Infection Flashcards
(Ped) 63 A 6 year old boy presents with worsening left knee pain, but no history of trauma. X-ray reveals a 1.5 cm lytic, oval lesion in the proximal tibial metaphysis. There is a surrounding rim of sclerosis with a lucent channel extending towards the growth plate. What is the most likely diagnosis?
(a) Brodie abscess
(b) Chondroblastoma
(c) Ewing’s sarcoma
(d) Osteoid osteoma
(e) Multiple myeloma
(a) Brodie abscess
Brodie abscess is a subacute pyogenic osteomyelitis, most commonly caused by Staphylococcus aureus. It is a metaphyseal lesion, but may cross to the epiphysis before growth plate fusion; the proximal or distal tibia location is typical. The finding of a lucent channel extending to the physis (‘serpentine’ sign) is pathognomonic for Brodie abscess.
@# 70 A 35 year old intravenous drug abuser presents complaining of pain in his great toe. On questioning, he has been using foot veins to inject drugs. Which of the following statements is incorrect regarding his risk of osteomyelitis?
(a) Staphylococcus aureus is the likeliest organism
(b) Initial plain radiographs may be normal
(c) Localized soft tissue swelling occurs within 2 weeks
(d) A sequestrum is not seen until at least a month after the insult
(e) Radiographs are not sensitive detectors of osteomyelitis
(a) Staphylococcus aureus is the likeliest organism
Pseudomonas is the commonest responsible organism in drug users.
S. aureus is the commonest responsible organism in non-diabetics.
Diabetic patients typically have multiple responsible organisms.
Plain films can be normal for up to 2 weeks.
The earliest sign is soft tissue swelling. Other signs include osteolysis, endosteal erosion, and the formation of an involucrum, followed by a sequestrum.
- A 60-year-old diabetic man with a 7-day-old compound fracture of the right tibia and fibula develops fever and septicaemia. Radiography of the leg shows a fracture of the mid shaft of tibia and fibula, along with extensive air in soft tissues extending to ankle and knee. What is the most likely diagnosis?
(a) Air secondary to compound fracture
(b) Aerobic bacterial infection
(c) Clostridium infection
(d) Staphylococcus infection
(e) Beta-haemolytic streptococci
- (c) Clostridium infection
Gas in the soft tissues after compound fractures is a manifestation of infection. Gas gangrene after Clostridium infection is a classical example and causes extensive oedema, necrosis of tissues with gas production resulting in a severe toxic state. Other gas-forming organisms include anaerobic bacteria, coliforms and Bacteroides.
- A patient who is HIV positive presents with knee and ankle pain and swelling. Clinical examination is otherwise unremarkable. Initial radiographs reveal only a joint effusion. The complaint resolves after 4 weeks. What is the most likely diagnosis?
A. Septic arthritis.
B. Psoriatric arthritis.
C. HIV-associated arthritis.
D. Acute symmetric polyarthritis.
E. Hypertrophic pulmonary osteoarthropathy (HPOA).
- C. HIV-associated arthritis.
This is oligoarticular, asymmetric and peripheral. It primarily affects the knees and ankles. It has a short duration of 1–6 weeks; radiography may reveal a joint effusion.
Acute symmetric polyarthritis also occurs in HIV. It behaves clinically like RA, but patients are negative for rheumatoid factor. Features that help differentiate it from RA are periostitis and proliferative new bone formation. Occasionally an erosive variety with little or no proliferative bone formation occurs.
Psoriatric arthritis has a higher prevalence among AIDS patients than in the general population.
HPOA is associated with P carinii pneumonia (PCP) in AIDS. Plain fi lms reveal periosteal reaction.
Kaposi’s sarcoma uncommonly affects the bone, but does so most commonly in Africa.
Non- Hodgkin lymphoma (NHL) is the second most common tumour in HIV infection. It can produce lytic, sclerotic, or mixed lesions with a wide zone of transition; they are usually lytic.
Other musculoskeletal complications in AIDS include infections (cellulitis, osteomyelitis, septic arthritis, pyomyositis, necrotising fasciitis), Reiter’s syndrome, undifferentiated spondyloarthropathy, polymyositis, osteonecrosis (especially of the femoral head), osteoporosis, rhabdomyolysis, and anaemia.
- An 81-year-old male diabetic is referred from the endocrinology team for an MRI of foot. This patient was seeing a podiatrist, who became concerned that the foot had become increasingly deformed and was acutely red and swollen around the tarso-metatarsal joints. The patient is asymptomatic as he has peripheral neuropathy. The clinical query is whether this patient has osteomyelitis/septic arthritis in this region, or neuropathic arthropathy. Which of these MRI features would be more typically associated with osteomyelitis than acute neuropathic arthropathy?
A. Focal involvement.
B. Predominant midfoot involvement.
C. Associated bony debris.
D. High T2WI and STIR, low T1WI. Enhancement present.
E. Bony changes are in a periarticular and subchondral location.
- A. Focal involvement.
Whilst differentiating these conditions can be difficult and they frequently overlap, there are certain features that can be of value.
Neuropathic arthropathy (NA) seldom affects a single bone/ joint in the foot, and is most common in the midfoot region.
As such a more focal abnormality, or abnormality affecting the metatarsal heads, or other points of pressure, should indicate osteomyelitis.
Whilst high T2WI/STIR, low T1WI and enhancement are seen in osteomyelitis, it is also seen in acute NA and as such is not a good differentiating factor.
The converse is not true, where low signal on T1WI and T2WI, typical of chronic NA, would make the presence of osteomyelitis unlikely.
50 A 27-year-old Afro-Caribbean patient with known sickle cell disease presented with ongoing pain left arm pain following a crisis and was found to have osteomyelitis of his humerus. What is the most likely causative organism?
a Proteus mirabilis
b Escherichia coli
C Staphylococcus aureus
d Mycoplasrna pneumoniae
e Corynebacteriurn diphtheriae
50 Answer C: Staphylococcus aureus
Some series suggest that Salmonella is the most likely cause but others have found that Staphylococcus is the commonest cause in this population.
9 A 10-year-old schoolboy had a fall and bruised his right knee badly. There was an open wound that was not treated until the following day. After a further two days he became systemically unwell with a fever. His knee was extremely tender, swollen, and the movement was restricted. Which of the following is a feature of septic arthritis?
a Usually due to Haernophilus
b Periarticular, soft tissue swelling is rare
C Blurring of the periarticular fat planes is common
d The joint space widens after a few weeks
e A joint effusion is not usually present
9 Answer C: Blurring of the periarticular fat planes is common
Septic arthritis usually occurs in hip, knee, shoulder, elbow and ankle. Staphylococcus aureus, followed by group A Streptococcus, are the most common causes.
Other radiographic features include periarticular soft-tissue swelling, an effusion, periarticular osteopenia and, later, joint space narrowing.
Ultrasound may help identify septic arthritis before cartilage lysis occurs. hallmark is joint eff. in a patient with signs of a joint infection.
66 A 12-year-old boy presented with ankle pain and a radiograph showed a metaphyseal lucency with dense surrounding sclerosis with a thin lucent channel extending towards the growth plate. The lesion was thought to be a Brodie’s abscess. What is the most likely causative organism?
a Proteus mirabilis
b Escherichia coli
c Staphylococcus aureus
d Salmonella species
e Streptococcus milleri
66 Answer C: Staphylococcus aureus
Brodie’s abscesses are more common in children and tend to affect the end of tubular bones, most commonly the distal tibia or femur.
(Ped) 24 A five-year-old girl is systemically unwell with left leg pain and a limp. On examination she is exquisitely tender over the left femur. Staphylococcus aureus is grown from her blood cultures. A plain radiograph of the left leg confirms the diagnosis of osteomyelitis. Where is the abnormality likely to be?
a Femoral metaphysis
b Femoral epiphysis
C Femoral diaphysis
d Distal femoral physis
e Multicentric involvement
24 Answer A: Femoral metaphysis
Osteomyelitis is often the result of haematogenous spread in the paediatric population.
In neonates there is commonly multicentric involvement.
In children from 18 months to 18 years the metaphyseal vessels loop sharply without penetrating the growth plate, therefore the metaphysis is most commonly affected.
QUESTION 28
An elderly diabetic patient with an established peripheral senso1y neuropathy has deep ulcers on his right foot. Plain films show destruction of the architecture of the midfoot with extensive sclerosis, consistent with a Charcot arthropathy. Which imaging feature would suggest coexistent infection?
A Collapse of the plantar arch on the lateral radiograph
B Enhancement of Tl w signal following administration of gadolinium
C Evidence of bone oedema on fluid sensitive sequences
D Reduced bone marrow signal on STIR
E Slow progression of bone destruction on serial radiographs
B Enhancement of Tl w signal following administration of gadolinium
The detection, or exclusion, of osteomyelitis in the context of Charcot arrhropathy is difficult. Bone marrow oedema is a feature of both infection and Charcot changes, but enhancement following gadolinium is suspicious for coexistent infection.
QUESTION 35
A 19-year-old student returns to the UK following 4 months’ travelling around the world. Radiographs reveal multiple oval areas of calcification, up to 1 cm in long axis, aligned in the direction of muscle fibres. What is the most likely diagnosis?
A Cysticercosis
B Dracunculus (guinea worm) infection
C Hydatid disease
D Loiasis
E Schistosomiasis
A Cysticercosis
@# A 75-year-old diabetic man underwent a left below knee amputation 3 months ago for osteomyelitis of the distal tibia. Since then, he has experienced recurrent episodes of fever and malaise. MRI is contraindicated due to a metallic aortic valve. Which is the best investigation to exclude an occult focus of osteomyelitis?
A CT
B US
C Scintigraphy using gallium
D Scintigraphy using indium-labelled white cells
E Scintigraphy using technetium (Tc-99m) monodiphosphonate
E Scintigraphy using technetium (Tc-99m) monodiphosphonate
Although an indium-labelled white cell study is more specific, a bone scintigram using Tc-99m monodiphosphonate is a more sensitive test to exclude osteomyelitis.
QUESTION 59
An 80-year-old diabetic man is admitted from the Emergency Department with clinical and radiographic features consistent with a septic arthritis of the right hip. There is no history of trauma or previous surgery. Initial blood cultures indicate a systemic bacteraemia. What is the most likely organism to be cultured?
A Clostridium difficile
B Haemophilus influenzae
C Pseudomonas aeruginosa
D Staphylococcus aureus
E Streptococcus pneumoniae
D Staphylococcus aureus
Streptococcus pneumoniae and Haemophilus influenzae are potential causes of primary bacteraemia and haematogenous infection of joints, but substantially less common than Staphylococcus aureus.
- Regarding imaging appearances of osteomyelitis: (T/F)
(a) Klebsiella is the commonest organism isolated in adult
(b) Chronic osteomyelitis is characterised by prominent cortical thinning
(c) The diaphysis are often spared in patients with sickle cell disease.
(d) Radiographic findings become evident approximately 3 days after onset infection
(e) Periosteal reaction is the earliest sign of acute osteomyelitis
Answers:
(a) Not correct
(b) Not correct
(c) Not correct
(d) Not correct
(e) Not correct
Explanation:
Radiographic findings of osteomyelitis become evident approximately at 1-2 weeks after onset of infection.
Soft tissue swelling and loss of normal fat planes is the earliest sign of acute osteomyelitis.
The staphylococcus is the commonest organism involved.
Chronic osteomyelitis is characterised by prominent cortical thickening.
In sickle cell disease, diaphysis is the primary focus of infection.
