Correlation between different components of synovial fluid and pathogenesis of rheumatic diseases

Biochemical analysis of synovial fluid is important in orientating the diagnosis of joint effusions. Its composition reflects the metabolic status of synovial tissue correlated with different rheumatic pathologies. The aim of this study was to compare the information provided by usual biochemical tests and proton magnetic resonance spectroscopy (MRS) analysis of synovial fluid, in order to detect potential characteristics of joint effusion correlated to the pathogenesis of arthritis.

This study included 99 synovial fluid samples obtained from patients with different etiology of arthritis--rheumatoid arthritis (RA), osteoarthritis (OA), gout, seronegative spondylarthropathies and septic arthritis, which underwent routine laboratory tests available in the Department of Rheumatology, Cantacuzino Clinical Hospital, Bucharest. Patients were admitted in the hospital between January 2003 and June 2005. Synovial samples were examined in parallel using MRS determination. Spectra have been recorded on a Bruker Avance DRX 400 MHz spectrometer.

We obtained a good correlation between biochemical analysis and MRS determination. RA samples have offered the most important information regarding the complex composition of pathological synovial fluid. In addition to the markedly elevated lactate (p < 0.009) and diminished glucose concentration (p < 0.02) in RA samples vs. OA, MRS analysis provides evidence for reduced mean chain length of very-low-density-lipoprotein (VLDL)-associated triacylglycerols (p < 0.05), high levels of ketone bodies (p < 0.05), ceramide (p < 0.02) and citrulline (p < 0.04). OA samples have shown a characteristically increased level of N-glucosamine (p < 0.04) and creatine (p < 0.04). For the other pathologies, there are no characteristic markers detected, except for the extremely increased level of lactate and the decreased concentration of glucose in septic arthritis.

This study gave us the possibility to provide a complex exploration of the biochemical environment of synovial fluid using the MRS method, that offers us the opportunity to understand more about the pathogenesis of rheumatic diseases, to provide information regarding the degree of inflammation, immune infiltration and apoptosis in RA, cartilage degradation and muscular secondary atrophy in OA. The most valuable information is focused on the possibility to have a simultaneous detection of more than 26 different metabolites in synovial fluid samples.