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Open Access Research article

Microstructure and mineral composition of dystrophic calcification associated with the idiopathic inflammatory myopathies

Naomi Eidelman1*, Alan Boyde2, Andrew J Bushby3, Peter GT Howell4, Jirun Sun59, Dale E Newbury6, Frederick W Miller7, Pamela G Robey8 and Lisa G Rider7

Author Affiliations

1 Paffenbarger Research Center, American Dental Association Foundation, National Institute of Standards and Technology, 100 Bureau Drive, Stop 8546, Gaithersburg, MD 20899, USA

2 Biophysics OGD, Dental Institute, Queen Mary University of London, New Road, London E1 1BB, UK

3 Department of Materials, Queen Mary University of London, Mile End Road, London E1 4NS, UK

4 Prosthetic Dentistry Unit, UCL Eastman Dental Institute, 256 Gray's Inn Road, London WC1X 8LD, UK

5 Polymers Division, National Institute of Standards and Technology, 100 Bureau Drive, Stop 8543, Gaithersburg, MD 20899, USA

6 Surface and Microanalysis Science Division, National Institute of Standards and Technology, 100 Bureau Drive, Stop 8371, Gaithersburg, MD 20899, USA

7 Environmental Autoimmunity Group, Office of Clinical Research, 10 Center Drive, MSC 1301, National Institute of Environmental Health Sciences, National Institutes of Health, Bethesda, MD 20892, USA

8 National Institute of Dental and Craniofacial Research, National Institutes of Health, 30 Convent Drive, Bethesda, MD 20892, USA

9 Current address: Paffenbarger Research Center, American Dental Association Foundation, National Institute of Standards and Technology, 100 Bureau Drive, Stop 8546, Gaithersburg, MD 20899, USA

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Arthritis Research & Therapy 2009, 11:R159  doi:10.1186/ar2841

Published: 26 October 2009

Abstract

Introduction

Calcified deposits (CDs) in skin and muscles are common in juvenile dermatomyositis (DM), and less frequent in adult DM. Limited information exists about the microstructure and composition of these deposits, and no information is available on their elemental composition and contents, mineral density (MD) and stiffness. We determined the microstructure, chemical composition, MD and stiffness of CDs obtained from DM patients.

Methods

Surgically-removed calcinosis specimens were analyzed with fourier transform infrared microspectroscopy in reflectance mode (FTIR-RM) to map their spatial distribution and composition, and with scanning electron microscopy/silicon drift detector energy dispersive X-ray spectrometry (SEM/SDD-EDS) to obtain elemental maps. X-ray diffraction (XRD) identified their mineral structure, X-ray micro-computed tomography (μCT) mapped their internal structure and 3D distribution, quantitative backscattered electron (qBSE) imaging assessed their morphology and MD, nanoindentation measured their stiffness, and polarized light microscopy (PLM) evaluated the organic matrix composition.

Results

Some specimens were composed of continuous carbonate apatite containing small amounts of proteins with a mineral to protein ratio much higher than in bone, and other specimens contained scattered agglomerates of various sizes with similar composition (FTIR-RM). Continuous or fragmented mineralization was present across the entire specimens (μCT). The apatite was much more crystallized than bone and dentin, and closer to enamel (XRD) and its calcium/phophorous ratios were close to stoichiometric hydroxyapatite (SEM/SDD-EDS). The deposits also contained magnesium and sodium (SEM/SDD-EDS). The MD (qBSE) was closer to enamel than bone and dentin, as was the stiffness (nanoindentation) in the larger dense patches. Large mineralized areas were typically devoid of collagen; however, collagen was noted in some regions within the mineral or margins (PLM). qBSE, FTIR-RM and SEM/SDD-EDS maps suggest that the mineral is deposited first in a fragmented pattern followed by a wave of mineralization that incorporates these particles. Calcinosis masses with shorter duration appeared to have islands of mineralization, whereas longstanding deposits were solidly mineralized.

Conclusions

The properties of the mineral present in the calcinosis masses are closest to that of enamel, while clearly differing from bone. Calcium and phosphate, normally present in affected tissues, may have precipitated as carbonate apatite due to local loss of mineralization inhibitors.