Thyroid hormones tied to cognitive impairments in Parkinson’s: Study
Changes in hormone levels may be biomarkers for cognitive dysfunction
Changes in the levels of thyroid hormones in the bloodstream are related to cognitive impairments in people with Parkinson’s disease, according to a new study by researchers in China.
“Our findings provided definite proof that changes in thyroid hormone levels have clinical implications for cognitive outcomes” in Parkinson’s, the team wrote.
In particular, the levels of the hormone FT3, fully called free triiodothyronine, were found to be significantly decreased among patients.
These results “suggest that thyroid hormone levels, particularly FT3, may serve as potential markers for cognitive dysfunction in [Parkinson’s],” the researchers wrote.
Details of the discovery were outlined in “Associations between Thyroid Hormones and Cognitive Impairment in Patients with Parkinson’s Disease,” a study published in the journal eNeuro.
Thyroid gland dysfunction linked to Parkinson’s clinical manifestations
Beyond the disease’s hallmark motor symptoms, people with Parkinson’s also may experience various nonmotor symptoms, such as anxiety and depression, sleeping problems, fatigue, and cognitive impairments.
Cognitive changes in Parkinson’s can vary widely from person to person, and range from mild cognitive impairment to dementia. Such changes are characterized by deficits in executive function — skills that help people manage everyday tasks — trouble maintaining attention, slowed thinking, and difficulties in word-finding, learning, and memory.
Thyroid hormones, produced by the thyroid gland in the neck, are essential modulators of several bodily processes, including metabolism, body temperature, heart rate, growth, and mood. Thyroid gland dysfunction has been shown to affect cognitive function and to correlate with clinical manifestations in Parkinson’s disease.
However, “the correlation of serum thyroid hormone levels to cognitive impairments in Parkinson’s disease (PD) patients remains unclear,” the researchers wrote.
To learn more, a team at the Cangzhou Central Hospital in China collected blood samples from 106 Parkinson’s patients without cognitive changes and 94 with cognitive impairments. Of those 94, 55 had mild cognitive impairment and were designated as PD-MCI, and 39 had Parkinson’s disease dementia, or PDD. The thyroid hormones measured were FT3, thyroid-stimulating hormone or TSH, and free thyroxine, known as FT4.
Cognitive functions were assessed using the Montreal Cognitive Assessment (MoCA) and the Mini-Mental State Examination (MMSE) alongside standard clinical tests for disease stage, duration, and motor function.
Compared with patients without cognitive changes, those with cognitive impairment had a longer disease duration, were at a more advanced stage (Hoehn and Yahr staging), and had worse motor function, as assessed by the Unified Parkinson’s Disease Rating Scale (UPDRS) Part 3. Age, sex, smoking status, and the occurrence of diabetes and high blood pressure were similar between the two groups.
Different hormone levels found in patients with cognitive impairments
Blood tests revealed significantly lower levels of FT3 and higher levels of FT4 and TSH in patients with cognitive impairments compared with those with normal cognition.
The accuracy in distinguishing between individuals with and without cognitive impairment was 66% for FT3 at a cutoff level of 3.78 picomoles/mL (pmol/mL), 71% for FT4 at a cutoff of 18.61 pmol/mL, and 69% for TSH at a cutoff of 2.99 U/mL. When the levels of all three hormones were combined, the accuracy improved to 82%.
Likewise, significantly lower FT3 and elevated FT4 and TSH levels were noted in those with dementia compared with mild cognitive changes, which provided “additional support for the association between thyroid hormone levels and the severity of cognitive impairment in [Parkinson’s] patients, “the researchers wrote.
This study provided supporting evidence on the clinical significance of investigating the intricate interplay between thyroid hormones and cognitive impairments in [Parkinson’s] patients. … This emphasizes the potential utility of these hormone levels as promising biomarkers for the detection of cognitive deficits in individuals with [Parkinson’s].
In line with these findings, low scores on the MoCA assessment, a sign of cognitive impairment, significantly correlated with low FT3 and high FT4 and TSH blood levels. Similar findings were reported for MMSE scores and increased levels of S100-beta, a marker for neurodegeneration.
“This study provided supporting evidence on the clinical significance of investigating the intricate interplay between thyroid hormones and cognitive impairments in [Parkinson’s] patients,” the team concluded. “This emphasizes the potential utility of these hormone levels as promising biomarkers for the detection of cognitive deficits in individuals with [Parkinson’s].”
About the Author
