Prevalence, hormonal correlates, severity, and neural basis of neurocognitive impairment in patients with hypothyroidism: Systematic review and meta-analyses.

The aims of this review were to assess the associations between neuropsychological test results and thyroid hormone levels, as well as the imaging abnormalities in the brain associated with hypothyroidism. For this systematic review and meta-analysis, 85 prior studies met the inclusion criteria. Among these studies, the prevalence of neurocognitive impairment assessed with the Mini-Mental State Examination (MMSE) in hypothyroidism was 0.29 [95% CI:0.26-0.33]. The pooled correlation strength between thyroid-stimulating hormone and the MMSE was r = -0.46 [95% CI:-0.69 to -0.15]. Patients with hypothyroidism performed lower than controls on the MMSE (standardized mean difference (SMD) = -1.134, [95% CI:-2.020 to -0.248]), Wechsler Memory Scale (SMD = -1.286 [95% CI:-2.110 to -0.462]), and had longer P300 latency (SMD = 1.124, [95% CI: 0.746-1.502]). Qualitative analysis of neuroimaging data indicated that drug-naïve individuals diagnosed with hypothyroidism have numerous structural and functional alterations. Meta-regressions showed that the results are dependent on both hormone levels and sociodemographic variables. Neurocognitive difficulties in individuals with hypothyroidism is a complex phenomenon that requires further investigation. HIGHLIGHTS: Neurocognitive impairment (NCI) occurs in about one third of patients with hypothyroidism. Thyroid-stimulating hormone level is negatively associated with neuropsychological test results. Memory functions in patients with hypothyroidism were lower than in the control group. Sociodemographic and clinical characteristics were moderators of NCI. Studies indicate abnormalities in the structure and metabolism of the central nervous system in patients with hypothyroidism.