Coexisting rheumatoid arthritis and ankylosing spondylitis discussion of 3 cases with review of the literature

Summary Coexisting rheumatoid arthritis (RA) and ankylosing spondylitis (AS) have rarely been reported. We aim to evaluate such association in our RA and AS hospitalized patients during the 5 past years. We selected 130 RA and 87 AS patients and found 3 genuine associations which are here reported, 3 AS patients with positive rheumatoid factors (RF) and 4 HLA B27 RA patients. HLA B27 frequency in our RA patients (6,6%) and positive RF in our AS patients (8,3%) does not differ from the HLA B27 or RF frequency in a control series of 172 osteoarthritis or fibromyalgia patients (respectively 8%-in the Caucasian-and 9,8% in this control series).Coexisting RA and AS is discussed with regard to these 3 cases; 44 similar cases are found in the literature and reviewed here. The mechanisms leading to this curious association are discussed. Besides these patients, the sacroiliac joint involvement in RA is also analyzed as well as the positivity of RF in AS. The low frequency of coexisting RA with AS suggests that these 2 conditions probably occur by chance. A similar explanation can certainly be advanced for positive RF in AS and HLA B27 in RA patients since the same frequency for B27 and RF has been observed in controls. Finally, these different case reports and unusual biological or roentgenographic features in RA or AS demonstrate the possibility of confusion between these two rheumatic conditions.