Background: Many nonthyroidal illnesses, such as major trauma, severe burn injury, sepsis or immune deficiency are associated with a reduced T3 concentration without increased serum TSH secretion. The pathopysiologic meaning of this phenomenon was controversely discussed since its investigation 20 years ago. The identification of the Type I 5-iodthyronine-deiodinase as a selenoenzyme brought many new aspects into this discussion.
Patients and methods: To investigate the correlation of T3 blood levels and the selenium concentrations in consideration of the severity of the nonthyroidal illness 20 patients with major trauma where included in this study. In all these patients frequently T3, T4, fT3, fT4, TSH, Se (whole blood), Se (plasma) and Glasgow-Coma-Scale (GCS), APACHE II and MOF-Score where measured until the 28th day of illness.
Results: Five patients (20%) died during the study until the 8th day of measurement. Survivors and nonsurvivors initial showed a low T3 and fT3 level in serum. While the T3 serum concentrations of nonsurvivors remained on a low level the thyronine concentrations of survivors distinctly increased. The measured thyroid hormone concentrations were significantly correlated with MOF-score, APACHE II and inversely with GCS. There was no significant correlation between low T3/fT3 blood levels and low selenium concentrations in all observed patients.
Conclusion: The selenium deficiency in all patients with major trauma seems to be not the single cause of the low T3 syndrome. The distinctly suppression of TSH could be caused by the action of various cytokines such as IL-6 and TNF-alpha. Further investigations should improve the effectivity of substitution of selenium and/or thyroid hormones in the therapy of patients with severe nonthyroidal illness.