T Niessink, M Janssen, C Otto, Tl Jansen
Affiliation(s):
Viecuri Medical Centre
Background: The gold standard diagnostic measure for crystal-induced arthritis is polarized light microscopy, the application of which remains challenging for rheumatologists. Glass artefacts, small crystal sizes, amorphic deposits, and poor training in handling of the microscope affect the reliability of the outcome. Uncertainties may be problematic as the choice of treatment in individual patients is dependent on the identification.
Objective: In this study we re-evaluate (two-stepped analysis) synovial fluid samples in which the crystal identification of the rheumatologist was not certain on their polarized light microscopic diagnosis with Raman spectroscopy. Raman spectroscopy is a highly specific technique and allows for an objective identification of individual particles.
Methods: 400 synovial fluid samples were evaluated by expert rheumatologists for the presence of pathological crystals (MSU and CPP). In uncertain cases, we performed an additional analysis with Raman spectroscopy (iRPoLM, Hybriscan Technologies B.V.) to either confirm the suspected crystal-based diagnosis or identify other deposits and confounders which might have confused the clinician when using the polarized light microscope.
Results: Within 400 samples, the rheumatologists were uncertain of the diagnosis in 90 (22.5%). Uncertain identification of MSU (n = 30) was indeed MSU in one case (3.3%) as confirmed by Raman spectroscopy, uncertain identification of CPP (n = 45) was indeed CPP in nine cases (20%). In one case, CPP was erroneously identified as MSU, and in one case, no crystals were identified where actually CPP was present. The most prominent confounders were calcium carbonate (calcite, dolomite) crystals, which were present in 34.4% of all samples with uncertain identifications. Microplastics were present in 31.1% of all samples. Table 1 gives an overview of all results. (table1 - Fig. 1)
Conclusion: We here demonstrate that an uncertain crystal diagnosis with PLM is common and that additional analysis with Raman spectroscopy significantly improves the reliability of synovial fluid analysis due to the inherent chemical specificity of the technique.