Botulinum toxin A improves muscle tone in hemiparesis

By Lucy Piper, Senior medwireNews Reporter

A single injection of abobotulinumtoxinA into upper limb muscles significantly reduces muscle tone in patients with hemiparesis following stroke or traumatic brain injury, study findings show.

Four weeks after a single injection session of abobotulinumtoxinA 500 U or 1000 U in the most spastic muscle groups around the elbow, wrist or finger flexors, muscle tone had reduced by an average of –0.9 and –1.1, respectively, on the Modified Ashworth Scale (MAS) compared with after placebo injections.

Significant beneficial effects were seen within 1 week of injection and persisted for at least 12 weeks, lead researcher Jean-Michel Gracies (Hospital Albert-Chenevier Mondor, Créteil, France) and colleagues note.

The improvements resulted in physicians giving patients receiving abobotulinumtoxinA significantly better ratings on the Physician Global Assessment scale, with average scores at 4 weeks of 1.4 and 1.8 with the 500 and 1000 U doses, respectively, versus 0.6 with placebo.

However, there were no significant differences among the three groups on the Disability Assessment Scale or the 36-item Short Form Health Survey.

“This finding is in line with previous reports about botulinum toxin, which so far has not shown improvements in active function after one injection session only,” say the researchers, although they add that there can often be a delay between tone reduction and functional improvement.

“This negative result might indicate that active function in the paretic upper limb depends on factors other than muscle overactivity in elbow, wrist, and finger flexors, including muscle shortening at these joints, together with limitations in supination and shoulder flexion”, they suggest in The Lancet Neurology.

Of the 238 patients participating in the study and randomly assigned to one of the three treatment groups, 79 were given abobotulinumtoxinA 1000 U, 80 the 500 U dose and 79 placebo. The average reductions in MAS score at 4 weeks were –1.4, –1.2 and –0.3, respectively.

Treatment-emergent events, most commonly mild muscle weakness, were seen in 7% of patients given abobotulinumtoxinA 500 U and 9% of those given the higher dose, compared with 2% of placebo-treated patients.

Three serious adverse events occurred in each group, but none of these were considered to be treatment related.

In an associated comment, Gert Kwakkel and Carel Meskers, from Vrije Universiteit Medical Center in Amsterdam, the Netherlands, praise the researchers for their “properly powered” trial involving 34 different rehabilitation or neurology clinics in nine different countries.

But they question the use of MAS, an indirect measure of spasticity, as a primary outcome and say that the benefits of abobotulinumtoxinA for improving upper limb capacity remain a mystery.

“Biochemical and neurophysiological measurements, preferably done during meaningful tasks, are needed to investigate this association”, they conclude.

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