Influence of thyroid hormone supply on EEG frequency spectrum

In 5 patients after total thyroidectomy followed by radioiodine ablation the frequency analysis of EEG based on fast Fourier transformation was performed and the results obtained during hypothyroid state and after the substitution treatment with thyroid hormones were compared. During the hypothyroid state the most remarkable finding was the increase of percentage representation of fast frequencies in beta 1 and beta 2 bands, while such values in alpha band including a dominant frequency in that band were reciprocally decreased. After the period of treatment with triiodothyronine during which clinically euthyroid state has been achieved (i.e. decrease of Achilles tendon reflex time, decrease of TSH and of T3 level) no significant changes in the distribution of EEG frequencies spectrum were found, but in all patients a dominant frequency in alpha band was increased at least for 1 Hz. Only after the treatment with thyroxine (Eltroxin Glaxo) the interrelations between individual frequencies of EEG spectrum returned to the normal range and a further increase in dominant alpha frequency was found. The correlation between a dominant frequency in alpha band and thyroxine level in serum was highly significant. These findings are in agreement with our previous observations in 43 subjects where a dominant alpha frequency in healthy controls was always higher than that in hypothyroid subjects and was significantly related to T4 level. The findings of continuing EEG signs of brain hypothyroidism even after achieving of clinical euthyroidism and normal peripheral parameters under increased serum T3 and low T4 level are in full agreement with experimental observations on the importance of local deiodination of T4 in brain tissue and on the risk of hypothyroxinemia.(ABSTRACT TRUNCATED AT 250 WORDS)