Concurrence of rheumatoid arthritis and systemic lupus erythematosus: report of 11 cases.

The concurrence of rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) has been reported infrequently. Eleven patients are described here with both RA and SLE, in whom the diagnoses were separated by one to 24 years. Because of the difficulty in diagnosing RA occurring subsequent to SLE, only patients with classical RA as their initial diagnosis were included. Further difficulties arise because arthritis is common to both diseases and may be deforming in SLE, antinuclear antibodies (ANA) are not uncommon in RA, and rheumatoid factor (RF) may be seen in SLE. Nonetheless, judicious application of the American Rheumatism Association (ARA) criteria allows both diagnoses to be made in the individual patient. In our patients there was erosive arthritis in nine, rheumatoid nodules in five, and urinary abnormalities in 10. Serological evidence of RA and SLE with positive RF and ANA and raised DNA antibodies was universal, all patients had haematological evidence of SLE, and all but one decreased serum complement levels. These cases suggest that the concurrence of RA and SLE is not as rare as previously considered and may occur more often than expected by chance alone.