Electroencephalographic changes during and after treatment of hyperthyroidism.
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EEG and thyroid function tests have been studied in 32 hyperthyroid patients before, during and after antithyroid treatment. EEG abnormalities such as increase in alpha rhythm, slow rhythms, spikes and sharp waves and fast activity were found in 81 % of the patients before treatment. A statistically significant correlation was found between the degree of EEG abnormalities and the severity of hyperthyroidism. During treatment and the period of observation which was extended to an average of 2\m=1/2\year, a slight decrease in the occurrence of all abnormalities was observed, but even in the period 24\p=n-\36months after the start of the therapy, 65 % of the patients still had abnormal EEG's. These persistent abnormalities in EEG suggest that hyperthyroidism might cause irreversible damage to the brain cells. It should be realized that hyperthyroidism may be the cause of considerable EEG abnormalities however not only in the acute state of the disease but also several years after an otherwise successful antithyroid treatment. It has been recognized for many years that abnormalities in the electroence¬ phalogram (EEG) are very frequent findings in patients with hyperthyroidism. Thus an increase in the alpha rhythm frequency, slow rhythms, paroxysmal activity with diffuse spikes and sharp waves and an increased incidence of fast activity are the abnormalities most often described (Ross Sc Schwab 1939; Downloaded from Bioscientifica.com at 12/02/2018 09:20:25PM via free access Condon et al. 1954; Skanse Se Nyman 1956; Vague et al. 1957, 1961; Jackson Sc Renfrew 1966; Wilson Sc Johnson 1964). Previous investigators have described an almost complete regression of abnormalities in EEG following antithyroid treatment (Skanse Sc Nyman 1956; Vague et al. 1961; Wilson Sc Johnson 1964). Changes in EEG however have not been correlated to total thyroxine or free thyroxine in serum and studies of a larger group of hyperthyroid patients with frequent EEG recordings during antithyroid treatment have not been found in the literature. MATERIAL AND METHODS The group studied comprised 32 patients i.e. 29 women aged 14 to 77 years and 3 men aged 16 to 49 years. The diagnosis was based on the clinical picture and on several thyroid function tests. (BMR, PBI, serum thyroxine, normal range 4.5-13.5 //g/100 ml (Siersbœk-Nielsen 1967), resin-T3-test (Triosorb Abbott) normal range 22.2-34.4% (Hansen & Buhl-Jergcnscn 1965), IS1I uptake in the thyroid gland). The severity of the hyperthyroidism was estimated using a »free thyroxine index« (serum thyroxine in //g/100 ml X resin-T3-test in %). Patients with values below 700 were classified as mild, between 700 and 1100 as moderate and over 1100 as severe cases. The patients were treated with propylthiouracil (PTU) in conventional doses. Eleven of the patients were thyroidectomized after 3 to 6 months treatment with PTU. The remainder of the patients received long term treatment with PTU for a period of approximately 24 months. In 5 patients hyperthyroidism relapsed after with¬ drawal of PTU and in one patient shortly after thyroidectomy. EEG's were recorded with an 8-channel Kaiser electroencephalograph and the recordings were analyzed blindly by two of us (M. St. and P. Z. O.). The EEG parameters were quantitated: the dominant alpha activity was the mean of values measured with a ruler 6-10 places in the vertex occipital lead. The slow activity of 3-4 cps and 5-6 cps was recorded as present or not. Paroxysmal activity re¬ flected diffuse sharp waves or spikes with or without high voltage slow waves and was graded from 0 to ++. Fast activity was measured as the activity above 14 cps in the fronto-central and parieto-occipital leads, and only an activity with a mean amplitude above 15 //V was considered. Finally the total abnormalities of a record was graded into 4 classes according to common usage and taking all the parameters into considerations The thyroid function tests and EEG's were performed before and 2 weeks, 6 weeks, 3 months, 6 months, 9 months, 12 months, 18 months and between 24 and 36 months after beginning of antithyroid treatment. The average period of observation was 32 months.