Rheumatic disease presenting as septic arthritis: a report of 10 cases.

To determine the forms and characteristics of rheumatic diseases whose initial presentation mimics septic arthritis. Retrospective study of 398 patients hospitalized between 1979 and 2005 for arthritis diagnosed and treated as septic. In 10 cases, initial presentation of a rheumatic disease was highly suggestive of septic arthritis, and the patient was treated as such. Three had rheumatoid arthritis, 3 spondyloarthropathies, 2 unclassified rheumatic diseases, 1 Wegener granulomatosis and 1 cytosteatonecrosis. Mean time to diagnosis of rheumatic arthritis was 6 months. There were 7 males and 3 females aged from 15 to 77 years. Six had fever, and 3 had leucocytosis. Average ESR was 68 mm/1 h, and C-reactive protein was above 100 mg/l in 6 patients. Five patients had radiological signs suggestive of septic arthritis. Joint fluid count was above 100,000 WBCs/mm(3) in 2/5. Synovial biopsy suggested septic arthritis in 5 out of 6. These cases of pseudoseptic arthritis were indistinguishable from true septic arthritis. Follow-up is required in septic arthritis with negative culture findings to exclude rheumatic disease.