Metabolic Bone Diseases — MCQs

Metabolic Bone Diseases Indian Medical PG Practice Questions and MCQs

Question 61: Erlenmeyer flask deformity of bones is seen in?

A. Achondroplasia
B. Osteopetrosis (Correct Answer)
C. Osteogenesis Imperfecta
D. Paget's disease

Explanation: **Explanation:** **Osteopetrosis** (Albers-Schönberg disease/Marble Bone Disease) is the correct answer. The underlying pathology is a **functional defect in osteoclasts**, leading to impaired bone resorption and remodeling. Because the metaphyses of long bones (especially the distal femur and proximal tibia) fail to remodel and narrow during growth, they remain abnormally wide and flared. This radiographic appearance resembles an **Erlenmeyer flask**. **Analysis of Incorrect Options:** * **Achondroplasia:** Characterized by impaired endochondral ossification. Classic radiographic findings include "bullet-shaped" vertebrae, "trident hand," and a "champagne glass" pelvis, but not the Erlenmeyer flask deformity. * **Osteogenesis Imperfecta:** A collagen type 1 defect leading to "brittle bones." Radiographs typically show osteopenia, multiple fractures, and "popcorn calcifications" at the metaphysis, rather than symmetric metaphyseal flaring. * **Paget’s Disease:** Involves excessive, disorganized bone remodeling. Key features include cortical thickening, "picture frame" vertebrae, and "cotton wool" appearance of the skull. **High-Yield Clinical Pearls for NEET-PG:** * **Differential Diagnosis for Erlenmeyer Flask Deformity (Mnemonic: LEAD):** * **L:** Lipid storage diseases (Gaucher’s disease – *Most common cause*) * **E:** Enchondromatosis (Ollier’s disease) * **A:** Anemias (Thalassemia major) * **D:** Dysplasias (Osteopetrosis, Pyle’s disease) * **Osteopetrosis Key Features:** "Bone-within-bone" appearance (Endobone), "Sandwich vertebrae," and pancytopenia due to marrow space obliteration. * **Gaucher’s Disease:** If both Gaucher’s and Osteopetrosis are in the options, Gaucher’s is statistically the most common cause of this deformity, but Osteopetrosis is the classic "textbook" association for metabolic bone exams.

Question 62: What is the gold standard for the diagnosis of osteoporosis?

A. DEXA (Correct Answer)
B. Single beam densitometry
C. Quantitative computed tomography
D. Bone histomorphometry

Explanation: **Explanation:** **DEXA (Dual-Energy X-ray Absorptiometry)** is considered the **gold standard** for diagnosing osteoporosis because it provides a precise, non-invasive measurement of Bone Mineral Density (BMD) with minimal radiation exposure. It measures the T-score (standard deviations from the mean peak bone mass of a young healthy adult), which is the primary metric used by the WHO to define osteoporosis (T-score ≤ -2.5). **Analysis of Options:** * **Single-beam densitometry (B):** This is an older technique (e.g., Single Photon Absorptiometry) primarily used for peripheral sites like the forearm. It is less accurate than DEXA and cannot assess the hip or spine, which are critical for fracture risk assessment. * **Quantitative CT (C):** While QCT provides a true 3D volumetric density and can differentiate between cortical and trabecular bone, it involves significantly higher radiation doses and is more expensive, making it less suitable for routine screening. * **Bone histomorphometry (D):** This involves a bone biopsy (usually from the iliac crest). While it is the gold standard for assessing bone *quality* and turnover at a cellular level, it is invasive and not used for the clinical diagnosis of osteoporosis. **High-Yield Clinical Pearls for NEET-PG:** * **WHO Criteria:** Normal (T-score > -1), Osteopenia (-1 to -2.5), Osteoporosis (≤ -2.5), Severe Osteoporosis (≤ -2.5 + fragility fracture). * **Z-score:** Used for children, pre-menopausal women, and men <50. It compares BMD to age-matched controls. * **Common Sites for DEXA:** Hip (Neck of femur) and Lumbar spine (L1-L4). * **FRAX Tool:** Used to estimate the 10-year probability of a major osteoporotic fracture.

Question 63: Looser's zones are seen in which of the following conditions?

A. Osteoporosis
B. Hyperparathyroidism
C. Osteomalacia (Correct Answer)
D. Renal osteodystrophy

Explanation: **Explanation:** **Looser’s zones** (also known as pseudofractures, Milkman’s lines, or cortical infractions) are the pathognomonic radiological hallmark of **Osteomalacia**. 1. **Why Osteomalacia is correct:** Osteomalacia is characterized by a defect in the mineralization of the organic bone matrix (osteoid), usually due to Vitamin D deficiency. Looser’s zones represent stress fractures where the body has attempted repair by laying down new osteoid, but because of the mineral deficiency, this osteoid remains uncalcified. On X-ray, these appear as narrow, transverse radiolucent lines oriented perpendicular to the cortex, often symmetrical and bilateral. Common sites include the axillary border of the scapula, femoral neck, pubic rami, and ribs. 2. **Why other options are incorrect:** * **Osteoporosis:** This involves a decrease in total bone mass (both matrix and mineral are lost), but the bone present is normally mineralized. It typically presents with wedge fractures or codfish vertebrae, not pseudofractures. * **Hyperparathyroidism:** Characterized by increased bone resorption. Classic radiological findings include subperiosteal bone resorption (radial side of middle phalanges) and "Salt and Pepper" skull. * **Renal Osteodystrophy:** While this is a complex spectrum that can include osteomalacia, the specific term "Looser's zones" is classically associated with pure Osteomalacia/Rickets. Renal osteodystrophy is more famously associated with the "Rugger Jersey Spine." **High-Yield Clinical Pearls for NEET-PG:** * **Biochemical Triad of Osteomalacia:** Low/Normal Calcium, Low Phosphate, and **Elevated Alkaline Phosphatase (ALP)**. * **Looser’s Zones vs. Stress Fractures:** Unlike true fractures, Looser’s zones do not show callus formation unless treated with Vitamin D. * **Milkman’s Syndrome:** A term used when a patient presents with multiple symptomatic pseudofractures.

Question 64: What is the primary metabolic bone disorder in scurvy?

A. Decreased mineralization
B. Decreased osteoid matrix formation (Correct Answer)
C. Increased bone resorption
D. Decreased bone mass with normal mineralization and osteoid formation

Explanation: **Explanation:** The primary defect in **Scurvy (Vitamin C deficiency)** is the failure of **osteoid matrix formation**. Vitamin C (ascorbic acid) is a mandatory cofactor for the enzyme *prolyl hydroxylase* and *lysyl hydroxylase*, which are responsible for the hydroxylation of proline and lysine residues during collagen synthesis. Without this step, stable triple-helix collagen molecules cannot form. Since the organic bone matrix (osteoid) is composed of 90% Type I collagen, its production is severely impaired. **Analysis of Options:** * **Option A (Decreased mineralization):** This is the hallmark of **Rickets and Osteomalacia**. In scurvy, the mineralization process itself is normal; the problem is that there is no matrix available to be mineralized. * **Option C (Increased bone resorption):** While some secondary resorption may occur, it is not the primary pathology. Scurvy is characterized by a failure of bone *formation* (osteoblastic activity) rather than excessive destruction. * **Option D (Decreased bone mass with normal mineralization/osteoid):** This describes **Osteoporosis**, where the quality of the bone is normal, but the quantity is reduced. In scurvy, the quality of the matrix itself is defective. **High-Yield Clinical Pearls for NEET-PG:** * **Radiological Signs:** Look for **Fraenkel’s line** (dense zone of provisional calcification), **Trummerfeld zone** (scurvy line/lucent zone), **Pelkan spur**, and **Wimberger’s ring sign** (dense epiphysis periphery). * **Clinical Presentation:** Gingival bleeding, perifollicular hemorrhages, and subperiosteal hematomas (causing extreme pain and "pseudoparalysis"). * **Key Distinction:** Unlike Rickets, the **Zone of Provisional Calcification** in Scurvy is **thickened and dense** because the body continues to calcify the available cartilage, but cannot convert it to bone due to lack of osteoid.

Question 65: Amber coloured tooth translucency, blue sclerae, bone fragility, and a history of previous bone fractures are characteristic findings in which condition?

A. Osteoporosis
B. Osteogenesis imperfecta (Correct Answer)
C. Osteitis deformans
D. Osteitis fibrosa cystica

Explanation: **Explanation:** The clinical triad of **blue sclerae, bone fragility (multiple fractures), and dental abnormalities** is the hallmark of **Osteogenesis Imperfecta (OI)**, also known as "Brittle Bone Disease." **Why Osteogenesis Imperfecta is correct:** OI is a genetic disorder caused by mutations in the **COL1A1 and COL1A2 genes**, leading to a defect in **Type I Collagen** synthesis. * **Bone Fragility:** Defective collagen leads to poor mineralization and frequent fractures with minimal trauma. * **Blue Sclerae:** The sclera is thin due to collagen deficiency, allowing the underlying choroidal veins to show through. * **Amber Teeth:** This refers to **Dentinogenesis Imperfecta**, where the teeth appear translucent or brownish-blue because of defective dentin (which is rich in Type I collagen). **Why other options are incorrect:** * **Osteoporosis:** Characterized by low bone mass and micro-architectural deterioration, but it does not present with blue sclerae or dentinogenesis imperfecta. It is typically an age-related or secondary metabolic condition. * **Osteitis Deformans (Paget’s Disease):** Involves excessive bone remodeling leading to thickened but weak bones. Key features include increased serum Alkaline Phosphatase and "mosaic" patterns on histology, not collagen defects. * **Osteitis Fibrosa Cystica:** This is a complication of **Hyperparathyroidism**. It presents with "brown tumors" and subperiosteal resorption, caused by overactive osteoclasts due to high PTH levels. **High-Yield Clinical Pearls for NEET-PG:** * **Inheritance:** Most commonly Autosomal Dominant. * **Classification:** **Sillence Classification** is used. **Type II** is the most severe (lethal in utero/perinatal); **Type I** is the most common and mildest. * **Associated Finding:** Otosclerosis leading to progressive conductive hearing loss in adulthood. * **Radiology:** Look for "Wormian bones" in the skull and "popcorn calcifications" near growth plates.

Question 66: All of the following are known causes of osteoporosis except?

A. Fluorosis (Correct Answer)
B. Hypogonadism
C. Hyperthyroidism
D. Hyperparathyroidism

Explanation: **Explanation:** The core concept in this question is distinguishing between diseases that decrease bone density (**Osteoporosis**) and those that increase it (**Osteosclerosis**). **Why Fluorosis is the correct answer:** Fluorosis is a condition caused by chronic ingestion of high levels of fluoride. Fluoride is a potent stimulator of osteoblasts; it replaces the hydroxy group in hydroxyapatite crystals to form **fluorapatite**. This leads to **Osteosclerosis** (increased bone density), though the bone formed is structurally brittle. On X-ray, fluorosis presents with increased radiodensity, especially in the axial skeleton, and calcification of ligaments (e.g., sacrotuberous ligament), which is the opposite of the "lucent" bones seen in osteoporosis. **Why the other options are incorrect:** * **Hypogonadism:** Estrogen and testosterone are crucial for inhibiting osteoclast activity. A deficiency (e.g., post-menopausal state or Turner syndrome) leads to accelerated bone resorption, making it a leading cause of secondary osteoporosis. * **Hyperthyroidism:** Excess thyroid hormone (T3/T4) increases the rate of bone turnover with a shorter cycle, favoring resorption over formation, thus leading to decreased bone mineral density. * **Hyperparathyroidism:** Parathyroid hormone (PTH) stimulates osteoclasts via the RANKL pathway. Chronic elevation leads to significant bone loss, classically manifesting as *Osteitis Fibrosa Cystica* or generalized osteoporosis. **High-Yield Clinical Pearls for NEET-PG:** * **Osteoporosis:** Characterized by normal mineralization but **decreased bone mass/quantity**. * **Osteomalacia:** Characterized by **defective mineralization** of the osteoid. * **Fluorosis Hallmark:** "Chalky white" teeth with mottling (dental fluorosis) and increased bone density with "dagger sign" on spinal X-ray due to interspinous ligament calcification. * **Drug of choice for Osteoporosis:** Bisphosphonates (Alendronate/Zoledronic acid).

Question 67: Which bony changes are seen in hyperparathyroidism?

A. Multiple bone cysts
B. Subperiosteal bone resorption
C. Brown's tumor
D. All of the above (Correct Answer)

Explanation: **Explanation:** Hyperparathyroidism (HPT), particularly the primary form, leads to an overproduction of Parathyroid Hormone (PTH). PTH increases osteoclastic activity to mobilize calcium from bones into the blood, resulting in a spectrum of skeletal changes collectively known as **Osteitis Fibrosa Cystica**. * **Subperiosteal Bone Resorption:** This is the **most sensitive and pathognomonic** radiographic sign of hyperparathyroidism. It is most commonly seen on the radial aspect of the middle phalanges of the index and middle fingers. * **Brown’s Tumor (Osteoclastoma):** These are non-neoplastic lytic lesions caused by intense localized bone resorption. The "brown" color is due to vascularity, hemorrhage, and hemosiderin deposition within the fibrous tissue. * **Multiple Bone Cysts:** Chronic PTH elevation leads to the replacement of marrow with fibrous tissue and the formation of cystic spaces (Osteitis Fibrosa Cystica), making the bone weak and prone to pathological fractures. **Why "All of the above" is correct:** Since hyperparathyroidism triggers a systemic increase in bone remodeling and resorption, it manifests through all three features: subperiosteal resorption (early sign), bone cysts, and Brown's tumors (late signs). **High-Yield Clinical Pearls for NEET-PG:** * **Salt and Pepper Skull:** A classic radiological appearance caused by multiple tiny lucent areas in the calvarium. * **Rugger Jersey Spine:** Seen in secondary hyperparathyroidism (Renal Osteodystrophy), characterized by bands of sclerosis at the vertebral endplates. * **Looser’s Zones:** These are pseudofractures more characteristic of Osteomalacia, not HPT. * **Biochemical Triad:** Hypercalcemia, Hypophosphatemia, and elevated Serum Alkaline Phosphatase (SAP).

Question 68: A 'petrified man' refers to a condition characterized by extensive calcification and ossification. Which of the following conditions is most likely associated with this description?

A. Generalized myositis ossificans (Correct Answer)
B. Ehlers-Danlos syndrome
C. Osteogenesis imperfecta
D. Cherubism

Explanation: ### Explanation **1. Why the Correct Answer is Right:** **Generalized Myositis Ossificans**, also known as **Fibrodysplasia Ossificans Progressiva (FOP)**, is a rare genetic connective tissue disease. It is characterized by the progressive transformation of soft tissues (muscles, tendons, and ligaments) into heterotopic bone. Over time, this extra-skeletal bone formation bridges joints, leading to permanent immobility. The term **'Petrified Man'** is used because the patient’s body literally turns into a "stone-like" state, locking the skeleton into a fixed position. A classic diagnostic hallmark is a congenital malformation of the **great toe (hallux valgus)**. **2. Why the Incorrect Options are Wrong:** * **B. Ehlers-Danlos Syndrome:** This is a disorder of collagen synthesis characterized by joint **hypermobility** and skin hyperextensibility. It is the opposite of "petrification," as patients are excessively flexible ("Rubber Man" syndrome). * **C. Osteogenesis Imperfecta:** Also known as "Brittle Bone Disease," this involves a defect in Type I collagen leading to frequent fractures and blue sclera, not extensive soft tissue calcification. * **D. Cherubism:** This is a rare genetic disorder of the jaws where bone is replaced by painless, cystic fibro-optical lesions, giving the child a "cherubic" (angelic) facial appearance. It does not involve generalized bodily ossification. **3. NEET-PG High-Yield Pearls:** * **Inheritance:** FOP is usually caused by a mutation in the **ACVR1 gene**. * **Pattern of Ossification:** It typically follows a cranio-caudal and axial-to-appendicular pattern (starts at the neck/shoulders and moves down). * **Contraindication:** **Biopsy or surgery** of the lesions is strictly contraindicated as trauma triggers "flare-ups" and accelerates explosive new bone formation. * **Radiology:** Look for "bridging" of the spine and limb joints by ectopic bone.

Question 69: Which of the following biochemical findings are typically seen in osteoporosis?

A. Low calcium, high phosphate, high alkaline phosphatase
B. Low calcium, low phosphate, low alkaline phosphatase
C. Normal calcium, normal phosphate, normal alkaline phosphatase (Correct Answer)
D. Low calcium, low phosphate, normal alkaline phosphatase

Explanation: ### Explanation **1. Why Option C is Correct:** Osteoporosis is defined as a **quantitative** decrease in bone mass (low bone mineral density) with a normal **qualitative** composition of the remaining bone. Because the underlying pathology is an imbalance between bone resorption and formation rather than a primary mineral or endocrine defect, the serum levels of **Calcium, Phosphate, and Alkaline Phosphatase (ALP) remain within the normal range.** This is a classic "trap" in exams; despite the bones being brittle and prone to fractures, the routine biochemical profile is unremarkable. **2. Why Other Options are Incorrect:** * **Option A:** High ALP with low calcium/phosphate is characteristic of **Osteomalacia** (in adults) or **Rickets** (in children), where there is a defect in mineralization. * **Option B:** This profile is not typical of any major metabolic bone disease. Low ALP is rare and seen in conditions like Hypophosphatasia. * **Option D:** Low calcium and phosphate with normal ALP can be seen in early stages of Vitamin D deficiency before the compensatory rise in ALP occurs, but it does not define osteoporosis. **3. NEET-PG High-Yield Clinical Pearls:** * **Gold Standard Investigation:** DEXA Scan (Dual-Energy X-ray Absorptiometry). * **DEXA Diagnostic Criteria:** * T-score **≤ -2.5**: Osteoporosis. * T-score between **-1.0 and -2.5**: Osteopenia. * **Most Common Site of Fracture:** Vertebral body (compression fracture), followed by the neck of the femur and Colles' fracture. * **Biochemical Markers:** While routine labs are normal, specialized **Bone Turnover Markers** may be elevated (e.g., Urinary deoxypyridinoline or Serum N-telopeptide for resorption; Osteocalcin for formation). * **First-line Treatment:** Bisphosphonates (e.g., Alendronate), which act by inhibiting osteoclasts.

Question 70: A 8-year-old boy is being treated for rickets. Which of the following investigations shows the earliest evidence for healing?

A. Serum calcium
B. Serum phosphates
C. Radiological examination of long bones (Correct Answer)
D. Serum alkaline phosphatase

Explanation: In Rickets, the hallmark of healing is the mineralization of the previously uncalcified osteoid at the growth plate. **Why Radiological Examination is Correct:** The **earliest** objective evidence of healing in rickets is seen on an X-ray of the wrist or knee. Within **1 to 3 weeks** of starting Vitamin D therapy, a new line of calcification appears at the zone of provisional calcification (the **"Line of Heubner"**). This represents the rapid deposition of calcium salts in the metaphyseal osteoid, making it the most reliable early indicator of a therapeutic response. **Analysis of Incorrect Options:** * **Serum Calcium (A):** Calcium levels often remain near normal in rickets due to secondary hyperparathyroidism. While they may rise slightly during treatment, they are not a specific or earliest indicator of bone healing. * **Serum Phosphates (B):** Phosphate levels rise as the disease resolves, but this biochemical shift precedes the structural repair of the bone and is less definitive than radiological changes. * **Serum Alkaline Phosphatase (D):** ALP is a marker of osteoblastic activity. In rickets, ALP is significantly elevated. During healing, ALP levels actually **remain high or may even transiently increase** before slowly returning to normal over several months. It is the *last* parameter to normalize. **NEET-PG High-Yield Pearls:** * **Earliest sign of healing:** Radiological appearance of the "Line of Heubner." * **Last sign to normalize:** Serum Alkaline Phosphatase (ALP). * **Most sensitive biochemical marker for diagnosis:** Serum ALP. * **Radiological features of active rickets:** Cupping, splaying, and fraying of the metaphysis.

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

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free