Objective: Testing the hypothesis that late onset essential tremor (LOET) patients show age-typical differences of the pupillary responses when compared with early onset ET (EOET) and healthy controls (HC) with a similar age at assessment.

Background: LOET is characterized by shorter life expectancy and more advanced aging parameters and may therefore be regarded as an ‘aging-related’ tremor. Brainstem functions involved in pupillary responses are hypothesized to reflect such earlier aging. The pupillary light response (PLR) and a task evoked pupillary response (TEPR) were used to test this hypothesis.

Method: The PLR and TEPR during the paced auditory serial addition test (PASAT) were tested in 57 normal subjects, 13 patients with LOET (onset age>50yrs), 16 patients with EOET and 15 age matched HC. Standard parameters of the PLR were measured: baseline pupil diameter, minimum pupil diameter after pupil reaction to light, constriction amplitude, maximum velocity, maximum acceleration, latency from stimulus onset to the maximum constriction acceleration, time for maximum velocity, time for maximum constriction, relative constriction amplitude. TEPR was measured during PASAT as the percentage change in pupil size (PCPS). Data were analysed with mixed model ANOVA and post-hoc testing.

Results: In HC the pupil diameter, latency, maximum acceleration/velocity and percentage amplitude were significantly correlated with age. Mixed model ANOVA comparing same aged EOET, LOET and controls with post-hoc testing showed significantly longer T1- (F(2, 37)=7.747, p<0.01) and T2- (F(2, 36)=7.430, p<0.01) measures in LOET compared to controls (for T1: p<0.001, T2: p<0.01) and EOET patients (p<0.05 each), while no differences were found between EOET and controls. A multiple linear regression was calculated to predict T1 for all ET patients based on the onset age, age, tremor severity (Fahn A) and a cognitive composite score. The R² for the overall model was 0.282, and the whole model showed no statistical significance (F(2, 21)=2.058, p>0.05). Only the onset age significantly predicted T1 (ß=0.516, p<0.05), while other parameters showed no significant predictive values. The task evoked pupillary response showed no significant differences between the groups.

Conclusion: LOET showed a prolonged latency of the PLR compared to EOET possibly indicating pathophysiological differences on brainstem level or a “premature aging” in these patients.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/pupillary-response-to-light-and-tasks-in-early-and-late-onset-essential-tremor-patients/