Day #56 - Acute Monoarthritis Redux

We again approached this issue today.

The differential diagnosis of subacute-acute monoarthritis includes:

• Septic arthritis (gonococcal, non-gonnococcal bacterial, tuberculosis, fungal)
• Crystal (gout, pseudogout AKA CPPD, hydroxyapatate)
• Osteoarthritis flare

More rarely an acute monoarthritis can be a presentation of

• Seropositive and seronegative arthridities including reactive arthritis and post-streptococcal arthritis
• Hemarthrosis (in hemophilia and acquired hemophilia)

We use the history and physical to help us form an opinion on the etiology, but ultimately because septic arthritis is so damaging if missed, a synovial fluid analysis is required if there is suspicion of septic arthritis.

A previous blog discussed septic arthtiris and synovial fluid analysis.

Day #4 - Acute Monoarthritis

Today the discussant spoke about the approach to acute monoarthritis. It was a very articulate presentation and your participation was excellent.

To clarify the point on treatment:

• CEFTRIAXONE 2g IV q24h will cover most organisms including GC, most streptococci, Staph. aureus and many gram negatives. It is not the ideal agent for Staph. aureus, so if it turns out to be methicillin *sensitive* staph. aureus you should change to ANCEF (1g IV q8) or CLOXAILLIN (2g IV q6)
  
• Is MRSA a possibility or is this a prosthetic joint? --> ADD VANCOMYCIN (renal dose)
• Is there reason to worry about pseudomonas? --> I would suggest VANCO+CEFTAZADIME and ID consult.
  

• Prosthetic Joint = Call ortho. Probably should not be admitted to medicine if septic prosthetic joint is the main reason they are in hospital -- they need to go to the OR for wash-out and, in my experience, this is much less likely if they are admitted to GIM instead of orthopedics. Should get ID consult as well.
  

This article from JAMA is an excellent reference on making an evidence based diagnosis of septic arthritis on history, physical and laboratory examination.

VIDEO: How to do an arthrocentesis of the knee

Highlights include:

Risk Factors: Age, DM, rheumatoid arthritis, joint surgery, hip/knee prosthesis, HIV infection, skin infection, (unprotected sexual intercourse for GC)

History: Pain and swelling are present >80% of the time; fever is present only 60% rigors and chills less than that.

Synovial Fluid Exam (LR less than 0.1 rules out; LR >10 rules it in)

• WBC <=25,000 unlikely septic arthritis (LR 0.32) unless immunosuppressed
• WBC >=25,000 LR 2.9
• WBC >=50,000 LR 7.7
• WBC >100,000 LR 28

• PMNs <90%>
• PMNs >90% LR 3.4
  

Important to note that measurement of glucose, protein, lactate do not appear to be helpful according to the literature. Also note that LDH in the joint may have some utility in ruling out as LDH <250>