Reliability of computerized image analysis for the evaluation of serial synovial biopsies in randomized controlled trials in rheumatoid arthritis

Rheumatoid arthritis (RA) is characterized by chronic and symmetric inflammation of synovial joints [1,2]. Although the aetiology of RA is still unknown, it is thought of as an autoimmune disease with the synovial tissue (ST) being its primary target. The microscopic appearance of RA ST includes marked intimal lining layer hyperplasia due to increased numbers of fiboblast-like synoviocytes and intimal macrophages, and accumulation of macrophages, T cells, B cells, plasma cells, dendritic cells, mast cells, natural killer cells and neutrophils in the synovial sublining layer [3]. Developments in synovial biopsy techniques, especially arthroscopy, have resulted in easier access to human ST. It is now possible to select ST from many sites within large and small joints, even in the earliest phases of disease, enhancing studies of aetiology, prognosis and response to treatment [4].Analysis of biomarkers in ST is increasingly being used in the evaluation of new targeted therapies in RA patients [5]. Numerous studies have suggested consistent associations between rapidity and magnitude of both clinical and immunohistological responses. It was shown that, especially within the ST, the number of infiltrating sublining macrophages can be used as a biomarker of clinical efficacy in relatively small studies of short duration [6,7]. Therefore, change in synovial sublining macrophages may be used as a biomarker for the evaluation of novel antirheumatic therapies. In addition to screening for possible efficacy, this approach provides insight into the mechanism of action of treatment.Within this setting, reliable and validated methods for studying the ST are pivotal. The use of computerized or digital image analysis (DIA) has greatly facilitated the evaluation of ST. The major advantage of DIA is standardization of image acquisition and processing, minimizing variance, and the ability to quantify the actual stained area together with staining intensity in a time efficient manner [8