Thyroid Dysfunction Could Increase Risk of Parkinson Disease

Nipith Chareonngam, MD

Patients with thyroid disorders may be at an increased risk of Parkinson disease, according to the results of a new study.

Presented at the American Academy of Clinical Endocrinology (AACE) annual meeting, results of the systematic review and meta-analysis indicate patients with hypothyroidism and hyperthyroidism were at a 1.5 times greater risk of developing Parkinson disease.

“Studies suggest patients with thyroid dysfunction may have an increased risk of developing Parkinson disease. However, the results from existing studies are inconsistent,” said Nipith Charoenngam, MD, a postdoctoral research fellow at Boston Medical Center, during his presentation. “Therefore, we aimed to investigate the association between hypo and hyperthyroidism with risk of Parkinson disease using the method of systematic review and meta-analysis.”

Citing an interest in building upon previous researching linking thyroid dysfunction and Parkinson disease, Charoenngam and a team of colleagues from Massachusetts-based institutions designed a systematic review and meta-analysis with the intent of assessing this association in eligible cohort and case-control studies published through 2021. With this in mind, investigators performed a search of the Medline and EMBASE databases form inception through December 2021, which yielded 3147 particles for potential inclusion in the analysis.

For inclusion in the analysis, studies needed to consist of 1 cohort of patients with hypothyroidism or hyperthyroidism and another cohort of patients without hypothyroidism or hyperthyroidism. Additionally, cohort studies were required to report effect estimates with 95% confidence intervals comparing incident Parkinson disease between the groups. Case-control studies were considered eligible if they included cases with Parkinson Disease and controls without Parkinson Disease. Additionally, these studies were required to explore a patientshistory of hypothyroidism and/or hyperthyroidism as well as report the odds ratios for associations between presence of hypothyroidism and/or hyperthyroidism and Parkinson Disease.

Of the 3147 articles identified, a pair of independent reviews by a trio of investigators results in a group of 3 cohort studies and 6 case-control studies being deemed eligible for inclusion in the investigators’ meta-analysis. The earliest study included in the meta-analysis was a case-control study published in 1981. Outside of this study, the remaining 5 case-control studies were published from 1999-2020. The 3 cohort studies included were published in 2012, 2020, and 2021. Of note, all 6 case-control studies included patients with hypothyroidism and 5 contained patients with hyperthyroidism.

Upon analysis, results indicated there was an increased likelihood of Parkinson disease was greater among those with hypothyroidism (pooled OR, 1.56 [95% CI, 1.38-1.77], moderate heterogeneity; I2, 66.9%) and those with hyperthyroidism (pooled OR, 1.57 [95% CI, 1.40-1.77], insignificant heterogeneity; I2, 0.0%). Investigators pointed out funnel plots for both meta-analyses were fairly symmetric, which led them to believe there was little evidence of publication bias.

“Possible explanations include, first, the dysfunction of dopaminergic neurons in the presence of thyroid hormone deficiency. Also, oxidative stress in the neuron due to thyroid hormone excess could be the explanation for the association between hyperthyroidism and Parkinson Disease,” added Charoenngam. “Also, shared genetic predisposition and neuroinflammation in autoimmune thyroid disease could be possible explanations as well.”

This study, “Thyroid Dysfunction and Risk of Parkinson’s Disease: a Systematic Review and Meta-Analysis,” was presented at AACE 2022.