Background & Objective: Subclinical hypothyroidism is defined by an increased serum TSH(Thyroid Stimulating Hormone) level in the presence of normal concentrations of circulating thyroid hormones and may be a predisposing factor for depression and psychomotor disorders. The aim of this study was to evaluate the effcts of L-thyroxine replacement on anxiety, depression and other neuropsychiatric aspects in patients with subclinical hypothyroidism.

Method: twenty-seven patients(19 females and 8 males) ranging from 17 to 61 years old(mean: 38±13.5 years) with basal serum TSH levels of 5.0-16.3 mu/l(mean: 8.4±5.2mu/l) and normal FT4I were enrolled. After being matched for age, TSH level and antithyroid antibodies, patients were randomly allocated into two treatment groups, LT4(Levo Thyroxine) and placebo including 13 and 14 cases respectively. In the LT4 group, dosage was titrated to achieve a serum TSH level between 0.3-3.5 mu/l. Intelligence Quotient(IQ) was assessed using Raven test, memory and psychomotor speed through Caughlan test, anxiety and depression via HADS(Hospital Anxiety Depression Scale) before and after treatment. Patients had follow-up visits for 11-14 months(mean: 12±0.6 months).

Results: Ten patients in the LT4 group and 13 in the placebo group completed the study. Mean TSH levels changed from 9.6±7.1 to 1.3±1.2mu/l(P<0.002) and from 7.6±3.1 to 18±15.8mu/l(P<0.024) in the LT4 and placebo groups respectively. No significant difference in IQ, recent and late memory, anxiety and depression was observed in both groups before and after intervention.

Conclusion: There is not obvious relationship between subclinical hypothyroidism, cognitive disorders and depression. Further studies to evaluate these problems are recommended.