Tophus

Author: Mikael Häggström

Preparation

A tophus specimen should be sent dry to the pathology department, and not be put in formalin.

Gross processing

A large tophus.

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. With characteristic crystals on a touch prep, sections may possibly be submitted in formalin.

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.
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  In contrast, pseudogout, also called calcium pyrophosphate dihydrate (CPPD) crystal deposition disease) displays rhombus-shaped or parallelogram-shaped crystals with negative birefringence.
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  To look for crystals in a regular light microscope, look without condenser (right image) if possible, wherein crystal outlines are more clear than with condenser (left image). CPPD crystals are depicted.

Main page

• Main page of Patholines