HLA phenotyping is usually considered as costly and unnecessary for the diagnosis of inflammatory rheumatoid diseases. The aim of our work was to assess the diagnostic value of HLA phenotyping compared with the diagnostic value of sex and age at the onset of disease in cases where there is a doubt between rheumatoid polyarthritis and spondyloarthropathy with peripheral involvement.
The relative prevalence of inflammatory rheumatoid diseases was calculated for 138 patients hospitalized for diagnosis of rheumatoid disease. We considered however that in these patients the etiology of the inflammatory rheumatoid disease with synovitis, after search for etiology, could be either spondyloarthropathy with peripheral involvement or early-stage rheumatoid polyarthritis. Positive and negative predictive values were calculated by comparison between these two diseases. The sensitivity of HLA B27 in spondyloarthropathy with peripheral involvement was determined in a population of 83 hospitalized patients with confirmed diagnosis. The prevalence of HLA DR4 in rheumatoid polyarthritis was determined in 375 hospitalized patients with confirmed diagnosis. Predictive values were calculated using Bayes formula.
The analysis of the positive and negative predictive values for HLA B27 showed that the diagnostic value of this allele was much greater than age at disease onset and sex in spondyloarthropathy with peripheral involvement. For rheumatoid arthritis, comparison of the diagnostic value of HLA DR4 versus age at disease onset and sex showed the lower performance of HLA DR4. However, the positive predictive value of HLA DR4 in rheumatoid polyarthritis was similar to that for these factors and equivalent to that of HLA B27. The positive predictive value for the combinations HLA DR4+ HLA B27- and HLA B27+ HLA DR4- was 0.90 for rheumatoid polyarthritis and spondyloarthropathy with peripheral involvement respectively.
The validity of these promising findings should be confirmed in prospective studies.