[CRST syndrome. Ultrastructural and physico-chemical studies of calcifications (author's transl)].

The subcutaneous calcifications in a case of CRST syndrome were studied by electron microscopy and by several physico-chemical tests in order to establish their structure and development. Samples of powder, obtained by crushing and homogenisation of the deposits, were subjected to the following analyses: - radiocrystallography by X-ray of the raw and heated material - infra-red spectroscopy before and after heating - quantitative chemical analysis and differential thermal micro-analysis. Connective tissue fibres seemed to play an important part in the development of the calcifications. The initial deposits of calcium first appeared in the central part of elastic fibres whose general morphology remained nevertheless undisturbed. In the older deposits disorganised elastic (and possibly collagen) fibres and areas of bone formation were found. Evidence of an inflammatory reaction was always minimal or nil. There was considerable variation in the calibre of collagen fibres in the non-calcified zones, the smaller fibres predominating. These appearances, sometimes noted in scleroderma, seem to be associated with increased collagen synthesis. X-ray diffraction and infra-red spectroscopy studies show that the deposits consist essentially of type B hydroxyapatite carbonate, confirmed by differential thermic analysis. On electron microscopy the calcifications were shown to comprise straight, needle-like crystals, 100-600 nm in length and 30-100 nm broad, characteristic of the apatites. Very occasionally, target-pattern deposits conforming to whitlockite were encountered. Chemical analysis revealed a high proportion of calcium with a Ca/P ratio greater than 1-666 as is typical of synthetic hydroxyapatite carbonates. The deposits also contained up to 20% by weight of organic material.