Pneumococcal polyarticular septic arthritis in a patient with rheumatoid arthritis.

Rheumatoid arthritis is the most commonly reported host-related risk factor for septic arthritis. This risk is highest in severe, seropositive, long-standing (mean, 10 years) rheumatoid arthritis responsible for extraarticular symptoms and treated with systemic glucocorticoids. The clinical presentation of the joint infection is often atypical, leading to diagnostic wanderings. In 25% of cases, the infection is polyarticular, with 3.5 involved joints on average. Staphylococcus aureus is the most common causative organism. Streptococcus pneumoniae causes 5% of all cases of septic arthritis and is more often responsible for polyarticular infections than other organisms. Polyarticular septic arthritis carries a poor prognosis, with a mortality rate of 50% in rheumatoid arthritis patients. Despite its low incidence, polyarticular septic arthritis should be routinely considered in the differential diagnosis of rheumatoid flares. We report a case of pneumococcal septic arthritis involving five joints in a patient with known rheumatoid arthritis. Three other cases with involvement of more than four joints have been published.