TSH-suppressive therapy is widely used in treatment of thyroid differentiated carcinoma. A common consequence of therapy is subclinical hyperthyroidism which may cause dysfunction of cardiovascular system, metabolism and reduction of bone mass. Thyroid hormones are also involved in regulation of brain function. Therefore, thyroid dysfunctions are associated with frequent comorbid cognitive dysfunctions and depression.

The aim of our study was to assess the cognitive functions in patients treated with suppressive doses of levothyroxine due to thyroid papillary carcinoma.

Twenty three patients with subclinical hyperthyroidism in the course of substitutive treatment with levothyroxine due to total thyroidectomy and 131I therapy were involved in the study. The control group consisted of 13 healthy, euthyroid subjects.

A battery of neuropsychological tests was administered to assess: 1. Working memory and executive functions (the Wisconsin Card Sorting Test- WCST, The Controlled Oral Word Association Test-FAS), 2. Psychomotor speed (the Trial Making Test- TMT) 3. Attention (the Stroop test) and 4. Short term memory (the Digit Span test). Psychometric evaluation was made using 17 items the Hamilton Depression Rating Scale and Beck Depression Inventory.

Patients compared to control group performed poorer in WCST. They made significantly more perseverative errors. Patients were found to perform less well than controls in FAS and in TMT-B. The mean score of HDRS and BI (3,4 and 6,6 respectively) suggest that patients were not depressed during examination.

Our results suggest that suppressive treatment with levothyroxine may affect executive functions, working memory, psychomotor speed.