We recently had a case of a middle age man with SLE on chronic prednisone, ESRD on PD, presenting with acute on chronic shoulder pain x 10 days. Presentation was initially concerning for septic arthritis, and joint washout revealed gross purulence from the shoulder joint. Cultures were sent but no additional fluid studies were obtained.

A subsequent TTE, and later a TEE, confirmed a mitral valve vegetation concerning for concurrent infective endocarditis. However, multiple sets of blood cultures, fungal cultures, synovial fluid culture from the initial I&D/wash out, and even 16S PCR of the synovial fluid were all negative. This is a rare case of culture negative endocarditis which is later thought to be more likely Libman Sacs!

Septic Arthritis

• Epidemiology
  • Risk factors: Advanced age, pre-existing joint dz, recent surgery or injection, SSTI, IVD, indwelling catheter, immunosuppression.
  • Most cases arise from hematogenous seeding, hence bacteremia is common.
  • Direct inoculation: usually due to trauma, surgery/injections, or wounds.
• Microbiology
  • Usually mono-microbial, and Staph aureus is the most common cause of septic arthritis in adults.
  • GNR can be seen in older adults or in immunocompromised patients
• Presentation
  • Monoarthritis is most common
    • Edematous, painful, warmth, limited ROM
    • Older patients may not be febrile
  • 20% of cases can present as oligoarticular or polyarticular infection. Polyarticular septic arthritis is more likely to occur in pts with RA
  • Most common affected joint is the knee
  • Could be a manifestation of infective endocarditis, esp amongst IVDU
• Diagnosis
  • Synovial fluid analysis and culture, should be obtained prior to abx
  • Positive gram stain or culture is gold standard and diagnostic
    • PCR only required in rare cases since most non-gonococcal cultures obtained prior to antibiotics return positive. Negative cultures can result due to recent abx or atypical organism.
  • In pts with purulent synovial fluid (WBC 50k-150k) but culture negative, a presumptive dx can be made.
    • Likelihood of septic arthritis inc with inc leukocyte count
  • Blood cultures should be obtained
  • Should also evaluate for endocarditis given most common organism is staph aureus
  • Imaging:
    • Always get a radiograph to evaluate for concurrent bone/joint involvement
    • CT/MRI can be useful if looking for an effusion
• DDx
  • Infectious
    • Gonococcal arthritis
    • Lyme disease
    • TB arthritis
    • Viral (usually polyarticular), i.e. Zika, Dengue, chikungunya, parvo, rubella, adenovirus
  • Non-infectious
    • Crystal dz
    • Reactive arthritis
• Management
  • Joint drainage, severe infectious may require repeated aspiration or even wash out.
  • Abx
    • Most cases are staph, MRSA cases on the rise
    • Suspect pseudomonas if pt is immunocompromised or has h/o IVDU
    • Intra-articular abx: typically not used
    • Duration:
      • Staph aureus with bacteremia: At least 4 weeks
      • Staph aureus without bacteremia: at least 14 days IV, followed by 1-2 weeks PO
      • Bone involvement: 4-6 weeks
      • Any organisms, any bone involvement: 4-6 weeks
      • Other organisms: Typically at least 4 weeks

Culture Negative Endocarditis

• Definition: Endocarditis without an identified organism in at least 3 independent blood cultures with negative growth after 5 days
• Epidemiology
  • 2-7% of IE cases
  • 3 most common causes:
    • Previous abx
    • Inadequate samples
    • Atypical organisms (fastidious bacteria i.e. zoonotic microbes, fungal)
• Microbiology
  • Farm animal exposure: Brucella, Coxiella (Q-fever)
  • Homeless: Bartonella Quintana
  • Cat: Bartonella hensale
  • Ingestion of unpasteurized milk: Brucella, Coxiella
  • Immunocompromised: Fungi, Coxiella
  • HACEK: Most common agents of culture negative endocarditis
    • Haemophilis aphrophulus
    • Actinobacillus
    • Cardiobacterum hominis
    • Eikenella corrdens
    • Kingella
• Diagnosis
  • PCR, histology, special cultures are helpful.
  • PCR
    • 16S Ribosomal DNA: Bacteria
    • 18S Ribosomal DNA: Fungi
• Non-infectious DDx
  • APLS, associated with Q fever
  • Acute rheumatic fever
  • Atrial myxoma
  • Libman Sachs endocarditis (non-bacterial thrombotic endocarditis or NBTE)
    • Seen in:
      • SLE
      • Advanced cancer
      • Hypercoagulable state
  • Vasculitis
  • Mural thrombus

NBTE (Non-bacterial thrombotic endocarditis)

• Epidemiology
  • Rare affected all age group with no sex preference, most commonly 40s – 80s
  • Most commonly associated with pts with concurrent SLE or advanced malignancy (lung cancer, pancreatic cancer, gastric cancer)
  • Other associated conditions: APLS, rheumatic heart disease, RA.
• Pathophysiology
  • A form of non-infectious endocarditis characterized by deposition of thrombi on halve valves, most commonly mitral or aortic
• Presentation
  • Usually asx but high risk of thromboembolic events
  • May present with acute stroke or coronary ischemia
• Diagnosis
  • Exclusion: Demonstration of vegetations on echo in absence of systemic infection in patients with risk factors.
• Management
  • Systemic anticoagulation
    • Clinical experience and retrospective studies had shown this is beneficial due to high rate of emboli in pts with NBTE
  • Treat underlying condition
  • Surgery
    • Surgical excision for NBTE vegetation, can be considered in only selective cases and generally avoided.