Context: Several studies have evidenced the association between subclinical hyperthyroidism and cognitive impairment in the elderly. However, the effect of long-term TSH suppressive therapy on the cognitive function in elderly patients with differentiated thyroid carcinoma (DTC) is still unclear.
Objective: Our aim was to investigate the effect of long-term TSH suppression on the cognitive function of elderly patients with DTC.
Design, setting, and participants: A cross-sectional case-control study including 50 DTC patients aged 65 years or older (mean age 70.9 ± 5.0 y) who have received a TSH-suppressive therapy for at least 5 years and 90 control subjects matched for age, sex, education period, and depressive mood was conducted. Major Outcome Measure: Comprehensive cognitive domains were compared between the patient and control groups. The association between serum thyroid hormone concentration and cognitive function was investigated.
Results: The patient group had higher serum free T4 levels and suppressed TSH levels compared with the control group. Age, sex, education period, the Korean version of the Geriatric Depression Scale scores, and Cumulative Illness Rating Scale scores were not different between the 2 groups. All assessed neuropsychiatric tests were comparable in both groups. In the patient group, those with higher serum free T4 levels performed better on Mini-Mental State Examination and Trail Making Test A. The association between serum free T4 and Trail Making Test A was maintained after adjusting for age, education period, the Korean version of the Geriatric Depression Scale, and Cumulative Illness Rating Scale. In the control group, serum free T4 and TSH levels were not associated with any of the assessed cognitive domains.
Conclusion: Our results demonstrated the safety of long-term TSH suppression on the cognitive function in elderly DTC patients. Furthermore, the positive correlations between serum free T4 levels and some cognitive domains suggest the potential beneficial effects of exogenous levothyroxine on the cognitive function of patients who lack endogenous thyroid hormone.