Context: Hyperthyroidism is frequently associated with emotional distress. The underlying cerebral processes of the endocrine induced mood changes are unclear.

Objective: To investigate, for the first time, the neuronal correlates of thyrotoxicosis associated psychic symptoms using positron emission tomography (PET)

Design: Cross-sectional trial

Setting: The study was performed at joint nuclear medicine and thyroid clinics

Patients: Twelve patients with untreated Graves' hyperthyroidism were evaluated

Methods: Levels of emotional distress were self-rated by means of the Hospital Anxiety and Depression Scale (HADS). 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 were analyzed.

Results: 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). In contrast, activation foci were registered in the posterior cingulate and in the inferior parietal lobe. These foci highly 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 FT3/FT4 levels negatively correlated with regional glucose metabolism in the medial posterior cingulate.

Conclusions: Thyrotoxicosis and associated psychic symptoms are correlated to regional metabolic changes in main structures of the limbic / paralimbic system.