Brain glucose metabolism changes following thyroid function normalization in hyperthyroidism

Objectives The consequences of endocrine-induced brain metabolism changes after thyroid function normalization are unclear. We hypothesized that the changes of regional cerebral glucose metabolism are related to thyroid hormone levels in hyperthyroid patients, and some of these changes can be reversed with antithyroid therapy.

Methods Relative regional cerebral glucose metabolism was compared between 10 new-onset, untreated hyperthyroid patients and 20 healthy control participants using brain fluorodeoxyglucose PET scan. Levels of emotional distress were evaluated using the SAS and SDS. Patients were treated with methimazole. A follow-up PET scan was performed to assess metabolic changes of the brain when thyroid functions were normalized.

Results Compared to controls, patients exhibited lower activity in the limbic system, frontal lobes, and temporal lobes, before antithyroid treatment. There were positive correlations between scores of depression and regional metabolism in the cingulate and paracentral lobule. The severity of depression and anxiety covaried negatively with pretreatment activity in the inferior temporal and inferior parietal gyrus respectively. Compared with the hyperthyroid status, patients with normalized thyroid functions showed an increased metabolism in the left parahippocampal, fusiform, and right superior frontal gyrus. The decrease in both FT3 and FT4 were associated with increased activity in the left parahippocampal and right superior frontal gyrus.

Conclusions The changes of regional cerebral glucose metabolism are related to thyroid hormone levels in hyperthyroid patients, and some cerebral hypometabolism can be improved after antithyroid therapy.

Research Support This work was supported by grants from the Natural Science Foundation of China (No.3080034)