EEG changes in untreated hyperthyroidism and under the conditions of thyreostatic treatment

20 patients with hyperthyroidism were observed with repeated EEG measurements before and during treatment (ObsidanR; MethimazolR). 17 patients, before starting antithyroid therapy, had slight to moderate EEG abnormalities. A prevalence for moderate disturbances occurred for patients with a higher degree of hyperthyroidism. The dominant EEG frequency was higher than in euthyroid controls, but no exact correlation to T3-values could be observed. 16 patients showed abnormal reactivity to photic stimulation. One-week therapy by propranolol produced only a slight synchronizing effect in EEG's, where T3-values decreased. After 4 weeks selective therapy by MethimazolR all patients were euthyroid, but some EEG abnormalities persisted in 12 patients in a lower degree. The dominant EEG frequency decreased to control-group ranges and abnormal photic reactivity was reduced. After 6 months some EEG disturbances re-increased tentiatively, in 3 relapses excessively. These observations confirm the prognostic value of EEG measurements for the recognition of occurrence and persistence of cerebral disturbances in severe metabolic dysfunctions.