CALCIUM PYROPHOSPHATE DEPOSITION DISEASE: DIAGNOSTIC VALUE OF POLARIZED OPTICAL MICROSCOPY

Background: Pseudogout, also known as calcium pyrophosphate deposition (CPPD) disease, is a common but often underdiagnosed crystal-induced arthropathy. It occurs when CPPD crystals deposit in articular cartilage and synovial fluid. Because its clinical manifestations often mimic gout or septic arthritis, accurate differentiation is essential for appropriate patient management. Recognition of the unique pathophysiology and crystal morphology of pseudogout is therefore critical for laboratory diagnosis. Methods: This narrative review summarizes and integrates findings from selected, well-established sources to provide clinical and laboratory perspectives, highlight best practices, and identify areas requiring standardization. The existing evidence regarding the diagnostic application of polarized optical microscopy (POM) in pseudogout was evaluated. Key themes include the principles of POM, optimal specimen collection and handling, techniques for accurate crystal identification, and recommended laboratory workflow practices. Additionally, the review discusses factors that influence diagnostic accuracy, such as technician proficiency and the use of standardized microscopic evaluation protocols. Results: The findings indicate that polarized light microscopy remains the gold standard for identifying CPPD crystals. Rhomboid-shaped crystals exhibiting weakly positive birefringence are characteristic of pseudogout and allow reliable differentiation from monosodium urate crystals observed in gout. Proper specimen preparation - particularly timely examination of fresh synovial fluid - and adherence to standardized microscopy practices significantly enhance diagnostic yield. In addition, targeted technician training in crystal recognition improves interobserver consistency and reduces misclassification. Conclusion: Polarized light microscopy is an indispensable tool for the accurate laboratory diagnosis of pseudogout. Increasing awareness of crystal morphology, improving specimen-handling practices, and investing in consistent technician training can substantially enhance diagnostic accuracy. Standardizing the use of POM across clinical laboratories will support earlier detection and improved clinical management of pseudogout.