Background Arthropathy induced by calcium pyrophosphate dihydrate [Ca2P2O7.2H2O] () crystals (chondrocalcinosis, pseudogout, pyrophosphate arthropathy) is characterized by intraarticular or periarticular deposition of . Crystals accumulate in the synovial membranes with or without calcification in articular hyaline and/or fibrocartilage, joint capsules, bursae, and tendon sheaths. Almost any joint may be involved by , although the knees, wrists, and hips are most often affected. crystals have a rhomboid shape in which adjacent sides are of unequal lengths and angles are not at 90 degrees. crystals may be identified by polarization optical methods as positively birefringent small (<40μm) rhomboid crystals, arranged separately or in aggregates of amorphous calcium phosphate, or carbonate deposits. In diagnostic pathology Alizarin Red staining (specific for calcium) or the von Kossa reaction (specific for phosphate and carbonate)are used to demonstrate calcium and phosphate. With these methods amorphous calcium phosphate, or carbonate deposits – accompanied by crystals – stain red, or black, resp., but crystals do not stain. The masses of amorphous calcium phosphate and carbonate may mask the crystals, without any detectable birefringence.
Objectives The of this study was to demonstrate the advantages of examining unstained histologic sections under polarized light in comparison with haematoxylin-eosin stained ones.
Methods At the National Institute of Rheumatology and at the Hospital of the Order of the Brothers of Saint John of God surgical specimens were examined histologically between 1985 and 2010, among them 10 (0.01%) with chondrocalcinosis and deposits. Seventeen tissue samples of 10 patients with deposits were studied in serial sections stained with haematoxylin-eosin and in unstained sections viewed under polarized light.
Results In formaldehyde fixed and haematoxylin-eosin stained sections, viewed under polarized light, CPPD crystals were detected in of 10 patients (60.0%), whereas in unstained sections crystals were present in 9 of them (90.0%).
CPPD crystals were demonstrable in 75.0% of formalin fixed tissue specimens (in 3 of 4 patients) which were considered negative with haematoxylin-eosin stain.
Conclusions The simplest and most effective technique to demonstrate crystals is “not-staining” (1). Textbooks of histologic methods and histochemistry do not mention this simple technique (2-5).
It appears that in case of clinically or histologically suspected metabolic or crystal induced diseases it is adventageous to examine tissue sections stained with haematoxylin-eosin as well as in unstained sections. The probability of identifying crystals is much higher in unstained sections viewed under polarized light than in haematoxylin-eosin stained ones. This approach may also be useful in other crystal deposition induced diseases.
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Disclosure of Interest None declared