Metabolic Bone Diseases Practice Questions

Q: The windswept deformity is seen in which of the following conditions?

Rickets. **Explanation:** **Windswept deformity** is a classic clinical presentation of **Rickets**. It is characterized by a combination of **genu valgum (knock-knee)** in one leg and **genu varum (bow-leg)** in the other. This occurs because the softened, unmineralized osteoid in rickets cannot withstand the mechanical stresses of weight-bearing, leading to progressive bowing and angular deformities of the long bones. **Analysis of Options:** * **Rickets (Correct):** Nutritional or Vitamin D-resistant rickets leads to defective mineralization of the epiphyseal growth plate. Along with windswept deformity, other features include rachitic rosary, Harrison’s sulcus, and craniotabes. * **Achondroplasia:** This is a quantitative defect in cartilage formation (FGFR3 mutation) leading to rhizomelic dwarfism. While genu varum is common, the specific "windswept" combination is not characteristic. * **Ankylosing Spondylitis:** This is a chronic inflammatory arthritis primarily affecting the axial skeleton (SI joints and spine), leading to a "Bamboo spine." It does not cause pediatric long-bone bowing. * **Scurvy:** Caused by Vitamin C deficiency, it affects collagen synthesis. Clinical features include subperiosteal hemorrhages, "scorbutic rosary" (sharp), and gingival bleeding, but not windswept limbs. **High-Yield Clinical Pearls for NEET-PG:** * **Windswept Deformity:** Also seen in **Skeletal Dysplasias** and **Metabolic Bone Diseases** (like Osteomalacia in adults). * **Radiological Signs of Rickets:** Cupping, splaying, and fraying of the metaphysis (best seen at the lower end of the radius and ulna). * **Looser’s Zones (Pseudofractures):** A hallmark radiological finding of Osteomalacia/Rickets. * **Windswept Hip:** In Cerebral Palsy, this refers to one hip being adducted and the other abducted.

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: 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.

Question 1

The windswept deformity is seen in which of the following conditions?

Accepted Answer

Rickets

Answer

Achondroplasia

Answer

Ankylosing spondylitis

Answer

Scurvy

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

Codfish vertebrae are seen in which of the following conditions?

Accepted Answer

Osteoporosis

Answer

Osteopetrosis

Answer

Morquio syndrome

Answer

All of the above

Question 4

This condition is associated with which of the following?

Accepted Answer

All of the above

Answer

Osteopetrosis

Answer

Marfan syndrome

Answer

Osteogenesis imperfecta

Question 5

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

Metabolic Bone Diseases — MCQs

Metabolic Bone Diseases — MCQs

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