Immunopathology — MCQs
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Type 4 hypersensitivity to Mycobacterium tuberculosis antigen may manifest as?
Anti-endothelial antibodies are seen in which of the following conditions?
A 26-year-old man has had myalgias and a fever for the past week. On physical examination, his temperature is 38.6°C. He has diffuse muscle tenderness, but no rashes or joint pain on movement. Laboratory studies show elevated serum creatine kinase and peripheral blood eosinophilia. Larvae of Trichinella spiralis are present within the skeletal muscle fibers of a gastrocnemius biopsy specimen. Two years later, a chest radiograph shows only a few small calcifications in the diaphragm. Which of the following immunologic mechanisms most likely contributed to the destruction of the larvae?
Which immunoglobulin combination is predominantly involved in the pathogenesis of cryoglobulinemic vasculitis?
A 30-year-old lady presents to the outpatient department with an erythematous butterfly rash on her cheeks. Which of the following antibodies should be assayed initially for her suspected condition?
Which part of the IgE antibody is responsible for binding to mast cells and basophils?
Antibody-dependent cell-mediated cytotoxicity (ADCC) is a mechanism by which target cells are killed. Which immune cells are primarily involved in ADCC?
A 30-year-old male develops tachycardia, hypotension (BP 70/40 mm Hg), and hematuria within 10 minutes of starting a blood transfusion in the OT. What is the most probable cause?
Which condition has a >90% association with HLA-B27?
Extranodal marginal zone lymphomas of MALT type can involve the thymus in the setting of which of the following conditions?
Immunopathology Indian Medical PG Practice Questions and MCQs
Question 61: Type 4 hypersensitivity to Mycobacterium tuberculosis antigen may manifest as?
- A. Iridocyclitis
- B. Polyarteritis nodosa
- C. Phlyctenular (Correct Answer)
- D. Giant cell arteritis
Explanation: **Explanation:** **Type IV (Delayed-type) Hypersensitivity** is a T-cell mediated immune response that occurs 48–72 hours after exposure to an antigen [1]. In the context of *Mycobacterium tuberculosis*, the body mounts a cell-mediated immune response involving Th1 cells and macrophages [1]. **Why Phlyctenular is correct:** **Phlyctenular keratoconjunctivitis** is a classic example of a localized Type IV hypersensitivity reaction to endogenous microbial proteins, most commonly the **tuberculoprotein** (from *M. tuberculosis*). It manifests as a small, greyish-white nodule (phlycten) on the cornea or conjunctiva, representing a lymphocytic infiltration rather than a direct infection of the eye. **Analysis of Incorrect Options:** * **A. Iridocyclitis:** While TB can cause uveitis, it is typically due to direct infection or a complex immune response, but it is not the "classic" manifestation of Type IV hypersensitivity specifically linked to the tuberculoprotein in the same way phlyctenules are. * **B. Polyarteritis Nodosa (PAN):** This is a systemic necrotizing vasculitis associated with **Type III hypersensitivity** (immune complex deposition), frequently linked to Hepatitis B virus, not TB [3]. * **D. Giant Cell Arteritis (GCA):** This is a granulomatous inflammation of large arteries. While it involves T-cells, it is an idiopathic autoimmune condition of the elderly and is not a hypersensitivity reaction to TB antigens. **High-Yield NEET-PG Pearls:** * **Mantoux Test:** The quintessential clinical test for Type IV hypersensitivity using PPD (Purified Protein Derivative) [1]. * **Granuloma Formation:** The hallmark of TB pathology, driven by Type IV hypersensitivity (Interferon-gamma and TNF-alpha) [2]. * **Other Type IV examples:** Contact dermatitis (poison ivy, nickel), Erythema multiforme, and the Lepromin test. * **Phlyctenule causes:** TB is the most common cause in developing countries; *Staphylococcus aureus* is the most common cause in developed countries. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 216-218. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, p. 109. [3] 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. 172-173.
Question 62: Anti-endothelial antibodies are seen in which of the following conditions?
- A. Kawasaki disease (Correct Answer)
- B. Giant cell arteritis
- C. Systemic lupus erythematosus (SLE)
- D. Microscopic polyangiitis
Explanation: **Explanation:** **Kawasaki Disease (Correct Answer):** Kawasaki disease is an acute, febrile, self-limiting systemic necrotizing vasculitis of unknown etiology, primarily affecting small to medium-sized vessels (especially coronary arteries) in children [1]. The pathogenesis involves a delayed-type hypersensitivity response or an oligoclonal B-cell response. A hallmark finding is the presence of **Anti-Endothelial Cell Antibodies (AECA)**, which target vascular endothelial cells, leading to inflammation and potential aneurysm formation [1]. **Analysis of Incorrect Options:** * **Giant Cell Arteritis:** This is a granulomatous large-vessel vasculitis [1]. Its pathogenesis is primarily T-cell mediated (Th1 and Th17 pathways) and strongly associated with HLA-DR4, rather than specific anti-endothelial antibodies. * **Systemic Lupus Erythematosus (SLE):** While SLE involves various autoantibodies (ANA, Anti-dsDNA, Anti-Smith), it is characterized by Type III hypersensitivity (immune complex deposition) [2]. While AECA can occasionally be found in SLE, they are not the defining or diagnostic serological marker as they are in the context of Kawasaki disease vasculitis. * **Microscopic Polyangiitis:** This is a small-vessel vasculitis characterized by the presence of **p-ANCA** (anti-myeloperoxidase antibodies). It is a "pauci-immune" vasculitis, meaning there is little to no antibody/complement deposition in the vessel walls [3]. **High-Yield Clinical Pearls for NEET-PG:** * **Kawasaki Disease Mnemonic (CRASH and Burn):** **C**onjunctivitis, **R**ash (polymorphous), **A**denopathy (cervical), **S**trawberry tongue, **H**ands/Feet (edema/desquamation), and **Burn** (high fever >5 days). * **Complication:** It is the leading cause of acquired heart disease in children (Coronary artery aneurysms). * **Treatment:** IVIG and high-dose Aspirin (one of the few pediatric indications for Aspirin). **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of Infancy and Childhood, pp. 515-516. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of Infancy and Childhood, pp. 514-515. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of Infancy and Childhood, pp. 518-519.
Question 63: A 26-year-old man has had myalgias and a fever for the past week. On physical examination, his temperature is 38.6°C. He has diffuse muscle tenderness, but no rashes or joint pain on movement. Laboratory studies show elevated serum creatine kinase and peripheral blood eosinophilia. Larvae of Trichinella spiralis are present within the skeletal muscle fibers of a gastrocnemius biopsy specimen. Two years later, a chest radiograph shows only a few small calcifications in the diaphragm. Which of the following immunologic mechanisms most likely contributed to the destruction of the larvae?
- A. Abscess formation with neutrophils
- B. Antibody-mediated cellular cytotoxicity (ADCC) (Correct Answer)
- C. Complement-mediated cellular lysis
- D. Formation of Langhans giant cells
Explanation: ### Explanation **Correct Option: B. Antibody-mediated cellular cytotoxicity (ADCC)** The clinical presentation of fever, myalgia, muscle tenderness, and **peripheral eosinophilia**, combined with the biopsy finding of *Trichinella spiralis* larvae, confirms a diagnosis of **Trichinosis**. Helminthic parasites are too large to be phagocytosed by macrophages or neutrophils. The primary immune defense against such multicellular parasites is **ADCC**. In this mechanism: 1. The host produces **IgE antibodies** against the parasite. 2. IgE coats the larvae (opsonization) [1]. 3. **Eosinophils** bind to the Fc portion of the IgE via their surface receptors (FcεRI) [1]. 4. This triggers eosinophil degranulation, releasing **Major Basic Protein (MBP)** and eosinophil cationic protein, which are directly toxic to the larvae, leading to their destruction. --- ### Why Other Options are Incorrect: * **A. Abscess formation with neutrophils:** Neutrophils are the hallmark of acute bacterial infections and pyogenic inflammation. They are ineffective against large tissue-invasive helminths. * **C. Complement-mediated cellular lysis:** While the classical pathway can be activated, the thick cuticle of most helminths is resistant to the Membrane Attack Complex (MAC). ADCC is the more specific and effective mechanism for larval destruction [1]. * **D. Formation of Langhans giant cells:** These are characteristic of **Granulomatous inflammation** (Type IV Hypersensitivity), typically seen in tuberculosis or sarcoidosis. While a granulomatous reaction may eventually surround dead larvae, it is not the primary mechanism for the initial destruction of the parasite. --- ### NEET-PG High-Yield Pearls: * **Eosinophils & Parasites:** Whenever you see "Eosinophilia" + "Parasite" in a question, think **Type I Hypersensitivity** (IgE) and **ADCC** [1]. * **Major Basic Protein (MBP):** This is the specific "weapon" within eosinophil granules responsible for killing helminths. * **Trichinella spiralis:** Classically presents with the triad of **periorbital edema, myositis, and eosinophilia**. Larvae typically encyst in "nurse cells" within striated muscle (diaphragm, masseter, gastrocnemius). **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 210-211.
Question 64: Which immunoglobulin combination is predominantly involved in the pathogenesis of cryoglobulinemic vasculitis?
- A. IgA and IgG
- B. IgM and IgG (Correct Answer)
- C. IgA and IgE
- D. IgE and IgM
Explanation: **Explanation:** Cryoglobulinemic vasculitis is a small-vessel vasculitis caused by the deposition of immune complexes that precipitate at cold temperatures. The pathogenesis is centered on **Type II and Type III cryoglobulins**, which are characterized by the interaction between **IgM and IgG**. [1] 1. **Why IgM and IgG is correct:** In the most common forms (Mixed Cryoglobulinemia), **IgM** acts as a monoclonal or polyclonal rheumatoid factor (RF). This IgM antibody specifically binds to the Fc portion of circulating **IgG** antibodies. These IgM-IgG complexes activate the classical complement pathway, leading to systemic inflammation and vasculitis, particularly in the skin, joints, and kidneys. [1], [2] 2. **Why other options are wrong:** * **IgA and IgG:** This combination is characteristic of IgA nephropathy or Henoch-Schönlein Purpura (IgA vasculitis), not cryoglobulinemia. [1] * **IgA and IgE:** IgE is primarily involved in Type I hypersensitivity (atopy/anaphylaxis) and parasitic infections; it does not form cryoprecipitates. * **IgE and IgM:** There is no recognized clinical vasculitis syndrome defined by this specific combination. **NEET-PG High-Yield Pearls:** * **Association:** Over 90% of mixed cryoglobulinemia cases are associated with **Hepatitis C Virus (HCV)** infection. * **Clinical Triad (Meltzer’s Triad):** Palpable purpura, arthralgia, and generalized weakness. * **Complement Levels:** Characteristically shows **low C4** levels due to constant activation of the classical pathway. [3] * **Classification:** Type I (Monoclonal IgG or IgM) is usually associated with hematologic malignancies (Multiple Myeloma/Waldenström’s); Types II and III (Mixed) involve the IgM-IgG complex. [1] **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of Infancy and Childhood, pp. 520-521. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 214-215. [3] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Cardiovascular Disease, pp. 278-279.
Question 65: A 30-year-old lady presents to the outpatient department with an erythematous butterfly rash on her cheeks. Which of the following antibodies should be assayed initially for her suspected condition?
- A. Anti-ds-DNA (Correct Answer)
- B. Anti-Ro Antibody
- C. Anti-Centromere Antibody
- D. Anti-mitochondrial Antibody
Explanation: **Explanation:** The clinical presentation of a **butterfly rash** (malar rash) in a young female is a classic hallmark of **Systemic Lupus Erythematosus (SLE)** [1], [2]. **Why Anti-dsDNA is the correct choice:** While the Anti-Nuclear Antibody (ANA) is the best *screening* test due to its high sensitivity, **Anti-dsDNA** is highly *specific* for SLE [5]. In the context of the provided options, Anti-dsDNA is the most definitive marker for confirming the diagnosis. Furthermore, its titers correlate with **disease activity** and the presence of **lupus nephritis**, making it clinically indispensable for both diagnosis and monitoring. **Analysis of Incorrect Options:** * **Anti-Ro (SS-A) Antibody:** Associated with Sjögren’s syndrome and Neonatal Lupus (congenital heart block). While present in some SLE patients (especially those with subacute cutaneous lupus), it is not as specific as Anti-dsDNA. * **Anti-Centromere Antibody:** This is the marker for **Limited Scleroderma (CREST Syndrome)**. It is not typically associated with the malar rash of SLE. * **Anti-mitochondrial Antibody (AMA):** This is the hallmark of **Primary Biliary Cholangitis (PBC)** and has no diagnostic value in immunodermatological or connective tissue disorders like SLE. **High-Yield Clinical Pearls for NEET-PG:** * **Most Sensitive Test for SLE:** ANA (Indirect Immunofluorescence is the gold standard) [3]. * **Most Specific Tests for SLE:** Anti-Smith (Sm) and Anti-dsDNA. * **Drug-Induced Lupus:** Anti-Histone antibodies are the characteristic marker. * **Mnemonic for SLE (MD SOAP HAIR):** Malar rash [1], Discoid rash [4], Serositis, Oral ulcers, Arthritis, Photosensitivity, Hematologic, ANA, Immunologic (dsDNA/Sm), Renal. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Osteoarticular And Connective Tissue Disease, pp. 685-686. [2] Kumar v, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, p. 226. [3] Kumar v, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 226-227. [4] Kumar v, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 233-234. [5] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Disorders Involving Inflammatory And Haemopoietic Cells, pp. 639-640.
Question 66: Which part of the IgE antibody is responsible for binding to mast cells and basophils?
- A. Light chain
- B. Immunoglobulin fold
- C. Fc region (Correct Answer)
- D. Complement binding site
Explanation: **Explanation:** The correct answer is **C. Fc region**. **1. Why the Fc region is correct:** The immunoglobulin molecule consists of two functional components: the **Fab region** (Fragment antigen-binding) and the **Fc region** (Fragment crystallizable). The Fc region, composed of the constant domains of the heavy chains ($C_H2$, $C_H3$, and in the case of IgE, $C_H4$), determines the biological activity of the antibody [1]. In Type I Hypersensitivity reactions, the Fc portion of IgE binds with high affinity to specific receptors called **Fc̵RI** located on the surface of mast cells and basophils [2]. This "sensitizes" the cells; subsequent exposure to an allergen causes cross-linking of these bound IgE molecules, leading to degranulation. **2. Why other options are incorrect:** * **A. Light chain:** The light chain (Kappa or Lambda) contributes to the formation of the antigen-binding site (Fab) but does not mediate cell surface binding. * **B. Immunoglobulin fold:** This is a structural motif (a sandwich of beta-sheets) common to all antibody domains. It provides structural integrity but is not a specific binding site for cell receptors. * **D. Complement binding site:** While the Fc region of IgG and IgM can bind complement (C1q), **IgE does not fix complement** via the classical pathway. **High-Yield Clinical Pearls for NEET-PG:** * **IgE Structure:** Unlike IgG, IgE has an extra constant domain (**$C_H4$**) instead of a hinge region. * **Receptor Affinity:** **Fc̵RI** is the high-affinity receptor (mast cells/basophils), while **Fc̵RII (CD23)** is the low-affinity receptor (B-cells/macrophages) [2]. * **Prausnitz-K1stner (PK) reaction:** A classic experiment demonstrating that the "reaginic" factor (IgE) in serum is responsible for immediate hypersensitivity. * **Omalizumab:** A monoclonal antibody used in severe asthma that works by specifically binding to the Fc region of free IgE, preventing it from attaching to mast cells. **References:** [1] 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. 155-156. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 210-211.
Question 67: Antibody-dependent cell-mediated cytotoxicity (ADCC) is a mechanism by which target cells are killed. Which immune cells are primarily involved in ADCC?
- A. NK cells
- B. NK cells only
- C. Macrophages
- D. NK cells, neutrophils, and macrophages (Correct Answer)
Explanation: **Explanation:** **Antibody-dependent cell-mediated cytotoxicity (ADCC)** is a mechanism of cell-mediated immune defense where an effector cell of the immune system actively lyses a target cell, whose membrane-surface antigens have been bound by specific antibodies (usually **IgG**). 1. **Why Option D is correct:** The process is triggered when the **Fc receptor (FcR)** on the surface of an effector cell binds to the **Fc portion** of an antibody attached to a target cell. While **Natural Killer (NK) cells** are the most well-known mediators of ADCC (via CD16/FcγRIII), they are not the only ones. **Macrophages, neutrophils, and eosinophils** also possess Fc receptors and can execute ADCC [1]. For instance, eosinophils use ADCC to kill helminths (mediated by IgE), while macrophages and neutrophils use it to destroy tumor cells or opsonized pathogens. 2. **Why other options are incorrect:** * **Options A & B:** These are incomplete. While NK cells are the primary mediators of ADCC against tumor and virus-infected cells, selecting "NK cells only" ignores the significant role of the myeloid lineage (neutrophils and macrophages) in this process [1]. 3. **High-Yield NEET-PG Pearls:** * **Antibody involved:** Primarily **IgG** (specifically IgG1 and IgG3). **IgE** is involved in ADCC against parasites (mediated by eosinophils). * **Key Receptor:** **CD16** (Fc\u03b3RIII) is the characteristic marker on NK cells responsible for ADCC. * **Mechanism:** Unlike CTLs (CD8+ T cells), ADCC does not require MHC restriction. It relies on the recognition of the antibody's Fc region. * **Clinical Relevance:** Many therapeutic monoclonal antibodies (e.g., **Trastuzumab** for breast cancer, **Rituximab** for B-cell lymphoma) work partly by inducing ADCC. **References:** [1] 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. 164-165.
Question 68: A 30-year-old male develops tachycardia, hypotension (BP 70/40 mm Hg), and hematuria within 10 minutes of starting a blood transfusion in the OT. What is the most probable cause?
- A. Anesthetic drug hypersensitivity
- B. Disseminated Intravascular Coagulation (DIC)
- C. Graft-versus-Host Disease (GVHD)
- D. ABO incompatibility (Correct Answer)
Explanation: ### Explanation **Correct Answer: D. ABO incompatibility** The clinical presentation of sudden **hypotension, tachycardia, and hematuria** (signifying hemoglobinuria) immediately following the start of a blood transfusion is a classic manifestation of an **Acute Hemolytic Transfusion Reaction (AHTR)**, most commonly caused by ABO incompatibility [1]. * **Mechanism:** This is a **Type II Hypersensitivity reaction**. Pre-formed host IgM antibodies (isohemagglutinins) attack the donor RBC antigens, leading to complement activation and **intravascular hemolysis** [1]. Intravascular hemolysis is manifested by anemia, hemoglobinemia, and hemoglobinuria [2]. * **Clinical Correlation:** In an anesthetized patient (in the OT), typical symptoms like chills or back pain are masked. The earliest signs are often **unexplained hypotension** and **oozing from puncture sites** (due to triggered DIC). **Why other options are incorrect:** * **A. Anesthetic drug hypersensitivity:** While it causes hypotension and tachycardia (Anaphylaxis), it does not explain **hematuria** (hemoglobinuria), which is a hallmark of red cell lysis. * **B. Disseminated Intravascular Coagulation (DIC):** While DIC can occur *as a complication* of ABO incompatibility [1], it is a secondary process rather than the primary "cause" of the immediate reaction. * **C. Graft-versus-Host Disease (GVHD):** Transfusion-associated GVHD is a delayed complication (occurring 1–2 weeks post-transfusion) caused by donor T-lymphocytes attacking an immunocompromised host. **High-Yield Clinical Pearls for NEET-PG:** * **Most common cause of AHTR:** Clerical/Administrative error (mislabeling) [1]. * **Direct Coombs Test:** Will be **positive** in AHTR. * **Immediate Management:** Stop the transfusion immediately, maintain IV access with normal saline, and support blood pressure. * **Delayed Hemolytic Reaction:** Usually due to **Kidd (Jk) system** antibodies; occurs 3–10 days post-transfusion. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Red Blood Cell and Bleeding Disorders, pp. 673-674. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Red Blood Cell and Bleeding Disorders, pp. 639-640.
Question 69: Which condition has a >90% association with HLA-B27?
- A. Enteropathic arthritis
- B. Reactive arthritis
- C. Rheumatoid arthritis
- D. Ankylosing spondylitis (Correct Answer)
Explanation: ### Explanation **Ankylosing Spondylitis (AS)** is the correct answer because it has the strongest known association with the **HLA-B27** allele among all Seronegative Spondyloarthropathies [1], [3]. Approximately **90–95%** of patients with AS are HLA-B27 positive [1]. The allele is thought to play a role in disease pathogenesis through molecular mimicry or the "misfolding protein response," leading to chronic inflammation of the sacroiliac joints and spine. **Analysis of Incorrect Options:** * **Enteropathic Arthritis:** Associated with Inflammatory Bowel Disease (IBD). While HLA-B27 is present in about 50–70% of cases with axial involvement (spondylitis), the overall association is much lower than in AS. * **Reactive Arthritis (Reiter’s Syndrome):** This condition follows certain GI or GU infections. It has a strong association with HLA-B27, but it is typically around **70–80%**, not exceeding 90% [2]. * **Rheumatoid Arthritis:** This is an autoimmune disease primarily associated with **HLA-DR4** (specifically the "shared epitope"), not HLA-B27. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for HLA-B27:** Remember **"PAIR"** (Psoriatic arthritis, Ankylosing spondylitis, IBD-associated arthritis, Reactive arthritis) [3]. * **Ankylosing Spondylitis:** Look for "Bamboo spine" on X-ray and the "Schober’s test" for restricted lumbar motion. * **HLA-B27 Prevalence:** While 90% of AS patients are HLA-B27 positive, only about 2–5% of all HLA-B27 positive individuals actually develop AS. * **Other HLA Associations:** * HLA-DR3/DR4: Type 1 Diabetes Mellitus. * HLA-DQ2/DQ8: Celiac Disease. * HLA-B51: Behcet’s Disease. **References:** [1] 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. 49-50. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Osteoarticular And Connective Tissue Disease, pp. 680-681. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, pp. 1214-1215.
Question 70: Extranodal marginal zone lymphomas of MALT type can involve the thymus in the setting of which of the following conditions?
- A. HIV
- B. Systemic Lupus Erythematosus (SLE)
- C. Sjogren's syndrome (Correct Answer)
- D. Crohn's disease
Explanation: **Explanation:** **Extranodal Marginal Zone Lymphoma (MALToma)** typically arises in the setting of chronic inflammation or autoimmune stimulation [1]. In the thymus, MALToma is rare but is characteristically associated with **Sjogren’s syndrome**. 1. **Why Sjogren’s Syndrome is correct:** Sjogren’s syndrome is a systemic autoimmune disease characterized by lymphocytic infiltration of exocrine glands. Patients with Sjogren’s have a **44-fold increased risk** of developing B-cell lymphomas, most commonly MALTomas [1]. While these usually occur in the parotid glands, they can also manifest in the thymus due to the chronic autoimmune-mediated follicular hyperplasia that provides a substrate for malignant transformation of marginal zone B-cells. 2. **Why other options are incorrect:** * **HIV:** While HIV is associated with various aggressive B-cell lymphomas (like DLBCL or Burkitt lymphoma), it is not specifically linked to thymic MALToma. * **SLE:** Although SLE is an autoimmune condition, it is more commonly associated with generalized lymphadenopathy rather than organ-specific MALTomas of the thymus [3]. * **Crohn’s Disease:** This is associated with an increased risk of intestinal lymphomas (specifically Enteropathy-associated T-cell lymphoma), not thymic MALToma. **High-Yield NEET-PG Pearls:** * **MALToma Associations:** * **Stomach:** *H. pylori* (Most common site; often regresses with antibiotics) [2]. * **Salivary Glands/Thymus:** Sjogren’s syndrome. * **Thyroid:** Hashimoto’s thyroiditis. * **Orbit:** *Chlamydia psittaci*. * **Cytogenetics:** The most common translocation in MALToma is **t(11;18)(q21;q21)**, involving the *API2-MALT1* fusion gene. * **Immunophenotype:** CD20+, CD19+, **CD5-**, and **CD10-**. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 235-236. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Alimentary System Disease, pp. 356-357. [3] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Diseases Of The Urinary And Male Genital Tracts, pp. 554-555.
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