Ultra-microcrystals in pyrophosphate arthropathy. Crystal identification and case report

A patient with pyrophosphate arthropathy is reported who had no calcifications on joint radiographs, and no crystals were found in polarized light microscopy of the synovial fluid. Using techniques for idenfication of crystals at the ultrastructural level, abundant small (less than or equal to 1 mu) pyrophosphate crystals were recognized and identified. The possibility of "ultramicrocrystal depositions", including pyrophosphate arthropathy, is important to consider in acute arthritides since small crystals might cause more intense inflammation and be the cause of arthritides, hitherto not possible to classify.