Raters described suspected crystals by shape ( rod or rhomboid), birefringence strength ( none, weak, moderate, strong) and color ( blue or yellow-orange), and certainty that the object was a CPP crystal ( low, medium, or high certainty). Raters examined each slide until a minimum of 10 suspected CPP crystals were photographed, with a minimum of four FOV photographs, or until a maximum of thirty minutes was reached. Suspected crystals were photographed using polarized light and the 100x objective. Raters scanned each slide with 10x or 40x objectives using either white or polarized light until regions suspicious for CPP crystals were identified. For evaluation of the study samples, raters used a standardized protocol to score each suspected crystal. All raters first underwent training with sample slides, which included CPP crystal-rich and crystal-free preparations. Slide assessment was conducted by four independent raters two were crystal-experienced and two were less crystal-experienced. Crystal identification by multi-rater assessment and crystal inclusion criteria Additionally, crystals that were not originally seen under direct CPLM, but visualized on enhanced digital images, were confirmed using advanced microscopic imaging with SCPLM.Ģ.3. To accomplish this, we rigorously evaluated crystals, first by multi-rater assessment of slides, followed by digital photomicrograph analysis, and subsequent expert confirmation of crystals. We undertook this project to better define the size and shape of CPP crystals as a reference database for these projects. To address the inherent challenges of CPLM for crystal arthropathy diagnosis, our group developed advanced microscopic imaging methods, including a lens-free polarized imaging system that directly images crystals using a light source and complementary metal-oxide-semiconductor (CMOS) and a single-shot computational polarized light microscopy (SCPLM) system that uses an industrial polarization CMOS image sensor. Given the abundance of issues associated with CPP identification by CPLM, there is clear need for a more reliable diagnostic tool. found that fewer than 20% of CPP crystals identified under ordinary light microscopy showed birefringence under polarized light. Furthermore, CPP crystals are weakly birefringent, making them difficult to detect by polarized light microscopy. Likewise, in an early report of clinical CPP arthropathy, while no crystals were detected by CPLM, abundant crystals smaller than 1 μm were identified at the ultrastructural level with electron microscopy and X-ray spectrometry. The low sensitivity of CPLM also relates to limitations of the sample and the instrument the CPP crystal concentration threshold for detection with CPLM is higher than estimates of in vivo crystal concentrations, and CPP crystals smaller than 1 μm fall below the limit of CPLM detection. demonstrated that analyst training improved the consistency of CPP crystal identification. There is ample room for improvement in crystal identification, particularly CPP crystals, amongst rheumatologists, other clinicians, and lab technicians. Several quality control studies have underscored the poor inter-laboratory reliability of CPP identification, including false negatives, false positives and misclassification of crystals, ,, ]. ![]() As a result, diagnostic accuracy is highly user-dependent. However, CPP crystal size and weak birefringence makes crystal identification challenging. ![]() ![]() The identification of CPP crystals is essential for an accurate and clinically meaningful diagnosis of CPPD disease.Ĭompensated polarized light microscopy (CPLM) of synovial fluid is the gold standard diagnostic method for CPP crystal-associated arthropathy. The presence of radiographic chondrocalcinosis is neither sensitive nor specific for clinically significant disease. It has been regarded as a great mimicker due to its clinical heterogeneity, resembling both acute inflammatory monoarthritis and chronic polyarticular arthritis. Calcium pyrophosphate deposition (CPPD) disease is arthritis due to deposition of calcium pyrophosphate (CPP) crystals in synovial fluid or tissues, which can cause significant morbidity and is often underdiagnosed.
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