The objective of this study was to begin to relate the microstructure of
calcinosis samples to clinical and laboratory characteristics of the
juvenile dermatomyositis (JDM) patients. Laboratory x-ray microCT (micro-Computed Tomography) noninvasively mapped microstructure for the first time in JDM calcifications.
Synchrotron x-ray diffraction (transmission geometry) identified the
mineral phase and crystallite size in the deposits. Samples were obtained from four children who had active JDM longer than 80 months and who were typed for TNFalpha-308 allele polymorphisms. Uniform
mineral (giving the appearance of an extruded solid) was observed in one patient, and irregular blocks of differing sizes filled the samples from two other patients. The sample from the fourth patient appeared to combine features of the other two types. These spatial distributions of
mineral were quite different from those in a bone reference sample. The only
mineral observed in the JDM samples was
hydroxyapatite (HAP), and the diffraction peaks of the JDM samples were slightly narrower than those of a trabecular bone reference sample. Diffraction peak widths of the JDM specimens revealed crystallite sizes (approximately 220-240 A) that are comparable to values reported in the literature for bone. Three children were positive for TNFalpha-308 GA polymorphism. The data suggest several possible origins for blocky vs. uniform structure of the JDM calcifications, including differences in duration of untreated
inflammation, in TNFalpha-308 polymorphism, and in mechanical constraint at the calcification site. Information from additional samples is required to determine the relative role of each of these factors. Taken together, non-invasive microCT and x-ray diffraction characterization on the same samples offer an informative window into the dystrophic mineralization process in JDM.