The nail plate biopsy may pick up gout crystals and other crystals.

The rewarding use of nail clippings processed histologically for the diagnosis of some nail diseases is well established. A new application of the nail plate biopsies (NPBs) is the detection of crystals in the subungual horn. Besides other subungual crystals, urate crystals are heretofore undescribed. This presentation adds to the advantages of an NPB: the detection of some cases of gout on which urate crystals are extruded subclinically. While searching for fungi, 2 cases of gout were diagnosed histologically, aided by unstained thick sections. A history of gout was then confirmed. No tophi were noted in or near the nail field. Chasing for crystals opens the study of fluids that may exude or transude into nail structures, a kind of "nail window" into hematic or metabolic abnormalities. In sum, the abundance of cytologic and histologic findings in an NPB can expand the armamentarium of physicians to evaluate nail diseases and even systemic diseases in a noninvasive manner.