Euthyroid sick syndrome and inhibitory effect of sera on the activity of thyroid 5'-deiodinase in systemic sclerosis.

Abstract

The low FT3 or FT3/FT4 ratio observed supports the hypothesis that euthyroid sick syndrome is often present in SSc. Anti-thyroid antibody is also frequently detected in SSc and the positive sera inhibit the activity of thyroid 5'-deiodinase, which can contribute to the low FT3 or FT3/FT4 ratio. Anti-thyroid peroxidase antibodies may play an additive role in the development of low FT3 levels via the inhibiting effect of thyroid 5'-deiodinase. The low FT3 levels may directly influence the already impaired microcirculation in SSc by increasing the systemic vascular resistance.