Effect of Botulinum Toxin on Clonus: A Systematic Review

To conduct a systematic review of the literature that examined the effect of botulinum toxin type A on clonus.

A literature search of multiple databases (PubMed, Cochrane, Google Scholar, Embase) was performed to identify articles published in English in the past 30 years (1986-2016).

Two reviewers independently applied the following inclusion criteria: (1) any adult patients older than 18 years with upper motor lesion; (2) any location and duration of clonus; and (3) subjective and objective measurements of clonus tested at least 2 weeks after botulinum toxin injection.

Two reviewers independently extracted the data and assessed the methodological quality. A consensus method was used to solve disagreements.

The systematic review resulted in 164 articles, of which 14 met the inclusion criteria: 3 were randomized controlled trials, 1 was nonrandomized, and 6 were case series and 3 case studies. All studies (181 patients) showed improvement in clonus: 6 of 14 results were statistically significant. Different scales were used for clonus measurement, such as clonus score, patient diaries, clonus spasm score, and electromyogram duration.

Overall, there was preliminary evidence indicating improvement in clonus after botulinum injection. The major drawback with studies reviewed here was a large variation in the type of clonus assessment tools, which also lacked validity, reliability, and sensitivity to small changes in clonus.