Abstract
BACKGROUND AND PURPOSE: Essential tremor with a midline distribution (Mid-ET) may represent a distinct subtype of essential tremor (ET) that primarily affects midline structures, often indicating advanced disease stage and increased severity. Recent studies have highlighted the complexity of Mid-ET, but research on neurological soft signs (NSS) in Mid-ET remains insufficient. METHODS: The patients with ET included in this cross-sectional study were divided into two subgroups based on whether or not the ET had a midline distribution: Mid-ET and No-Mid-ET. Comparative analyses were performed to assess clinical features and NSS prevalence in these subgroups. RESULTS: Among 1,160 patients, 567 (48.9%) were Mid-ET and 593 (51.1%) were No-Mid-ET. The prevalence rates of head, face (including the jaw), and voice tremors were 31.9%, 23.0%, and 25.8%, respectively. In Mid-ET, tremor often affects multiple midline structures simultaneously. In the entire cohort, 24.7%, 16.6%, and 7.6% of patients exhibited tremors in one, two, and three midline structures, respectively. The prevalence of common NSS, including mild cognitive impairment, impaired tandem gait, and questionable dystonic posturing, was significantly higher in the Mid-ET than the No-Mid-ET subgroup (all p<0.001). Furthermore, we found that female sex (p<0.001), olfactory dysfunction (p=0.003), and questionable dystonic posturing (p=0.004) were associated with Mid-ET. CONCLUSIONS: Mid-ET and No-Mid-ET presented significant clinical differences. The presence of questionable dystonic posturing may contribute to the distinct characteristics of Mid-ET, suggesting the presence of pathophysiological differences between the subgroups. Further investigations are warranted to determine the potential pathophysiological link between NSS and Mid-ET.