Abstract Background and Objectives In clinical practice, we have observed that patients with Parkinson disease (PD) often have blepharoclonus, but its prevalence is not well described in the literature. Understanding the relative frequencies of blepharoclonus in PD and atypical parkinsonian syndromes may shed light on the diagnostic utility of this clinical sign. We aimed to assess (1) the frequency of blepharoclonus in patients with PD in a single-center cohort; (2) the association of blepharoclonus with disease stage, tremor severity, and non-motor symptoms; and (3) the frequency of blepharoclonus in synucleinopathy vs non-synucleinopathy–associated parkinsonism. Methods We prospectively enrolled 85 patients, 75 with PD and 10 with atypical parkinsonism. Blepharoclonus was considered present if eyelid fluttering was sustained for >5 seconds after gentle eye closure. For each patient, demographics were collected, and we completed selected questions from the MDS-UPDRS (Unified Parkinson's Disease Rating Scale) part 2, REM Sleep Behavior Disorder Questionnaire, and MDS-UPDRS part 3 tremor assessments and recorded the presence/absence of dyskinesia. Results 63 of 75 patients with PD (84%) had blepharoclonus. Among the 10 patients with atypical parkinsonism, 5 had synucleinopathy syndromes. Blepharoclonus was present in 3 of 5 patients with synucleinopathy and 0 of 5 patients with non-synucleinopathy–associated parkinsonian syndromes. Discussion Blepharoclonus is prevalent in our PD cohort, suggesting possible utility as a clinical marker for PD. The absence of blepharoclonus in a patient with parkinsonism may suggest a non-synucleinopathy (e.g., tauopathy). Analysis of a larger cohort of both PD and atypical parkinsonism would be needed to establish whether blepharoclonus distinguishes PD from atypical parkinsonism, or synucleinopathy from non-synucleinopathy. https://www.neurology.org/doi/10.1212/CPJ.0000000000200240
