Role of event-related potentials in evaluation of cognitive function in subclinical hypothyroid patients

Context: Hypothyroidism has been associated with neurocognitive deficit, but status of cognitive function in subclinical hypothyroidism is unclear. Also, cognitive impairment found in these patients has been associated with aging. Aims: The purpose of this study was to evaluate cognitive function in hypothyroid and subclinical hypothyroid patients using objective methods and to correlate it with age, thyroid stimulating hormone (TSH) level, and education status of patients. Settings and Design: It was a cross-sectional study conducted on 90 female participants aged 30-50 years. Thirty patients diagnose with subclinical hypothyroidism (group 1) were compared with 30 age- and sex-matched hypothyroid patients (group 2) and euthyroid controls (group 3). Subjects and Methods: Cognitive function was evaluated using three parameters such as mini mental scale examination (MMSE), event-related potentials - P300latency and amplitude, auditory and visual reaction time. Statistical Analysis Used: SPSS version 17 was used for statistical analysis. The data were also analyzed for variables related to age, TSH, and education level. Results: Significant delay in P300latency and prolonged reaction time was found in both subclinical hypothyroid and hypothyroid group compared to controls (P < 0.001). P300amplitude and MMSE score showed no significant difference in all groups. In hypothyroid patients, P300latency at Fz, Pz was positively correlated with age while nonsignificant correlation was observed in subclinical hypothyroid patients. TSH and education level of patients showed no significant correlation with cognitive function tests. Conclusions: Delayed P300latency and prolonged reaction time in both subclinical hypothyroid and hypothyroid patients shows that cognitive function is affected adversely. Event-related potentials may be more sensitive than clinical evaluation by MMSE, for early diagnosis of mild cognitive impairment in subclinical hypothyroidism