Bone and Soft Tissue Pathology Practice Questions

Q: Which of the following genes is responsible for Fibrous dysplasia?

GNAS1. ### Explanation **Correct Answer: A. GNAS1** **Mechanism and Pathophysiology:** Fibrous dysplasia is a non-neoplastic bone lesion where normal bone is replaced by fibrous tissue and haphazardly arranged bony trabeculae. The underlying molecular defect is a **somatic gain-of-function mutation** in the **GNAS1 gene** (located on chromosome 20q13) [1]. This gene encodes the **alpha subunit of the stimulatory G-protein (Gśα)**. The mutation leads to constitutive activation of adenylate cyclase, resulting in an intracellular overproduction of **cyclic AMP (cAMP)** [1]. In bone-forming cells, elevated cAMP promotes excessive proliferation and prevents the maturation of osteoblasts, leading to the formation of immature "woven" bone embedded in a cellular fibrous stroma. **Analysis of Incorrect Options:** * **GNAS2, GNAS3, and GNAS4:** These are not recognized genes associated with human skeletal pathology. The GNAS complex is highly imprinted and produces multiple transcripts, but the specific mutation linked to Fibrous Dysplasia and McCune-Albright syndrome is consistently identified in the **GNAS1** locus. **High-Yield Clinical Pearls for NEET-PG:** * **Histology:** Characterized by the **"Chinese letter" pattern** (curved, irregular trabeculae of woven bone) without osteoblastic rimming. * **Clinical Variants:** 1. **Monostotic:** Involves a single bone (most common). 2. **Polyostotic:** Involves multiple bones. 3. **McCune-Albright Syndrome:** Triad of Polyostotic fibrous dysplasia, **Café-au-lait spots** (Coast of Maine borders), and **Precocious puberty** (Endocrinopathies) [1]. 4. **Mazabraud Syndrome:** Polyostotic fibrous dysplasia associated with soft tissue myxomas. * **Radiology:** Classic **"Ground-glass appearance"** on X-ray. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, pp. 1126-1127.

Q: Which of the following is FALSE regarding cystic fibrosis?

Associated with chromosome 7p. **Explanation:** Cystic Fibrosis (CF) is the most common lethal genetic disease in Caucasian populations. The correct answer is **Option C** because the **CFTR gene** is located on the **long arm of chromosome 7 (7q31.2)**, not the short arm (7p). In genetics, 'p' stands for *petit* (short arm) and 'q' stands for the long arm. **Analysis of Options:** * **Option A (True):** CF is caused by mutations in the **Cystic Fibrosis Transmembrane Conductance Regulator (CFTR)** gene, which encodes a cAMP-regulated chloride channel [1]. * **Option B (True):** It follows an **Autosomal Recessive** inheritance pattern. Parents are typically asymptomatic carriers. * **Option D (True):** Defective chloride transport leads to abnormally thick, viscid mucus [1]. This impairs mucociliary clearance, leading to **recurrent respiratory infections**, bronchiectasis, and colonization by pathogens like *Pseudomonas aeruginosa* [1]. **NEET-PG High-Yield Pearls:** * **Most Common Mutation:** **ΔF508** (a three-base pair deletion of phenylalanine at position 508), which leads to protein misfolding and degradation in the ER (Class II defect) [1]. * **Diagnosis:** Sweat Chloride Test (Gold Standard) showing chloride levels **>60 mEq/L** [1]. * **Clinical Triad:** Chronic sinopulmonary disease, pancreatic insufficiency (steatorrhea), and male infertility (bilateral absence of vas deferens - CBAVD) [1]. * **Meconium Ileus:** A classic neonatal presentation of CF. * **Nasal Polyps:** CF should be suspected in any child presenting with nasal polyposis. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of Infancy and Childhood, pp. 475-479.

Q: The term 'ragged red fibers' is applied to describe the skeletal muscle fibers in which of the following conditions?

Mitochondrial myopathy. **Explanation:** **Mitochondrial Myopathy (Correct Answer)** The term **'Ragged Red Fibers' (RRF)** is a hallmark histological finding in mitochondrial myopathies (e.g., MERRF, MELAS) [1]. These fibers represent a compensatory proliferation of abnormal mitochondria in the subsarcolemmal and intermyofibrillar spaces of skeletal muscle. On **Gomori Trichrome stain**, these mitochondrial aggregates appear as irregular, reddish-purple granular deposits at the periphery of the muscle fiber, giving it a "ragged" appearance. **Analysis of Incorrect Options:** * **Myotonic Dystrophy:** Characterized by **ring fibers**, sarcoplasmic masses, and an increase in internal nuclei. It is an autosomal dominant disorder caused by CTG repeat expansions. * **Nemaline Myopathy:** Defined by the presence of **'Nemaline rods'** (Z-band material) within the sarcoplasm, visible on Gomori Trichrome stain as small blue-dark purple rods. * **Spinal Muscular Atrophy (SMA):** A neurogenic atrophy characterized by **groups of small, rounded atrophic fibers** (group atrophy) interspersed with hypertrophied fibers, resulting from the loss of lower motor neurons in the anterior horn of the spinal cord. **High-Yield Pearls for NEET-PG:** * **Stain of Choice:** Modified Gomori Trichrome is essential to visualize RRFs. * **Biochemical marker:** These fibers are often **SDH (Succinate Dehydrogenase) positive** (as SDH is nuclear-encoded) but **COX (Cytochrome c Oxidase) negative** (if the mutation affects mtDNA-encoded COX subunits). * **Clinical Triad:** Mitochondrial diseases often present with the triad of ophthalmoplegia, proximal muscle weakness, and lactic acidosis. * **MERRF:** Myoclonic Epilepsy with Ragged Red Fibers is the classic syndrome associated with this finding [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Central Nervous System, pp. 1305-1306.

Q: What is the commonest site for glomangioma?

Nail bed. **Explanation:** **Glomus tumor (Glomangioma)** is a benign, exquisitely painful vascular neoplasm arising from the modified smooth muscle cells of the **glomus body** [1]. The glomus body is a specialized arteriovenous anastomosis involved in thermoregulation. 1. **Why the Nail Bed is Correct:** Glomus bodies are found in highest concentration in the dermis of the distal portions of the fingers and toes. Therefore, the **subungual region (nail bed)** is the most characteristic and commonest site for these tumors. They typically present as a small, firm, red-blue nodule under the nail. 2. **Why Other Options are Incorrect:** * **Head and Neck / Chest Wall:** While glomus tumors can occur anywhere in the skin or soft tissues, these are not the primary or most frequent locations. * **Retroperitoneal:** This is an extremely rare site. Deep-seated glomus tumors are uncommon and usually occur in the gastrointestinal tract (specifically the stomach) rather than the retroperitoneum. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Triad:** Paroxysmal pain, localized point tenderness, and sensitivity to cold. * **Hildreth’s Sign:** Relief of pain upon application of a tourniquet (positive in glomus tumors). * **Histology:** Nests of uniform, round "glomus cells" with "punched-out" nuclei surrounding thin-walled vascular vascular spaces. * **Immunohistochemistry (IHC):** Glomus cells are positive for **Alpha-Smooth Muscle Actin (α-SMA)** and Type IV Collagen (pericellular staining), but negative for endothelial markers like CD31 (which stain the vessels, not the tumor cells). **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of Infancy and Childhood, pp. 523-524.

Question 1

What is the characteristic finding in muscular dystrophy?

Accepted Answer

Muscle necrosis

Answer

Inflammatory cell infiltrate

Answer

Heterogenicity of fiber size

Answer

Nuclear proliferation beneath sarcolemma

Question 2

Which of the following genes is responsible for Fibrous dysplasia?

Accepted Answer

GNAS1

Answer

GNAS2

Answer

GNAS3

Answer

GNAS4

Question 3

Which of the following is FALSE regarding cystic fibrosis?

Accepted Answer

Associated with chromosome 7p

Answer

Associated with the CFTR gene

Answer

Autosomal recessive inheritance

Answer

Recurrent respiratory tract infection

Question 4

A 60-year-old man, treated for lung cancer, presents with a rash on his chest and pain in his upper arms and calves. He has difficulty raising his arms and climbing stairs. Muscle biopsy reveals perivascular infiltrates of lymphocytes and plasma cells extending between muscle fibers. Immunofluorescence shows immune complexes in the walls of intramuscular blood vessels. What is the most likely diagnosis?

Accepted Answer

Dermatomyositis

Answer

Becker muscular dystrophy

Answer

Lambert-Eaton myasthenic syndrome

Answer

Myasthenia gravis

Question 5

The term 'ragged red fibers' is applied to describe the skeletal muscle fibers in which of the following conditions?

Accepted Answer

Mitochondrial myopathy

Answer

Myotonic dystrophy

Answer

Nemaline myopathy

Answer

Spinal muscular atrophy

Question 6

What is the commonest site for glomangioma?

Accepted Answer

Nail bed

Answer

Head and neck

Answer

Chest wall

Answer

Retroperitoneal

Question 7

Osteogenic metastases is characteristic of which of the following?

Accepted Answer

Prostate carcinoma

Answer

Colon carcinoma

Answer

Thyroid carcinoma

Answer

Breast carcinoma

Question 8

Which tumor is not seen in the anterior mediastinum?

Accepted Answer

Neurofibroma

Answer

Teratoma

Answer

Thymic tumors

Answer

Thyroid tumors

Question 9

Which type of osteogenesis imperfecta is characterized by normal dentition and sclera?

Accepted Answer

Type 1A

Answer

Type 2

Answer

Type 3

Answer

Type 4B

Question 10

Synovial fluids of normal joints are usually devoid of collagen. Patients with rheumatoid diseases have various types of collagen in their synovial fluid, depending on the tissue being damaged. If a patient has type II collagen in their synovial fluid, which of the following tissues is being eroded?

Accepted Answer

Articular Cartilage

Answer

Vascular Endothelium

Answer

Compact Bone

Answer

Vascular Smooth Muscle

Bone and Soft Tissue Pathology — MCQs

Bone and Soft Tissue Pathology — MCQs

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