drug-induced vasculitis

Question 4

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?

Accepted Answer

Immunodeficiency

Answer

Gout

Answer

Dwarfism

Answer

Intellectual disability

Question 5

A 7-year-old boy presents with a palpable, non-blanching rash that started 3 days prior and involves the lower limbs and buttocks, following a previous viral upper respiratory tract infection. His blood pressure is normal, and kidney function tests are normal. What is the diagnosis?

Accepted Answer

Henoch-Schonlein purpura

Answer

Meningococcemia

Answer

Hemolytic uremic syndrome

Answer

Cutis marmorata

Question 6

A neonate presents with recurrent seizures, hypocalcemia, and recurrent infections. What is the diagnosis?

Accepted Answer

DiGeorge syndrome (22q11.2 deletion syndrome)

Answer

Bardet-Biedl syndrome

Answer

Gitelman syndrome (hypokalemic metabolic alkalosis)

Answer

Idiopathic hypercalciuria (calcium wasting)

Question 7

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?

Accepted Answer

Henoch-Schönlein purpura

Answer

Acute rheumatic fever

Answer

Juvenile rheumatoid arthritis

Answer

Pyogenic arthritis

Question 8

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?

Accepted Answer

A distinctive-appearing 8-month-old boy with an interrupted aortic arch, hypocalcemia, and cleft palate

Answer

A 1-year-old boy with severe eczema, recurrent middle-ear infections, lymphopenia, and thrombocytopenia

Answer

A 9-year-old boy with an eczema-like rash and recurrent severe staphylococcal infections

Answer

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

Immunology and Allergies — MCQs

Immunology and Allergies — MCQs

On this page

Practice by Chapter

Want unlimited practice?