Metabolic Bone Diseases Practice Questions

Q: Bone density is decreased in which of the following conditions?

Osteoporosis. **Explanation:** **1. Why Osteoporosis is the Correct Answer:** Osteoporosis is defined as a systemic skeletal disorder characterized by **low bone mass** and micro-architectural deterioration of bone tissue. In this condition, there is a proportional decrease in both the bone mineral (calcium/phosphate) and the bone matrix (collagen). Because the total amount of bone tissue per unit volume is reduced, the **bone mineral density (BMD)** is significantly decreased, leading to increased bone fragility and risk of fractures. **2. Why the Other Options are Incorrect:** * **Avascular Necrosis (AVN):** In the early stages, the bone density may appear normal. However, as the bone dies and attempts to repair (creeping substitution), it often appears **more dense (sclerotic)** on X-ray compared to surrounding osteoporotic bone. * **Osteopetrosis:** Also known as "Marble Bone Disease," this is a genetic disorder where osteoclast function is defective. This leads to a failure of bone resorption, resulting in **increased bone density** (though the bone is paradoxically brittle). * **Fracture and Collapse of Cancellous Bone:** When bone collapses (as seen in vertebral compression fractures), the trabeculae are crushed together. This compaction leads to a localized **increase in radiodensity** on imaging. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard for Diagnosis:** DEXA Scan (Dual-Energy X-ray Absorptiometry). * **WHO Criteria:** Osteoporosis is defined as a **T-score ≤ -2.5**. * **Biochemical Profile:** In primary osteoporosis, Serum Calcium, Phosphate, and Alkaline Phosphatase (ALP) levels are typically **Normal**. * **Most Common Site of Fracture:** Vertebral body (compression fracture), followed by the neck of the femur and Colles' fracture.

Q: A 40-year-old female presents with urine darkening on standing, joint pain and stiffness, and pigment deposition in joints. What is the probable diagnosis?

Alkaptonuria. **Explanation:** The clinical presentation of **urine darkening on standing**, joint stiffness, and pigment deposition (ochronosis) is pathognomonic for **Alkaptonuria**. **1. Why Alkaptonuria is Correct:** Alkaptonuria is an autosomal recessive disorder caused by a deficiency of the enzyme **Homogentisate 1,2-dioxygenase**. This leads to the accumulation of **Homogentisic Acid (HGA)**. * **Urine Findings:** When urine is exposed to air (standing), HGA oxidizes into a melanin-like polymer, turning the urine black. * **Ochronosis:** HGA binds to connective tissues (cartilage, sclera, ears), causing bluish-black pigmentation. * **Arthropathy:** Long-term deposition in large joints (spine, hips, knees) leads to degenerative "Ochronotic arthritis," typically manifesting in the 4th decade of life. **2. Why Other Options are Incorrect:** * **Phenylketonuria (PKU):** Caused by Phenylalanine Hydroxylase deficiency. It presents with intellectual disability, "mousy" body odor, and hypopigmentation, not joint pigment deposition. * **Tyrosinemia:** Involves defects in the tyrosine catabolic pathway (e.g., Fumarylacetoacetate hydrolase). It primarily presents with liver failure, renal rickets (Fanconi syndrome), and a "cabbage-like" odor, but not black urine or ochronosis. **3. NEET-PG High-Yield Pearls:** * **Radiology:** Characterized by **intervertebral disc calcification** and narrowing at multiple levels (bamboo spine appearance, but unlike Ankylosing Spondylitis, it spares the sacroiliac joints). * **Diagnosis:** Confirmed by detecting Homogentisic acid in urine using **Gas Chromatography-Mass Spectrometry (GC-MS)**. * **Screening:** Benedict’s test is positive (reducing sugar), and Ferric Chloride test gives a transient deep blue/green color.

Q: Codfish vertebrae are seen in which of the following conditions?

Osteoporosis. **Explanation:** **Codfish vertebrae** (also known as biconcave vertebrae) occur when the intervertebral discs bulge into the weakened vertebral bodies. This happens because the decreased bone mineral density makes the vertebral endplates unable to resist the pressure of the nucleus pulposus, resulting in a characteristic "hourglass" or fish-like appearance on a lateral X-ray. **1. Why Osteoporosis is Correct:** In **Osteoporosis**, there is a quantitative reduction in bone mass. The trabecular bone in the spine becomes thin and fragile. The expansive pressure of the intervertebral discs causes the softened superior and inferior endplates to bow inward, creating the classic biconcave "Codfish" deformity. **2. Analysis of Incorrect Options:** * **Osteopetrosis (Option A):** This is characterized by increased bone density ("marble bone disease"). Instead of biconcavity, it typically shows the **"Rugger-Jersey spine"** or **"Bone-within-a-bone"** (sandwich vertebrae) appearance due to defective osteoclast activity. * **Morquio Syndrome (Option C):** This mucopolysaccharidosis is characterized by **Platyspondyly** (generalized flattening of the vertebrae) and a characteristic **anterior tongue-shaped protrusion** (central beaking) of the vertebral bodies, rather than biconcavity. **Clinical Pearls for NEET-PG:** * **Codfish Vertebrae Differential:** While most common in **Osteoporosis**, it can also be seen in **Osteomalacia** and **Hyperparathyroidism**. * **Rugger-Jersey Spine:** Classically seen in **Renal Osteodystrophy** and Osteopetrosis. * **H-shaped Vertebrae (Lincoln Log):** Seen in **Sickle Cell Anemia** due to microvascular infarction of the central endplate. * **Picture Frame Vertebrae:** Pathognomonic for **Paget’s Disease**.

Q: This condition is associated with which of the following?

All of the above. ***All of the above*** - **Blue sclerae** can occur in all three conditions due to different mechanisms affecting **collagen structure** or **bone metabolism**. - The **thinning of scleral tissue** allows the underlying **choroidal pigment** to show through, creating the characteristic blue appearance. *Osteopetrosis* - **Defective osteoclast function** leads to **dense, brittle bones** and can cause **cranial nerve compression**. - Blue sclerae occurs less commonly but can result from **abnormal bone remodeling** affecting orbital structures. *Marfan syndrome* - **Connective tissue disorder** affecting **fibrillin-1 protein**, leading to **aortic dilatation** and **lens dislocation**. - Blue sclerae occurs due to **defective collagen synthesis** causing **scleral thinning** and increased translucency. *Osteogenesis imperfecta* - **Type I collagen defect** causes **brittle bones**, **short stature**, and **hearing loss**. - Blue sclerae is the **most classic association** due to **severe collagen abnormalities** causing marked **scleral transparency**.

Q: An X-ray shows heterotopic calcification around the bilateral knee joints in a young man. What is the next investigation?

Serum alkaline phosphatase. **Explanation:** The presence of heterotopic calcification (calcification in non-osseous tissues) around major joints in a young patient is a hallmark of **Fibrodysplasia Ossificans Progressiva (FOP)** or, more commonly in clinical practice, **Hypophosphatasia**. **Why Serum Alkaline Phosphatase (ALP) is the correct answer:** In the context of metabolic bone disease presenting with ectopic calcification, **Hypophosphatasia** is a key differential. It is characterized by a genetic deficiency of the tissue-nonspecific alkaline phosphatase (TNSALP) enzyme. Low levels of ALP lead to an accumulation of inorganic pyrophosphate (a potent inhibitor of mineralization), which paradoxically results in both rickets/osteomalacia and ectopic calcification. Therefore, checking Serum ALP is the critical diagnostic step to identify the low levels pathognomonic of this condition. **Analysis of Incorrect Options:** * **Serum Phosphate & Calcium (A & B):** While these are often deranged in secondary tumoral calcinosis or renal osteodystrophy, they are typically normal in the early screening of primary genetic ossification disorders like FOP or Hypophosphatasia. * **Serum PTH (C):** PTH is useful for diagnosing hyperparathyroidism or pseudohypoparathyroidism. While these can cause metastatic calcification, they usually present with other systemic symptoms and are not the primary investigation for isolated heterotopic ossification in a young male. **NEET-PG High-Yield Pearls:** * **Hypophosphatasia:** Look for "Low Serum ALP" + "High Urinary Phosphoethanolamine." * **Fibrodysplasia Ossificans Progressiva (FOP):** Characterized by the "Stone Man" syndrome and a classic association with a **short hallux (great toe)**. * **Heterotopic Ossification (HO):** Most commonly occurs post-trauma or surgery (e.g., total hip arthroplasty). Prophylaxis includes NSAIDs (Indomethacin) or low-dose radiation.

Q: The bodies of the vertebrae are biconcave and are called "codfish spine" most commonly seen in which of the following conditions?

Osteomalacia. **Explanation:** The **"Codfish Spine"** appearance refers to the biconcave deformity of the vertebral bodies. This occurs when the bone mineral density is significantly reduced, making the vertebrae soft. Under the constant pressure of the nucleus pulposus (intervertebral discs), the weakened vertebral endplates bulge inward, resembling the anatomy of a fish's spine. **Why Osteomalacia is correct:** In **Osteomalacia** (and Osteoporosis), there is a failure of bone mineralization or a loss of bone mass. This leads to "soft bones." The biconcave shape is a classic radiological hallmark of these metabolic bone diseases. While it is seen in both, Osteomalacia is the most characteristic answer in this context due to the global softening of the osteoid. **Analysis of Incorrect Options:** * **Scurvy:** Characterized by Vitamin C deficiency leading to defective collagen synthesis. Radiological features include the *Wimberger sign* (ring epiphysis), *Frankel line* (white line of scurvy), and *Pelkan spur*, but not typically codfish vertebrae. * **Fluorosis:** Causes **Osteosclerosis** (increased bone density). The spine appears chalky white ("Marble bone" appearance) with ligamentous calcification, rather than biconcave softening. * **Hyperparathyroidism:** Classically associated with subperiosteal bone resorption (especially in phalanges), **"Rugger-Jersey Spine"** (bands of sclerosis), and "Salt and Pepper" skull. **NEET-PG High-Yield Pearls:** * **Codfish Spine:** Seen in Osteomalacia, Osteoporosis, and sometimes Sickle Cell Anemia (due to infarction). * **Rugger-Jersey Spine:** Pathognomonic for Chronic Kidney Disease - Mineral Bone Disorder (CKD-MBD) / Hyperparathyroidism. * **Picture Frame Vertebra / Ivory Vertebra:** Seen in Paget’s Disease. * **Bamboo Spine:** Classic for Ankylosing Spondylitis.

Q: Pelkan spur is seen in which of the following conditions?

Scurvy. **Explanation:** **Scurvy (Vitamin C deficiency)** is the correct answer. The underlying pathology involves a failure of osteoid formation due to defective collagen synthesis. While the cartilaginous matrix at the growth plate calcifies normally, it cannot be converted into bone, leading to a brittle, calcified zone known as the **Zone of Provisional Calcification**. **Pelkan Spur** refers to the lateral bony outgrowths (spicules) seen at the ends of long bones. These occur because the weakened, brittle zone of provisional calcification fractures and pushes outward under the stress of weight-bearing or muscle pull, creating a "spur" appearance on X-ray. **Why other options are incorrect:** * **Rickets:** Characterized by a failure of mineralization of the osteoid. Classic X-ray findings include cupping, splaying, and fraying of the metaphysis, but not Pelkan spurs. * **Hemophilia:** Primarily affects joints (hemarthrosis). Chronic cases show joint space narrowing, subchondral cysts, and squaring of the patella (Jordan’s sign), but not metaphyseal spurs. **High-Yield Clinical Pearls for Scurvy (NEET-PG):** * **Wimberger’s Sign:** A thin, sclerotic ring around a radiolucent epiphysis. * **Frankel’s Line:** A dense, white line of provisional calcification at the metaphysis. * **Trummerfeld Zone:** A radiolucent "scurvy line" proximal to Frankel’s line (representing a zone of debris/fracture). * **Subperiosteal Hemorrhage:** A hallmark clinical feature that causes exquisite pain and "pseudoparalysis" in infants.

Q: Looser zones/pseudofractures are commonly seen in which of the following areas except?

Radius. **Explanation:** **Looser zones**, also known as **pseudofractures** or Milkman’s lines, are pathognomonic radiological features of **Osteomalacia** (in adults) and Rickets (in children). They represent cortical stress fractures that have healed with unmineralized osteoid rather than mature bone. **Why Radius is the Correct Answer:** Looser zones typically occur at sites of mechanical stress or where major arteries cross the bone, causing pulsatile pressure. They are characteristically found in the **Scapula** (lateral border), **Ribs**, **Pubic rami (Pelvis)**, and the **medial aspect of the femoral neck**. The **Radius** is not a common site for these lesions; instead, the radius is more frequently associated with "Colles' fractures" in osteoporosis or "cupping and splaying" of the distal metaphysis in Rickets. **Analysis of Incorrect Options:** * **Scapula:** The lateral border of the scapula is one of the most classic locations for Looser zones due to the mechanical pull of the muscles. * **Ribs:** Multiple pseudofractures are frequently seen in the ribs of patients with severe Vitamin D deficiency. * **Pelvis:** The pubic rami and the ischium are high-stress areas where these radiolucent lines are commonly identified. **High-Yield Clinical Pearls for NEET-PG:** * **Radiological Appearance:** They appear as narrow, transverse radiolucent lines oriented perpendicular to the bone cortex. * **Symmetry:** Looser zones are often **bilateral and symmetrical**. * **Biochemical Profile:** Low/Normal Calcium, Low Phosphate, and **Elevated Alkaline Phosphatase (ALP)**. * **Most Common Site:** The axillary border of the scapula and the superior/inferior pubic rami.

Q: Which of the following is NOT a type of vitamin D-resistant rickets?

Osteomalacia. **Explanation:** The core concept of **Vitamin D-Resistant Rickets (VDRR)** refers to a group of metabolic disorders where clinical and radiological features of rickets persist despite physiological doses of Vitamin D. These are typically genetic conditions involving phosphate wasting or end-organ resistance. **Why Osteomalacia is the correct answer:** Osteomalacia is not a "type" of rickets; rather, it is the **adult counterpart** of rickets. While rickets occurs in children before the fusion of epiphyses (affecting the growth plate), osteomalacia occurs in adults after the epiphyses have closed (affecting bone remodeling). Furthermore, most cases of osteomalacia are Vitamin D-deficient (nutritional), not Vitamin D-resistant. **Analysis of Incorrect Options:** * **B. Familial Hypophosphatemia:** This is the most common form of VDRR. It is an X-linked dominant condition caused by a mutation in the PHEX gene, leading to renal phosphate wasting. * **C. Refractory Rickets:** This is a clinical synonym for Vitamin D-resistant rickets. It describes rickets that does not respond to standard doses (e.g., 600,000 units) of Vitamin D. * **D. Phosphate Diabetes:** This is an older clinical term used to describe the primary renal tubular defect in phosphate reabsorption seen in VDRR. **High-Yield NEET-PG Pearls:** * **Most common type of VDRR:** X-linked Hypophosphatemic Rickets. * **Biochemical hallmark:** Low serum phosphate, normal serum calcium, and elevated alkaline phosphatase. * **Treatment:** Unlike nutritional rickets, VDRR requires **oral phosphate supplements** and **calcitriol** (active Vitamin D), not just Vitamin D2/D3. * **Radiological sign:** "Looser’s zones" (pseudofractures) are characteristic of osteomalacia/rickets.

Question 1

A 45-year-old man presents with back pain and facial pain. Physical examination reveals coarse facial features and kyphosis. Laboratory examination shows elevated alkaline phosphatase. Radiographic studies demonstrate skull thickening with narrowing of foramina, and bowing of the femur and tibia. Bone biopsy reveals a mosaic pattern of bone spicules with prominent osteoid seams. Which of the following neoplasms occurs with increased frequency in patients with this disorder?

Accepted Answer

Osteosarcoma

Answer

Astrocytoma

Answer

Hodgkin's lymphoma

Answer

Meningioma

Question 2

Bone density is decreased in which of the following conditions?

Accepted Answer

Osteoporosis

Answer

Avascular necrosis of bone

Answer

Osteopetrosis

Answer

Fracture and collapse of cancellous bone

Question 3

A 40-year-old female presents with urine darkening on standing, joint pain and stiffness, and pigment deposition in joints. What is the probable diagnosis?

Accepted Answer

Alkaptonuria

Answer

Phenylketonuria

Answer

Tyrosinemia

Answer

Tyrosinemia

Question 4

Codfish vertebrae are seen in which of the following conditions?

Accepted Answer

Osteoporosis

Answer

Osteopetrosis

Answer

Morquio syndrome

Answer

All of the above

Question 5

This condition is associated with which of the following?

Accepted Answer

All of the above

Answer

Osteopetrosis

Answer

Marfan syndrome

Answer

Osteogenesis imperfecta

Question 6

An X-ray shows heterotopic calcification around the bilateral knee joints in a young man. What is the next investigation?

Accepted Answer

Serum alkaline phosphatase

Answer

Serum phosphate

Answer

Serum calcium

Answer

Serum PTH

Question 7

The bodies of the vertebrae are biconcave and are called "codfish spine" most commonly seen in which of the following conditions?

Accepted Answer

Osteomalacia

Answer

Scurvy

Answer

Fluorosis

Answer

Hyperparathyroidism

Question 8

Pelkan spur is seen in which of the following conditions?

Accepted Answer

Scurvy

Answer

Rickets

Answer

Hemophilia

Answer

All of the above

Question 9

Looser zones/pseudofractures are commonly seen in which of the following areas except?

Accepted Answer

Radius

Answer

Scapula

Answer

Ribs

Answer

Pelvis

Question 10

Which of the following is NOT a type of vitamin D-resistant rickets?

Accepted Answer

Osteomalacia

Answer

Familial hypophosphatemia

Answer

Refractory rickets

Answer

Phosphate diabetes

Metabolic Bone Diseases — MCQs

Metabolic Bone Diseases — MCQs

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