In which rheumatic conditions are the affected joints erythematous?
Septic arthritis, rheumatic fever, and neoplasia.
Red joints are very rare in JIA and in most other rheumatic conditions, and they should be a “red flag” for the above diagnoses. The arthritis of rheumatic fever is also characterized by its migratory nature and by pain often out of proportion to the apparent severity of findings on joint examination (e.g., degree of swelling). However, arthritis as part of rheumatic fever is highly responsive to nonsteroidal antiinflammatory drug (NSAID) therapy.
Typical Joint Fluid Findings in ArthritisAdapted from Cassidy JT et al: Textbook of Pediatric Rheumatology, 6th ed. Philadelphia, WB Saunders, 2011.
| Group/Condition | WBC Count (/mL) | PMN (%) | Miscellaneous Findings |
|---|---|---|---|
| Noninflammatory | |||
| Normal | <200 | <25 | — |
| Traumatic arthritis | <2000 | <25 | Debris |
| Osteoarthritis | 1000 | <25 | — |
| Inflammatory | |||
| SLE | 5000 | 10 | LE cells |
| Rheumatic fever | 5000 | 10–50 | — |
| JIA | 15,000–20,000 | 75 | — |
| Reactive arthritis | 20,000 | 80 | Reiter cells |
| Pyogenic | |||
| Tuberculous arthritis | 25,000 | 50–60 | Acid-fast bacteria a |
| Septic arthritis | 50,000–300,000 | >75 | Low glucose, bacteria |
JIA, juvenile idiopathic arthritis; LE, lupus erythematosus; SLE, systemic lupus erythematosus; PMN, polymorphonuclear neutrophils; WBC, white blood cell.Crystal-induced synovitis is rare in childhood apart from genetic (familial hyperuricemia, FMF), neoplastic (leukemia), enzymatic (Lesch-Nyan), and nephropathic origins.These are guidelines and some inflammatory arthritides like JIA can have a synovial fluid WBC count >100,000/mL (pseudoseptic).
a Synovial fluid yield is low; synovial biopsy should be considered if tuberculosis is high on the differential.
