Elisa Bruno, Alessandra Nicoletti, Graziella Quattrocchi, Roberta Allegra, Graziella Filippini, Carlo Colosimo, Mario Zappia

Essential tremor (ET) is one of the most common movement disorders. The management is primarily based on pharmacological agents and in clinical practice propranolol and primidone are considered the first-line therapy. However, these treatments can be ineffective in 25% to 55% of people and are frequently associated with serious adverse events (AEs). For these reasons, it is worthwhile evaluating other treatments for ET. Topiramate has been suggested as a potentially useful agent for the treatment of ET but there is uncertainty about its efficacy and safety. To assess the efficacy and safety of topiramate in the treatment of ET. We carried out a systematic search without language restrictions to identify all relevant trials in the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (January 1966 to January 2017), Embase (January 1988 to January 2017), National Institute for Health and Care Excellence (1999 to January 2017), ClinicalTrials.gov (1997 to January 2017) and World Health Organization International Clinical Trials Registry Platform (ICTRP; 2004 to January 2017). We searched BIOSIS Citation Index (2000 to January 2017) for conference proceedings. We handsearched grey literature and the reference lists of identified studies and reviews. We included all randomised controlled trials (RCTs) of topiramate versus placebo/open control or any other treatments. We included studies in which the diagnosis of ET was made according to accepted and validated diagnostic criteria. We excluded studies conducted in people presenting with secondary forms of tremor or reporting only neurophysiological parameters to assess outcomes. Two review authors independently collected and extracted data using a data collection form. We assessed the risk of bias and the quality of evidence. We used a fixed-effect meta-analysis for data synthesis. This review included three trials comparing topiramate to placebo (309 participants). They were all at high overall risk of bias. The quality of evidence ranged from very low to low. Compared to placebo, participants treated with topiramate showed a significant improvement in functional disability and an increased risk of withdrawal (risk ratio (RR) 1.78, 95% confidence interval (CI) 1.23 to 2.60). There were more AEs for topiramate-treated participants, particularly paraesthesia, weight loss, appetite decrease and memory difficulty. This systematic review highlighted the presence of limited data and very low to low quality evidence to support the apparent efficacy and the occurrence of treatment-limiting AEs in people with ET treated with topiramate. Further research to assess topiramate efficacy and safety on ET is needed.