ASSESSMENT OF COGNITIVE FUNCTIONS AMONG SUBJECTS WITH SUBCLINICAL HYPOTHYROIDISM

Abstract

Objective: The consequences of overt hypothyroidism on CNS are well known. In contrast, there is less evidence regarding the effects of subclinical hypothyroidism (SCH) on cognitive functions. Studies have shown a variable association between SCH and cognitive dysfunction. This study was done to assess the prevalence of cognitive impairment among subjects with SCH. Methods: The participants were 100 subjects (aged 40-60 years) with SCH and similar number of age-matched euthyroid controls. Subclinical hypothyroidism was defined as serum TSH level > 4.5 mIU/L with normal FT3 and FT4. Participants were interviewed by a single observer. Cognitive function was assessed by mini mental state examination (MMSE) and clock drawing test (CDT). MMSE scores ≤24 is indicative of cognitive impairment. For CDT a score of ≥3 represents a cognitive deficit, while a score of 1 or 2 was considered normal. Results: The mean age of patient group was 47.4 years, and BMI of 26.1kg/m2 which were comparable to controls who had a mean age of 46.1 years (P=0.16) and mean BMI of 25.9 kg/m2 (P=0.25). All other baseline variables including sex ratio, co-morbidities, family history of dementia, smoking, alcohol use, education and exercise were also comparable in both groups. The mean TSH was 7.8 mIU/L in patients and 2.7 mIU/L in controls (P< 0.05). The mean MMSE score was 26.1 in patient group and 27.7 in controls (P=0.31) The patients had mean CDT of 2.32 and controls 2.44 (P=0.61). Cognitive impairment by MMSE (score ≤24) was found in 22.0% of patients and in 16.0% of controls (P=0.14), also the cognitive impairment by CDT (score of ≥3) was present in 27.0% of patients and 25.0% of controls (P=0.29). Conclusion: In the present study we have found that the prevalence of cognitive impairment in subjects with SCH is similar to the age matched controls. Therefore the potential benefit of levothyroxine therapy if used with an aim of improving cognitive functions becomes doubtful.