BACKGROUND: There is a significant need for a targeted therapy for essential 
tremor (ET), as medications have not been developed specifically for ET, and the 
ones prescribed are often not well-tolerated, so that many patients remain 
untreated. Recent work has shown that, unlike previous experience, kinematically 
guided individualized botulinum toxin type A (BoNT-A) injections provide benefit 
along with minimal weakness. Ours is the first long-term (96-week) safety and 
efficacy study of BoNT-A as monotherapy for ET using kinematically driven 
injection parameters.
METHODS: Ten ET patients were administered six serial BoNT-A treatments every 16 
weeks and were assessed at 6 weeks following treatment. During each study visit, 
the Fahn-Tolosa-Marin (FTM) scale, the Unified Parkinson's Disease Rating Scale, 
and the Quality of Life for Essential Tremor Questionnaire (QUEST) were 
administered along with kinematic assessment of the treated limb. Participants 
performed scripted tasks with motion sensors placed over each arm joint. Dosing 
patterns were determined using the movement disorder neurologist's 
interpretation of muscles contributing to the kinematically analyzed upper limb 
tremor biomechanics.
RESULTS: There was a 33.8% (p<0.05) functional improvement (FTM part C) and a 
39.8% (p<0.0005) improvement in QUEST score at week 96 compared to pretreatment 
scores at week 0. Although there was a 44.6% (p<0.0005) non-dose-dependent 
reduction in maximal grip strength, only 2 participants complained of mild 
weakness. Following the fourth serial treatment, mean action tremor score was 
reduced by 62.9% (p=0.001) in the treated and by 44.4% (p=0.03) in the untreated 
arm at week 96 compared to week 48.
CONCLUSIONS: Individualized BoNT-A dosing patterns to each individual's tremor 
biomechanics provided an effective monotherapy for ET as function improved 
without functionally limiting muscle weakness.