Metabolic Bone Diseases — MCQs

An 80-year-old man presents with slowly progressive enlargement of his head circumference, deformities of long bones and spine, and chronic pain of the affected skeletal segments. Laboratory studies show elevated serum alkaline phosphatase and high urine hydroxyproline. X-ray findings are consistent with Paget disease. Which of the following is the most likely pathogenetic mechanism of this condition?

Metabolic Bone Diseases Indian Medical PG Practice Questions and MCQs

Question 71: Milkman's fracture is a type of:

A. Pseudofracture (Correct Answer)
B. Clavicular fracture
C. Humeral fracture
D. Metacarpal fracture

Explanation: **Explanation:** **Milkman’s fracture** is a classic radiological feature of **Osteomalacia** (softening of bones due to Vitamin D deficiency in adults). Despite the name, it is not a true traumatic fracture but a **Pseudofracture**, also known as a **Looser’s zone**. ### Why the correct answer is right: Pseudofractures are narrow, radiolucent lines that appear perpendicular to the bone cortex. They represent **unmineralized osteoid** (stress fractures that have healed with non-mineralized callus) at sites where major arteries cross the bone, causing mechanical pulsation. They are typically bilateral, symmetrical, and occur in non-weight-bearing areas. ### Why the other options are wrong: * **B, C, and D (Clavicular, Humeral, Metacarpal fractures):** While these bones can technically sustain fractures, Milkman’s fracture refers specifically to a pathological radiological sign of metabolic bone disease, not a traumatic injury to a specific anatomical bone. While Looser's zones can occur in the clavicle or humerus, the term "Milkman's fracture" is synonymous with the *type* of lesion (pseudofracture) rather than the *location*. ### NEET-PG High-Yield Pearls: * **Common Sites:** Axillary border of the scapula (most common), inner cortex of the femoral neck, pubic rami, and ribs. * **Radiological Triad of Osteomalacia:** Generalized rarefaction (decreased bone density), Looser’s zones, and "Protrusio Acetabuli." * **Biochemical Profile:** Low/Normal Calcium, Low Phosphate, and **Elevated Alkaline Phosphatase (ALP)**. * **Clinical Sign:** "Waddling gait" due to proximal muscle weakness and pelvic girdle pain.

Question 72: Which of the following conditions shows the Looser's zone or Pseudofracture?

A. Vitamin C deficiency
B. Osteoporosis
C. Thyroiditis
D. Osteomalacia (Correct Answer)

Explanation: **Explanation:** **1. Why Osteomalacia is Correct:** Looser’s zones (also known as **pseudofractures** or Milkman’s lines) are the pathognomonic radiological hallmark of **Osteomalacia** (in adults) and Rickets (in children). They represent cortical stress fractures that have healed with **unmineralized osteoid** rather than mature bone. On X-ray, they appear as thin, radiolucent lines oriented perpendicular to the bone cortex, often symmetrical. Common sites include the axillary border of the scapula, inner cortex of the femoral neck, pubic rami, and ribs. **2. Why Other Options are Incorrect:** * **A. Vitamin C deficiency (Scurvy):** Characterized by defective collagen synthesis. Classic radiological signs include the **White line of Frankel**, Wimberger’s ring sign, and Pelkan spurs, but not pseudofractures. * **B. Osteoporosis:** This involves a decrease in total bone mass (both matrix and mineral are lost proportionally). While it increases the risk of true pathological fractures (e.g., Colles' or vertebral compression fractures), it does not typically present with Looser’s zones. * **C. Thyroiditis:** This is an inflammatory condition of the thyroid gland. While hyperthyroidism can lead to secondary osteoporosis, thyroiditis itself is not a primary cause of pseudofractures. **3. NEET-PG Clinical Pearls:** * **Biochemical Triad of Osteomalacia:** Low/Normal Calcium, Low Phosphate, and **Elevated Alkaline Phosphatase (ALP)**. * **Gold Standard Diagnosis:** Bone biopsy showing increased osteoid volume/thickness. * **Milkman’s Syndrome:** A specific clinical eponym for multiple spontaneous pseudofractures associated with osteomalacia. * **Differential Diagnosis for Looser's Zones:** Osteomalacia, Rickets, Paget’s disease, and occasionally Renal Osteodystrophy.

Question 73: Osteogenesis imperfecta has an abnormality in which type of collagen?

A. Collagen 3
B. Collagen 2
C. Collagen 4
D. Collagen 1 (Correct Answer)

Explanation: **Explanation:** **Osteogenesis Imperfecta (OI)**, also known as "Brittle Bone Disease," is a genetic disorder characterized by increased bone fragility. The fundamental defect lies in the synthesis of **Type 1 Collagen**, which is the primary structural protein in bone, skin, tendons, and sclera. Most cases are autosomal dominant and result from mutations in the **COL1A1** or **COL1A2** genes. These mutations lead to either a quantitative deficiency or a qualitative defect (structural abnormality) in the collagen triple helix, resulting in weak osteoid and frequent fractures. **Analysis of Options:** * **Option D (Correct): Type 1 Collagen** is the "bone" collagen (Mnemonic: Type **One** is in B**one**). It provides tensile strength to the organic matrix. * **Option B: Type 2 Collagen** is primarily found in hyaline **cartilage** and vitreous humor (Mnemonic: Type **Two** is in Car-**two**-lage). * **Option A: Type 3 Collagen** (Reticulin) is found in extensible connective tissues like blood vessels, skin, and fetal tissues. It is deficient in the Vascular type of Ehlers-Danlos Syndrome. * **Option C: Type 4 Collagen** is a major component of the **Basement Membrane** (Mnemonic: Type **Four** is on the **Floor**). Defects here lead to Alport Syndrome. **High-Yield Clinical Pearls for NEET-PG:** 1. **Clinical Triad:** Fragile bones (multiple fractures), **Blue Sclera** (due to thinning of collagen allowing uveal pigment to show through), and **Early Otosclerosis** (hearing loss). 2. **Dental Findings:** Dentinogenesis imperfecta (translucent, weak teeth). 3. **Sillence Classification:** Type I is the most common and mildest; Type II is the most severe (perinatal lethal). 4. **Radiology:** Look for "Popcorn calcifications" at metaphyses and "Codfish vertebrae" (biconcave).

Question 74: All the following are true about osteoporosis except?

A. There is bending of long bones
B. There is hypercalcemia (Correct Answer)
C. There are vertebral compression fractures
D. Milkman's fracture

Explanation: **Explanation:** In **Osteoporosis**, there is a reduction in total bone mass (both mineral and matrix), but the **chemical composition of the remaining bone is normal**. Therefore, serum levels of Calcium, Phosphate, and Alkaline Phosphatase remain **characteristically normal**. The presence of hypercalcemia (Option B) should instead prompt an investigation for conditions like primary hyperparathyroidism or malignancy. **Analysis of Options:** * **Option A (Bending of long bones):** While more characteristic of Osteomalacia (where bone is soft due to poor mineralization), severe osteoporosis can lead to skeletal deformities and bowing due to the inability of the thinned cortex to support weight. * **Option C (Vertebral compression fractures):** This is a hallmark of osteoporosis. The axial skeleton is highly susceptible, leading to "codfish vertebrae" or wedge fractures, often resulting in kyphosis (Dowager’s hump). * **Option D (Milkman’s fracture):** Also known as **Looser’s zones** or pseudofractures. While classically the pathognomonic sign for **Osteomalacia**, some examiners include it in osteoporosis discussions in the context of "fragility fractures" or mixed metabolic pictures. However, in the context of this question, the biochemical normalcy of osteoporosis makes "Hypercalcemia" the most definitively "false" statement. **NEET-PG High-Yield Pearls:** 1. **Gold Standard Investigation:** DEXA Scan (T-score ≤ -2.5 defines Osteoporosis). 2. **Biochemical Profile:** In Osteoporosis, Ca, PO₄, and ALP are all **Normal**. 3. **Most Common Site of Fracture:** Vertebral body (overall); Neck of femur (clinically significant). 4. **Singh’s Index:** Used to grade osteoporosis based on the disappearance of trabecular patterns in the proximal femur.

Question 75: Which of the following is NOT true about Osteogenesis imperfecta?

A. Impaired healing of fractures (Correct Answer)
B. Deafness
C. Laxity of joints
D. Fragile bones prone to fracture

Explanation: **Explanation:** Osteogenesis Imperfecta (OI), also known as "Brittle Bone Disease," is a genetic disorder primarily caused by mutations in the **COL1A1 and COL1A2 genes**, leading to a quantitative or qualitative defect in **Type I Collagen**. **Why Option A is the Correct Answer:** Contrary to what might be expected in a disease with "fragile bones," **fracture healing in OI is generally normal** in terms of timing and callus formation. The defect lies in the structural integrity of the bone matrix (collagen), not in the cellular mechanisms of the healing cascade (osteoblasts and fibroblasts). In fact, some patients may even develop "Hyperplastic Callus" (especially in Type V OI), which can sometimes be mistaken for osteosarcoma. **Analysis of Incorrect Options:** * **B. Deafness:** This is a classic feature (Otosclerosis). Conductive or sensorineural hearing loss occurs due to the involvement of the auditory ossicles, which are also composed of bone. * **C. Laxity of joints:** Type I collagen is a major component of ligaments and tendons. Its defect leads to significant ligamentous laxity and joint hypermobility. * **D. Fragile bones:** This is the hallmark of the disease. The defective collagen matrix leads to decreased bone density and extreme cortical thinning, making bones highly susceptible to multiple fractures from minimal trauma. **NEET-PG High-Yield Pearls:** * **Blue Sclera:** The most iconic clinical sign, caused by the thinning of the scleral collagen allowing the underlying choroidal veins to show through. * **Dentinogenesis Imperfecta:** "Opalescent teeth" due to deficiency in dentin. * **Classification:** The **Sillence Classification** is used to grade severity (Type II is the most severe/lethal perinatally). * **Treatment:** **Bisphosphonates** (like Pamidronate) are the mainstay to increase bone mineral density and reduce pain. Surgical management often involves **Sillence (telescopic) nails**.

Question 76: Osteomalacia is associated with which of the following?

A. Decreased osteoid volume
B. Decreased osteoid surface
C. Increased osteoid maturation time (Correct Answer)
D. Increased mineral apposition rate

Explanation: **Explanation:** Osteomalacia is a metabolic bone disease characterized by **defective mineralization** of the organic bone matrix (osteoid). In a healthy state, osteoblasts secrete osteoid, which undergoes a "maturation" period before being mineralized. **Why the correct answer is right:** In Osteomalacia, the mineralization process is delayed or absent due to deficiencies (commonly Vitamin D, Calcium, or Phosphate). This leads to an **increased osteoid maturation time** (the lag time between osteoid deposition and its subsequent mineralization). Because the matrix is produced but not hardened, there is a characteristic accumulation of unmineralized bone. **Analysis of incorrect options:** * **A & B (Decreased osteoid volume/surface):** These are incorrect because Osteomalacia actually shows **increased** osteoid volume and surface. Since the osteoid is not being mineralized into mature bone, it "piles up," leading to thickened osteoid seams. * **D (Increased mineral apposition rate):** The mineral apposition rate (MAR) refers to the speed at which the mineralization front moves. In Osteomalacia, mineralization is sluggish or halted, resulting in a **decreased** mineral apposition rate. **NEET-PG High-Yield Pearls:** * **Histology Gold Standard:** Presence of widened osteoid seams (increased width and volume) and a decreased calcification rate. * **Radiology:** Look for **Looser’s zones** (Pseudofractures/Milkman’s fractures), which are pathognomonic. They are typically bilateral and symmetrical, found in the femoral neck, axillary border of the scapula, and pubic rami. * **Biochemistry:** Typically shows **low/normal Calcium**, **low Phosphate**, and **elevated Alkaline Phosphatase (ALP)**. * **Rickets vs. Osteomalacia:** Rickets occurs in children (before epiphyseal closure) and affects the growth plate; Osteomalacia occurs in adults (after epiphyseal closure).

Question 77: Triradiate pelvis is typically seen in which of the following conditions?

A. Rickets (Correct Answer)
B. Chondrodystrophy
C. Osteoporosis
D. Hyperparathyroidism

Explanation: ### Explanation **Correct Answer: A. Rickets** **Mechanism:** Triradiate pelvis (also known as a "heart-shaped" or "beaked" pelvis) is a classic radiological feature of **Rickets** (in children) and **Osteomalacia** (in adults). The underlying pathology is a failure of mineralization of the bone matrix (osteoid), leading to soft, pliable bones. Under the physiological stress of weight-bearing and the upward thrust of the femoral heads, the softened acetabula are pushed inward (protrusio acetabuli), while the sacrum is pushed downward. This structural collapse results in the characteristic three-rayed or "triradiate" appearance of the pelvic inlet. **Analysis of Incorrect Options:** * **B. Chondrodystrophy (e.g., Achondroplasia):** Typically presents with a **"Champagne glass"** appearance of the pelvis, characterized by a broad, short ilium and a narrow greater sciatic notch. * **C. Osteoporosis:** Characterized by a decrease in total bone mass (both matrix and mineral). While it leads to fractures (especially of the neck of femur and vertebrae), it does not typically cause the plastic deformation required to form a triradiate pelvis. * **D. Hyperparathyroidism:** Leads to subperiosteal bone resorption and "Salt and Pepper" skull. While it can cause osteopenia, the specific triradiate deformity is not a hallmark feature. **High-Yield Clinical Pearls for NEET-PG:** * **Rickets Radiological Signs:** Cupping, fraying, and splaying of metaphyses (best seen at the lower end of the radius/ulna), and **Harrison’s sulcus**. * **Looser’s Zones (Pseudofractures):** Pathognomonic for Osteomalacia; these are radiolucent lines oriented perpendicular to the cortex. * **Protrusio Acetabuli:** Also seen in Rheumatoid Arthritis, Paget’s disease, and Marfan syndrome. * **Pelvic Shapes:** * *Triradiate:* Rickets/Osteomalacia. * *Champagne Glass:* Achondroplasia. * *Mickey Mouse Ear:* Down Syndrome (iliac wings).

Question 78: All of the following drugs can be used in the treatment of postmenopausal osteoporosis EXCEPT:

A. Alendronate
B. Teriparatide
C. Calcium
D. Thyroxine (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Thyroxine** **Why Thyroxine is the Correct Answer:** Thyroxine is not a treatment for osteoporosis; in fact, **excessive thyroxine is a known risk factor for secondary osteoporosis.** High levels of thyroid hormone (hyperthyroidism or over-replacement therapy) increase bone turnover by stimulating osteoclastic activity more than osteoblastic activity. This leads to a shortened remodeling cycle and a net loss of bone mineral density (BMD). Therefore, it is contraindicated as a treatment and must be monitored carefully in osteoporotic patients. **Analysis of Other Options:** * **A. Alendronate:** A nitrogen-containing **Bisphosphonate**. It is the first-line treatment for postmenopausal osteoporosis. It works by inhibiting osteoclast-mediated bone resorption. * **B. Teriparatide:** A recombinant human **Parathyroid Hormone (rhPTH 1-34)**. It is an anabolic agent that stimulates new bone formation (osteoblastic activity) when given in intermittent pulses. * **C. Calcium:** Essential supplementation in osteoporosis management. It ensures adequate mineralization of the bone matrix and suppresses compensatory PTH secretion which would otherwise cause bone resorption. **NEET-PG High-Yield Pearls:** * **Drug of Choice (DOC):** Bisphosphonates (e.g., Alendronate, Zoledronic acid) are the first-line agents for most patients. * **Anabolic vs. Antiresorptive:** Teriparatide and Romosozumab are **anabolic** (build bone), while Bisphosphonates, Denosumab, and SERMs are **antiresorptive** (prevent breakdown). * **Denosumab:** A monoclonal antibody against **RANKL**, administered subcutaneously every 6 months. * **Side Effect Note:** Long-term bisphosphonate use is associated with **Atypical Femur Fractures** and **Osteonecrosis of the Jaw (ONJ)**.

Question 79: Sudeck's atrophy is associated with which of the following conditions?

A. Osteoporosis
B. Osteophyte formation
C. Osteopenia (Correct Answer)
D. Osteochondritis

Explanation: **Explanation:** **Sudeck’s atrophy**, also known as **Complex Regional Pain Syndrome (CRPS) Type 1**, is a condition characterized by post-traumatic reflex sympathetic dystrophy. The hallmark radiographic feature of this condition is **patchy, periarticular osteopenia** (rarefaction of bone). 1. **Why Osteopenia is correct:** Following an injury (often a distal radius fracture), abnormal sympathetic activity leads to increased local blood flow and rapid bone resorption. This results in a localized decrease in bone mineral density, which appears on X-rays as "ground-glass" appearance or patchy demineralization, specifically termed **osteopenia**. 2. **Why other options are incorrect:** * **Osteoporosis:** While both involve low bone density, osteoporosis is typically a systemic metabolic process. Sudeck’s is a localized, post-traumatic phenomenon. In exam nomenclature, "osteopenia" is the preferred term for the specific radiographic finding in CRPS. * **Osteophyte formation:** These are bony outgrowths associated with degenerative conditions like Osteoarthritis, not sympathetic dystrophy. * **Osteochondritis:** This refers to inflammation or necrosis of bone and cartilage (e.g., Perthes disease), which has a different pathophysiology involving ischemia. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Triad:** Burning pain, autonomic dysfunction (swelling/sweating), and trophic changes (skin thinning/hair loss). * **Common Site:** Most frequently seen after a **Colles’ fracture**. * **Diagnosis:** Primarily clinical; **Triple-phase bone scan** is the most sensitive imaging modality (shows increased uptake). * **Treatment:** Early mobilization is preventive; Vitamin C supplementation post-fracture is thought to reduce incidence.

Question 80: An 80-year-old man presents with slowly progressive enlargement of his head circumference, deformities of long bones and spine, and chronic pain of the affected skeletal segments. Laboratory studies show elevated serum alkaline phosphatase and high urine hydroxyproline. X-ray findings are consistent with Paget disease. Which of the following is the most likely pathogenetic mechanism of this condition?

A. Generalized reduction in bone mass
B. Genetic deficiency of carbonic anhydrase II
C. Monoclonal proliferation of plasma cells
D. Paramyxovirus infection of osteoclasts (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Paramyxovirus infection of osteoclasts** **Pathogenesis:** Paget disease (Osteitis Deformans) is characterized by disordered bone remodeling. The primary defect lies in **hyperactive osteoclasts**. The current leading theory for its etiology is a **slow virus infection** (specifically **Paramyxoviruses** like Measles or Respiratory Syncytial Virus) in genetically susceptible individuals. These viruses act as triggers, leading to the formation of giant, multinucleated osteoclasts (containing up to 100 nuclei) that exhibit increased sensitivity to RANKL and Vitamin D. This results in three phases: Osteolytic, Mixed, and Osteosclerotic (burnt-out) phases. **Analysis of Incorrect Options:** * **A. Generalized reduction in bone mass:** This describes **Osteoporosis**, where bone quality is normal but quantity is decreased. Paget disease involves localized, disordered overgrowth, not generalized loss. * **B. Genetic deficiency of carbonic anhydrase II:** This is the hallmark of **Osteopetrosis** (Marble Bone Disease). Carbonic anhydrase II is essential for osteoclasts to create an acidic environment to dissolve bone; its deficiency leads to dense, brittle bones. * **C. Monoclonal proliferation of plasma cells:** This refers to **Multiple Myeloma**, which presents with "punched-out" lytic lesions and hypercalcemia, rather than the sclerotic/mixed bone changes seen in Paget disease. **NEET-PG High-Yield Pearls:** * **Clinical Triad:** Increasing hat size (skull enlargement), bowing of femur/tibia, and hearing loss (due to nerve compression in the foramen). * **Markers:** **Elevated Serum Alkaline Phosphatase (ALP)** reflects high osteoblastic activity; **High Urine Hydroxyproline** reflects high osteoclastic bone resorption. Serum Calcium and Phosphate are typically **normal**. * **X-ray Signs:** "Blade of grass" or "Flame-shaped" lytic lesions; "Cotton wool" appearance of the skull; "Picture frame" vertebrae. * **Complication:** The most dreaded late complication is **Osteosarcoma** (<1% of cases). * **Treatment:** **Bisphosphonates** (Drug of choice) to inhibit osteoclasts.

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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