X-ray diffraction analysis of spontaneously draining calcinosis in scleroderma patients

Calcium hydroxyapatite (HA) is reported to be the major constituent of soft tissue calcinosis in patients with scleroderma (systemic sclerosis, SSc). Mechanical stress and local tissue hypoxia are thought to be important in the pathogenesis of SSc calcinosis. We sought to analyse spontaneously draining material from calcinosis sites in SSc patients using X-ray diffraction (XRD).

With approval from our local Institutional Review Board (IRB), eligible SSc patients consented to submit their spontaneously draining calcinosis samples for XRD analysis. All patients met the American College of Rheumatology (ACR) criteria for definite SSc. XRD data were used to determine how much solid phase was present (e.g. HA vs. other calcium phosphate phases) and the percentage of crystalline components. Pertinent clinical data were collected.

Draining calcinosis was submitted mostly from the hands of 10 female patients with advanced SSc, whose mean disease duration was 16 (range 9-29) years; six had diffuse cutaneous SSc and four had limited SSc. All 10 developed calcinosis later in their disease course; seven had extensive deposits affecting multiple sites. XRD confirmed that HA was the only crystalline material. However, HA was the minor component and most samples contained more than 50% organic material. Solid samples generally contained more HA and fluid samples contained HA in suspension.

In this large series of SSc calcinosis analysis, XRD confirmed that HA was the only inorganic material that formed less than 50% of most draining samples. More research is needed to fully characterize and improve our understanding of calcinosis formation in SSc.