Electroencephalographic Changes Accompanying Thyroid Deficiency in Man1

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Abstract
Serial electroencephalograms were recorded during deprivation and replacement of thyroid hormone in patients who had little functional thyroid tissue and were therefore dependent on exogenous hormone for maintenance of a euthyroid state. The frequency and amplitude of the EEG alpha rhythm, and the photic driving response to flickering light were measured: 1) before and after hormone withdrawal (interval 4–6 weeks); 2) before and after hormone replacement (interval 4–6 weeks); and 3) after replacement with varying dosages of desiccated thyroid and triiodothyronine. Significant changes in the resting alpha rhythm and photically evoked responses were found for these limited periods of deprivation and replacement. Of special interest was the reduction of the brain's response to high frequency flickering light during thyroid deficiency. Of the measures studied, alpha frequency was the most responsive to changes in thyroid status—slowing with deprivation, increasing after replacement and fluctuating consistently with dosage changes. The finding of EEG changes during thyroid deficiency, in the absence of electrical abnormalities according to the usual criteria, suggests that physiologic normality cannot be assumed without knowing the extent to which the electrical recording deviates from the individual–s “personal norm.” The results indicate that the EEG is potentially useful in the detection of central nervous system effects of thyroid deficiency and in monitoring the efficacy of hormone replacement therapy

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