Metabolic Bone Diseases Practice Questions

Q: Myopathy is seen in all except?

X-linked hypophosphatemic rickets. **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.

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

Pelvis, Vertebrae, Skull. **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).

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

Type 1. **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.

Q: Marble bone is characteristic of which condition?

Osteopetrosis. **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).

Q: All are features of osteogenesis imperfecta except?

Absent clavicle. **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).

Question 1

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

Accepted Answer

Severe infantile osteopetrosis

Answer

Cherubism

Answer

Robinow syndrome

Answer

Pycnodysostosis

Question 2

Myopathy is seen in all except?

Accepted Answer

X-linked hypophosphatemic rickets

Answer

Oncogenic osteomalacia

Answer

Nutritional osteomalacia

Answer

Myopathy is not seen in any of the above conditions

Question 3

Paget's disease involves which of the following bones?

Accepted Answer

Pelvis, Vertebrae, Skull

Answer

Pelvis, Vertebrae

Answer

Pelvis, Skull, Phalanges

Answer

Vertebrae, Skull, Phalanges

Question 4

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

Accepted Answer

Extent and severity

Answer

Poor outcome

Answer

Diagnosis

Answer

Recurrence

Question 5

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?

Accepted Answer

They have a near normal life expectancy.

Answer

They are predisposed to pneumonia.

Answer

They have a short hallux.

Answer

Increased expression of BMP4 gene is seen.

Question 6

Which type of osteogenesis imperfecta is characterized by blue sclera?

Accepted Answer

Type 1

Answer

Type 2

Answer

Type 3

Answer

Type 4

Question 7

Marble bone is characteristic of which condition?

Accepted Answer

Osteopetrosis

Answer

Marfan's syndrome

Answer

Osteogenesis imperfecta

Answer

Melorheostosis

Question 8

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

Accepted Answer

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.'

Answer

Bone mineral density less than 1 standard deviation below the mean of a young, healthy adult.

Answer

Bone mineral density at least 2.5 standard deviations below the mean of a young, healthy adult.

Answer

T score less than -2.5.

Question 9

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?

Accepted Answer

Prednisolone

Answer

Methotrexate

Answer

Indomethacin

Answer

Salbutamol

Question 10

All are features of osteogenesis imperfecta except?

Accepted Answer

Absent clavicle

Answer

Known as brittle bone disease

Answer

Blue sclera

Answer

Wormian bones

Metabolic Bone Diseases — MCQs

Metabolic Bone Diseases — MCQs

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