Transcranial sonography (TCS) in Parkinson's disease (PD) and essential tremor (ET) in relation with putative premotor symptoms of PD

Background: Hyperechogenicity of substantia nigra (SN+) is a common finding in transcranial ultrasound studies of parkinsonian patients. However, this feature is also found in 13-16% of ET patients. The possible links between ET and PD are of special interest, particularly with the familial aggregated data supporting this association. However, few studies have been conducted regarding the factors associated with the emergence of PD in the ET population. In this study, we investigated the possible association between SN+ and putative premotor symptoms of PD in patients with ET. Methods: A total of 47 patients with PD and 64 patients with ET were enrolled in the study. All patients underwent TCS and completed a structured interview for putative premotor symptoms of PD. Results: As expected, there were significant differences observed in the frequency and size of SN+, and the prevalence of the putative premotor symptoms of PD. More interestingly, in the ET group a significant association between SN+ and each premotor symptom was observed and a trend was also found that ET cases with more putative premotor symptoms of PD had a greater size of SN+. In contrast, in the PD group, SN+ was not influenced by the cumulative effect of premotor symptoms. Conclusion: The results of this study suggest that SN+ in patients with ET is influenced by the putative premotor symptoms of PD.