Impaired Sustained Attention in Patients with Subclinical Hypothyroidism

<b>Background:</b> Subclinical hypothyroidism (SCH) is of particular importance due to its high prevalence and its association with cognitive deficits. Patients often express complaints of neuropsychological symptoms and cognitive impairments including lack of attention. Also, patients treated with levothyroxine (LT-4) often report persistent complaints related to mental slowing or lack of attention despite normal TSH levels.<b>Purpose:</b> To investigate the effects of different ranges of TSH on sustained attention in SCH.<b>Methods:</b> Included in the study were 136 participants that were divided into four groups: Group 1, 35 healthy individuals; Group 2, 33 newly diagnosed patients with SCH; Group 3, 36 patients on LT-4 with uncontrolled or elevated TSH; Group 4, 32 euthyroid patients (ongoing LT-4). Laboratory measurements and clinical assessment were done. Rapid visual processing (RVP) task was performed on standardized battery (Cambridge Automated Neuropsychological Test Battery).<b>Results:</b> There was significant impairment in sustained attention (<i>P</i>=<0.05) in Group 2 patients who had neuropsychological symptoms and SCH diagnosed with a TSH range of ≥2.5mIU/L.<b>Conclusion:</b> Our findings encourage screening for sustained attention along with thyroid profile in those who report neuropsychological symptoms. TSH mean range of ≥2.5 mIU/L was established as a more reasonable threshold for evaluating sustained attention and initiating LT-4 in SCH.