I think this card is misleading and fails to capture the key defining features that help to distinguish between septic arthritis and inflammatory arthritis.
All of this woman's symptoms point to rheumatoid arthritis:
- Fever
- Joint paint
- Arthrocentesis showing WBCs < 50k with neutrophilic predominance
However, the answer to the card is "Gonococcal septic arthritis".
After going through the 2 UWorld questions tagged in the card (qid: 3153 and 15847), I believe this card is based on qid: 15847.
In the Uworld question stem, the patient has the same symptoms, but with the added information that points to gonococcal septic arthritis: she also has non-tender pustules, and the synovial fluid reveals a WBC count of 30,000.
In the article "Approach to Septic Arthritis" by Horowitz et al. (PMID: 21916390), table 3 states that the WBC count from a synovial fluid analysis in the setting of gonococcal arthritis typically reveals a value ranging from 34,000 to 68,000.
Also, if you look at UWorld qid: 3153 (which is another case of gonococcal arthritis), the explanation says "The diagnosis of DGI requires sampling from multiple areas because Neisseria gonorrhoeae is a fastidious organism and culture results are frequently negative. Two sets of blood cultures should be obtained, and synovial fluid sampling is required when joint effusion is present. Synovial fluid leukocyte count usually is ~50,000/mm3 with a preponderance of neutrophils, but organisms may be absent on Gram stain."
Thus, this card is misleading. Gonococcal septic arthritis will present with an elevated synovial fluid white count (although it may be less than 50,000). However, the symptoms listed in the card as is give is no way to differentiate between inflammatory arthritis and gonococcal septic arthritis.
Suggested change: "Synovial fluid analysis reveals WBC between 34,000 and 68,000" or something like that.
Or add that she has tenosynovitis and dermatitis (erythematous papules and pustules).