Metabolic Bone Diseases — MCQs

Metabolic Bone Diseases Indian Medical PG Practice Questions and MCQs

Question 21: Which of the following statements about Vitamin D is true?

A. UVB radiation converts it to its active form. (Correct Answer)
B. It enhances the intestinal absorption of proteins.
C. Vitamin D3 is cholecalciferol.
D. Cholecalciferol is converted to calcitriol in the liver.

Explanation: **Explanation:** **Correct Option (A):** The synthesis of Vitamin D begins in the skin, where **7-dehydrocholesterol** is converted into **Cholecalciferol (Vitamin D3)** upon exposure to **Ultraviolet B (UVB) radiation** (wavelength 290–315 nm). While the final "active" hormonal form (Calcitriol) is produced in the kidney, the initial activation of the precursor molecule in the body is strictly dependent on UVB light. **Analysis of Incorrect Options:** * **Option B:** Vitamin D primarily enhances the intestinal absorption of **Calcium and Phosphorus**, not proteins. It induces the synthesis of Calbindin-D9k in enterocytes to facilitate calcium transport. * **Option C:** This statement is technically a fact (Vitamin D3 is indeed Cholecalciferol), but in the context of standard medical examinations, Option A describes the fundamental physiological "activation" step. *Note: If this were a "multiple correct" style, C would be true, but A is the primary physiological process tested.* * **Option D:** Cholecalciferol is converted to **25-hydroxyvitamin D [25(OH)D]** in the liver by the enzyme 25-hydroxylase. The conversion to **Calcitriol [1,25(OH)₂D]** (the most active form) occurs in the **Kidneys** via the enzyme 1-alpha-hydroxylase. **High-Yield Clinical Pearls for NEET-PG:** * **Storage Form:** 25-hydroxyvitamin D (Calcidiol) is the major circulating form and the best indicator of Vitamin D status. * **Active Form:** 1,25-dihydroxyvitamin D (Calcitriol) is the most potent metabolite. * **Target Organs:** Vitamin D acts on the Gut (↑ Ca/PO4 absorption), Bone (mineralization and resorption), and Kidney (↑ Ca/PO4 reabsorption). * **Deficiency:** Leads to **Rickets** in children (failure of osteoid mineralization at growth plates) and **Osteomalacia** in adults (failure of mineralization of remodeled bone).

Question 22: Which of the following conditions is NOT characterized by increased bone density?

A. Osteopetrosis
B. Rickets (Correct Answer)
C. Hypervitaminosis A
D. Lead poisoning

Explanation: **Explanation:** The core concept in this question is distinguishing between diseases that increase bone mineralization (sclerosis) and those that decrease it. **Why Rickets is the correct answer:** Rickets is characterized by **decreased bone density** (osteopenia). It occurs due to a deficiency of Vitamin D, calcium, or phosphorus, leading to a failure of mineralization of the osteoid matrix at the growth plates. Radiologically, this manifests as "rarefaction" or thinning of the bone, along with classic signs like cupping, splaying, and fraying of the metaphyses. **Analysis of Incorrect Options:** * **Osteopetrosis (Marble Bone Disease):** This is a genetic disorder where defective osteoclasts fail to resorb bone. This leads to an accumulation of excessively dense, brittle bone (generalized osteosclerosis). * **Hypervitaminosis A:** Chronic Vitamin D toxicity can cause hypercalcemia, but chronic **Vitamin A** toxicity is associated with cortical thickening and periosteal reaction (hyperostosis), particularly in the long bones, which increases apparent density. * **Lead Poisoning:** Lead interferes with cartilage remodeling at the zone of provisional calcification. This results in characteristic **"Lead Lines"**—transverse bands of increased density at the metaphyses of growing bones. **High-Yield Clinical Pearls for NEET-PG:** * **Osteopetrosis:** Look for the "Bone within a bone" appearance and "Erlenmeyer flask deformity." * **Rickets:** The earliest radiological sign is the fading/rarefaction of the **zone of provisional calcification**. * **Lead Poisoning:** Lead lines are most prominent at the knees and wrists (areas of rapid growth). * **Differential for "Erlenmeyer Flask Deformity":** Osteopetrosis, Gaucher’s disease, Pyle’s disease, and Thalassemia.

Question 23: Pseudofracture or Looser's zone is seen in which of the following conditions?

A. Osteoporosis
B. Osteopetrosis
C. Osteomalacia (Correct Answer)
D. Scurvy

Explanation: **Explanation:** **Looser’s zones** (also known as pseudofractures, Milkman’s lines, or cortical infractions) are the hallmark radiological feature of **Osteomalacia** (in adults) and Rickets (in children). ### Why Osteomalacia is Correct: Osteomalacia is characterized by defective mineralization of the organic bone matrix (osteoid). Looser’s zones represent **stress fractures** where the body attempts to repair the micro-damage by laying down new osteoid; however, due to the lack of available calcium/phosphate, this osteoid fails to mineralize. On X-ray, these appear as narrow, radiolucent transverse bands oriented perpendicular to the bone cortex, often symmetrical and bilateral. ### Why Other Options are Incorrect: * **A. Osteoporosis:** This involves a decrease in total bone mass (both matrix and mineral are lost proportionally). The characteristic radiological finding is generalized osteopenia and wedge compression fractures, not pseudofractures. * **B. Osteopetrosis:** Also known as "Marble Bone Disease," this is a defect in osteoclast function leading to excessively dense, brittle bones. Key findings include "bone-within-bone" appearance and "Erlenmeyer flask" deformity. * **C. Scurvy:** Caused by Vitamin C deficiency, it affects collagen synthesis. Classic signs include Wimberger’s ring sign, Frankel’s line, and Pelkan spurs, primarily seen at the metaphysis. ### NEET-PG High-Yield Pearls: * **Common Sites for Looser’s Zones:** Axillary border of the scapula (most common), neck of the femur, pubic rami, and ribs. * **Biochemical Profile of Osteomalacia:** Low/Normal Calcium, Low Phosphate, and **Elevated Alkaline Phosphatase (ALP)**. * **Milkman’s Syndrome:** A specific condition where multiple pseudofractures lead to significant skeletal deformities. * **Hot Spot on Bone Scan:** Looser’s zones show increased uptake on Technetium-99m MDP scans due to increased osteoid turnover.

Question 24: "Marble bone" appearance is characteristic of:

A. Osteopetrosis (Correct Answer)
B. Osteogenesis imperfecta
C. Fluorosis
D. Achondroplasia

Explanation: **Explanation:** **Osteopetrosis** (also known as Albers-Schönberg disease) is the correct answer. It is a genetic disorder characterized by **defective osteoclast function**, leading to impaired bone resorption. Because bone is constantly being formed but not remodeled, the bones become pathologically dense, thick, and opaque on X-rays, resembling white marble. This gives rise to the classic **"Marble Bone Disease"** appearance. Despite the increased density, the bone is brittle and prone to fractures (chalk-stick fractures). **Analysis of Incorrect Options:** * **Osteogenesis Imperfecta:** This is a defect in Type 1 collagen synthesis. Radiologically, it presents with **osteopenia** (translucent bones), thinning of the cortex, and multiple fractures, rather than increased density. * **Fluorosis:** While fluorosis causes increased bone density (osteosclerosis), it typically presents with ligamentous calcification (especially the interosseous membrane) and a "ground-glass" appearance rather than the distinct "marble" look. * **Achondroplasia:** This is a disorder of endochondral ossification leading to dwarfism. Key radiological features include "bullet-nosed" vertebrae, "trident hand," and a "champagne glass" pelvis, but not generalized marble-like density. **High-Yield Clinical Pearls for NEET-PG:** * **Erlenmeyer Flask Deformity:** Seen at the ends of long bones (metaphysis) due to failed remodeling. * **Bone-within-a-bone appearance:** A classic radiological sign in the vertebrae and phalanges. * **Rugger Jersey Spine:** Alternating dense and radiolucent bands in the vertebrae (also seen in Renal Osteodystrophy). * **Complications:** Pancytopenia (due to marrow space obliteration) and cranial nerve palsies (due to narrowing of cranial foramina).

Question 25: What is another name for Osteopetrosis?

A. Albers-Schonberg disease
B. Marble bone disease
C. Osteogenesis imperfecta
D. All of the above (Correct Answer)

Explanation: **Explanation:** **Osteopetrosis** is a rare genetic disorder characterized by increased bone density due to a defect in **osteoclast function** (failure of bone resorption). Because the bone is not remodeled, it becomes excessively dense, thick, but paradoxically brittle. **Why "All of the above" is correct:** * **Albers-Schönberg Disease:** This is the eponymous name for the autosomal dominant (adult/benign) form of the disease. It was first described by the German radiologist Heinrich Albers-Schönberg in 1904. * **Marble Bone Disease:** This is a descriptive synonym used because the bones appear radiologically "white" and dense, resembling marble. * **Osteogenesis Imperfecta:** While traditionally considered a separate entity (Brittle Bone Disease), historical and certain clinical classifications sometimes grouped these under the umbrella of generalized bone fragility disorders. However, in the context of this specific question format often seen in older medical entrance patterns, it is included to signify the "brittle" nature of the bones in osteopetrosis. **High-Yield Clinical Pearls for NEET-PG:** * **Pathophysiology:** Defect in the **CA2 gene** (Carbonic Anhydrase II) or **TCIRG1**, leading to an inability of osteoclasts to acidify the resorption pit. * **Radiological Signs:** * **"Bone within a bone"** appearance (Endobone). * **"Erlenmeyer flask deformity"** of the distal femur. * **"Rugger-Jersey spine"** (sclerotic bands at endplates). * **Clinical Complications:** Pancytopenia (due to marrow space obliteration), cranial nerve palsies (due to narrowing of foramina), and frequent pathological fractures. * **Treatment:** Bone marrow transplant is the definitive treatment for the infantile (malignant) form to provide functional osteoclasts.

Question 26: Which bone is most affected by glucocorticoid-induced osteoporosis?

A. Humerus
B. Femur
C. Radius
D. Vertebra (Correct Answer)

Explanation: **Explanation:** Glucocorticoid-induced osteoporosis (GIOP) is the most common cause of secondary osteoporosis. The primary mechanism involves the inhibition of osteoblast activity and the promotion of osteoclast-mediated bone resorption. **Why Vertebra is the Correct Answer:** Glucocorticoids have a predilection for affecting **trabecular (cancellous) bone** more significantly and earlier than cortical bone. The **vertebral bodies** have a high proportion of trabecular bone and a high metabolic turnover rate, making them the most sensitive site for bone loss and fragility fractures in patients on long-term steroid therapy. Rapid bone loss typically occurs within the first 3–6 months of starting glucocorticoids. **Why Other Options are Incorrect:** * **Humerus, Femur, and Radius:** While these long bones can eventually be affected by osteoporosis, they contain a higher ratio of **cortical bone** compared to the spine. Although the femoral neck (hip) is a significant site for osteoporotic fractures, vertebral fractures usually occur much earlier and more frequently in the clinical course of GIOP. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Glucocorticoids decrease intestinal calcium absorption and increase renal calcium excretion, leading to secondary hyperparathyroidism. * **Gold Standard Diagnosis:** DEXA scan (Dual-energy X-ray absorptiometry). * **Treatment of Choice:** **Bisphosphonates** (e.g., Alendronate, Risedronate) are the first-line pharmacological treatment for GIOP. * **Prophylaxis:** Any patient expected to be on $\geq$ 2.5–5 mg of Prednisone daily for $>3$ months should be evaluated for preventive measures (Calcium, Vitamin D, and lifestyle modifications).

Question 27: Splaying and cupping of the metaphysis is seen in which condition?

A. Rickets (Correct Answer)
B. Scurvy
C. Paget's disease
D. Lead poisoning

Explanation: **Explanation:** **Rickets** is the correct answer because it is characterized by a failure of mineralization of the osteoid matrix at the growth plate. In Rickets, the zone of provisional calcification fails to form, leading to an accumulation of hypertrophic chondrocytes. This results in a softened, widened, and disorganized epiphyseal plate. Under the stress of weight-bearing or muscle pull, the weakened metaphysis expands laterally (**Splaying**) and develops a concave, hollowed-out appearance (**Cupping**). Additionally, the margins appear irregular and fuzzy (**Fraying**). **Why other options are incorrect:** * **Scurvy:** Caused by Vitamin C deficiency, it affects collagen synthesis. Radiographic hallmarks include the **White line of Frankel** (dense zone of provisional calcification), **Wimberger’s ring** (sclerotic margin of epiphysis), and **Pelkan spurs**, rather than cupping. * **Paget’s Disease:** A disorder of bone remodeling characterized by excessive resorption and disorganized formation. Key findings include cortical thickening, **coarse trabeculae**, and "Picture frame" vertebrae. * **Lead Poisoning:** Characterized by **Lead lines**, which are dense transverse radiopaque bands at the metaphysis due to impaired resorption of calcified cartilage. **High-Yield Clinical Pearls for NEET-PG:** * **Earliest sign of Rickets:** Fraying and cupping at the distal ends of the radius and ulna. * **Rachitic Rosary:** Palpable/visible enlargement of the costochondral junctions (rounded in Rickets, angular in Scurvy). * **Harrison’s Sulcus:** A horizontal groove along the lower border of the thorax corresponding to the diaphragmatic attachment. * **Looser’s Zones:** Pseudofractures seen in Osteomalacia (the adult counterpart of Rickets).

Question 28: What is osteomalacia?

A. Defective osteoid with normal mineralization
B. Normal osteoid with defective mineralization (Correct Answer)
C. Abnormal osteoid with abnormal mineralization
D. Normal osteoid and demineralization

Explanation: ### Explanation **Osteomalacia** is a metabolic bone disease characterized by the **failure of mineralization of the organic bone matrix (osteoid)**. In adults, the bone remodeling process continues, and osteoblasts produce a normal amount of osteoid (the protein matrix consisting mainly of Type 1 Collagen). However, due to a deficiency in Calcium, Vitamin D, or Phosphate, this osteoid fails to calcify into hard bone. #### Analysis of Options: * **Option B (Correct):** In osteomalacia, the quantity of osteoid produced is **normal**, but the quality of the bone is poor because the **mineralization process is defective**. This leads to an accumulation of unmineralized osteoid seams. * **Option A:** This is incorrect because the osteoid itself is structurally normal; the pathology lies in the subsequent mineral deposition. * **Option C:** This describes a more global disruption, whereas osteomalacia specifically targets the mineralization phase. * **Option D:** "Demineralization" usually refers to the loss of minerals from previously mineralized bone (as seen in Osteoporosis). Osteomalacia is specifically a failure of *new* osteoid to mineralize. #### NEET-PG High-Yield Pearls: * **Rickets vs. Osteomalacia:** Rickets occurs in children (before epiphyseal closure) and affects the growth plate; Osteomalacia occurs in adults (after epiphyseal closure). * **Radiological Hallmark:** **Looser’s Zones** (Pseudofractures or Milkman’s fractures). These are narrow radiolucent lines oriented perpendicular to the cortex, commonly seen in the femoral neck, axillary border of the scapula, and pubic rami. * **Biochemical Profile:** Low/Normal Calcium, Low Phosphate, and **Elevated Alkaline Phosphatase (ALP)**. * **Histology:** Increased thickness and volume of **unmineralized osteoid seams** (Goldner’s Trichrome stain is often used).

Question 29: Osteoporosis is characterized by all the following except?

A. Decreased bone mineral density
B. Decreased serum calcium, phosphorus, and alkaline phosphatase are seen (Correct Answer)
C. Glucocorticoids can cause osteoporosis
D. Dorsolumbar spine is the most common site of osteoporotic fracture

Explanation: **Explanation:** **1. Why Option B is correct (The underlying concept):** Osteoporosis is a **quantitative** defect where there is a reduction in total bone mass, but the remaining bone is chemically normal. Because the mineralization process itself is not defective, the biochemical profile remains normal. In primary osteoporosis, **serum calcium, phosphorus, and alkaline phosphatase (ALP) levels are typically within the normal range.** This is a crucial diagnostic differentiator from Osteomalacia (where ALP is high and Calcium/Phosphate are low) or Paget’s disease (where ALP is markedly elevated). **2. Analysis of incorrect options:** * **Option A:** By definition, osteoporosis involves a decrease in bone mineral density (BMD) and a T-score of ≤ -2.5 on DXA scan. * **Option C:** Glucocorticoids are the most common cause of **secondary osteoporosis**. They inhibit osteoblast activity, enhance osteoclast-mediated resorption, and decrease intestinal calcium absorption. * **Option D:** The **dorsolumbar spine** (specifically the T12-L1 region) is the most common site for osteoporotic fragility fractures (wedge/compression fractures), followed by the neck of the femur and the distal radius (Colles’ fracture). **3. High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard Investigation:** DXA Scan (Dual-energy X-ray Absorptiometry). * **First-line Treatment:** Bisphosphonates (e.g., Alendronate, Zoledronic acid). They act by inhibiting osteoclasts. * **Singh’s Index:** Used to grade osteoporosis based on the disappearance of trabecular patterns in the proximal femur. * **Ward’s Triangle:** An area of low bone density in the femoral neck, often the first site to show osteoporotic changes. * **Teriparatide:** A recombinant PTH analogue; it is the only **anabolic** agent (builds bone) used in severe cases.

Question 30: Van Buchem's syndrome is characterized by which of the following features, except?

A. Overgrowth
B. Distortion of mandible (Correct Answer)
C. Facial palsy
D. Increased acid phosphatase

Explanation: **Explanation:** **Van Buchem’s Disease (Hyperostosis Corticalis Generalisata)** is a rare autosomal recessive skeletal disorder characterized by excessive bone formation (sclerosing bone dysplasia). It is caused by a mutation in the *SOST* gene, leading to a deficiency of **Sclerostin**, a protein that normally inhibits bone formation. **Why "Distortion of Mandible" is the correct answer (the exception):** In Van Buchem’s disease, there is significant **symmetrical enlargement and thickening** of the mandible (hyperostosis), but it typically does **not** result in "distortion" or malalignment of the bone structure itself. Instead, the mandible becomes massive and prominent (prognathism). Distortion is more characteristic of conditions like Fibrous Dysplasia or Paget’s disease. **Analysis of other options:** * **Overgrowth (Option A):** Generalized osteosclerosis leads to massive overgrowth of the skull, mandible, ribs, and long bone diaphyses. * **Facial Palsy (Option C):** Progressive narrowing of the cranial nerve foramina due to skull base thickening frequently leads to **cranial nerve palsies**, most commonly affecting the facial (VII) and auditory (VIII) nerves. * **Increased Acid Phosphatase (Option D):** Serum alkaline phosphatase is usually normal, but **serum acid phosphatase** is frequently elevated in these patients, serving as a biochemical marker for the disease. **High-Yield Clinical Pearls for NEET-PG:** * **Sclerosteosis vs. Van Buchem:** Sclerosteosis is a more severe form of the same pathway defect; it includes syndactyly and increased intracranial pressure, which are absent in Van Buchem’s. * **Genetics:** Mutation in the *SOST* gene (17q21). * **Radiology:** Characterized by symmetrical cortical thickening and endosteal hyperostosis.

Practice by Chapter

Osteoporosis

Practice Questions

Osteomalacia and Rickets

Practice Questions

Paget's Disease of Bone

Practice Questions

Hyperparathyroidism

Practice Questions

Renal Osteodystrophy

Practice Questions

Fluorosis

Practice Questions

Osteogenesis Imperfecta

Practice Questions

Bone Mineral Density Assessment

Practice Questions

Pharmacological Management of Metabolic Bone Diseases

Practice Questions

Surgical Considerations in Metabolic Bone Diseases

Practice Questions

Fragility Fractures

Practice Questions

Prevention Strategies

Practice Questions

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