Ultrasound-guided biopsy of synovial tissue is an increasingly performed procedure for diagnostic and research purposes.
In clinical practice, synovial tissue analysis may assist in the diagnostic work-up in selected (rare) joint diseases, including neoplastic or granulomatous diseases, deposition diseases including crystal-associated arthritis or infection, when synovial fluid analysis and culture are not conclusive.
As demonstrated by several studies, including the 1987 ACR classification criteria for rheumatoid arthritis (RA) study, synovial tissue analysis helps in distinguishing inflammatory from non-inflammatory arthritis and between different forms of immune-mediated inflammatory arthritis (IA). Despite morphological and immunohistochemistry analyses are accurate in differentiating RA from spondyloarthritis, at this moment the usefulness of these tests to establish the diagnosis in clinical practice is not justified.
Further applications of synovial tissue analysis include disease activity assessment at joint and patient level, as well as prognostic stratification, but no specific prognostic biomarkers are enough specific and predictive to be included in a standard patient assessment. However, in the setting of drug development, the evaluation of biological activity of experimental drugs at the site where the disease process takes place is now a well-recognized approach, and evaluation of serial synovial biopsies assists in screening for potential efficacy of novel compounds provides insights into the mechanism of therapy.
Form a technical point of view, needle biopsy is simple, cheap and minimally invasive, while arthroscopic biopsy is regarded as the gold standard sampling method, since it provides adequate synovial tissue samples selected under direct vision from both large and small joints even from clinically uninvolved joints. The availability of more recent office-based mini-invasive ultrasound-guided techniques are increasing the diffusion of the synovial tissue analysis in inflammatory arthritis research and clinical practice.
Depending on the indication for the biopsy procedure, the tissue needs to be handled substantially differ. Under the assumption that inflammation in one inflamed joint is generally comparable to that in other inflamed joints, in order to minimize sampling error, multiple sampling (typically at least six samples from different areas throughout the joint) need to be applied. As recently demonstrated in validation studies on US-guided derived synovial samples, both at large and small joints: good quality tissue collection is feasible; quantification of digital synovial inflammation by image analysis is a valid, sensitive and time efficient; and quantitative PCR and different microarray analysis techniques can be used to analyze US synovial tissue samples for research purposes.
Future advances in the field of minimally invasive ultrasound-guided synovial biopsy will include new technical developments, identification of novel biomarkers, able to improve diagnostic/prognostic characterization of individuals at the onset of the disease, and even more importantly, to personalize treatment based on potential treatment selection biomarkers.
Disclosure of Interest None declared