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The gold-standard technique to diagnose gout and pseudogout is detection of crystals in joint fluid aspirates under compensated polarised light microscopy (CPLM). Detecting monosodium urate (MSU) and calcium pyrophosphate (CPP) crystals is diagnostic of gout and pseudogout, respectively1 2
The crystals are identified and differentiated from one another using the CPLM by assessment of their (A) colour, (B) shape and (C) birefringence.1 2 However, this method has limitations including possible low sensitivity in detecting rare and small crystals and differentiating them from contaminants, and it can be unreliable.1 2 Also, CPLM requires two filters that need to be manually adjusted and rotated and needs special training.2 The limitations of CPLM are compounded by examiner inexperience.2 The accurate identification of MSU and CPP crystals is vital, as missing small or rare crystals might lead to confusion in the diagnosis and delay in treatment.2 3
A new polarising microscope technology known as the polychromatic polscope (PPM)4 allows the detection of birefringent particles with low retardance at all orientations of their slow axis. This means that theoretically, the detection of crystals could be accomplished regardless of the angle at which they are lying on the slide. PPM can be deployed on a standard light microscope with only minor …
Footnotes
Handling editor Josef S Smolen
Twitter @jumah_husam
Contributors Conducting the research: HJ and SA designed the study. HJ collected the cases and analysed the data/results. SA reviewed the slides and did the interpretation. Preparing the manuscript: HJ wrote the manuscript. MS cowrote and critically revised the manuscript. AK, BL, YL, DO, KWE, AL and SA critically revised the manuscript. All authors contributed importantly to this study.
Funding We acknowledge funding from the Morgridge Institute for Research and NIH R01 R01CA238191 to KWE, and NIH R01GM101701 to MS.
Competing interests MS: NIH R01GM101701. KWE: The Morgridge Institute for Research, NIH R01CA238191, Bruker (Consultant to KWE, stock or stock options with KWE) and Elephas (Consultant to KWE, stock or stock options with KWE). BL: Studentship stipends made to personal account (University of Wisconsin-Madison), travel reimbursement made to personal account (Morgridge Institute for Research), and Studentship stipends made to personal account (University of Wisconsin-Madison).
Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.
Provenance and peer review Not commissioned; externally peer reviewed.