Detection of silica and calcium carbonate deposits in granulomatous areas of skin sarcoidosis by μFourier transform infrared spectroscopy and Field Emission Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy analysis

Sarcoidosis is a multisystem inflammatory disease affecting different organs particularly lung, skin, eyes and joints. Characterized by noncaseating epithelioid granulomas, sarcoidosis is considered to be caused by a complex interplay between genetics and environmental agents while it still remains a disease of unknown etiology. 10 skin biopsies from patients with cutaneous sarcoidosis were included in the study. After polarized light examination (PLE) through optical microscopy, these skin biopsies have been investigated through μFourier transform (FTIR) infrared spectroscopy and Field Emission Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (FE-SEM/EDX). Three biopsies showed a refractive material at PLE. FTIR and FE-SEM/EDX analyses indicate the presence of silica at the center of the granulomas in these three biopsies. Another striking result is related to the presence of calcite, a calcium carbonate at the periphery of the granulomas. To our best knowledge, this is the first time that the presence of this calcium carbonate has been reported. Such description at the submicrometer scale paves the way for a better understanding of the physicochemical processes related to sarcoidosis and will help clinicians to develop new diagnostic tools.