Euthyroid sick syndrome: recent advances in its pathophysiology.

Introduction. - Patients with nonthyroidal disease frequently exhibit abnormal thyroid function tests; this is referred to as euthyroid sick syndrome. The clinical significance of this syndrome is unknown: abnormal endocrine reaction with reduced triiodothyronine (T3) at the tissue level, or adaptation to stress protecting the body against exaggerated catabolism. Current knowledge and key points. - Recent advances in the underlying mechanisms concern the role of deiodinase and of the transport of thyroid hormone in tissues. Various factors acting on deiodinase or on transport system, such as medications and nutritional factors, have been implicated. Considerable interest has raised concerning the role of cytokines. Some cytokines may act at every level of the thyrotropic Mis, but their real action in vivo remains unclear. Nutritional factors have a great impact on thyroid hormone metabolism, but the mechanism of the decrease in T3 induced by starvation is not identified. The role of the decrease in type I hepatic deiodinase has been recently challenged. Future prospects and projects, - Despite its complexity, euthyroid sick syndrome is a model for the study of thyroid hormone metabolism regulation. Characterisation of the thyroid hormone transport proteins will lead to significant advances in the understanding of the syndrome. (C) 1998 Elsevier, Paris