Associations between Thyroid Hormones and Cognitive Impairment in Patients with Parkinson’s Disease

This study aims to explore the correlation of serum thyroid hormone levels to cognitive impairments in Parkinson's disease (PD) patients. In this retrospective study, 106 Chinese patients without cognitive impairments and 94 patients with cognitive impairments, including 55 with mild cognitive impairment (PD-MCI) and 39 with Parkinson's disease dementia (PDD), were analyzed. Clinical data regarding the PD assessments, including disease duration, Unified Parkinson's Disease Rating Scale (UPDRS) Part III scores, and Hoehn and Yahr staging, were analyzed. Cognitive functions were evaluated using the Montreal Cognitive Assessment (MoCA) score. Serum levels of thyroid-stimulating hormone (TSH), free thyroxine (FT4) and free triiodothyronine (FT3), were measured using ELISA. Significantly altered Hoehn and Yahr staging, disease duration, and UPDRS Part III scores were observed in PD patients with cognitive impairment compared to those without. Serum levels of FT3 were significantly decreased, while FT4 and TSH levels were significantly elevated in PD patients with cognitive impairment compared to those without. Combined detection of TSH, FT3, and FT4, showed value in distinguishing PD patients with and without cognitive impairment. Furthermore, a comparison of serum levels between PD-MCI and PDD patients revealed significant association between thyroid hormone levels and the degree of cognitive impairment in PD patients. Our findings suggest a relationship between changes in serum thyroid hormone levels and cognitive impairments in PD patients. Thyroid hormone levels, particularly FT3, may serve as potential markers for cognitive dysfunction in PD. Significance Statement The correlation of serum thyroid hormone levels to cognitive impairments in Parkinson's disease (PD) patients remains unclear. The current results demonstrate a relationship between changes in serum thyroid hormone levels and cognitive impairments in PD patients. Our findings suggest that thyroid hormone levels, particularly FT3, may serve as potential markers for cognitive dysfunction in PD.