Staining Method to Demonstrate Urate Crystals in Formalin-Fixed, Paraffin-Embedded Tissue Sections

Abstract

T histologic appearance of tophi is usually diagnostic. The tophi typically have a characteristic feathery appearance and foreign body giant cells around aggregates of needle-shaped empty spaces in a basophilic matrix formed by washed urate crystals.1,2 However, some lesions may have less characteristic histologic features because of minimal crystal deposits, small size of the biopsy specimen, minimal or absent foreign body giant cell response, abundance of basophilic matrix with scant crystals, or the formation of a prominent palisading granuloma-like pattern. In such cases, special techniques are important to demonstrate the presence of urate crystals in tissue. Different staining methods are described to demonstrate urate crystals in tissue, including deGalantha stain3 and Gomori methenamine-silver stain.4 These stains share the nonspecificity of routine hematoxylin-eosin (HE) stain without any advantage. Traditionally, alcohol fixation is preferred over formalin fixation.5 The present study describes a simple method that visualizes urate crystals in formalin-fixed, paraffin-embedded tissue sections under a light microscope and allows the confirmation by a polarizing microscope.