Conversely, analyzing the distribution of CD138+ cells within the synovial tissue, Abneg RA patients showed higher IHC scores for CD138+ cells (1.58 ± 1.09) compared to PsA patients (0.72 ± 0.71; p < 0.001) independently of the treatment scheme (Fig. 3f–i). This evidence concerns the gene SDC1 and rheumatoid arthritis.