Introduction: Subclinical hypothyroidism has been reported to be associated with disturbed cognitive function. In this study, changes of subtests of the Wechsler Memory Scale and memory quotient were investigated in subjects with subclinical hypothyroidism following treatment with levothyroxine. The aim of the study was a randomized double blind placebo-controlled clinical trial.
Material and methods: Sixty subjects (51 females and 9 males) with subclinical hypothyroidism were enrolled. Memory quotient was evaluated at the beginning of the study and three months after enrollment, using Wechsler's memory test. Subclinical hypothyroidism was defined as serum TSH level between 4.5 mU/l and 10 mU/l in the presence of normal free-T4 (0.8-2 ng/dl) and positive anti-TPO-Ab. The intervention and control groups received levothyroxine and placebo respectively for 3 months. Re-evaluation was done using the Wechsler Memory Scale at the end of the study.
Results: The mean age was 34 ±10 years, mean TSH level was 8.25 ±3.64 muIU/l. Memory quotient was similar in both groups at the beginning of the study: 105.70 ±2.1 in intervention group vs. 105.87 ±2.1 in control group (p = 0.89). At the end of the study, the memory quotient rose by 9.3 points in the intervention group and by 3.23 in the controls (p = 0.002). Analysis of the scores of Wechsler Memory subtests in the intervention group indicated significant improvement of mental control (p = 0.002), logical memory (p < 0.001), associate learning (p = 0.014), age corrected score (p = 0.002), and memory quotient (p < 0.001).
Conclusions: This study showed the efficacy of levothyroxine for cognitive function of subjects with subclinical hypothyroidism.
Keywords: Memory Quotient; Subclinical Hypothyroidism; Wechsler Memory Test; levothyroxine.