gms | German Medical Science

Introduction: In rheumatoid arthritis (RA), a chronic inflammatory autoimmune reaction leads to inflammation of the synovium resulting in the breakdown of cartilage and bone. Despite various treatment options, the disease cannot be cured, which is why remission is the therapeutic goal. As the prognostic outcomes of patients in remission still vary widely, a better understanding of remission is needed.

Objectives: Investigation of histological differences in the synovium that define remission in RA.

Methods: RA patients (age 43–81 years) receiving joint replacement surgery were clinically classified into remission vs. active disease based on clinical (e.g. information on painful joints, pain degree, medication) and laboratory parameters (e.g. ESR, CRP, leucocytes). Before the synovial tissues were scored using the Krenn score [1], they were stained with hematoxylin and eosin. Three synovitis characteristics (hyperplasia, activation of synovial stroma, inflammatory infiltrates) were scored (score 0–3). The Krenn score is defined by the sum of the three values.

Results: Clinical classification of 37 synovial endstage tissues led to the inclusion of 20 active patients and 17 in remission. The patients in remission showed lower values for all parameters. In particular, they showed reduced inflammatory infiltrates, a thinner lining, less activation of synovial stroma and a lower Krenn score (4.5 vs. 5.7). Especially hyperplasia (P=0.0337) and total Krenn score (P=0.0381) were significantly reduced. As expected, patients with active disease showed more inflammatory infiltrates and a more pronounced hyperplasia resulting in a higher Krenn score. Statistical analyses of the Krenn Score were carried out using GraphPad Prism version 6 (*P<0.05).

Conclusion: As it is difficult to include arthroscopy and synovial tissue evaluation in clinical monitoring and these procedures are not established for routine clinical assessment, the characterisation of synovium after joint replacement surgery was used to compare synovial tissue activity of patients in clinical remission compared to active disease. Patients in remission showed a lower degree of inflammation and, most prominent, cellular activation (hyperplasia) compared to active disease. Evaluation of cellular alterations contributing to the different response to treatment will provide valuable information about subgroups not responding to certain medication preventing remission.