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MSK-Derm by Minnie > SM 242a - Bone and Joint Infections > Flashcards

SM 242a - Bone and Joint Infections Flashcards

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1
Q

Which bones are likely to be infected with osteomyelitis due to hematogenous spread?

Which organism is a likely culprit?

A

Long bones, vertebrae

S. aureus

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2
Q

How is osteomyelitis treated?

A

Get diagnostic tests before starting an antibiotic

  • You want to choose the right antibiotic
  • Less urgent than septic arthritis
    • However, if the patient is septic treat empirically immediately
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3
Q

Describe the clinical presentation of a disseminated gonococcal infection (DGI)

A
  • One of two major presentations
    • Tenosynovitis, dermatitis, and polyarthralgia
    • Purulent monoarticular arthritis
  • More common in women than men
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4
Q

Which organisms is the most common cause of osteomyelitis?

A

Staphylococcus aureus

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5
Q

Describe the clinical manifestation of osteomyelitis

A

Nonspecific presentation

  • Pain around the involved site
  • Fever, chills, local swelling, erythema in the proximity of the involved bone is infrequent
  • Occasionally can see a draining sinus tract over the involved bone
    • This is pathognomonic for osteomyelitis
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6
Q

Which bacteria are likely to cause septic arthritis after a cat or dog bite?

A

Pasteurella multocida, Capnocytophaga spp.

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7
Q

A 65 year-old male presents with several weeks of progressive back pain and several hours of left lower extremity weakness. MRI shows L4-L5 diskitis, osteomyelitis, and epidural fluid collection with posterior displacement of the spinal cord. Should treatment be delayed until deep tissue specimens can be obtained for culture?

A

No!

Neurologic signs (left lower extremity weakness) = an emergency. Need to treat immediately to avoid permanent injury and paraplegia

Treat immediately with broad spectrum antibiotic while the patient waits for emergent surgery to decompress the spinal cord (via surgery or percutaneous drainage)

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8
Q

A 25 year-old woman presents with several days of right knee pain, swelling and low grade fever. Arthrocentesis shows 70,000 white blood cells with 95% neutrophils. A gram stain of the joint fluid shows no microorganisms. Blood and synovial fluid cultures are negative.

Is any further evaluation necessary?

A

Yes!

  • >50,000 WBCs and >90% neutrophils indicates a joint infection
  • Synovial fluid and blood cultures can be negative, especially since the bacteria may exist in biofilms
  • Fever indicates septic arthritis

Most likely culprits are S. aureus and N. gonorrhoeae. Futher testing for N. gonorrhoeae is indicated. Treat empirically with vancomycin for S. aureus and ceftrioxone for N. gonorrhoeae

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9
Q

What are the clinical manifestations of septic arthritis?

A
  • Monoarticular in 80% of cases
    • Usually a knee in adults or a hip in children
  • Pain and loss of function
  • Swelling and redness, increased warmth
  • Fever and malaise
  • In peripheral joints…
    • Focal tenderness, inflammation, effusion
    • Limited ROM
  • Axial joints
    • Focal tenderness
    • Distance source of infection in ~50% of patients
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10
Q

In which populations is Pseudomonas aeruginosa a likely culprit for joint infection?

A
  • IV drug users

Note: often involves fibrocartilaginous joints (pubic symphysis, sternoclavicular and SI joints)

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11
Q

When are prosthetic joint infections usually contracted?

A

During placement of the new joint

Usually due to contamination of the prosthesis by skin microorganisms during surgery

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12
Q

What is the key diagnostic test and result for septic arthritis?

A

Arthrocentesis with >50,000 WBCs, >90% neutrophils

Culture positive in 80-90% of patients

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13
Q

Eikenella corrodens might cause joint infection after which exposure?

A

Human bite

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14
Q

What is the most common culprit in septic arthritis?

A

Staphyloccous aureus

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15
Q

Why is Nesseria gonorrhoeae infection difficult to treat?

A

Surface glycoproteins on the bacteria undergo phase and antigenic variation; this allows them to evade the immune system

  • The longer an infection persists untreated, the greater the opportunity for invasive, serum-resistant strains to emerge
  • Infection is often asymptomatic, and therefore persists untreated
    • More commonly asymptomatic in women than in men
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16
Q

What factors promote bacterial attachment to synovial joints?

A
  • Bacterial adhesins (**S. aureus)
  • Host inflammatory factors
  • Extracellular proteins promote bacterial attachment
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17
Q

Which bones are likely to be infected with osteomyelitis due to contiguous spread?

Which organism is a likely culprit?

A

Foot, sacrum

Polymicrobial

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18
Q

Which organism is likely to cause osteomyelitis in immunocompromised patients?

A

Aspergilllus

Mycobacterium avium complex

Candida albicans

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19
Q

Describe the clinical presentation of lyme disease

A

Early infection

  • Erythema migrans
    • Expanding, annular erythematous skin lesion
  • Disseminated infection
    • Fever, chills, secondary annular skin lesions
    • Meningitis
    • Cranial neuritis -> Facial palsy, carditis, migratory arthrits

Late infection

  • ​Arthritis
  • Chrnoic encephalopathy
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20
Q

What pathologies could result in an arthrocentesis with >100,000 WBCs?

A
  • Septic arthritis
  • RA flare
  • Leukemia
  • Gout
  • Reaction to intraarticular injection
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21
Q

What imaging studies are useful in the evaluation of septic arthritis?

A

CT and MRI

Both are sensitive for early septic arthritis. Will show fluid as well as surrounding bone involvement

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22
Q

Which imaging modalities are choice for the diagnosis of osteomyelitis?

A

CT and MRI

23
Q

Why is S**taphylococcus aureus a common culprit of joint infections?

A

S**taphylococcus aureus produces adhesins that permit adherence of the bacteria to cartilage

24
Q

The high relapse rate with osteomyelitis is secondary to…

A. Underlying immunosuppression

B. Inadequate treatment

C. Biofilm formation on devascularized bone

D. Delayed diagnosis

A

C. Biofilm formation on devascularized bone

25
Q

How are prosthetic joint infections treated?

A

Several options, but two-stage exchange is the gold standard

  • Debridement with retention of prosthesis and abx
  • One- or two-stage exchange + abx
  • Long-term antimicrobial suppression (palliative)
  • Implant removal without replacement + abx
    • Amputation may be needed
26
Q

Why are prosthetic joint infections difficult to treat?

A

Biofilms tend to form on the surface of prosthetic material

This dampens the immune response and limits antibiotic penetration

27
Q

Describe the pathogenesis of osteomyelitis

A

Bacteria escapes host defences through

  • Adherence to damaged bone
  • Persistence within osteoblasts
    • Can lay dormant for years
  • Formation of biofilm over bacteria and underlying bone surfaces
    • Forms on areas of de-vascularized bone
    • Prevents eradication of the bacteria
28
Q

Which organism is associated with osteomyelitis caused by animal or human bites?

A
  • Pasteurella moltocida from animal bites
  • Eikenella corrodens from human bites
29
Q

What is Pott’s disease?

Describe the clinical presentation

A

Tuberculous spondylitis = vertebral osteomyelitis due to M**ycobacterium tuberculosis

  • Systemic symptoms are often absent
  • Back pain or stiffness is commonly the only symptom
  • Delayed diagnosis is common
  • Abnormal chest x-ray in <50% of patients
30
Q

Which organism is associated with osteomyelitis in patients with sickle cell disease?

A

Salmonella

Streptococcus pneumoniae

31
Q

Which virus is associated with “persistent, symmetric polyarthritis”?

A

Human Parvovirus B19

32
Q

Pasteurella multocida or Capnocytophaga spp. may cause joint infection after which exposure?

A

Dog or cat bite

33
Q

What is the treatment for diabetic foot infection?

A
  • Revascularization when indicated
  • Surgical debridement of infected bone and soft tissue
  • Broad-spectrum antibiotic therapy targeting aerobic and anaerobic bacteria
34
Q

Why are joints particularly susceptible to infection during bacteremia?

A

The vascular synovial membrane lacks a limiting basememnt membrane; this makes them susceptible to bacterial deposition

35
Q

Which viruses are most commonly associated with viral arthritis?

A
  • Chikungunya virus
  • Hepatitis B virus
  • Hepatitis C virus
  • Human parvovirus B19
    • Persistent, symmetric polyarthritis
36
Q

Which bacteria are likely to cause septic arthritis after a human bite?

A

Eikenella corroens

37
Q

If a patient presents with persistent joint pain that is difficult to diagnose (negative cultures, no improvement), fungal cultures should be sent.

Which fungal organisms are likely to be culprits in healthy hosts?

In immunocompromised hosts?

A
  • Healthy hosts
    • Blastomyces dermatitidis
    • Coccidioides spp.
  • Immunocompromised hosts
    • Candida spp.
    • Cryptococcus
    • Aspergillus
38
Q

What samples are best for the diagnosis of osteomyelitis?

A

Tissue samples or a syringe of pus

These will yield more accurate results than a swab

39
Q

Describe the presentation of viral arthritis casued by human parvovirus B19

A

Persistent, symmetric polyarthritis

40
Q

Drainage of infected synovial fluid in cases of septic arthritis is necessary because…

  1. Inflammatory synovial fluid destroys cartilage
  2. Antibiotics will not penetrate into synovial fluid
  3. Undrained fluid will ultimately drain to the skin via disfiguring sinus tracts
A

a. Inflammatory synovial fluid destroys cartilage

41
Q

Describe the typical clinical presentation of a contiguous osteomyelitis infection

A
  • Affects sacrum, pelvis, or foot
    • May be adjacent to neuropathic ulcers
  • More common in adults than children
  • Usually polymicrobial
42
Q

Describe the typical clinical presentation of hematogenous osteomyelitis

A
  • Usually affects the long bones, vertebrae, or sternoclavicular joint
  • More common in children than adults
  • Usually monobacterial
43
Q
A
44
Q

What is the treatment for septic arthritis?

A
  • Joint drainage
    • Either repeated arthrocentesis or arthroscopic lavage
  • Antibiotic therapy
    • Empiric: Direct against S. aureus and N. gonorrhoeae
      • ​Vancomycin + Ceftriaxone
    • Otherwise, base on blood or synovial fluid culture
45
Q

Which bacteria is associated with Lyme disease?

How is it transmitted?

A

Borrelia burgdorferi

Tick bite (Ixodes tick)

46
Q

How do biofilms contribute to the pathogenesis of osteomyelitis and septic arthritis?

A

Biofilms consist of an organized group of microorganisms in an extracellular polymeric matrix

  • Facilitates gene transfer
    • Microorganisms can pass on virulence factors and abx resistance
  • Evades host immune response
    • Rapid changes in antigen expression
  • Reduces antibiotic efficacy
    • Slows diffusion
    • Prevents mechanism from working effectively
47
Q

Which organism is associated with osteomyelitis due to a foreign body?

A

Coagulase-negative staphylococci

48
Q

Describe the clinical presentation of vertebral osteomyelitis

A
  • Invection involves…
    • Vertebral disks, adjacent vertebrae, or both
    • +/- epidural or psoas abscesses
  • Localized insidious pain and tenderness in the spine
  • Fever in 50% of patients
  • Motor and ensory deficits in 15%
    • Spinal cord or nerve root compression
    • This is an emergency!! Surgery + abx!!
49
Q

Which organism is associated wtih nosocomial osteomyelitis?

A

Enterobacteriaceae

50
Q

In which populations is Kingella kingae a likely culprit for joint infection?

A
  • Children
51
Q

What are the risk factors for septic arthritis?

A
  • Abnormal joint
  • Previous intraarticular steroid injection
  • Immunosuppression
  • Diabetes melitus
  • Malignancy
  • Chronic renal failure
  • Intravenous drug abuse
52
Q

Why do synovial cultures of prosthetic joints have poor sensitivity for infection?

A
  • Prosthetic joints have a lot of surface area
    • The infected part might hide from biopsy
  • Bacteria tend to form biofilms on prosthetic joints
    • The bacteria may not be floating freely in the synovial fluid
53
Q

Which organism is associated with osteomyelitis caused by nail puncture wounds to the foot?

A

Pseudomonas aeruginosa

Usually from the sweat in sneakers/gym shoes

54
Q

In which populations is E. coli a likely culprit for joint infection?

A
  • Neonates
  • Elderly
  • IV drug users
  • Immunocompromised hosts

MSK-Derm by Minnie (48 decks)

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