Thyroid hormone level is associated with motor symptoms in de novo Parkinson’s disease

Sympathetic denervation has been observed not only in the myocardium but also in the thyroid of patients with Parkinson’s disease (PD). We investigated whether sympathetic denervation as indicated by decreased cardiac ¹²³I-meta-iodobenzylguanidine uptake is associated with the levels of thyroid hormones and whether the levels of thyroid hormones affect clinical manifestations in patients with PD. The subjects were 75 patients with de novo PD and 20 age-matched healthy controls. We examined the levels of thyroid-stimulating hormone, free triiodothyronine, and free thyroxine, and evaluated the associations of these levels with cardiac ¹²³I-meta-iodobenzylguanidine uptake and motor symptoms. The results showed that the free triiodothyronine level was below the normal range in 29 patients (approximately 40 %) and was significantly lower in the patients with PD than in the controls. The decreased free triiodothyronine level was associated with akinetic-rigid motor subtype and washout ratio of cardiac ¹²³I-meta-iodobenzylguanidine scintigraphy. The free triiodothyronine level negatively correlated with disease severity. Thyroid-stimulating hormone level was within normal range. However, its level was lower in patients with tremor-dominant type or mixed type than in those with akinetic-rigid type. All correlations of these variables with the levels of thyroid hormones remained statistically significant on multiple regression analysis. Our results suggest that the thyroid hormone level, especially the free triiodothyronine level, is closely related to motor symptoms in patients with de novo PD. Further studies are needed to clarify whether the decreased hormone levels have functional roles in motor and non-motor symptoms.