Preservation of tophi in the modified Gomori methenamine silver procedure for urates

There are several variations of laboratory procedures to preserve and demonstrate monosodium urate (MSU) crystals in tissue for the diagnosis of gout. MSU is water soluble and washed away in most staining solutions, so these procedures generally necessitate two slides; one which is silver stained and one which is left unstained to confirm the negative birefringence of MSU when viewed under polarized light. The modified Gomori’s methenamine silver (GMS) for urates is an underutilized procedure which provides sensitive, high-contrast staining of MSU crystals. Additionally, we have observed that MSU deposits are preserved in the stained sections, allowing for examination by polarized light and subsequent diagnosis with only one slide. We have found this modification of the GMS stain to be the most sensitive and efficient method for the diagnosis of gout histologically due to the procedure’s relatively short duration as well as the sharp black staining of MSU crystals and preservation of MSU birefringence on a single slide.