Alivernini S, et al. - Researchers examined 34 psoriatic arthritis (PsA) patients [12 DMARD naive and 22 non-responder to methotrexate (MTX-IR)] with peripheral joint involvement and 55 seronegative rheumatoid arthritis [Ab^neg RA; 27 DMARD naive and 28 MTX-IR] for synovial tissue (ST) biomarkers differentially expressed in PsA and Ab^neg RA. In addition, they tested the predictive value of the biomarkers for therapeutic response. Regardless of the therapeutic scheme, they noted higher immunohistochemistry (IHC) score of CD117+ cells in PsA patients than Ab^negRA patients. Conversely, higher IHC score of CD138+ cells was noted in Ab^neg RA patients, irrespective to the therapeutic scheme. Analyzing the response rate to the therapeutic scheme, at the study entry, they identified lower IHC score of CD3+ cells naive among PsA patients reaching minimal disease activity status at 6 months follow-up compared to PsA patients not reaching this outcome; conversely, at the study entry, lower IHC score of sublining CD68+ cells was observed in naive Ab^neg RA patients reaching DAS remission status at 6 months follow-up compared to Ab^neg RA patients not reaching this outcome. These findings support the utility of histological analysis of ST in solving the clinical overlap between the two diseases and in providing prognostic data about the therapy success.