Positron Emission Tomography Reveals Correlations between Brain Metabolism and Mood Changes in Hyperthyroidism

Hyperthyroidism is frequently associated with emotional distress. The underlying cerebral processes of the endocrine-induced mood changes are unclear.The objective of this study was to investigate, for the first time, the neuronal correlates of thyrotoxicosis-associated psychic symptoms using positron emission tomography (PET).The study was designed as a cross-sectional trial.The study was performed at joint nuclear medicine and thyroid clinics.Twelve patients with untreated Graves' hyperthyroidism were evaluated.Levels of emotional distress were self-rated by means of the Hospital Anxiety and Depression Scale. Both patients and 20 age- and gender-matched euthyroid controls underwent a brain fluorodeoxyglucose PET scan. Subsequently, the functional relationship between brain metabolism and the psychometric scores was analyzed.Compared with controls and visualized by fluorodeoxyglucose PET, hyperthyroid patients showed a decreased (P < 0.0001) glucose metabolism in the limbic system (uncus and inferior temporal gyrus). Activation foci in the posterior cingulate and in the inferior parietal lobe were correlated with both anxiety and depression scales (P < 0.001). Compared with patients with normal anxiety levels, those with increased anxiety yielded an enhanced glucose metabolism (P < 0.001) in the bilateral sensory association cortex. Serum free T3/free T4 levels negatively correlated with regional glucose metabolism in the medial posterior cingulate.Thyrotoxicosis and associated psychic symptoms are correlated to regional metabolic changes in the main structures of the limbic/paralimbic system.