Cerebral function in hypothyroid patients. A study of the vigilance level in patients with hypothyroidism before and during substitution therapy.

Abstract

Mental performance was studied in 6 hypothyrotic patients before, seven weeks after and one year after initiation of thyroxine substitution therapy. Performance as measured by critical flicker-fusion (CFF) and vernier visual acuity (KVAT) improved significantly after 7 weeks of substitution therapy, and improved still further, although not significantly, after 1 year. Performance as measured by two reaction time tasks was not significantly improved, either after 7 weeks or after 1 year. The results were interpreted in terms of the complexity of the measures used, more complex measures being more affected by the disease through summing of several ‘unit impairments’. Further, 3 subjects were studied in detail with repeated measurements of CFF. 1 subject was studied with T4 substitution, another with T3 substitution and 1 subject with T4 substitution and T4 substitution plus T4 propylthiouracil blocking of T4 to T3 metabolism. With T4 substitution there was a distinct increase in performance, with a delay of 2-3 weeks after a dose change. With T3 substitution in a dose corresponding to T4 to T3 metabolism there was no change in performance.