Changes in brain size with treatment in patients with hyper- or hypothyroidism.

Background And Purpose: Although neuropsychological symptoms and signs are common in thyroid disease, their organic substrate is unknown. We performed brain MR imaging in patients with hyperthyroidism or hypothyroidism before and after treatment and correlated the results with hormonal markers.

Methods: Eight patients with hyperthyroid disease and three with hypothyroid disease underwent imaging within 1-2 days of a thyroid hormone testing. Images were registered, and brain and ventricular sizes were measured by using a semiautomated contour and thresholding technique. Changes in brain and ventricular volume were correlated with serum levels of total thyroxine (T(4)), unbound triiodothyronine (free T(3)), and thyroid-stimulating hormone (TSH) before and after treatment.

Results: With treatment, brain size decreased by 6,329-31,183 mm(3) in the hyperthyroid group and increased by 2,599-48,825 mm(3) in the hypothyroid group. Conversely, with treatment, ventricular size increased by 325-6,279 mm(3) in the hyperthyroid group and decreased by 760-2,376 mm(3) in the hypothyroid group. There was a highly significant correlation between reduction in brain size and reduction in T(4), as well as between the increase in ventricular size and reduction in T(4). There was a significant correlation between reduction in ventricular size and reduction in free T(3). There were highly significant correlations between reduced levels of TSH and increase in brain size, as well as between increased levels of TSH and increase in ventricular size.

Conclusion: In thyroid disease, the size of the brain and ventricles significantly change after treatment, and these changes are correlated with T(4), free T(3), and TSH levels. The mechanism of these changes is uncertain, but it may involve osmolyte regulation, the sodium and water balance, and alterations in cerebral hemodynamics.