Background There is a need to identify subgroups of patients with RA having a more uniform phenotype. HLA-B27 is a good candidate to affect the RA phenotype because it is associated with differential clinical aspects of other diseases, both B27-associated and non-associated1-3.
Objectives We aimed to determine with a standardized ultrasonographic (US) evaluation whether the HLA-B27+ patients with RA have specific entheseal lesions or not.
Methods HLA-B27 was determined in 523 patients with RA. For each positive patient a B27- patient was selected matched for gender, age and age of disease onset. They were examined for clinical characteristic of the HLA-B27 associated diseases, including Schober test, BASDAI, BASFI, lateral trunk flexion and pelvic anteroposterior radiographs. US evaluation was performed by an experimented rheumatologist with General Electric LogiqQ7 equipment using a 10-14 MHz linear array transducer. The power Doppler settings were standardized with a pulse repetition frequency (PRF) of 500 Hz with a low wall filter and 35-40 dB of gain. Scoring was done with the Madrid Sonography Enthesitis Index (MASEI)4. This index evaluates 6 features in 6 entheses. A value ≥18 has been defined as characteristic of spondyloarthritis. Radiographs were evaluated independently by two rheumatologists. All the personnel involved in recruiting and evaluating the patients was blind to their HLA-B27 status. The patients consented in writing and the study was approved by the ethics committee.
Results There were 44 HLA-B27+ patients with RA among the 523 studied. They were similar to the HLA-B27- patients in gender, age of disease onset, erosive arthritis, anti-CCP and shared epitope prevalence. However, they were less frequently positive for RF (P=0.002). Anamnesis and exploration were possible in 41 HLA-B27+ and in 41 matched B27- patients. None of the explorations showed significant differences. However, there were 3 patients with sacroileitis in the group of HLA-B27+ patients and none among the B27- (P=0.13). US entheseal evaluation did not show any difference in the mean MASEI value. The number of patients with MASEI ≥18 was 13 HLA-B27+ and 10 HLA.B27-. In addition, there were not differences in any of the 6 individual features analyzed separately.
Conclusions Carrying HLA-B27 did not significantly modify the clinical phenotype of RA patients. In particular, no specific US pathology was found in the entheses. However, our study has shown that there are common entheseal abnormalities in patients with RA and, as a consequence, the MASEI ≥18 threshold lacks specificity for spondyloarthritis in these patients. Only, a lower frequency of RF was observed in the B27+ patients. In addition, there were 3 patients with sacroileitis that suggest a low frequency of mixed phenotypes, insufficient for significant differences in our study.
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Disclosure of Interest None Declared
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