Objective: Calcific deposits develop in 20-40% of children with juvenile dermatomyositis (juvenile DM), contributing to disease morbidity and mortality. This study was undertaken to define the structure and composition of these deposits and to characterize their association with chronic inflammation.
Methods: We examined calcific deposits from 5 children with juvenile DM (2 boys and 3 girls). The crystal structure and mineral content of the deposits was analyzed by x-ray diffraction, Fourier transform infrared spectroscopy, and imaging. The protein content of the deposits, following solubilization, was assayed by Western blotting.
Results: All 5 children had both a young age at disease onset (mean +/- SD 3.3 +/- 1.9 years) and, despite therapy, persistent cutaneous inflammation (mean +/- SD duration 81.3 +/- 58.7 months). The bone proteins, osteopontin, osteonectin, and bone sialoprotein, were identified in the protein extracts; the only mineral detected was hydroxyapatite, but the tissue was distinct from bone, with an extremely high mineral content and an irregular distribution of mineral.
Conclusion: These results indicate that chronic cutaneous inflammation may contribute to the formation of hydroxyapatite-containing pathologic calcifications in children with juvenile DM.