Seen here are needle-shaped crystals under polarized light using a red compensator. Most of the crystals are yellow, indicating negative birefringence, while those oriented perpendicularly are blue, because the axis of the compensator is in the direction of the yellow crystals. This appearance is consistent with sodium urate crystals from the joint (or tophus) of a patient with gout. Without the compensator, the crystals appear bright white. The more rhomboidally-shaped crystals of calcium pyrophosphate dihydrate (CPPD) seen with the condition known as pseudogout are positively birefringent. In this case, the "red compensator" is a standard glass microscope slide upon which two strips of clear (not semi-transparent) adhesive tape ("scotch tape") have been layered. The trick is getting strips of the appropriate thickness. The long axis of the slide becomes the axis of this cheap "red compensator".
There were 49 correct entries out of 97 total entries for case 49.
| Our winner is: Liron Pantanowitz, Pathology, Harvard Medical School
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