Metabolic Bone Diseases — MCQs

A 62-year-old female presents to the emergency with acute severe low back pain after sitting down quickly. She has a history of rheumatoid arthritis and bronchial asthma and reports being on multiple medications for several years. X-ray shows a fracture of the fifth lumbar vertebra. Which of the following drugs is likely responsible for the patient's condition?

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All are features of osteogenesis imperfecta except?

Metabolic Bone Diseases Indian Medical PG Practice Questions and MCQs

Question 41: Which of the following disorders is classified under defects in metabolic pathways?

A. Cherubism
B. Robinow syndrome
C. Severe infantile osteopetrosis (Correct Answer)
D. Pycnodysostosis

Explanation: **Explanation:** The classification of skeletal dysplasias distinguishes between defects in **structural proteins** (like collagen), **signaling pathways**, and **metabolic pathways**. **Why Severe Infantile Osteopetrosis is correct:** Osteopetrosis is a group of rare genetic disorders characterized by increased bone density due to **defective osteoclast function**. In the severe infantile (autosomal recessive) form, the primary defect lies in the **metabolic machinery** required for bone resorption. Specifically, mutations in the *TCIRG1* gene (encoding a subunit of the vacuolar proton pump) or the *CLCN7* chloride channel prevent osteoclasts from acidifying the resorption lacuna. This failure of the metabolic "proton pump" mechanism prevents the dissolution of bone mineral, classifying it as a defect in metabolic pathways. **Analysis of Incorrect Options:** * **Cherubism:** This is classified under **disorders of signaling pathways**. It is caused by mutations in the *SH3BP2* gene, leading to overactive osteoclasts and fibro-osseous lesions in the mandible and maxilla. * **Robinow Syndrome:** This is a defect in **signaling pathways** (specifically the Wnt signaling pathway, involving *ROR2* or *WNT5A* genes), resulting in short-limbed dwarfism and "fetal face" dysmorphism. * **Pycnodysostosis:** While also involving osteoclast dysfunction, it is specifically a **lysosomal storage disorder** (cathepsin K deficiency). In many classifications, it is grouped separately or under enzymatic defects, whereas infantile osteopetrosis is the classic representative of metabolic/proton-pump failure in standard orthopedic texts. **NEET-PG High-Yield Pearls:** * **Osteopetrosis (Albers-Schönberg disease):** Look for "Marble Bone disease," "Erlenmeyer flask deformity," and "Bone-within-a-bone" appearance on X-ray. * **Clinical Triad:** Anemia, hepatosplenomegaly (due to extramedullary hematopoiesis), and blindness (due to cranial nerve compression). * **Pycnodysostosis:** Famous for being the diagnosis of artist Henri de Toulouse-Lautrec; characterized by osteosclerosis, short stature, and persistent fontanelles.

Question 42: Myopathy is seen in all except?

A. X-linked hypophosphatemic rickets (Correct Answer)
B. Oncogenic osteomalacia
C. Nutritional osteomalacia
D. Myopathy is not seen in any of the above conditions

Explanation: **Explanation:** The presence or absence of myopathy is a critical clinical differentiator in metabolic bone diseases. **1. Why X-linked Hypophosphatemic Rickets (XLH) is the correct answer:** XLH is caused by a mutation in the **PHEX gene**, leading to increased levels of **FGF-23**. This results in renal phosphate wasting and impaired Vitamin D activation. Crucially, in XLH, **proximal muscle weakness (myopathy) is characteristically absent.** Patients typically present with lower limb deformities (bowing) and short stature, but they maintain normal muscle strength. **2. Analysis of Incorrect Options:** * **Nutritional Osteomalacia:** This is primarily caused by Vitamin D deficiency. Vitamin D plays a vital role in muscle metabolism and calcium homeostasis. Deficiency leads to significant **proximal myopathy**, often manifesting as a "waddling gait" and difficulty rising from a chair. * **Oncogenic Osteomalacia:** This is a paraneoplastic syndrome where tumors (usually mesenchymal) secrete FGF-23. Unlike the genetic form (XLH), acquired oncogenic osteomalacia is **strongly associated with severe muscle weakness** and bone pain. * **Option D:** This is incorrect because myopathy is a hallmark feature of most forms of osteomalacia, with XLH being the notable exception. **Clinical Pearls for NEET-PG:** * **The "Rule of XLH":** Low Serum Phosphate + High FGF-23 + Normal Calcium + **No Myopathy**. * **Waddling Gait:** Seen in nutritional osteomalacia due to proximal muscle weakness (Gluteus medius weakness). * **Looser’s Zones (Pseudofractures):** Radiographic hallmark of osteomalacia, typically seen at the axillary border of the scapula, pubic rami, and femoral neck.

Question 43: Paget's disease involves which of the following bones?

A. Pelvis, Vertebrae
B. Pelvis, Vertebrae, Skull (Correct Answer)
C. Pelvis, Skull, Phalanges
D. Vertebrae, Skull, Phalanges

Explanation: **Explanation:** Paget’s Disease (Osteitis Deformans) is a chronic disorder characterized by excessive and disorganized bone remodeling. It primarily affects the **axial skeleton** and long bones. The disease progresses through three stages: osteolytic, mixed, and osteosclerotic. **Why Option B is Correct:** Paget’s disease has a predilection for the axial skeleton. The most common sites involved are: 1. **Pelvis** (most common site, ~70%) 2. **Vertebrae** (Lumbar spine) 3. **Skull** (leads to increasing hat size and "Cotton wool" appearance on X-ray) 4. **Femur and Tibia** (leads to "saber shin" deformity) **Why Other Options are Incorrect:** * **Options C and D:** These include the **phalanges**. Paget’s disease characteristically **spares the small bones** of the hands and feet. If small bone involvement is seen, it is extremely rare and usually occurs only in very advanced, polyostotic cases. **High-Yield Clinical Pearls for NEET-PG:** * **Biochemical Marker:** Isolated elevation of **Serum Alkaline Phosphatase (ALP)** with normal Calcium, Phosphate, and PTH levels. * **Radiological Signs:** * **Skull:** *Osteoporosis circumscripta* (early), *Cotton wool spots* (late). * **Spine:** *Picture frame vertebra* or *Ivory vertebra*. * **Pelvis:** *Brim sign* (thickening of the pelvic brim). * **Complications:** The most dreaded complication is **Osteosarcoma** (secondary), seen in <1% of patients. Other complications include high-output heart failure and deafness (due to CN VIII compression). * **Drug of Choice:** **Bisphosphonates** (Zoledronic acid is highly effective).

Question 44: 24-hour estimation of urinary hydroxyproline levels is a good indicator for what in Paget's disease?

A. Poor outcome
B. Diagnosis
C. Recurrence
D. Extent and severity (Correct Answer)

Explanation: **Explanation:** In **Paget’s disease of bone (Osteitis Deformans)**, there is a marked increase in bone remodeling characterized by excessive osteoclastic resorption followed by disorganized osteoblastic bone formation. **Why "Extent and Severity" is correct:** Hydroxyproline is an amino acid found almost exclusively in collagen. When osteoclasts resorb bone matrix, collagen is broken down, and hydroxyproline is released into the bloodstream and excreted in the urine. Therefore, **24-hour urinary hydroxyproline** serves as a direct biochemical marker of **bone resorption rate**. In Paget's disease, the levels correlate directly with the metabolic activity of the disease and the total volume of bone involved (the "skeletal burden"). Higher levels indicate more widespread (polyostotic) and aggressive disease. **Analysis of Incorrect Options:** * **A. Poor outcome:** While high turnover suggests active disease, it does not necessarily predict a "poor outcome" in terms of mortality; Paget’s is often managed effectively with bisphosphonates. * **B. Diagnosis:** While suggestive, it is not diagnostic. Diagnosis is primarily based on **Radiology** (e.g., thickened cortex, coarse trabeculae, bone enlargement) and elevated **Serum Alkaline Phosphatase (ALP)**. * **C. Recurrence:** While it can be used to monitor treatment response, it is less specific for "recurrence" than Serum ALP, which is the preferred marker for monitoring follow-up. **High-Yield Clinical Pearls for NEET-PG:** * **Marker of Bone Formation:** Serum Alkaline Phosphatase (most commonly used clinical marker). * **Marker of Bone Resorption:** Urinary Hydroxyproline (classic) or **Urinary N-telopeptide/Deoxypyridinoline** (more specific modern markers). * **Radiological Sign:** "Blade of grass" or "Flame shaped" lytic lesion in long bones. * **Treatment of Choice:** Bisphosphonates (e.g., Zoledronic acid). * **Complication:** The most dreaded complication is **Osteosarcoma** (suspect if there is a sudden increase in pain or a new mass).

Question 45: A 16-year-old male presents with extensive heterotropic ossification over the neck, back, and shoulders and decreased chest movements. He gives a history of progressive immobility since the age of 3 years. Which of the following statements about his affecting condition is not true?

A. They have a near normal life expectancy. (Correct Answer)
B. They are predisposed to pneumonia.
C. They have a short hallux.
D. Increased expression of BMP4 gene is seen.

Explanation: The clinical presentation of progressive heterotopic ossification (HO) starting in early childhood, involving the axial skeleton (neck, back), and leading to restricted chest expansion is diagnostic of **Fibrodysplasia Ossificans Progressiva (FOP)**, also known as Munchmeyer’s disease. ### **Explanation of Options** * **A. They have a near-normal life expectancy (Correct Answer):** This statement is **false**. FOP is a severely disabling condition. Most patients become bedridden by their 20s and have a significantly reduced life expectancy (median age of death is approximately 40 years). Death usually occurs due to **Thoracic Insufficiency Syndrome** caused by the ossification of intercostal muscles and the chest wall. * **B. They are predisposed to pneumonia:** This is **true**. Progressive ossification of the thoracic cage leads to restrictive lung disease, poor cough reflex, and reduced vital capacity, making these patients highly susceptible to recurrent respiratory infections and pneumonia. * **C. They have a short hallux:** This is **true**. Congenital **malformation of the great toe** (short, monophalangic, or hallux valgus) is a classic pathognomonic feature present at birth, often preceding the onset of HO. * **D. Increased expression of BMP4 gene:** This is **true**. FOP is caused by a mutation in the **ACVR1 gene** (encoding the ALK2 receptor), which leads to over-activation of the Bone Morphogenetic Protein (BMP) signaling pathway, specifically **BMP4**, resulting in the transformation of connective tissue into bone. ### **High-Yield Clinical Pearls for NEET-PG** * **Inheritance:** Autosomal Dominant (most cases are sporadic mutations). * **Trigger:** Minor trauma, intramuscular injections, or viral illnesses can trigger "flare-ups" of ossification. * **Biopsy Warning:** **Never biopsy** these lesions; surgical trauma or needle sticks will trigger massive new heterotopic bone formation. * **Pattern:** Ossification typically follows a cranio-caudal and axial-to-appendicular pattern.

Question 46: Which type of osteogenesis imperfecta is characterized by blue sclera?

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

Explanation: **Explanation:** **Osteogenesis Imperfecta (OI)**, also known as "Brittle Bone Disease," is a genetic disorder of Type 1 collagen synthesis. The classification is primarily based on the **Sillence Classification**. 1. **Why Type 1 is correct:** **Type 1 OI** is the most common and mildest form. It is characterized by a **quantitative defect** (decreased production) of structurally normal Type 1 collagen. The hallmark clinical feature is **persistent blue sclera** throughout life. The blue appearance occurs because the abnormally thin scleral collagen allows the underlying choroidal veins to show through. 2. **Why other options are incorrect:** * **Type 2:** This is the most severe, **perinatal lethal** form. It involves a qualitative defect in collagen leading to multiple in-utero fractures and death in the neonatal period. While sclerae may be blue, the primary clinical identifier is lethality. * **Type 3:** This is the **severely deforming** type. Patients have multiple fractures and significant limb/spine deformities. Sclerae may be blue at birth but usually **turn white** as the patient ages. * **Type 4:** This is a moderate form with normal (white) sclerae. It is distinguished from Type 1 primarily by the absence of blue sclera and more frequent fractures. **High-Yield Clinical Pearls for NEET-PG:** * **Inheritance:** Most cases (Types 1-4) are **Autosomal Dominant**. * **Associated Features:** Dentinogenesis imperfecta (opalescent teeth), otosclerosis (conductive hearing loss), and wormian bones on skull X-ray. * **Treatment:** **Bisphosphonates** (e.g., Pamidronate) are the medical mainstay to increase bone mineral density. * **Surgery:** "Sofield-Millar" procedure (multiple osteotomies and intramedullary nailing) is used for long bone deformities.

Question 47: Marble bone is characteristic of which condition?

A. Osteopetrosis (Correct Answer)
B. Marfan's syndrome
C. Osteogenesis imperfecta
D. Melorheostosis

Explanation: **Explanation:** **Osteopetrosis (Option A)** is the correct answer. Also known as **Albers-Schönberg disease** or **Marble Bone Disease**, it is a rare genetic disorder characterized by defective **osteoclast function**. Because osteoclasts fail to resorb bone, the balance between bone formation and resorption is lost, leading to excessively dense, thick, and opaque bones. Despite their "marble-like" appearance on X-ray, these bones are structurally weak and prone to pathological fractures. **Why other options are incorrect:** * **Marfan’s Syndrome (Option B):** A connective tissue disorder caused by a mutation in the Fibrillin-1 gene. It presents with arachnodactyly (long fingers), tall stature, and ectopia lentis, not increased bone density. * **Osteogenesis Imperfecta (Option C):** Known as "Brittle Bone Disease," it is caused by a defect in Type I collagen. Radiologically, it presents with osteopenia (thin, translucent bones), the opposite of marble bone. * **Melorheostosis (Option D):** Characterized by a "flowing wax" appearance (dripping candle wax) on X-ray due to cortical thickening. It is usually localized to a single limb rather than a generalized "marble" appearance. **High-Yield Clinical Pearls for NEET-PG:** * **Radiological Signs:** "Bone-within-a-bone" appearance and "Rugger-Jersey spine" (though also seen in renal osteodystrophy). * **Complications:** Bone marrow obliteration leads to **pancytopenia** and extramedullary hematopoiesis (hepatosplenomegaly). Cranial nerve palsies occur due to narrowing of the neural foramina. * **Erlenmeyer Flask Deformity:** Seen at the ends of long bones (also seen in Gaucher’s disease).

Question 48: What is the World Health Organization (WHO) definition of osteoporosis?

A. Bone mineral density less than 1 standard deviation below the mean of a young, healthy adult.
B. Bone mineral density at least 2.5 standard deviations below the mean of a young, healthy adult.
C. T score less than -2.5.
D. Both 'Bone mineral density at least 2.5 standard deviations below the mean of a young, healthy adult' and 'T score less than -2.5.' (Correct Answer)

Explanation: **Explanation:** The World Health Organization (WHO) defines osteoporosis based on **Bone Mineral Density (BMD)** measurements compared to a reference population. The correct answer is **D** because it encompasses both the statistical definition and its clinical representation (the T-score). 1. **Why the correct answer is right:** The WHO criteria utilize the **T-score**, which represents the number of standard deviations (SD) a patient's BMD is above or below the mean BMD of a **young, healthy adult (peak bone mass)** of the same sex. Osteoporosis is defined as a BMD that is **2.5 SD or more below** this mean. Mathematically, this is expressed as a **T-score ≤ -2.5**. Since options B and C describe the same physiological threshold using different terminology, both are correct. 2. **Analysis of incorrect options:** * **Option A:** A BMD within 1 SD of the young adult mean (T-score between -1.0 and +1.0) is considered **Normal**. * **Option B & C:** While individually correct, they are incomplete on their own in the context of this multiple-choice question, as they represent the same diagnostic criteria. **High-Yield NEET-PG Pearls:** * **Osteopenia:** Defined as a T-score between **-1.0 and -2.5**. * **Severe (Established) Osteoporosis:** A T-score ≤ -2.5 **plus** the presence of one or more fragility fractures. * **Z-score:** Compares BMD to an **age-matched and sex-matched** population. It is used for children, pre-menopausal women, and men under 50. * **Gold Standard Investigation:** Dual-energy X-ray Absorptiometry (**DEXA Scan**). The most common sites scanned are the lumbar spine and the neck of the femur.

Question 49: A 62-year-old female presents to the emergency with acute severe low back pain after sitting down quickly. She has a history of rheumatoid arthritis and bronchial asthma and reports being on multiple medications for several years. X-ray shows a fracture of the fifth lumbar vertebra. Which of the following drugs is likely responsible for the patient's condition?

A. Methotrexate
B. Prednisolone (Correct Answer)
C. Indomethacin
D. Salbutamol

Explanation: **Explanation:** The patient presents with a **fragility fracture** (vertebral compression fracture) following minimal trauma. Her history of Rheumatoid Arthritis and Bronchial Asthma suggests chronic use of **Corticosteroids**, which are the most common cause of **secondary osteoporosis**. **1. Why Prednisolone is correct:** Prednisolone induces bone loss through multiple mechanisms: * **Decreased Bone Formation:** It directly inhibits osteoblast activity and increases osteocyte apoptosis. * **Increased Bone Resorption:** It increases RANK-L and decreases Osteoprotegerin (OPG), stimulating osteoclasts. * **Calcium Imbalance:** It inhibits intestinal calcium absorption and increases renal calcium excretion, leading to secondary hyperparathyroidism. * **Clinical Correlation:** Steroid-induced osteoporosis characteristically affects **trabecular bone** (like the vertebrae) more than cortical bone, leading to sudden compression fractures. **2. Why other options are incorrect:** * **Methotrexate:** While used for RA, it can cause "Methotrexate Osteopathy" (bone pain and stress fractures) only at very high doses (e.g., in oncology). At low doses for RA, it is not a primary cause of fragility fractures. * **Indomethacin:** This is an NSAID. While long-term use has GI and renal risks, it does not cause systemic bone loss; in fact, some studies suggest NSAIDs might slightly inhibit bone resorption. * **Salbutamol:** A beta-2 agonist used for asthma, it has no significant clinical association with decreased Bone Mineral Density (BMD). **3. NEET-PG High-Yield Pearls:** * **Gold Standard Diagnosis:** DEXA Scan (T-score ≤ -2.5 indicates osteoporosis). * **Prophylaxis:** Patients on >7.5mg prednisolone for >3 months should receive Calcium, Vitamin D, and potentially Bisphosphonates. * **First-line Treatment:** Bisphosphonates (e.g., Alendronate) are the drug of choice for steroid-induced osteoporosis. * **Teriparatide:** An anabolic agent (recombinant PTH) often used for severe cases with multiple fractures.

Question 50: All are features of osteogenesis imperfecta except?

A. Known as brittle bone disease
B. Blue sclera
C. Absent clavicle (Correct Answer)
D. Wormian bones

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 defective synthesis of **Type I Collagen**. Since Type I collagen is a major structural component of bone, skin, and sclera, its deficiency results in extreme bone fragility. **Why "Absent Clavicle" is the correct answer:** Absent or hypoplastic clavicles are a hallmark feature of **Cleidocranial Dysplasia**, not Osteogenesis Imperfecta. In Cleidocranial Dysplasia, patients can often approximate their shoulders in the midline due to the missing clavicles. In contrast, patients with OI have intact clavicles, though they are prone to fractures. **Analysis of other options:** * **A. Brittle bone disease:** This is the synonym for OI due to the characteristic susceptibility to multiple fractures from minimal trauma. * **B. Blue sclera:** This occurs because the thinning of the scleral collagen allows the underlying choroidal veins to show through. (Note: This is most common in Type I OI). * **C. Wormian bones:** These are accessory small bones found within the sutures of the skull. They are a classic radiological finding in OI (specifically more than 10 Wormian bones). **NEET-PG High-Yield Pearls:** * **Sillence Classification:** Used to categorize OI types (Type I is mildest/most common; Type II is perinatal lethal). * **Associated features:** Dentinogenesis imperfecta (translucent teeth), early-onset conductive hearing loss (otosclerosis), and ligamentous laxity. * **Differential for Wormian Bones:** Remember the mnemonic **"PORK CHOP"** (P-Pyknodysostosis, O-Osteogenesis Imperfecta, R-Rickets, K-Kinky Hair Syndrome, C-Cleidocranial Dysplasia, H-Hypothyroidism/Hypophosphatasia, O-One Down Syndrome, P-Pachydermoperiostosis).

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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