Metabolic Bone Diseases — MCQs

A 90-year-old male complains of hip and back pain. He has also developed headaches, hearing loss, and tinnitus. On physical exam, the skull appears enlarged with prominent superficial veins. There is marked kyphosis, and the bones of the leg appear deformed. Plasma alkaline phosphatase is elevated. A skull x-ray shows sharply demarcated lucencies in the frontal, parietal, and occipital bones. X-rays of the hip show thickening of the pelvic brim. What is the most likely diagnosis?

Q40Medium

A 60-year-old male presents with a bony abnormality at the upper tibia associated with sensorineural hearing loss. Laboratory examination reveals elevated serum alkaline phosphatase levels (440 mU/L) with normal serum calcium and phosphate. A skeletal survey shows "ivory vertebrae" and "cotton wool spots" on skull X-ray. What is the most likely diagnosis?

Metabolic Bone Diseases Indian Medical PG Practice Questions and MCQs

Question 31: What is the most common site of osteoporosis?

A. Humerus
B. Vertebrae (Correct Answer)
C. Scapula
D. Flat bones

Explanation: **Explanation:** **1. Why Vertebrae is the Correct Answer:** Osteoporosis is a systemic skeletal disorder characterized by low bone mass and micro-architectural deterioration. It primarily affects **trabecular (cancellous) bone** more than cortical bone because trabecular bone has a higher metabolic turnover rate and a larger surface area exposed to osteoclast activity. The **vertebral bodies** have the highest concentration of trabecular bone in the human body, making them the most common site for both asymptomatic bone loss and clinical fractures (vertebral compression fractures). **2. Analysis of Incorrect Options:** * **Humerus (A):** While proximal humerus fractures are common in osteoporotic elderly patients (part of the "fragility fracture" group), they occur less frequently than vertebral or hip fractures. * **Scapula (C):** The scapula is rarely affected by osteoporosis to a clinical degree because it is not a primary weight-bearing bone and has a different structural composition. * **Flat bones (D):** While some flat bones (like the pelvis) contain trabecular bone, the term is too broad. The vertebrae remain the statistically dominant site for osteoporotic changes. **3. NEET-PG High-Yield Pearls:** * **Most common site of fracture:** Vertebra (often asymptomatic/wedge fracture). * **Most common site of "Colles' fracture":** Distal Radius (often the first sign of osteoporosis in postmenopausal women). * **Most serious site of fracture:** Hip (Neck of femur/Intertrochanteric), associated with high mortality. * **Gold Standard Investigation:** DEXA Scan (Dual-Energy X-ray Absorptiometry). * **DEXA Sites:** Usually measured at the Lumbar Spine (L1-L4) and Hip (Total hip/Femoral neck). * **Diagnosis:** T-score ≤ -2.5 SD.

Question 32: Which of the following statements is WRONG regarding Hypophosphataemic Rickets?

A. Hypocalcemia
B. Normal Alkaline Phosphatase (ALP) (Correct Answer)
C. Elevated levels of Parathyroid Hormone
D. Intestinal malabsorption

Explanation: ### Explanation: Hypophosphataemic Rickets **Hypophosphataemic Rickets** (Vitamin D-resistant Rickets) is most commonly inherited as an X-linked dominant trait (XLH). The primary defect is a mutation in the **PHEX gene**, leading to increased levels of **FGF-23** (a phosphatonin). This results in renal phosphate wasting and impaired 1-alpha-hydroxylation of Vitamin D. #### 1. Why "Normal Alkaline Phosphatase" is the WRONG statement: In all forms of active rickets and osteomalacia, **Alkaline Phosphatase (ALP) is characteristically elevated**. ALP is a marker of osteoblastic activity; as the body attempts to mineralize the excessive unmineralized osteoid (the hallmark of rickets), ALP levels rise significantly. Therefore, a "Normal ALP" is clinically inconsistent with a diagnosis of active rickets. #### 2. Analysis of other options: * **Hypocalcemia:** While the primary defect is phosphate loss, serum calcium can be low or low-normal because the deficiency in 1,25-(OH)₂D (calcitriol) reduces intestinal calcium absorption. * **Elevated PTH:** Low serum calcium and low calcitriol levels trigger the parathyroid glands, leading to **Secondary Hyperparathyroidism**. * **Intestinal Malabsorption:** Due to the failure of the kidneys to convert Vitamin D to its active form (1,25-(OH)₂D), there is a secondary failure of calcium and phosphate absorption from the gut. #### 3. NEET-PG High-Yield Pearls: * **Biochemical Profile:** Low Serum Phosphate, Low/Normal Serum Calcium, **High ALP**, and Low/Normal 1,25-(OH)₂D. * **Hallmark:** "Phosphate wasting" despite low serum phosphate (decreased TmP/GFR). * **Clinical Feature:** Unlike nutritional rickets, these patients do **not** show signs of tetany (as calcium is rarely critically low) and do **not** respond to physiological doses of Vitamin D. * **Treatment:** Oral phosphate supplements and Calcitriol (active Vitamin D).

Question 33: Chronic fluorosis is caused by drinking water with fluoride content of:

A. 1-5 ppm
B. 5-10 ppm
C. > 10 ppm (Correct Answer)
D. 10-15 ppm

Explanation: **Explanation:** Fluorosis is a chronic condition caused by the prolonged ingestion of excessive fluoride, primarily through drinking water. The clinical manifestations are strictly dose-dependent: * **Correct Answer (C):** Chronic skeletal fluorosis, which leads to severe osteosclerosis, ligamentous calcification (especially the longitudinal ligaments of the spine), and crippling deformities, typically occurs when the fluoride concentration in drinking water exceeds **10 ppm (parts per million)** over a long period. At these levels, fluoride replaces the hydroxyl group in hydroxyapatite crystals to form fluorapatite, making the bone denser but more brittle. * **Incorrect Options (A & B):** * **1 ppm:** This is considered the **optimal level** for preventing dental caries. * **1.5 - 3 ppm:** This range is associated with **Dental Fluorosis** (mottling of enamel), which occurs during the period of tooth development in children. * **3 - 10 ppm:** While this can cause mild skeletal changes, the classic "chronic/crippling" skeletal fluorosis is defined by concentrations exceeding 10 ppm. **High-Yield Clinical Pearls for NEET-PG:** 1. **Radiological Hallmark:** The earliest sign is increased bone density (osteosclerosis), most prominent in the axial skeleton (spine, pelvis, and ribs). 2. **Physical Sign:** "Poker Back" deformity occurs due to calcification of the interspinous and longitudinal ligaments, leading to a rigid spine. 3. **Diagnostic Test:** 24-hour urinary fluoride excretion is the most reliable indicator of current fluoride intake. 4. **Genu Valgum:** In endemic areas, high fluoride intake combined with low calcium intake can lead to "Kenyan" or endemic genu valgum (knock-knees) in children.

Question 34: Which of the following conditions is NOT associated with "Umbau Zones"?

A. Osteomalacia
B. Rickets
C. Osteogenesis imperfecta
D. Osteomyelitis (Correct Answer)

Explanation: **Explanation:** **Umbau Zones** (also known as **Looser’s zones**, pseudofractures, or Milkman’s fractures) are radiolucent lines oriented perpendicular to the bone cortex. They represent stress fractures where the fractured bone is replaced by unmineralized osteoid rather than mature bone. **Why Osteomyelitis is the correct answer:** Osteomyelitis is an infectious inflammatory condition of the bone. Its hallmark radiological features include **sequestrum** (dead bone), **involucrum** (new bone formation), and **cloaca**. It does not involve the systemic defect in osteoid mineralization required to form Umbau zones. **Analysis of other options:** * **Osteomalacia:** This is the classic condition associated with Umbau zones. In adults, inadequate mineralization of the bone matrix leads to these characteristic pseudofractures, typically seen in the femoral neck, pubic rami, and axillary border of the scapula. * **Rickets:** As the pediatric counterpart to osteomalacia, severe rickets can also manifest with pseudofractures due to the same underlying pathology of defective mineralization. * **Osteogenesis Imperfecta (OI):** While OI is primarily a collagen defect, severe forms can present with "pseudo-Umbau zones" or actual stress fractures during the healing process of fragile bones. **NEET-PG High-Yield Pearls:** 1. **Common Sites for Umbau Zones:** Axillary border of the scapula (most classic), neck of the femur, pubic rami, and ribs. 2. **Radiological Appearance:** Transverse lucent bands that do NOT cross the entire bone width, often bilateral and symmetrical. 3. **Biochemical Profile in Osteomalacia:** Low/Normal Calcium, Low Phosphate, and **Elevated Alkaline Phosphatase (ALP)**. 4. **Milkman’s Syndrome:** A specific clinical entity characterized by multiple pseudofractures, often associated with Osteomalacia.

Question 35: A 70-year-old woman with a history of vertebral crush fracture presents to the osteoporosis outpatient clinic. Which of the following investigations is most useful to assess the extent of her osteoporosis?

A. Spinal x-rays
B. DEXA scan (Correct Answer)
C. Full blood count, bone and liver biochemistry blood tests
D. Vitamin D levels

Explanation: ### Explanation **1. Why DEXA Scan is the Correct Answer:** Dual-Energy X-ray Absorptiometry (DEXA) scan is the **gold standard** for diagnosing osteoporosis and assessing its extent. It measures Bone Mineral Density (BMD) at clinically relevant sites like the lumbar spine and proximal femur. The diagnosis is based on the **T-score** (comparison to a young healthy adult). According to WHO criteria: * **Normal:** T-score ≥ -1.0 * **Osteopenia:** T-score between -1.0 and -2.5 * **Osteoporosis:** T-score ≤ -2.5 * **Severe Osteoporosis:** T-score ≤ -2.5 plus a fragility fracture (as seen in this patient). **2. Why Other Options are Incorrect:** * **Spinal X-rays:** While useful for identifying existing fractures (like the crush fracture mentioned), X-rays are insensitive for early diagnosis. Bone loss is only visible on plain radiographs after **30–50% of bone mass** has already been lost. * **Biochemistry (FBC, Bone/Liver profile):** In primary osteoporosis, serum calcium, phosphate, and alkaline phosphatase (ALP) levels are typically **normal**. These tests are used to rule out secondary causes (e.g., osteomalacia, hyperparathyroidism, or malignancy) rather than to quantify osteoporosis. * **Vitamin D levels:** While Vitamin D deficiency is a risk factor for bone loss, its level does not quantify the extent of bone density loss already present. **3. NEET-PG High-Yield Pearls:** * **Most common site** of osteoporotic fracture: Vertebra (Compression/Crush fracture). * **Most common site** for DEXA measurement: Neck of femur (best predictor of hip fracture) and Lumbar spine (L1–L4). * **Z-score:** Used for pre-menopausal women and men <50 years (compares density to age-matched controls). * **FRAX Tool:** Used to calculate the 10-year probability of a major osteoporotic fracture.

Question 36: Which of the following are features of Paget's disease?

A. Affecting the skull generally leads to a progressive increase in circumference of the head (osteoporosis circumscripta).
B. Jigsaw puzzle appearance of the bone.
C. Leontiasis ossea.
D. All of the above. (Correct Answer)

Explanation: **Explanation:** Paget’s disease (Osteitis Deformans) is a chronic disorder characterized by excessive and disorganized bone remodeling. It progresses through three stages: osteolytic, mixed, and osteosclerotic. * **Option A:** In the early **osteolytic phase**, the skull shows well-defined radiolucent areas known as **Osteoporosis Circumscripta**. As the disease progresses to the sclerotic phase, the bone thickens, leading to a progressive increase in head circumference (often described as the patient needing a larger hat size). * **Option B:** Histologically, the rapid, haphazard bone formation and resorption result in prominent cement lines. This creates a characteristic **"Mosaic" or "Jigsaw puzzle" appearance** of the lamellar bone, which is a pathognomonic finding. * **Option C:** When Paget’s disease involves the facial bones (maxilla and mandible), it causes massive bony overgrowth. This results in a lion-like facial appearance known as **Leontiasis Ossea**. Since all three descriptions are classic clinical and pathological hallmarks of the disease, **Option D** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **Marker of Choice:** Serum **Alkaline Phosphatase (ALP)** is markedly elevated, while Calcium and Phosphate levels typically remain normal. * **Radiological Signs:** "Cotton wool" appearance of the skull, "Picture frame" vertebrae, and "Ivory vertebra." * **Treatment:** **Bisphosphonates** (Zoledronic acid) are the drug of choice. * **Complications:** The most dreaded complication is **Osteosarcoma** (secondary), and the most common cause of death in extensive disease is high-output heart failure.

Question 37: Lobstein disease is:

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

Explanation: **Explanation:** **Osteogenesis Imperfecta (OI)**, also known as **Lobstein disease** (specifically Type I), is a genetic disorder characterized by increased bone fragility and low bone mass. The underlying pathophysiology involves a mutation in the **COL1A1 or COL1A2 genes**, leading to a defect in the synthesis of **Type I Collagen**. Since Type I collagen is a primary component of the bone matrix, skin, and sclera, patients present with frequent fractures, blue sclera, and hearing loss. **Analysis of Options:** * **Fibrous Dysplasia:** This is a condition where normal bone is replaced by fibrous connective tissue (showing a "ground-glass" appearance on X-ray). It is associated with McCune-Albright syndrome, not Lobstein disease. * **Achondroplasia:** This is the most common cause of dwarfism, caused by a mutation in the **FGFR3 gene**. It affects endochondral ossification, leading to short-limbed stature. * **Osteopetrosis:** Also known as **Albers-Schönberg disease** or "Marble Bone Disease," it is caused by defective **osteoclast** function, leading to excessively dense but brittle bones. **High-Yield Clinical Pearls for NEET-PG:** * **Blue Sclera:** Occurs because the thinness of the Type I collagen allows the underlying choroidal veins to show through. * **Classification:** Sillence Classification is used to categorize the types of OI (Type II is the most severe/lethal perinatally). * **Radiological Sign:** "Zebra stripe sign" may be seen in patients treated with cyclic bisphosphonates. * **Dentinogenesis Imperfecta:** Often co-exists with OI, resulting in discolored, weak teeth.

Question 38: Blue sclera is seen in which of the following conditions?

A. Alkaptonuria
B. Osteogenesis imperfecta (Correct Answer)
C. Turner's syndrome
D. Kawasaki syndrome

Explanation: **Explanation:** **Osteogenesis Imperfecta (OI)**, also known as "Brittle Bone Disease," is the correct answer. It is primarily caused by a genetic defect in **Type 1 Collagen** synthesis (COL1A1 and COL1A2 genes). The sclera of the eye is normally composed of Type 1 collagen. In OI, the collagen is either deficient or structurally abnormal, leading to a **thinning of the scleral layers**. This allows the underlying **choroidal veins** to show through, giving the sclera a characteristic translucent blue or slate-gray appearance. **Analysis of Incorrect Options:** * **Alkaptonuria:** Characterized by **ochronosis** (dark pigmentation). It causes brownish-black pigmentation of the sclera and ear cartilage due to homogentisic acid deposition, not blue sclera. * **Turner’s Syndrome:** Associated with skeletal abnormalities like a short fourth metacarpal and cubitus valgus, but blue sclera is not a classic feature. * **Kawasaki Syndrome:** A systemic vasculitis characterized by **bilateral non-exudative conjunctival injection** (red eyes), not blue sclera. **High-Yield Clinical Pearls for NEET-PG:** * **Types of OI:** Type I is the most common and mildest form (presents with blue sclera); Type II is the most severe/lethal (perinatal death). * **Clinical Triad:** Fragile bones (multiple fractures), Blue sclera, and Early-onset Otosclerosis (conductive hearing loss). * **Other causes of Blue Sclera:** Ehlers-Danlos Syndrome, Marfan Syndrome, Pseudoxanthoma elasticum, and Iron deficiency anemia (rarely). * **Radiological Sign:** "Zebra stripe sign" (seen in children treated with cyclic bisphosphonates).

Question 39: A 90-year-old male complains of hip and back pain. He has also developed headaches, hearing loss, and tinnitus. On physical exam, the skull appears enlarged with prominent superficial veins. There is marked kyphosis, and the bones of the leg appear deformed. Plasma alkaline phosphatase is elevated. A skull x-ray shows sharply demarcated lucencies in the frontal, parietal, and occipital bones. X-rays of the hip show thickening of the pelvic brim. What is the most likely diagnosis?

A. Multiple myeloma
B. Paget's disease (Correct Answer)
C. Hypercalcemia
D. Metastatic bone disease

Explanation: ### **Explanation** **Correct Option: B. Paget’s Disease (Osteitis Deformans)** The clinical triad of **bone pain, skeletal deformities (bowing of legs/kyphosis), and cranial involvement** in an elderly patient is classic for Paget’s disease. * **Pathophysiology:** It is a disorder of bone remodeling characterized by excessive osteoclastic resorption followed by disorganized osteoblastic bone formation, resulting in "woven bone" that is mechanically weak and vascular. * **Clinical Features:** Skull enlargement (increasing hat size) leads to cranial nerve compression, causing **hearing loss** and tinnitus. Prominent scalp veins occur due to increased bone vascularity. * **Radiology:** The "sharply demarcated lucencies" in the skull represent **Osteoporosis Circumscripta** (early lytic phase). Thickening of the pelvic brim is known as the **"Brim Sign."** * **Biochemistry:** Characterized by isolated **elevated Alkaline Phosphatase (ALP)** with normal Calcium, Phosphate, and PTH levels. **Why Incorrect Options are Wrong:** * **A. Multiple Myeloma:** Presents with "punched-out" lytic lesions and bone pain, but typically features anemia, hypercalcemia, and renal failure. It does not cause bone enlargement or isolated ALP elevation. * **C. Hypercalcemia:** This is a biochemical finding, not a primary diagnosis. While it can cause bone pain (e.g., in hyperparathyroidism), it doesn't explain the focal skull enlargement or specific radiological signs like the Brim sign. * **D. Metastatic Bone Disease:** While common in the elderly, it usually presents with osteoblastic (prostate) or osteolytic (lung/breast) lesions. It does not typically cause generalized skull enlargement or the specific lytic pattern of osteoporosis circumscripta. ### **NEET-PG High-Yield Pearls** * **Most common site:** Pelvis > Lumbar spine > Skull > Tibia. * **Skull Signs:** "Cotton wool appearance" (sclerotic phase) and "Osteoporosis circumscripta" (lytic phase). * **Complications:** The most dreaded complication is **Osteosarcoma** (suspect if pain suddenly worsens or a soft tissue mass appears). High-output heart failure can occur due to extensive AV shunting in hypervascular bone. * **Treatment:** **Bisphosphonates** (Zoledronic acid is the drug of choice).

Question 40: A 60-year-old male presents with a bony abnormality at the upper tibia associated with sensorineural hearing loss. Laboratory examination reveals elevated serum alkaline phosphatase levels (440 mU/L) with normal serum calcium and phosphate. A skeletal survey shows "ivory vertebrae" and "cotton wool spots" on skull X-ray. What is the most likely diagnosis?

A. Fibrous dysplasia
B. Paget disease (Correct Answer)
C. Osteosclerotic metastasis
D. Osteoporosis

Explanation: **Explanation:** The clinical presentation and radiographic findings are classic for **Paget Disease of Bone (Osteitis Deformans)**. This condition is characterized by disordered bone remodeling where excessive osteoclastic resorption is followed by disorganized osteoblastic bone formation. **Why Paget Disease is correct:** 1. **Biochemical Markers:** The hallmark is an **isolated elevation of Serum Alkaline Phosphatase (ALP)** with normal calcium, phosphate, and PTH levels. 2. **Radiology:** "Cotton wool spots" in the skull represent mixed lytic and sclerotic patches. "Ivory vertebra" refers to a dense, radio-opaque vertebral body. 3. **Clinical Features:** Sensorineural hearing loss occurs due to the involvement of the petrous temporal bone or compression of the CN VIII in the internal auditory meatus. The tibia is a common site for bowing and enlargement. **Why other options are incorrect:** * **Fibrous Dysplasia:** Typically presents in younger patients with "ground-glass" appearance on X-ray and "shepherd’s crook" deformity of the femur. * **Osteosclerotic Metastasis:** While it can cause ivory vertebrae (commonly from prostate cancer), it would not explain the cotton wool skull or the specific pattern of hearing loss and tibial enlargement. * **Osteoporosis:** This is a "silent" disease characterized by decreased bone mass and normal lab values (including ALP), leading to fractures rather than bony enlargement or sclerosis. **NEET-PG High-Yield Pearls:** * **Most common site:** Pelvis > Femur > Skull > Tibia. * **Histology:** "Mosaic pattern" or "Jigsaw puzzle" appearance of lamellar bone with prominent cement lines. * **Treatment of choice:** Bisphosphonates (Zoledronic acid). * **Complication:** The most dreaded complication is **Osteosarcoma** (suspect if there is a sudden increase in pain or a new soft tissue mass).

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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