Septic Arthritis in a Patient with Rheumatoid Arthritis

77 y.o. F with past medical history of rheumatoid arthritis on etanercept (TNF-a inhibitor), DM, HTN presenting with whole body pain and fatigue consistent with flare of rheumatoid arthritis. Blood pressure was noted to be lower than normal. On exam, she was noted to have multiple painful small joints but also had a tender L knee with moderate effusion and limited active and passive range of motion.

Based on exam, it was clear that this patient had a flare of her rheumatoid arthritis. However, there were other factors which indicated there may be a second process going on, including her constitutional symptoms, hypotension and leukocytosis. Subsequent arthrocentesis of the left knee drained frank pus.

To find knee effusions, here is a demonstration of the “Bulge Sign Test” and the “Patellar Tap Test”:

Which patients are at risk for septic joints? In patients with known joint disease, certain factors play a key role in worsening the chances of septic arthritis. Diabetes, age >80, rheumatoid arthritis, skin infection have odds ratios of 3.3, 3.5, 4.0, 27.2 (!!) for development of septic arthritis (Risk factors for septic arthritis in patients with joint disease. A prospective study). So don’t be too fast to attribute a painful joint in an RA patient to their RA!

There are case reports of relapsing septic monoarthritis while on etanercept. This paper advocates discontinuation of etanercept (or other TNF-a inhibitors) while treating for septic arthritis.