Answer to Image of the Month September 2015

Submitted by Inchara YK


Gouty tophus

Gout is a disorder of purine metabolism characterised by elevated uric acid levels. Deposition of these crystals in skin and soft issue produces tophi. In the image provided (formalin-fixed tissue), circumscribed deposits of uric acid are seen as feathery eosinophilic structures surrounded by fibrosis and a giant cell response. Demonstration of the characteristic needle-shaped uric acid crystals in tophi requires alcohol fixation and anhydrous processing as monosodium urate is water soluble. These crystals are negatively birefringent when viewed under the polarizing microscope.


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