Prodromal Markers of Parkinson's Disease in Patients With Essential Tremor

Abstract

Background: Essential tremor (ET) is manifested as an isolated syndrome of bilateral upper limb action tremor. Parkinson's disease (PD) is the second most common neurodegenerative disease, with typical motor symptoms of bradykinesia, rigidity, and resting tremor. ET-PD describes the new-onset of PD in ET patients. Recently, numerous studies on epidemiology, genetics, pathology, clinical features, and neuroimaging studies are challenging the idea that ET is an isolated disease, suggesting that patients with ET have the tendency to develop PD. Methods: In this review article, we collected recent findings that reveal prodromal markers of PD in patients with ET. Results: Substantia nigra hyperechogenicity serves as a prodromal marker for predicting the development of PD in patients with ET and provides a reference for therapeutic strategies. Additional potential markers include other neuroimaging, clinical features, heart rate, and genetics, whereas others lack sufficient evidence. Conclusion: In consideration of the limited research of PD in patients with ET, we are still far from revealing the prodromal markers. However, from the existing follow-up studies on ET patients, Substantia nigra hyperechogenicity may enable further exploration of the relationship between ET and PD and the search for pathogenesis-based therapies.

Keywords: ET-PD; Parkinson's disease; essential tremor; prodromal markers; substantia nigra hyperechogenicity.

Figure 1

An overview of the risk markers of Parkinson's disease in patients with essential tremor. Essential tremor patients have an increased risk of the development of PD, especially those with SN hyperechogenicity in TCS. Similarly, ET patients with specific tremor or non-motor symptoms, additional HRV, genetic risk, or the other risk markers such as Tremor Stability Index are undergoing a higher risk of the development of PD afterward.