Levodopa induces thyroid function regulation in a patient with thyroid hormone resistance and Parkinson's disease: a case report

Abstract

Introduction: Thyroid hormone resistance (THR) is a rare genetic syndrome characterized by reduced sensitivity to thyroid hormones. Patients may be asymptomatic, although clinical manifestations depend on the THR subtype. This entity commonly has abnormal thyroid function tests and can be confirmed by molecular analyses.

Case presentation: The present study describes a 55 year-old female diagnosed with surgically resected papillary thyroid carcinoma. During the endocrinology consults, elevated thyroid hormone levels were detected without an adequate TSH response, and THR was suspected. Moreover, Parkinson's disease was diagnosed, and treatment with levodopa/carbidopa was initiated. Following this regimen, her TSH and total T3 levels were subsequently normalized, which suggests a potential effect of this agent on the normalization of these hormone levels in the blood. In this case, the role of levodopa was crucial to regulate the TSH concentration which was required to carry out the resection of a tumoral remnant.

Conclusion: The influence of dopamine in the endocrine system, specifically in the thyroid gland, is beneficial in conditions such as THR where abnormal TSH levels can be lowered, helping to balance the thyroid and hormones function.

Keywords: Parkinson’s disease; case report; dopamine; levodopa; thyroid hormone resistance.

Figure 1

Thyroid hormone levels (TSH, Free T4, Total T4, Total T3, and Free T3) over time. (A) TSH levels throughout time. TSH remained mostly in the normal range but managed to stay within the normal range and suppressed with the start of the medication. (B) Free T4 levels throughout time. The concentrations remained elevated despite the start of Levodopa/Carbidopa. (C) Total T4 levels throughout time. The concentrations remained elevated despite the start of the medication. (D) Total T3 levels throughout time. The concentrations normalized when Levodopa/Carbidopa was started. (E) Free T3 levels throughout time. Free T3 remained mostly in the normal range and there was no clear change in the TSH levels with the start of Levodopa/Carbidopa.

Figure 2

(A) Sagittal T1-weighted brain magnetic resonance imaging (MRI) sequence showing the findings of an partially empty sella turcica. (B) Coronal T2-weighted MRI sequence confirming the previously described findings.