Osteomyelitis and Infectious Diseases — MCQs
Osteomyelitis of spine is caused by the most common organism?
12 years male came with swelling of lower end tibia which is surrounded by rim of reactive bone. What is most likely diagnosis?
A 12-year-old girl begins to limp while playing soccer. She has pain in her right leg and upper right thigh. Her temperature is 102°F. X-ray of the femur reveals that the periosteum is eroded. Assuming that this case is managed as an infectious disease, which of the following is the most likely etiologic agent?
An 8-year-old boy complains of left leg pain for 3 days. On physical examination, his temperature is 38.9°C, and he exhibits irritability when his left leg is moved. A radiograph of the left leg shows changes suggesting acute osteomyelitis in the proximal portion of the left femur. Culture of the infected bone is most likely to grow which of the following organisms?
Which of the following statements about osteomyelitis is incorrect?
Most sensitive imaging modality for detecting early osteomyelitis
A 25-year-old male presents with localized pain in the tibia and swelling. Imaging reveals a bone abscess. Identify the condition.
Which of the following statements about chronic osteomyelitis is false?
All of the following are seen in osteopetrosis EXCEPT:
Which of the following statements about Prions is true:
Osteomyelitis and Infectious Diseases Indian Medical PG Practice Questions and MCQs
Question 1: Osteomyelitis of spine is caused by the most common organism?
- A. Streptococcus
- B. Pseudomonas
- C. Mycobacterium tuberculosis
- D. Staphylococcus aureus (Correct Answer)
Explanation: ***Staphylococcus aureus*** - **_Staphylococcus aureus_** is the most common causative organism for **hematogenous osteomyelitis** in adults, including osteomyelitis of the spine. - It frequently gains access to bone through the bloodstream, leading to infection of the vertebral bodies. *Streptococcus* - While various species of **_Streptococcus_** can cause bone infections, they are **less common** than **_Staphylococcus aureus_** in vertebral osteomyelitis. - **Group A Streptococcus** primarily causes soft tissue infections, and **_S. pneumoniae_** is more associated with pneumonia and meningitis. *Pseudomonas* - **_Pseudomonas aeruginosa_** is a common cause of osteomyelitis, particularly in specific risk groups such as intravenous drug users, patients with puncture wounds (especially through footwear), or those with implanted medical devices. - It is **not the most common** overall cause of general osteomyelitis of the spine. *Mycobacterium tuberculosis* - **_Mycobacterium tuberculosis_** causes tuberculous spondylitis **(Pott's disease)**, which commonly affects the spine, leading to characteristic vertebral destruction and kyphosis. - While significant globally, it is **not the most common bacterial cause** of acute pyogenic vertebral osteomyelitis.
Question 2: 12 years male came with swelling of lower end tibia which is surrounded by rim of reactive bone. What is most likely diagnosis?
- A. GCT
- B. Hyper PTH
- C. Brodie's Abscess (Correct Answer)
- D. Osteomyelitis
Explanation: ***Brodie's Abscess*** - A **Brodie's abscess** is a subacute or chronic osteomyelitis characterized by a localized bone abscess, typically with a surrounding **sclerotic rim of reactive bone**. - It often occurs in the **metaphysis of long bones** (like the lower end of the tibia) in children and adolescents, presenting with localized pain and swelling. *GCT* - **Giant cell tumor (GCT)** typically occurs in **skeletally mature adults** (20-40 years old) and is a lytic lesion often found in the **epiphysis** of long bones, rarely with a distinct sclerotic rim. - GCTs are generally more aggressive and demonstrate a **soap-bubble appearance** with cortical expansion rather than a thick reactive bone rim. *Hyper PTH* - **Hyperparathyroidism** causes bone changes such as **osteopenia**, **subperiosteal bone resorption**, especially in the phalanges, and **brown tumors** (lytic lesions). - It does not typically present as a localized lesion with a **sclerotic rim of reactive bone** in a child. *Osteomyelitis* - While chronic osteomyelitis can involve local bone destruction and reactive bone formation, a **Brodie's abscess** is a specific, well-circumscribed form of **subacute osteomyelitis**. - Acute osteomyelitis presents with more diffuse systemic symptoms (fever, malaise) and less defined reactive bone in its early stages compared to the distinct **sclerotic rim** seen in a Brodie's abscess.
Question 3: A 12-year-old girl begins to limp while playing soccer. She has pain in her right leg and upper right thigh. Her temperature is 102°F. X-ray of the femur reveals that the periosteum is eroded. Assuming that this case is managed as an infectious disease, which of the following is the most likely etiologic agent?
- A. Salmonella enteritidis
- B. Staphylococcus saprophyticus
- C. Listeria monocytogenes
- D. Staphylococcus aureus (Correct Answer)
Explanation: ***Staphylococcus aureus*** - *S. aureus* is the most common cause of **osteomyelitis** in children, accounting for the symptoms of bone pain, limp, fever, and periosteal erosion. - The organism frequently gains access to bone via **hematogenous spread** from a superficial infection or direct inoculation through trauma. *Salmonella enteritidis* - While *Salmonella* can cause osteomyelitis, especially in patients with **sickle cell disease**, there is no indication of this predisposing factor in the girl's history. - *Salmonella* osteomyelitis is less common than that caused by *S. aureus* in the general pediatric population. *Staphylococcus saprophyticus* - *S. saprophyticus* is primarily associated with **urinary tract infections (UTIs)**, particularly in young, sexually active females. - It is an uncommon cause of osteomyelitis and typically not the primary pathogen in bone infections. *Listeria monocytogenes* - *Listeria monocytogenes* is known to cause severe infections in **immunocompromised individuals**, neonates, and pregnant women. - While it can cause osteomyelitis, it is a rare cause in an otherwise healthy 12-year-old and would usually be associated with specific risk factors.
Question 4: An 8-year-old boy complains of left leg pain for 3 days. On physical examination, his temperature is 38.9°C, and he exhibits irritability when his left leg is moved. A radiograph of the left leg shows changes suggesting acute osteomyelitis in the proximal portion of the left femur. Culture of the infected bone is most likely to grow which of the following organisms?
- A. Hemophilus influenzae
- B. Neisseria gonorrhoeae
- C. Salmonella enterica
- D. Staphylococcus aureus (Correct Answer)
Explanation: ***Staphylococcus aureus*** - **_Staphylococcus aureus_** is the most common cause of **acute osteomyelitis** in children. - The clinical presentation with a febrile child, localized leg pain, and radiographic changes strongly points to **bacterial osteomyelitis**, with **_S. aureus_** being the predominant pathogen. *Hemophilus influenzae* - **_Hemophilus influenzae_** was once a significant cause of osteomyelitis in children before widespread **HiB vaccination**. - Its incidence has drastically decreased, making it a less likely cause compared to **_S. aureus_** in an 8-year-old. *Neisseria gonorrhoeae* - **_Neisseria gonorrhoeae_** typically causes **septic arthritis** or osteomyelitis in sexually active adolescents and adults, often in disseminated infections. - It is an **uncommon cause** of osteomyelitis in an 8-year-old child and highly unlikely without a history of sexual abuse or neonatal exposure. *Salmonella enterica* - **_Salmonella enterica_** can cause osteomyelitis, particularly in patients with **sickle cell disease** or other **hemoglobinopathies**. - Without any mention of underlying predisposing conditions like sickle cell disease, **_Salmonella_** is a less probable cause than **_S. aureus_**.
Question 5: Which of the following statements about osteomyelitis is incorrect?
- A. Sequestrum is a piece of dead bone
- B. Epiphysis most commonly involved region (Correct Answer)
- C. In sickle cell anemia salmonella is causative organism
- D. Involucrum is dense sclerotic bone overlying a sequestrum
Explanation: ***Epiphysis most commonly involved region*** - This statement is **incorrect** because osteomyelitis, particularly in children and adolescents, most commonly affects the **metaphysis** of long bones due to its rich, slow-flowing blood supply, which facilitates bacterial deposition. - The epiphysis is less commonly involved primarily due to the differences in vascularity and growth plate anatomy. *Sequestrum is a piece of dead bone* - This statement is **correct**. A **sequestrum** refers to a piece of dead or necrotic bone that has separated from the surrounding healthy bone, often seen in chronic osteomyelitis [1]. - It results from the inflammatory process and lack of blood supply, acting as a nidus for infection. *Involucrum is dense sclerotic bone overlying a sequestrum* - This statement is **correct**. An **involucrum** is a new shell of dense, sclerotic bone that forms around a sequestrum in chronic osteomyelitis, attempting to wall off the infection [1]. - It represents the body's attempt to heal and contain the infection, often leading to sinus tract formation [1]. *In sickle cell anemia salmonella is causative organism* - This statement is **correct**. Patients with **sickle cell anemia** are particularly susceptible to **Salmonella osteomyelitis**, which replaces Staphylococcus aureus as the predominant causative agent in this population. - The altered splenic function and compromised immune response in sickle cell disease contribute to this increased risk. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, pp. 1197-1198.
Question 6: Most sensitive imaging modality for detecting early osteomyelitis
- A. Nuclear bone scan
- B. CT scan
- C. MRI (Correct Answer)
- D. Plain radiograph
Explanation: **MRI** - **MRI** is the most sensitive imaging modality for detecting **early osteomyelitis** due to its superior ability to visualize **bone marrow edema** and soft tissue changes, which are the earliest signs of infection. - It can differentiate between **bone infection** and other processes like inflammation or tumor, even before cortical bone changes are evident. *Nuclear bone scan* - **Nuclear bone scans** (e.g., technetium-99m) are highly sensitive for detecting **increased bone turnover** but lack specificity for infection. - They can identify areas of **inflammation** or injury but cannot reliably distinguish between osteomyelitis and other conditions like **fractures** or **tumors**. *CT scan* - **CT scans** are excellent for visualizing **cortical bone destruction**, **sequestra**, and **involucrum** in later stages of osteomyelitis. - However, **CT scans** are not as sensitive as MRI for detecting early bone marrow changes and soft tissue involvement, making them less ideal for **early diagnosis**. *Plain radiograph* - **Plain radiographs** are often the first imaging study for suspected osteomyelitis but have **low sensitivity** in the early stages, with changes typically not visible until 10-14 days after infection onset. - Early findings may include **periosteal elevation** or soft tissue swelling, but **bone destruction** or new bone formation is usually required for a definitive diagnosis.
Question 7: A 25-year-old male presents with localized pain in the tibia and swelling. Imaging reveals a bone abscess. Identify the condition.
- A. Brodie abscess (Correct Answer)
- B. Osteoid osteoma
- C. Intracortical hemangioma
- D. Chondromyxoid fibroma
Explanation: ***Brodie abscess*** - A Brodie abscess is a **subacute or chronic osteomyelitis** characterized by a well-circumscribed, **radiolucent lesion** (an abscess cavity) often surrounded by a zone of **sclerosis**, representing the body's attempt to wall off the infection. - The presentation of localized pain and swelling in the tibia, with imaging revealing a bone abscess, is consistent with this condition, which is a common form of localized osteomyelitis. *Osteoid osteoma* - This is a **benign bone tumor** characterized by a small, radiolucent nidus surrounded by a large area of **sclerotic bone**. The pain from an osteoid osteoma is typically **worse at night** and dramatically relieved by NSAIDs. - While it can cause localized pain and swelling, the imaging features of a distinct abscess cavity are not characteristic of an osteoid osteoma. *Intracortical hemangioma* - An intracortical hemangioma is a **rare benign vascular lesion** within the cortex of a bone. - Imaging typically shows a **lytic lesion** with a characteristic **"honeycomb" or "sunburst" appearance**, not a well-defined abscess. *Chondromyxoid fibroma* - This is a rare, **benign cartilaginous tumor** that usually presents as an **eccentric lytic lesion** in the metaphysis of long bones, often with a scalloped border and sclerotic rim. - While it can cause localized pain and swelling, the imaging appearance of an abscess with sclerotic margins is not typical of a chondromyxoid fibroma.
Question 8: Which of the following statements about chronic osteomyelitis is false?
- A. Reactive new bone formation
- B. Cloaca is an opening in involucrum
- C. Involucrum is dead bone (Correct Answer)
- D. Sequestrum is hard and dense
Explanation: ***Involucrum is dead bone*** - This statement is false because the **involucrum** is the layer of **new bone formation** that surrounds a segment of necrotic (dead) bone, known as the **sequestrum**, in chronic osteomyelitis [1]. - The involucrum represents the body's attempt to wall off the infection and dead bone, and thus, it is living, *reactive bone*, not dead bone [1]. *Reactive new bone formation* - This statement is true; **reactive new bone formation** occurs around infected or necrotic bone in chronic osteomyelitis, forming the **involucrum** [1]. - This process is a hallmark of the body's response to chronic infection and attempts to contain it. *Cloaca is an opening in involucrum* - This statement is true; a **cloaca** is a **fistulous tract** or opening in the **involucrum** that allows pus and necrotic debris from the infected area to drain to the skin surface. - This drainage is a common clinical sign of chronic osteomyelitis. *Sequestrum is hard and dense* - This statement is true; the **sequestrum** is a piece of **necrotic (dead) bone** that has become separated from living bone due to ischemia and infection [1]. - Due to the loss of blood supply and avascular necrosis, it appears **dense, hard, and radiodense** on imaging, representing devitalized bone tissue that is walled off from the body's immune response. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, pp. 1197-1198.
Question 9: All of the following are seen in osteopetrosis EXCEPT:
- A. Osteomyelitis of the mandible
- B. Pancytopenia
- C. Decreased bone density (Correct Answer)
- D. Compression of cranial nerve
Explanation: ***Decreased bone density*** - Osteopetrosis is characterized by **increased bone density**, not decreased, due to the failure of osteoclasts to resorb bone, leading to accumulation of dense, immature bone [1]. - This creates the classic "**marble bone**" or "**stone bone**" appearance on radiographs [1]. - Therefore, decreased bone density is **contradictory** to the fundamental pathology of the disorder. *Osteomyelitis of the mandible* - Defective **osteoclast function** in osteopetrosis leads to **dense, brittle bone** with **compromised vascularity** that is highly susceptible to infection, particularly in the mandible and maxilla. - The poor blood supply and altered bone architecture make these bones prone to **osteonecrosis** and subsequent infection, manifesting as osteomyelitis. - This is a **well-recognized complication** of osteopetrosis. *Compression of cranial nerve* - **Cranial nerve compression** is a **major complication** of osteopetrosis due to **narrowing of skull foramina** from excessive bone formation [1]. - Common manifestations include **optic nerve compression** (leading to blindness), **facial nerve palsy**, and **hearing loss** from auditory nerve compression [1]. - This occurs due to encroachment of dense bone on nerve pathways [1]. *Pancytopenia* - **Pancytopenia** is a **classic finding** in osteopetrosis due to the **obliteration of bone marrow space** by unresorbed primary spongiosa, impairing hematopoiesis [1]. - This leads to compensatory **extramedullary hematopoiesis** in the liver and spleen. - Bone marrow failure is a significant feature requiring bone marrow transplantation in severe cases. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, pp. 1188-1189.
Question 10: Which of the following statements about Prions is true:
- A. They can be cultured in cell free media
- B. They are infectious proteins (Correct Answer)
- C. They have rich nuclear material
- D. They are made up of bacteria and virus
Explanation: ***They are infectious proteins*** - Prions are uniquely characterized as **infectious proteinaceous particles** that lack nucleic acids. - Their mechanism of pathogenicity involves inducing conformational changes in normal host proteins, leading to disease. *They can be cultured in cell free media* - Prions cannot be cultured in cell-free media because they are **not living organisms** and require host cells to propagate by converting normal proteins. - Their replication depends on the presence of the **normal prion protein (PrPC)** in the host. *They have rich nuclear material* - Prions are fundamentally **devoid of nucleic acids** (DNA or RNA), which is a defining characteristic distinguishing them from viruses, bacteria, and other microorganisms. - Their infectious nature is solely based on their **aberrant protein structure**. *They are made up of bacteria and virus* - Prions are distinct biological entities that are **neither bacteria nor viruses**; they are misfolded proteins. - They are much simpler in structure than even the smallest viruses, lacking the complex genetic material and cellular machinery found in bacteria and viruses.
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