[Low triiodothyronine syndrome in non thyroidal diseases. Distribution and serum TSH concentration studies (author's transl)].

Thyroid explorations were made in 57 patients complaining of serious illnesses in order to identify "low T3 syndrome". All these patients were clinically euthyroid as assessed by normal values of T4 concentration, RT3U ratio and FT4I. However, all the patients included in this study had significantly low serum T3 (42 +/- 29 ng/100 ml) and FT3I (0,44 +/- 0,30). Low T3 syndrome was particularly frequently seen in patients with cancer (8/10), hepatic cirrhosis (5/6), renal failure (6/7), old age (5/8) and in serious systemic diseases (6/12). Nevertheless, at adverse with other authors, we have observed less frequently the low T3 syndrome in anorexia nervosa (4/6) as well as during fasting (1/8). In 31 out of 35 patients with low or normal low T3 concentrations, the serum TSH values observed were within the normal limits in 28 cases. The etiologies of isolated decreased T3, mainly the deviation of peripheral conversion of T4 to reverse T3, are discussed. Normal metabolic state and normal TSH concentration encountered in the low T3 syndrome are equally commented.