Scanning electron microscopic study of microcrystals implicated in human rheumatic diseases.

Scanning electron microscopy has been used in conjunction with wavelength dispersive X-Ray spectroscopy and in correlation with X-Ray diffraction to define the populations of crystals present in rheumatic diseases. Microcrystals of monosodium urate, triclinic and monoclinic calcium pyrophosphate dihydrate, apatite, calcium hydrogen phosphate dihydrate and corticosteroids, among others, have been found in synovial fluid, in the intraarticular tissues (fibrocartilage, cartilage, and synovial membrane), and in the periarticular tissues (tendons and ectopic calcifications). Scanning electron microscopy in conjunction with wavelength dispersive X-Ray spectroscopy has made it possible to detect microcrystals, even isolated, to describe their morphologies, and to study their relations with the cells of the synovial fluid and with the collagenous and cellular structures of the synovial membrane and of the cartilage. It cannot replace X-Ray diffraction for the conclusive identification of microcrystals, but it can certainly help to improve the analysis of the various populations of crystals present in articular and periarticular rheumatic diseases.