Background Synovial biopsies have been collected by rheumatologists for several decades using arthroscopic guidance with the additional advantages of joint visualization and lavage. We aim to analyse the outcomes of the first 20 knee arthroscopic guided synovial biopsies (AGB) recently performed at our centre for diagnosis and (non-orthopedic) therapeutic purposes.
Methods AGB were performed according to standardised procedures. Nineteen were done for diagnostic purposes to patients with knee arthritis of unknown etiology, after application of a clinical algorithm. The remaining patient had a therapeutic indication. A macroscopic scoring for vascularization and proliferation was applied and synovial tissue processed for routine histology and microbiology assessment.
Results 20 patients were submitted to AGB. Eight had a previous diagnosis of inflammatory arthritis: RA (2), JIA (2), PsA (3) and SLE (1). In all cases, patients were in joint remission with the exception of knee arthritis, raising the suspicion of undercurrent septic arthritis AGB allowed the exclusion of joint infection in 7 of 8 patients and septic arthritis was the established diagnosis in one case. This favoured rapid systemic therapeutic adjustment and/or intra-articular corticosteroids administration to induce remission, in non-infectious cases. In a PsA DMARD treated patient, direct visualization of crystal deposits on synovial membrane supported the diagnosis of concomitant crystal induced arthritis. The remaining patients had no previous rheumatic disease and presented with monoarthritis (7) or oligoarthritis (5) of unknown etiology. Considering the monoarthritis group, Mycobacterium tuberculosis was isolated in two patients. For the remaining five, infection was excluded and a definite diagnosis of osteoarthritis (1), crystal induced arthritis (3) and psoriatic arthritis (1) was established. In the oligoarthritis group, neither synovial membrane macroscopic, histology nor microbiology analysis helped to clarify the diagnosis.
Conclusions In inflammatory arthritis, persistent synovitis of a single joint can be a red flag for joint infection, however, in this small series, the majority of patients exhibited uncontrolled disease activity rather than septic arthritis. The rate of joint tuberculosis was particularly high (10%) highlighting its endemic occurrence in Portugal and awareness for this etiology. The visualization of crystal deposits can be a complementary diagnostic tool in patients with crystal induced arthritis in which crystals are not identified in the synovial fluid. Despite application of commonly available synovial tissue study strategies (macroscopy, histology and microbiology) in 25% of patients it was not possible to establish a definite diagnosis indicating that further synovial tissue biomarkers for inflammatory arthritis diagnosis are required.