Tophus
Author:
Mikael Häggström [note 1]
Preparation
A tophus specimen should be sent dry to the pathology department, and not be put in formalin.[notes 1]
Gross processing
Preferably make a touch prep for polarized light microscopy. At least if urate crystals are not initially detected, take sections to be put in 100% alcohol and tell the histology lab to prepare it as per gout protocol.[notes 1] With characteristic crystals on a touch prep, sections may possibly be submitted in formalin.[notes 1]
Microscopy evaluation
On a touch prep, look for needle-shaped crystals of urate. On polarized light, these will have negative birefriengence.
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Light microscopy of a touch preparation of a gout tophus, showing needle-shaped crystals
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Uric acid crystals in polarized light, showing negative birefringence, with yellow color when aligned parallel to the axis of the red compensator, and blue when aligned perpendicularly to it.[1]
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In contrast, pseudogout (Calcium pyrophosphate dihydrate crystal deposition disease) displays rhombus-shaped or parallelogram-shaped crystals with negative birefringence.
![Uric acid crystals in polarized light, showing negative birefringence, with yellow color when aligned parallel to the axis of the red compensator, and blue when aligned perpendicularly to it.[1]](/index.php?title=Special:Upload&wpDestFile=Birefringence_microscopy_of_gout,_annotated.jpg){kind=link}
Notes
- ↑ For a full list of contributors, see article history. Creators of images are attributed at the image description pages, seen by clicking on the images. See Patholines:Authorship for details.
Main page
References
- ↑ Bruce M Rothschild. Gout and Pseudogout Workup. Medscape. Updated: Jun 30, 2020
Image sources