1. ¹Department of Radiology, National Naval Medical Center, Bethesda, Maryland, USA
2. ²Department of Radiology, Uniformed Services University of the Health Sciences, Bethesda, Maryland, USA
3. ³Department of Psychiatry, Uniformed Services University of the Health Sciences, Bethesda, Maryland, USA
4. ⁴Division of Nuclear Medicine, Russell H Morgan Department of Radiology and Radiological Science, Johns Hopkins Medical Institutions, Baltimore, Maryland, USA
5. ⁵Laboratory of Personality and Cognition, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA

Correspondence: Dr FV Schraml, Department of Radiology, National Naval Medical Center, 205 Piping Rock Drive, Silver Spring, MD, 20905, USA. E-mail: fvschraml@bethesda.med.navy.mil

Received 2 March 2005; Revised 19 May 2005; Accepted 13 June 2005; Published online 3 August 2005.

Abstract

Thyroid dysfunction is a well-known contributor to psychiatric morbidity. To investigate the mechanism(s) by which thyroid hormone availability affects cerebral activity, a group of thyroidectomized individuals were studied at two points in time: when markedly hypothyroid in preparation for a thyroid cancer metastatic survey and when clinically and/or biochemically euthyroid. The analysis consisted of single photon emission computed tomography (SPECT) using a lipophilic radiopharmaceutical, technetium-99m (Tc-99m) ethyl cysteinate dimer (ECD), and measurement of mood, anxiety, and psychomotor function, at both points in time. Both increases and decreases in regional cerebral radiotracer activity were found in the hypothyroid condition relative to the euthyroid condition, and the neuropsychological assessment demonstrated significantly greater depression, anxiety, and psychomotor slowing during the hypothyroid state. Increased radiotracer activity was seen in frontal and temporal regions, posterior cingulate gyrus, thalamus, and putamen. Decreased activity was seen in the occipital cortex, and the pre- and postcentral gyri. This distribution pattern is partially consistent with findings in persons with depression and anxiety unrelated to thyroid disease, supporting the link between the symptoms observed in our subjects and their marked hypothyroidism. Finally, these results support the need to consider the effect of the thyroid state on cellular mechanisms of uptake and retention of cerebral blood flow radiopharmaceuticals when studying 'noneuthyroid' individuals.